Category: Environmental geology and geohazards

Highly fractionated, silica-rich magma poses the greatest danger of explosive volcanic eruption, characterised by glowing pyroclastic flows that produce the strange rock ignimbrite. For example, in the Andes, ignimbrites extend for large distances from the calderas that emitted them. Fortunately rhyolite eruptions are rare, but that poses a scientific problem – they have not been as well studied as more common magmatic phenomena. Until May 2008 the latest rhyolite eruption had been in Alaska during 1912. In 2008 the Chilean volcano Chaitén erupted for the first time in 9 thousand years. There was no warning. Andesitic and dacitic volcanoes are restless for months before an eruption, though that is not much comfort as exactly when they ‘go off’ is still unpredictable. But any warning helps prepare local populations for the worst. A volcanoes precursory rumblings and shakings reflect the slow upward movement of magma. In the case of Chaitén, magma rose at about 1 m s^-1 that flabbergasted the volcanologists who rushed to study such a rare event (Castro, J.M. & Dingwell, D.B. 2009. Rapid ascent of rhyolitic magma at Chaitén volcano, Chile. Nature, v. 461, p. 780-783). The magma rose 5 km from its source in less than 4 hours. It is generally thought that the more silicic magma is, the more viscous and sluggish, which is certainly the case for rhyolite when it emerges: the melting of impurities in a coal fire produces a very silica-rich melt but such slag certainly does not dribble out of the fire box to pool on the hearth. High viscosity allows an erupting magma to retain gas escaping from solution as pressure drops, which is the source of the catastrophic blasts of massive ignimbrite events. Below the surface the Chaitén magma behaved in an extremely fluid manner, perhaps because it contained so much dissolved gas that it became a fluid froth at quite shallow depth. This unique observation is deeply disturbing for populations living in areas blanketed by ancient ignimbrites, as in the Andes. The very worst terrestrial events imaginable are ignimbrite eruptions that can blast out at such high velocities as to groove the ground and carry over thousands of km² in matter of minutes. Without warning, there is no escape.

Wenchuan earthquake (May 2008) analysed

On 12 May 2008 a magnitude 7.90 earthquake killed more than 80 thousand people and left many more injured and homeless in the Wenchuan area of Sichuan province China. In the worst affected areas up to 60% of the population were killed. The catastrophe occurred at the densely populated western boundary of the Sichuan basin with the Tibetan Plateau, and involved surface displacement that propagated rapidly north-eastwards along a 235 km long zone. There was virtually no warning sign and although crossed by major faults, high-magnitude seismicity was a rarity in the area. Several satellites now repeatedly deploy synthetic aperture radar sensing along their ground swath, so that interferometric methods (InSAR) are able to assess ground motions between separate times of overpass, with sub-centimetre precision. Together with direct measurement of motions at GPS ground stations, InSAR allows an unprecedented ‘post-mortem’ of this dreadful event (Shen, Z-K et al. 2009. Slip maxima at fault junctions and rupturing of barriers during the 2008 Wenchauan earthquake. Nature Geoscience, v. 2, p. 718-724). The structural architecture of the surrounding area is of five fault-bounded blocks that jostled during the event, resulting in profound shifts in the geometry of motion along two parallel faults that ruptured. The event was so sudden and large because what would otherwise have been barriers to propagation of strain failed at the same time. All the strain cascaded through several fault segments. This is not a scenario that could have been easily predicted, the authors judging it to have been a once-in-4000 years concatenation of crustal failure.

Seismic unpredictability is something that seismologists now recognise (Chui, G. 2009. Shaking up earthquake theory. Nature, v. 461, p. 870-872). Active faults turn out not to be ‘creatures of habit’, and nor can we assume that long-quiet segments are the most likely to fail in future. Ominously, there is a growing body of evidence that great earthquakes are able somehow to trigger others, often far distant. An example is the giant Sumatra-Andaman event of 26 December 2004, tsunamis from which caused a toll of hundreds of thousand lives around the Indian Ocean. It was followed quickly by swarms of small tremors on the San Andreas Fault 8000 km away. Rapid successions of great earthquakes around the world, such as the October 2005 Pakistan earthquake 9 months after that in the Indonesian area, can no longer be regarded as ‘bad luck’. Seismic waves are able to weaken far-off segments of active faults.

All forms of asbestos (various serpentines and some amphiboles), but especially the blue variety, are carcinogenic because their dusts consist of minute fibres. Most publicity about the hazard that this mineral presents is from cases that stem from its use as an insulator in housing, shipbuilding and other constructions in developed countries. Areas where it has been mined or outcrops naturally are equally risky if wind can pick up asbestos dust under dry conditions. A large proportion of this now banned industrial mineral was mined in South Africa and many cases of asbestosis and mesothelioma in former mining areas have come to light there since the fall of apartheid. The locations of former asbestos mines are well known, and some attempts are being made to bury the waste. The most tragic cases are where the mining companies have either folded or been engulfed by larger transnational corporations; several legal actions for compensation have been dragging through the courts for a decade or more. However, asbestos minerals are common at what were non-commercial levels in many ultramafic rocks. Such rocks occur in ophiolite complexes and Archaean greenstone belts on every continent, and although ultramafics are in a minority as regards rock outcroppings, they are far from rare. In its natural state such land can shed asbestos-rich dust when dry, and urban and communications developments expose the material to wind action.

Asbestos minerals fortunately have distinctive infrared spectra in the short-wave infrared (SWIR), preferentially absorbing photons at around 2.3 micrometres because of their abundance of magnesium-oxygen bonds that such wavelengths cause to vibrate. Remote sensing is therefore a potentially useful means of screening areas of human habitation for asbestos risks (Swayze, G.A. et al. 2009. Mapping potentially asbestos-bearing rocks using imaging spectroscopy. Geology, v. 37, p. 763-766). The authors, from the US geological Survey and the California Department of Conservation, used a sophisticated and costly form of aerial remote sensing that covers the visible and infrared part of the EM spectrum with hundreds of narrow-wavelength bands: so-called hyperspectral imaging. It is possible to highlight areas containing asbestos minerals by matching the measured and mapped surface spectra with laboratory standard spectra of the pure minerals. In the case of the test area in northern California, where suburban expansion is likely to occur or has done already, the geology is known in some detail and the expensive airborne hyperspectral surveys could be focused. The approach gave results sufficiently accurate for preventive measure to be taken; not only for asbestos-rich bare soils, but also the specific kind of vegetation that ultramafic soils encourage.

There is another, far cheaper means of assessing asbestos risks that is not so accurate, but capable of covering very large areas of poorly known geology, especially in less well-off parts of the world. This uses the satellite remote sensing conducted by the US-Japanese ASTER instrument carried on NASA’s Terra satellite. ASTER data include 5 narrow wavebands that bracket the 2.3-micrometre part of SWIR, so that it is capable of assessing the distribution of ultramafic rock outcrops using software similar to that for hyperspectral data. The USGS/California DoC survey could have tested ASTER data to see how effective it would be if more costly airborne data was unaffordable. Sadly the team didn’t foresee how a local test of concept might benefit a great many areas elsewhere by using an ASTER scene that would cover their entire study area, be free to USGS scientists and cost only US$85 for anyone working in the Third World.

Nuclear waste: planning blight writ large

The artificial radioactive isotopes generated in nuclear fission reactors have half lives that range from days (¹³¹I) to a few million years (¹³⁵Cs). They pose a thorny problem for disposal since the radiation that they emit collectively is likely to reach ‘safe’ levels only after tens to hundreds of thousand years, even if they were diluted by leakage into air or water or onto the land surface. They have to be contained, and that demands storage in rock. More over, underground disposal sites must ensure no leakage for geologically significant periods – a great many rare events, such as magnitude 9 earthquakes, large volcanic upheavals and rapid climate changes all become increasing likely the longer the delay time. Apart from Sweden and Finland, no country that uses nuclear energy has a deep disposal site. The focus has been on the temporary measure of reprocessing, and one major facility, that at Sellafield in the UK, is to close down.

In 1987 the US Congress designated only one potential site for investigation as a place for long term water storage in their vast, geologically diverse country: Yucca Mountain in Nevada. The reasoning was that the area is remote and arid, and not so far away from highly secure military sites, so it could be guarded unobtrusively. After 30 years of investigation, Yucca Mountain has been abandoned, with no equally-well researched fallback site (Ewing, R.C. & von Hippel, F.N. 2009. Nuclear waste management in the United States – starting over. Science, v. 325, 151-152). From a geological standpoint, that is not so surprising as Nevada is seismically active; there has been volcanism in the not-so-distant past, it does have groundwater, and that is present in the volcanic ash proposed for storage. Moreover, the water is oxidising and uranium in spent nuclear fuel easily dissolves under those conditions – storage was to be in titanium casks. Clay saturated in anoxic water is a better bet, while the Scandinavian approach seems safer still: galleries and boreholes in dry crystalline basement rock with canisters packed in clay.

Yucca Mountain has been wrangled over for 3 decades, and one component in its abandonment was a change in the proposed ‘regulatory period’ from 10 thousand to a million years. How compliance might be demonstrated for a period five time longer than our species has existed, and 500 time longer than the length of the Industrial Revolution is something of a problem for bureaucrats, as of course is judging the cost and time for decommissioning obsolescent nuclear plant. If nuclear energy is to play any role in cutting carbon emissions, the volume of nuclear waste is set to rise enormously, but this does not seem to concentrate the regulatory group mind wonderfully.

See also: Wald, M.L. 2009. What now for nuclear waste? Scientific American, v. 301 (August 2009), p. 40-47.

Methane: the dilemma of Lake Kivu

A massive discharge of carbon dioxide from the small but deep Lake Nyos in Cameroon in 1986 killed 1700 local people after a small earthquake and landslide disturbed the bottom water.  The lake is stagnant, and carbon dioxide released by exhalation from deep magma chambers beneath it had dissolved under pressure in in deepest levels. Once disturbed, the gas came out of solution to reduce bottom water density so a large volume rose to blurt out gas and deal silent death in the lake’s immediate surroundings.

Lake Kivu in the western branch of the East African Rift system borders the Democratic Republic of Congo (DRC) and Rwanda. With an area of 2700 km² and a depth of over 400 m it is far larger than Lake Nyos, but similar in having stagnant water below a depth of about 75 m, in which gases are dissolved under pressure. Lake Kivu contains an estimated 256 km³ of carbon dioxide derived from magmas beneath the Rift and 65 km³ of methane that probably arises by anoxic bacterial reduction of the CO₂. Cores into Lake Kivu’s sedimentary floor indicate massive biological die-offs at roughly millennial intervals, which probably result from magmatic destabilisation of the gas-rich lower waters. Experimental vent pipes have been installed in Lake Nyos and nearby Lake Monoun to remove gas from the deep water (see Taming Lake Nyos, Cameroon and Letting Cameroon’s soda-pop lakes go flat in EPN issues for April 2001 and March 2003, respectively), but such a solution for the much larger Lake Kivu would be far less predictable and extremely expensive (Nayar, A. 2009. A lakeful of trouble. Nature, v. 460, p. 321-323). Energy companies based in DRC and Rwanda are now starting to use the ‘soda siphon’ approach that relieved Cameroon’s deadly lakes to capture the methane potential in Lake Kivu. Perhaps that will dampen down the lake’s potential for explosive gas surges, but no one knows if it could instead destabilise its uneasy equilibrium. Furthermore, the deep cool water is nutrient rich and may set off planktonic blooms in Lake Kivu’s surface waters. DRC is notorious for bandit mining and politics and security even more unstable than the lake that it shares with its tiny neighbour Rwanda. Population density on the lake’s shore, always high because of the fisheries and agricultural potential, rose explosively in the aftermath of the Rwandan genocide of 1994.

An option much touted as a means of having our cake (power stations fired by fossil fuels, especially coal) and eating it (escaping runaway global warming while enjoying a high-energy lifestyle) is extracting carbon dioxide from flue gases, or even the atmosphere itself, and safely disposing of it in long-term storage. Carbon capture and storage (CCS) is not a well-tried technology. Yet some authorities claim it is at the least a means of ‘tiding-over’ an economy that depends to such a degree on fossil carbon burning as an energy source that it seems unlikely that alternative, carbon-neutral sources can be deployed in time to stave off increasingly awful and plausible climate and thereby social scenarios. There are others who are convinced that CCS is merely an excuse to continue with ‘business as usual’, and therefore fraught with dangers. Whichever, there are elements of CCS that do concern geoscientists, such as where should it be stored and in what form. Leaving aside some of the geological issues of storage, such as depleted natural petroleum fields or deep aquifers, what happens to CO₂ at depth? There are five possibilities: it remains as a gas; under high pressure it may take on liquid form (CO₂ can exist only as gas or ‘dry ice’ at atmospheric pressure); it reacts with the rock itself to form some kind of carbonate; under moderate pressure and low temperature it may combine with water to form a gas-hydrate ‘ice’, as does methane; or it may dissolve in water under high pressure.

The ideal form for long-term storage would be in the form of solid carbonate, but that demands bicarbonate ions combining with calcium, magnesium or perhaps sodium ions. One possibility is through dissolution in highly saline groundwater. The chemical reactions are not complex, but depend on the solubility of carbonates being exceeded because of massive increases in bicarbonate concentrations. However, experiments have had little success. Another means of solid storage is by the combination of atmospheric CO₂ with calcium hydroxide to form calcium carbonate, which is what happens when lime plaster slowly ‘cures’. The downside is that the only means of making Ca(OH)₂ is by kilning limestone: no free lunch there. To cut a long story short, a view is emerging that CO₂ pumped, in whatever form, into wet rock will end up dissolving in groundwater, to form vast quantities of ‘sparkling’ water, or ‘soda pop’ (Gilfillan, S.M.V. and 10 others 2009. Solubility trapping in formation water as dominant CO₂ sink in natural gas fields. Nature, v. 458, p. 614-618). The British, Canadian, US and Chinese team investigated nine natural gas fields in which CO₂ is present as well as petroleum gas, using noble gases and carbon isotopes as tracers of the chemical fate of the natural CO₂ as the reservoir rocks filled with oil and natural gas during maturation. They discovered that the bulk of CO₂ ended up dissolving to form a weakly acidic water under pressure. This is a recipe for filling huge analogies of soda siphons. They did discover that some CO₂ ended up as solid carbonate, but no more than 15%. As those who add Perrier or Volvic to their Scotch should know, carbonated springs are not unknown. Consequently, CCS that uses confined aquifers poses the danger of eventual leakage, whether CO₂ is stored as gas, liquid or in solution. Petroleum geologists often claim that no trap is leak proof, and extensive areas of gas leakage are known over most oil fields; they are an important sign for explorationists, if they can be detected. The other issue is that fans of CCS set much store in re-use of depleted commercial oil and gas fields for sequestration. Such fields have already been depressurised, and nobody knows whether or not they were leaky to gas and water.

See also: Aeschbach-Hertig, W. 2009. Clean coal and sparkling water. Nature, v. 458, p. 583-4.

Shortly before the start of the Younger Dryas cold period, around 12.9 ka, the Palaeoindian Clovis culture of North America seems to have come to an abrupt halt. The North American mammoths on which the Clovis people preyed also disappear from the fossil record. Some folk reckon that early immigrants from NE Asia devoured the last of the mammoths, as they ate their way through two continents en route to Tierra del Fuego. Equally imaginative scientists have been suggesting since 2007 that an extraterrestrial cataclysm was responsible for climate change and the demise of both mammoths and the Clovis people (see Whizz-bang view of Younger Dryas and Impact cause for Younger Dryas draws flak in EPN July 2007 and May 2008). Evidence found just beneath a sediment layer that marks the outset of the Younger Dryas included: excess iridium; tiny spherules; fullerenes containing extraterrestrial helium; nanodiamonds and evidence for huge wildfires. Neither crater nor shocked mineral grains have been found, and the proponents of this controversial idea have opted for a cometary airburst as culprit – an impact would have produced shocked debris. The authors have had a ‘bad press’, but remain undeterred and have published photomicrographs of diamonds in minute spherules made of amorphous carbon (Kennett, D.J. and 8 others 2009. Nanodiamonds in the Younger Dryas boundary sediment layer. Science, v. 323, p. 94). There is a problem or two with the hypothesis: mammoths, albeit little ones, lived on Wrangel Island in the Arctic Ocean until 1650 BC; had some kind of cosmic encounter in North America set global cooling in motion at 12.9 ka, then the best place to look for evidence would be in the Greenland ice cores, in which diamonds have yet to be found. No-one doubts that diamonds do occur in the sediments formed just before the Younger Dryas, but experts don’t accept them as irrefutable evidence for impacts (Kerr, R.A. 2009. Did the mammoth slayer leave a diamond calling card? Science, v. 323, p. 26). But the plot thickens. A Belgian and German team has discovered that forest topsoils, grasslands and swamps, no more than a few thousand years old, from 70 sites across Europe also contain nanodiamonds. Although one member of that team reportedly has no idea where they came from, a website (http://www.chiemgau-impact.com/) hints that a very young (2500 years) impact site in Bavaria may be the source. While the end-Clovis diamonds may not have triggered global cooling and killed off mammoths, they could well set off a research line aimed at documenting hazardous extraterrestrial events of the recent past and puzzling occurrences in the archaeological record.

See also: Herd, C.D.K et al. 2009. Anatomy of a young impact event in central Alberta, Canada: Prospects for the missing Holocene impact record. Geology, v. 36, p. 955-958.

Chinese dam implicated in the 2008 Sichuan great earthquake

Four years after the completion of the Koyna Dam in India’s Maharashtra State in 1963, the surrounding area experienced a magnitude 6.5 earthquake. Because the region is free of active tectonics, the earthquake was a surprise. The possibility that it could be linked to filling of the reservoir behind the Koyna Dam became a proven fact when the region subsequently became plagued by minor seismicity. In the immediate aftermath of the magnitude 7.9 Wenchuan earthquake in Sichuan, China on 12 May 2008, which killed 80 thousand people, there were alarms about the possible failure of weakened dams and lakes blocked by landslides in the Longmen Shan mountains. But now suspicion has fallen on the earthquake having been caused by the load that filling a new reservoir created only 5 km from the epicentre and 500 m from the fault that failed during the disaster (Kerr, R.A. & Stone, R. 2009. A human trigger for the great quake of Sichuan? Science, v. 323, p. 322). Calculations of the stress from this loading suggest that it was 25 times that of the tectonic stresses in the region.

Since the awful discovery in the 1980s that millions of people in the delta plains of the northern Indian subcontinent were at risk of chronic arsenic poisoning if they drank water drawn from wells in alluvium, that hazard has been found to exist in other alluvial areas close to sea level. The arsenic is of natural origin and is released when iron hydroxide, the most common sediment colorant and powerful medium for adsorption of many elements including arsenic, breaks down. Iron hydroxide is destabilised in strongly reducing environments, when its component Fe³⁺ gains an electron to become soluble Fe²⁺. The most common source of reducing conditions is vegetation buried in alluvial sediments. In Bangladesh and West Bengal, India, the problem is peat layers buried by rapid sedimentation since about 7 thousand years ago that filled channels cut by rivers when sea level was much lower during the ast glacial maximum. The risky areas in the Mekong Delta are more complex (Papacostas, N.C. et al. 2008. Geomorphic controls on groundwater arsenic distribution in the Mekong River Delta, Cambodia. Geology, v. 36, p. 891-894). Areas at risk are strongly focused by recent landforms associated with channel migration, rather than extending across entire flood plains as in Bangladesh. Features such as meander scrolls, point bars and islands that have grown to be incorporated in older floodplains show the highest arsenic concentration in groundwater. These accumulate organic debris in large amounts, whose decay releases arsenic from iron hydroxide veneers on sand grains. Older features of the same kinds show less arsenic contamination in their groundwater, suggesting that eventually either the reductants become exhausted or available arsenic is flushed out. So, careful mapping and dating of fluviatile geomorphology may be a means of screening for arsenic risk in the Mekong and other low-lying delta plains.

Since the Indian Ocean disaster of 26 December 2004, coastal areas world wide are increasingly examined for signs of past tsunamis. Much the most common focus is on large boulders on low-relief shorelines never subject to glaciation. On the Bahamas large blocks of coral scattered above sea level suggest past tsunamis perhaps caused by collapse of volcanoes on Atlantic islands such as the Canaries or Azores. Yet, ordinary storm waves, if focused by coastal inlets can literally blast large boulders from well-jointed outcrops and carry them hundreds of metres inland. So peculiar boulders on a coast do not necessarily show that a tsunami once struck, although many around the shores of eastern Britain may well have been dislodged by tsunami triggered by a submarine landslide off western Norway about 7 thousand years ago. In an attempt to get more reliable signs of past tsunamis, the devastated coasts of northern Sumatra and western Thailand have been searched for tangible signs of the 2004 event (Monecke, K. et al. 2008. A 1,000-year sediment record of tsunami recurrence in northern Sumatra. Nature, v. 455, p. 1232-1234. Jankaew, K. et al. 2008. Medieval forewarning of the 2004 Indian Ocean tsunami in Thailand. Nature, v. 455, p. 1228-1231).

Both teams homed in on boggy depressions or swales between fossil beach ridges on broad low-lying shores. There, debris carried by the huge 2004 waves could be trapped and then preserved by regrowth of vegetation. The generally low energy in the swales is also likely to prevent erosion, so that deep superficial sediment can build up that may preserve signs of past tsunamis. This focus paid dividends, in the form of coarse sand just beneath a regrown vegetation mat, with distinctive signs that the sand had been deposited by transport from the seaward side of swales. Coring and trenching then unearthed deeper, older sands with exactly the same structure. The surprise was the antiquity of the tsunami sands: layers carbon-dated around 1300-1400, 780-990 AD and 250 BC. Clearly, more extensive surveys of this kind are necessary wherever coastal conditions permit good preservation. That would give an idea of the periodicity of earthquakes and landslips energetic enough to produce coastal catastrophes around major ocean basins. Yet there is a danger: if, as suggested by the Thai and Indonesia data, several centuries have lapsed between such dreadful events, it presents an excuse not to install costly monitoring devices or permanently shift coastal townships to foretell or prevent future disasters.

See also: Bondevik, S. 2008. The sands of tsunami time. Nature, v. 455, p. 1183-1184.

Chinese PM is a geo

Like me, many EPN readers may have admired the swift, effective and open response of the government of the People’s Republic of China to the Szechuan earthquake disaster in May 2008. They may also be surprised to learn that Wen Jiabao, the prime minister of the PRC, is geologist who worked for 14 years with a provincial geological survey. To read an abbreviated transcript of a dialogue between the editor of Science and Wen Jiabao was refreshing, and quite probably unique in a world where most senior politicians are, to say the least, not science-savvy (Alberts, B. & Jiabao, W. 2008. China’s scientist premier Q&A. Science, v. 322, p. 362-364; full transcript at www.sciencemag.org/cgi/content/full/322/5900/362/DC1).

Millions of people in Bangladesh and West Bengal have unwittingly drunk groundwater that is contaminated with arsenic as a result of natural processes for up to 20 years. They are potential victims of the greatest mass poisoning in human history. Dreadful as the possible fate awaiting them might be – they may develop various cancers – discovery and ten years of research into their problems has alerted geoscientists to the hazard of environments like those in which they live. That arsenic poses great dangers is common knowledge, but until unmistakable signs of arsenic poisoning appeared there (black wart- and mole-like skin lesions), the hazard was thought to be restricted to former mining areas where oxidation of iron sulfides released the traces of arsenic locked within those minerals. From studies in West Bengal and Bangladesh has emerged a cause that was completely unexpected: it involves one of the commonest minerals at the Earth’s surface, goethite or FeOOH. This yellow-brown colorant of many sediments has the remarkable property of being able to adsorb or ‘mop-up’ a large range of elements dissolved in water with which it comes into contact. Among these is arsenic. In the oxidising conditions that sponsor the formation of goethite as a coating on sedimentary grains the mineral actually prevents a great deal of natural, geochemical pollution. Yet, exposed to reducing conditions, commonly developed when buried organic material begins to rot, goethite may dissolve and release its potentially toxic load into groundwater. This is precisely the source of arsenic at levels more than 100 times the safe level in some wells on the Ganges-Brahmaputra plains. The story does not stop there, however.

When sea level stood about 130 m lower than now, at the last glacial maximum, rivers rising in the Himalaya cut deep valleys in the coastal areas. As sea-levels rose these rapidly filled with new sediments, most of which were stained with goethite. But they were interbedded with thick organic-rich peats that formed during periods of slow sea-level rise. It is the peats and more finely dispersed vegetable matter that caused the reduction and solution of goethite, and thus the arsenic that it carried. Especially high arsenic levels develop in sediments derived from specific areas in the Himalaya. So a suite of conditions conducive to arsenic hazard have emerged from unravelling the tragedy of the northern plains of the Indian subcontinent. It is possible to use that suite as a means of predicting other risky areas, one of the first to be revealed being in the Red River delta of northern Vietnam: the population of Hanoi is at risk from well water drawn from the Red River sands and gravels. Systematic computer screening of known geology, topography and soil conditions in Southeast Asia is beginning to throw up other problematic areas (Winkel, L. et al. 2008. Predicting groundwater arsenic contamination in Southeast Asia from surface parameters. Nature Geoscience, v. 1, p. 536-542) where concentrations of arsenic in drinking water are highly likely to exceed the maximum recommended level of 10 μg l^-1 (parts per billion). The pilot study highlights the known areas, but also the deltas of Mekong River in Cambodia and southern Vietnam, the Irrawaddy in Burma (Myanmar) and the Chao Phraya basin of Thailand. Hopefully, geochemical testing will reveal in details which wells are at risk and which are not, in these three regions: it would be easy to reject perfectly safe groundwater that often occurs close to contaminated areas, as found in Bangladesh, without careful testing. The implicated mineral, goethite, is itself a cheap and abundant means of remediation if contaminated water is passed through goethite-rich filters. But the large areas at risk in SE Asia, together with others discovered by epidemiologists in northwestern India, the Indus plains of Pakistan and in Mongolia, create a chilling scenario for many other populous, sediment-rich areas elsewhere. Winkel et al’s approach surely needs to be refined and applied globally.

See also: Polizzotto, M.L. et al. 2008. Near-surface wetland sediments as a source of arsenic release to ground water in Asia. Nature, v. 454, p. 505-508. Harvey, C.F 2008. Poisoned waters traced to source. Nature, v. 454, p. 415-416.

Cause of Javan mud volcano

Since May 2006 the largely urban Sidoarjo area of eastern Java has been plagued by continuous eruption of hot mud and steam from a vent that suddenly appeared. Around 7 km² have been buried by up to 20 m of noxious mud, giving a total emission of about 0.05 km³ at a rate of 100 thousand m³ per day. Although nobody has been killed, the mud volcano is an economic and social disaster, 30 thousand people having been displaced. The area is one of active petroleum exploration, and locals blame a blow out from a nearby gas exploration well, though scientists and the exploration company point to the eruption having begun a couple of days after a magnitude 6.3 earthquake in the area around the capital Yogyakarta, 250 km away. If the latter, economic losses may be difficult to recover from insurers; if the former, there will be a rare old furore. So, a thorough evaluation of what the cause may have been is welcome (Tingay, M. et al. 2008. Triggering of the Lusi mud volcano: Earthquake versus drilling initiation. Geology, v. 36, p. 639-642). Being a mix of Australian, German and British geologists, the authors have no axe to grind. They consider that seismic influence was highly unlikely, in this case, although many mud volcanoes have formed close to earthquake epicentres in other areas. On the other hand, the well that was being drilled at the time suffered a loss of drilling mud shortly before the volcano began to erupt, suggesting escape to fractures at depth around the well. Moreover, the hole was not cased at depth. The most likely trigger was creating a passageway up the well for high-pressure fluids to escape from the 3 km deep target limestone sequence into shallower unconsolidated clays. They were liquefied and escaped as a lateral blow out

Beneath the Dragon’s Gate (Longmenshan) Mountains of Sichuan Province, China an apparently ‘stuck’ segment of a major fault complex failed on 12 May 2008 (Stone, R. 2008. An unpredictably violent fault. Science, v. 320, p. 1578-1580). Unprecedented access to the world’s media resulted in our exposure to the full horror of the results of major seismic events in mountainous terrain and on habitations, especially schools, whose building standards were unable to withstand ground shaking. &0 thousand souls died, thousands more are still unaccounted for and more than 1.5 million people have become refugees in a country that is rapidly emerging from Third World status. Now that aftershocks have subsided massive threats remain from the many landslide-blocked rivers and fractured dams. Yet we also witnessed enormous mobilisation of the People’s Army within hours of the earthquake and truly heroic attempts to rescue as many trapped people as possible. Without that swift response the casualties would undoubtedly have been worse.

China boasts one of the most sophisticated seismic warning systems outside of California and Japan, deploying robotic seismometers and GPS recorders in the most risky regions, and with a 10-thousand strong Earthquake Administration. Sadly, Chinese seismologists regarded the faults shown to be accumulating displacement most quickly as those most likely to fail. It is generally ‘stuck’ segments that fail catastrophically. China has a long-respected reputation for gathering data generally regarded as ‘non-scientific’, such as well water levels, and animal behaviour, that might give empirical clues to impending earthquakes. The Tangshan earthquake of 28 July 1976, which killed a quarter of a million people 160 km from Beijing, was preceded by reports of shifts in the water table, odd ‘earthlights’ and unusual animal behaviour. Paying serious attention to reports by ordinary people of such oddities is reported to have avoided untold numbers of deaths in the period since Tangshan, but not in the case of Sichuan. Strangely, a Taiwanese weather satellite detected decreased electrical activity in the ionosphere above Sichuan hours before the recent earthquake (see Clouds and large earthquakes in May 2008 issue of EPN). Geophysicists have noted increased emissions of radon in the period immediately preceding some major earthquakes which might conceivably have an effect on the ionosphere. Whatever, prediction of catastrophic earthquakes has had very few successes in terms of lives saved, and the signal lesson from Sichuan, as from that which destroyed the Japanese city of Kobe in 1995, is that building standards in zones of active faulting must take account of the risk of ground movement.

See also: Stone, R. 2008. Landslide, flooding pose threats as experts survey quake’s impact. Science, v. 320, p. 996-997.

Extraterrestrial impactors

July 2008

June 30, 2008 was the centenary of the mysterious Tunguska event that devastated more than 2000 km2 of forest 1000 km north of Lake Baikal in Siberia at 7 am a hundred years before. Much of the mystery stems from there being no sign of a crater and therefore of the process involved. Speculation about the cause of a massive explosion between 5-10 km above the surface still goes on (Steel, D, 2008. Tunguska at 100. Nature, v. 453, p. 1157-1159). Ideas have ranged over a gamut of high-energy physical processes involved in the explosion: a deuterium-rich, fluffy comet that was ignited as a thermonuclear explosion by hypersonic atmospheric entry; a lump of antimatter; a miniature black hole; explosive release and ignition of natural gas; a ‘Verneshot’, and even an alien space craft involved in an accident. The chances are that the explosion was more mundane, and akin to what occurs inside a diesel engine. Compressive heating of the air in front of a small asteroid or comet travelling at more than 15 km s-1 would generate temperatures around 50 thousand degrees. Flash vaporisation of a small comet or asteroid would add to a massive shock wave at the epicentre, rather than by an intact projectile. It is thought that many small craters, such as Meteor Crater in Arizona, result from impacts by strong metallic asteroids, whereas stony ones or comets easily disintegrate. Whatever, research still goes on at the site, now completely reforested.

The centenary spurred Nature to devote pages 1157-1175 in its 26 June 2008 issue to impact-induced features from Earth and other planets, together with three Letters and two reviews. Topics covered include the search for near-Earth objects and the Spaceguard survey, which is beginning to suggest that humanity can concentrate on global warming for the next century or so, and truly monster impact structures from the Moon and Mars, including evidence for one that may have ‘scalped’ northern Mars. In one of the reviews it is said that a sci-fi novel (Niven, R. & Pournelle, J. 1977. Lucifer’s Hammer. Harper Collins) inspired the Alvarez father-and-son team that first postulated an impact origin for the K-T mass extinction event. The second review is of a highly realistic sculptural depiction of a pope (John Paul II) knocked over by a meteorite: perhaps planetary science’s first involvement, literally, in what some might consider lèse majesté. So, in many ways, quite an event…

See also: Cohen, D. 2008. The day the sky exploded. New Scientist, v. 198, 28 June 2008 issue, p. 38-41.

The press announced in April that the USGS and other western US geoscience institutes had issues the first ever comprehensive earthquake forecast for California (see http://www.scec.org/ucerf/) , but it was cautiously phrased in terms of probabilities of destructive magnitudes (>6.7) over the next 30 years. That might be fine and dandy for administrators and civil engineers, but not so good for anyone who becomes a victim at the precise time this or that Californian fault ‘goes off’. People world-wide have rarely chosen where to live based on knowledge of geological risks; indeed most threatened communities have little choice, for many reasons. What would be useful is being warned that a devastating earthquake is definitely due where one lives, and it will happen sometime in the next few days or weeks. Even an hour’s warning will save many lives. But no geological survey will commit itself to that kind of pronouncement, except perhaps some of the many surveys in China. The fact that all kinds of phenomena, such as nervousness among animals, rising water levels in wells and so-on have been shown to occur shortly before many big earthquakes has prompted a kind of ‘barefoot’ monitoring that is officially co-ordinated in some parts of China. It is said that lives have been saved on a number or recent occasions.

It is easy for western scientists to make the analogy with homeopathy, and pooh-pooh such methodology. Also, there has been a succession of observations from space that could prove useful, such as ‘earth lights’ and magnetic-field fluctuations that accompany some seismic events (see Remote signs of earthquakes in EPN August 2003, Early warning of earthquakes in EPN December 2005). The latest odd, but conceivably useful connection is an association of unusual cloud formations with earthquakes in Iran (Guo, G. & Wang, B. 2008. Cloud anomaly before Iran earthquake. International Journal of Remote Sensing, v. 29, p. 1921-1928). The authors, from Nanyang Normal University in China, scrutinised free, hourly images from the geostationary Meteosat-5 satellite covering the whole of Iran, where seismicity is concentrated on a single large zone of deformation that trends NW-SE through the Zagros mountains. On several dates they found cloud formations parallel to the fault zone. Between 60 to 70 days later large eathquakes took place along the fault, including the highly destructive Bam earthquake of 26 December 2003. Indeed, a noticeable thermal anomaly in clouds directly above Bam occurred 5 days before the disaster.

How often do tsunamis occur?

Fortunately, truly destructive tsunamis on the scale of that of 26 December 2004 are rare events. So much so that nobody has a clear idea of their average frequency at different exposed shorelines; a vital statistic for risk analysis. Tsunamis produce high energy marine deposits, but unless they are preserved in accessible locations their incidence would be difficult to estimate, and they may be confused with tempestites generated by hurricanes. One characteristic of tsunamis is that they are waves that affect the entire ocean volume, unlike wind waves whose effects are restricted to a few tens to hundred of metres, which can create unique features. Canadian, US and Omani sedimentologists have examined a sediment deposited in Oman by a recorded tsunami generated by a large earthquake off Pakistan in 1945 and have discovered one such signature (Donato, S.V et al 2008. Identifying tsunami .deposits using bivalve shell taphonomy.  Geology, v. 36, p. 199-202). The deposit, a coquina rich in bivalve shells, contains an unusually high proportion of still-articulated shells, suggesting that living animals were ripped from the seabed and then flung into a lagoon. Along with oddities in fragmentation of other shells and the sheer size and extent of the coquina, this feature seems to be characteristic of tsunamites. Features in the Oman example closely match those in another on the eastern shore of the Mediterranean Sea in Israel.

In the centenary year of the 1906 San Francisco earthquake a lot of attention has been paid to the northern part of the infamous San Andreas Fault. That avoids the fact the its southerly extension to the south-east of Los Angeles has not ruptured in a devastating way for at least 250 years. Faults break after protracted build-up of elastic strain. Such strains are detectable using data from spaceborne radar systems. These have been available since 1992 from the European Space Agency ERS-1 and ERS-2 satellites. A sequence of data sets provides information about the annual rate of deformation (Fialko Y. 2006. Interseismic strain accumulation and the earthquake potential on the southern San Andreas fault system. Nature, v. 441, p. 968-971). Fialko shows that the parallel San Andreas and San Jacinto faults near the Salton Sea are building up strain at about 3 cm per year, so that about 7 to 10 metres will have accumulated since the last major earthquake in that part of the system. This exceeds the largest known seismic movement on the system, thereby suggesting that Los Angeles is likely to experience a ‘big one’ shortly.

Supervolcanoes

Outside of a major meteorite impact, the greatest danger posed by geological processes is a monster volcanic eruption. As well as the close-by effects of massive debris avalanches and ash falls, explosive eruptions blast sulphur gases into the stratosphere where they reside for a long time as sulphuric acid aerosols. Clouds of these tiny particles reflect a proportion of solar radiation back into space and so cause global cooling. The eruptions of Pinatubo and Krakatau in recent historic times did just that, as have several others with more devastating global effects such as famine. Yet these are tiny compared with eruptions known from the recent geological past that are marked by ash deposits over vast areas. About 71 ka ago, Toba in Indonesia  blasted out a 30 by 100 km caldera and its ash extends across much of south Asia and surrounding ocean floors. Genetic evidence from human Y-chromosomes suggests a massive decline in human numbers at the time, to create an evolutionary bottleneck. This near-extinction may have been connected in some way to eruption of the Toba supervolcano. Such events are a more likely risk than impacts, and a recent review of research into them highlights those that are well-known (Bindeman, I.N. 2006. The secrets of supervolcanoes. Scientific American, v. 294 (June 2006 issue), p. 26-33). The western USA has two potential threats: calderas in Yellowstone National Park and Long Valley. Between 760 and 640 ka both exploded to blanket the whole southern USA and northern Mexico with around 1000 cubic kilometres of ash. Bindeman’s own research sheds light on the details of magma evolution during such eruptions using isotopic signals in zircons contained within ash deposits..

That 18 April was 100 years since the Magnitude 7.9 earthquake that raised San Francisco to the ground and killed more than 3000 is no cause for celebration. Yet it focussed seismologists to commemorate the event, as if that was necessary following hard on the heels of two of the most shattering natural events of the last century. In fact San Francisco created the science of seismology, rocking as it did the most vibrant city in the world’s emerging superpower. It brought the San Andreas Fault into common parlance, and research on that huge and structurally odd fracture – one of the largest transcurrent systems on the continent – played a major role in the development of plate tectonics. In the US, a century of attention to seismic hazards has made it, along with Japan, the leader in attempts to forecast earthquakes and subdivide half a continent in terms of seismic risk (see Here is the earthquake forecast in the July 2005 issue of EPN).

The 1906 San Francisco earthquake is reviewed in issues of three generalist journals (Lubick, N. 2006. Breaking new ground. Nature, v. 440, p. 864-865. Holden, C. 2006. Reliving the ‘Frisco quake. Science, v. 312, p. 345. Marshall, J. 100 years on, you’d think San Francisco would be ready. New Scientist, v. 190 15 April 2006, p. 8-11). In each, different graphics show the estimated risk of earthquakes and the degree of seismic hazard in relation to the many large faults in California. Yet the Sumatra-Andaman earthquake that set the Indian Ocean tsunamis in motion on 26 December 2004, and that in Kashmir in October 2005, between 20 and 40 times more energetic than San Francisco, killed hundreds of times more people and devastated the lives of millions more. As well as more widely deploying well-known, sensible and moderate-cost measures to build and site habitations more safely as regards the shaking effects of seismic waves, a great deal is left to learn about the global nature of earthquake hazard. A first step is better understanding the actual processes to which great earthquakes are related, and lessons are beginning to stem from the research on the Sunda subduction zone, whose movement unleashed terror around the entire Indian Ocean (Briggs, R.W. and 13 others 2006. Deformation and slip along the Sunda megathrust in the great 2005 Nias-Simeulue earthquake. Science, v. 311, p. 1897-1901). The Nias earthquake involved failure of the Sunda subduction zone in a 400 km gap between that affected by the Sumtra-Andaman event of 2004 and a stretch further to the SE that had three great earthquakes between 1797 to 2000; i.e. a previously quieter sector had succumbed to tectonic forces. That emerged from seismic analysis at the University of Ulster (see Yet more Indian Ocean earthquakes? Sadly, yes in the April 2005 issue of EPN). Briggs et al. examined hundreds of patches of coral reef around the islands of Nias and Simeulue, using preciseGPS measurements of the elevation of coral heads that had been uplifted and killed by exposure to the air. Their results show that uplift was as high as 3 metres with some areas subsiding by around a metre, but the total movement by thrusting beneath the islands was of the order of 11 metres.

Indian analytical chemist Dipankar Chakraborti of Jadvapur University, Kolkata was born and raised in one of West Bengal’s many small villages on the delta plains of the Ganges. Paying a visit to a friend’s village in 1988, he found people bearing visible symptoms of chronic arsenic poisoning, which had not been diagnosed before. Analysing samples of well water, Chakraborti found extremely high levels of the poisonous element. For years he was reviled by government agencies who paid no heed to his discovery, calling him a ‘panic monger’ – when more recently showing that Bihar and Assam had similar problems he received death threats. Almost single-handed he campaigned for attention to the undoubted problem, until in the mid 1990s it became clear that arsenic in drinking water from recently sunk wells was a plague of biblical proportions across low-lying West Bengal and neighbouring Bangladesh.

Massive funding, both for establishing the extent and distribution of the contamination and for installing means of removing arsenic from well water, flowed form a host of international donors and agencies. To the outside world it has seemed that the tragedy was being remedied by hugely qualified teams of international scientists, and would eventually be held in check. As revealed in a recent interview (Pearce, F & Chakraborti, D. 2006. Drinking at the west’s toxic well. New Scientist, 1 April 2006 issue, p. 48-49), Chakraborti believes that intervention at national and international levels is doing far less than claimed, even exacerbating the problem by pouring in remedial filtration units without teaching villagers to maintain them. Locals’ are encouraged to trust the remedies, yet continue to drink highly contaminated water once the units clog with silts.

Timely review of nuclear waste disposal

The grand old man of biogeochemistry and the Gaia hypothesis, James Lovelock, seems to have lost patience with life’s ability – and that of alternative energy resources – to keep the Earth system in balance. His view that global warming is past the point of no return as regards ‘green’ remedies has been widely publicised in recent months: he has come out in favour of an increase in the contribution of energy by nuclear reactors. He may have fallen out with many environmentalists, but may also have become an ally of politicians who are looking to nuclear power as a way of maintaining ‘business as usual’ yet putting their money where their mouths are, as regards reducing carbon emissions.  Nuclear power may yet have a resurgence, but that would pose again the thorny problem of secure disposal of radioactive wastes. Sweden supplies almost 50% of its electricity using eleven nuclear power stations: the highest number per capita anywhere, despite the country’s otherwise ‘green’ outlook. Should nuclear power rise rapidly elsewhere, then Sweden’s approach to waste disposal may well become a model to follow.  What that system is summarised in a recent issue of New Scientist (Nielsen, R.H 2006. Final resting place. New Scientist, 4 March 2006, p. 38-41). Sweden has discovered quite a challenge at its experimental nuclear-waste disposal facility, even though most of the country’s rocks are hard and crystalline, and therefore seemingly ideal for disposal sterilised from the outside world. Despite the common view that crystalline basement is totally impermeable, in reality it is not. Water will be present in any rocks used to cache waste, unless they are beneath almost totally arid deserts, of which only the USA among developed countries has one. It is also becoming increasingly clear that even at great depths, extremophile organisms infest the rock. Among the most common are those that use the reduction of sulfate to sulfide ions as a metabolic energy source: they produce sulphuric acid. That seems a considerable risk to the integrity of whatever form the waste is stored in. The response of the Swedish researchers has been to look for lateral solutions that either kill off the bacteria using clay packing, or exploit the potentially preservative effects of others.

Because earthquakes result ultimately from the relative movement of lithospheric plates, and take the form of various kinds of ground motion it is easy to think of them just in mechanical terms.  However, such movements affect materials that respond in odd ways to motion and friction. One of the most obvious is the sound near a fault zone during an earthquake, which can range from a rumble to a piercing shriek, depending on the near-surface rocks being dragged past each other. There are other, more subtle effects.  For instance, if grains of quartz or dolomite are rubbed against one another they glow – a nice piece of natural magic for the dark days of winter.  There have been many reports of so-called ‘Earth lights’ along active fault zones before and during earthquakes, and they might result from this piezoluminescence. Rocks differ in their ability to conduct electricity, but Faraday’s laws of electromagnetism show that if a conductor is moved in a magnetic field, currents flow through it; the principle behind electricity generation.  In turn, motion in a magnetic field of a conductor in which electricity flows generates electromagnetic radiation, whose frequency depends on the rate of motion. Electromagnetic effects may also result from build-up of electrical charge derived from minerals in the crust, or from crushing of magnetic minerals. Along with even less well understood phenomena, such as the rise and fall of water levels and various gas discharges in wells, and animal behaviour, physical changes are potential means of earthquake warning, if they can be detected and properly understood, that could supplement and even supersede conventional approaches to early warning.

Minoru Tsutsui of the Kyoto Sangyo University in Japan has concentrated on the EM radiation known to precede earthquakes (Tsutsui, M. 2005. Identification of earthquake epicentre from measurements of electromagnetic pulses in the Earth. Geophys. Res. Lett., 32, L20303, doi:10.1029/2005GL023691). Previously published observations have been limited to noting EM pulses before major seismic events. These showed that in some cases nearby areas experienced increased EM noise up to a few months beforehand, to peak a few hours before events. The radiation is at very low frequencies, i.e. wavelengths are much longer than normal radio waves. Such ultra-low frequency (ULF) radiation passes extremely efficiently through rock, and ULF has been used for secret communications between submarines and their bases, as it passes through the whole Earth. In the context of seismic prediction, detecting ULF changes is not enough: the object is to predict the position of an earthquake’s focus as well as its timing. Tsutsui has developed a means of finding the direction in which ULF radiation moves, which has been calibrated using the ULF from lightning strikes and the position of the thunder clouds found using weather radar systems. A strong ULF EM pulse that accompanied a magnitude 5.5 earthquake, whose epicentre was known from studies of seismograph records, enabled the Kyoto team to try out their method.  It succeeded in accurately pinpointing the epicentre, thereby proving that ULF radiation is generated at the site of earth movements. But that is not sufficient to provide a warning system. The equipment and data analysis have to be refined and continually tested to detect and use ULF noise long before events, to see whether or not these preceding signals point to future epicentres.

As Charles Darwin noted in Voyage of the Beagle, following his experience of a major earthquake in Chile, nothing is more frightening than the unexpected movement of the ground on which one stands. Every victim of an earthquake suffers post-traumatic stress disorder, whether or not they are injured or lose people close to them – we all implicitly trust solidity. Yet many survive physically because they instinctively seek some kind of shelter; perhaps one advantage of panic in the face of such a sudden threat.  How much warning is needed in order to act according to a learned plan, in the manner of following a fire drill?  Would say 20 seconds be enough? With even such a short warning, automated shut-down mechanisms for gas supplies – much damage and fatality is caused by fires in the aftermath of earthquakes – and activation of road and rail warnings would be possible.  It would also enable people to escape from small buildings or to seek shelter in larger ones, given an ‘earthquake drill’, and an audible alert, such as a siren.

During research into the way in which faults rupture, based on seismograms of events of all detectable magnitudes, Erik Olson and Richard Allen of the University of Wisconsin, USA, made a potentially useful discovery (Olson, E.L. & Allen, R.M. 2005. The deterministic nature of earthquake rupture. Nature, v. 438, p, 212-215). Previously, the most widely held view was that the magnitude of an earthquake could not be calculated until all its energy had been released. Indeed, the magnitudes of the events that caused the 26 December 2004 Indian Ocean tsunamis and the massive loss of life in Kashmir and northern Pakistan in October 2005 were not calculated until hours afterwards. Olson and Allen found that the energy delivered by the first arrivals of fast seismic P waves correlated closely with the total energy of the full event, i.e. with its magnitude. The key to this finding was their analysis of the frequency of the early P waves, which show sufficiently good correlation with final magnitude for useful prediction of the most damaging events. P waves arrive around 20 to 30 seconds before the most energetic but slower surface waves, and they are rarely noticeable. If frequency analysis of the kind used by the authors were to be systematised at seismic stations, automatic warnings could be generated.  They would not be false alarms because they are based on actual seismicity, although imprecision might mean that some alarms were followed by smaller earthquakes than the theory predicts.

See also: Tata, P. 2005. Can Earth’s seismic radio help predict quakes? New Scientist, 19 November 2005, p.28-29.

 

The Boxing Day 2004 Indian Ocean tsunamis were recorded by tidal gauges across the planet, both as amplitude and time of arrival. Armed with such calibrating data, detailed ocean-floor bathymetry and means of modelling wave propagation, oceanographers and geophysicists from the US, Canada and Russia have been able to estimate just how the terrible waves travelled the globe (Titov, V. et al. 2005. The global reach of the 26 December 2004 Sumatra tsunami. Science, v. 309, p. 2045-2048). Highlighting their article wonderfully is a colour-coded map that shows offshore amplitude and arrival time for the world’s oceans and shores. Its most fascinating feature is the manner in which the worst of the disturbance was guided by ocean-ridge systems, principally the Ninety-East and Southwest Indian Ridges, but also the mid-Atlantic Ridge. That is of no comfort to the survivors of the disasters around the Bay of Bengal, although the Irriwaddy delta in Myanmar was spared by the influence of the northern part of the Ninety East Ridge. That Madagascar and East Africa, except for northern Somalia, suffered far less than anticipated is thanks to the peculiar effect of the ridge systems.

The fluoride saga

Archaeological work on Icelandic burial grounds of the 18^th century in the early 21^st century exhumed victims of the Laki eruption of XXXX. Many skeletons bore the distinctive signs of bizarre bone growth that characterises massive ingestion of fluoride ions. The victims had endured prolonged and worsening suffering after exposure to hydrogen fluoride-rich gases that seem to characterise Laki’s effusions. It is a now well-documented geotragedy. Equally well recorded are the lives of Iceland’s early inhabitants from the 8^th century onwards, but in the form of epic prose in Old Norse: the Sagas. Being prone to repeated volcanism, an obvious question is, “Did the Viking heroes experience the same problems?”

One of them was huge, both a righter of injustice and a tidy hand with the battleaxe. Egil Skallagrimsson was ‘a man who caught the eye’, reputedly being awesomely ugly and capable of jerking an eyebrow down to his chin line. Such attributes might seem to have been passed on to the legendary centre-half, ‘Skinner’ Normanton, who graced Barnsley football club in the 1950s. The traditions perhaps, but Egil’s visage was probably a result of chronic fluorosis rather than parentage (Weinstein, P. 2005. Palaeopathology by proxy: the case of Egil’s bones. Journal of Archaeological Science, v. 32, p. 1077-1082). His relatives Hallbjorn Half-troll and Grim Hairy-Cheeks seem from the saga to have been equally afflicted, yet successful. As befits a Viking battler, Egil had a thick skull; when exhumed by descendants in the 12^th century, it was found to be ridged like a scallop shell – the attending priest hit it with the back of an axe, to no avail. Some have inferred abnormal bone growth and deformities due to Paget’s disease, but that tends to produce massive but weak growths, following repeated crumbling of bone. Weinstein’s theory may be verifiable, since Egil’s Saga reveals the final resting place of this enigmatic giant.

Source: Pain, S. 2005. Egil the enigmatic. New Scientist, 17 September 2005, p. 48-49

It is now a decade since the enormity of natural arsenic contamination in groundwater below the great plains of northern India and Bangladesh came to light. In 1995 the World Health Organisation announced that this waterborne arsenic was causing the world’s largest case of mass poisoning. Since then other areas at risk have emerged in East and Central Asia and South America. The tragedy is that groundwater generally presents the safest option for drinking water because sediments filter water and encourage biogenic oxidation that remove common pathogens. That tens of million people in West Bengal and Bangladesh face stealthy poisoning results from channels cut in the low-lying plains during the last glacial maximum being filled rapidly with sediment as sea level rose during climatic recovery. Sedimentation buried large amounts of organic debris to form anoxic conditions in the shallower sediments. Reducing conditions encourage breakdown of the common colorant in sediments, iron hydroxide grain coatings that, having adsorbed most arsenic and other ions from water, releases them when it dissolves. That this should occur was unsuspected during a massive programme of well sinking to relieve endemic ill health from waterborne disease, yet early signs that arsenic had replaced pathogens as a hazard was widely ignored, despite a few warning voices who discovered the unmistakable signs of arsenicosis in the 1980s. They include disfiguring pigmented skin spots and horny growths on hands and feet.

By 1995, the rest of the world took notice, pouring in funds to document occurrences and causes, and to remediate a clearly catastrophic situation. There are three main strategies: to remove arsenic from well water using chemical filters; to return to water from surface sources, though with careful processing to remove pathogens; to sink wells below the level known to encourage arsenic release from iron hydroxide dissolution. For two decades affected populations had been bombarded with encouragement to turn to groundwater: against their better judgement – they termed it the Devil’s water. Once using wells they saw that infant mortality plummeted, so they developed a new enthusiasm for water deemed safe. Caught on the horns of a dilemma, when arsenicosis appeared they were reluctant to return to what appeared to be the greater of two evils. In only a few places were wells deepened to safe depths, and the externally sponsored drive for a solution centred on arsenic removal techniques. Even that was not widespread: of millions of risky wells some 2000 were equipped with arsenic extracting devices, at around US$ 1500 each. It now emerges that the technologies chosen are not doing their intended job (Hossain, M.A. (and 10 others) 2005. Ineffectiveness and Poor Reliability of Arsenic Removal Plants in West Bengal, India. Environmental Science & Technology, v. 39, p. 4300-4306). The team, led by Depankar Chakraborti, who first spoke out about arsenicosis in 1983, tested the efficacy of 18 different devices installed in West Bengal. Only two reduced arsenic levels to the maximum of 50 parts per billion accepted by the Indian government, which is itself five times more than that deemed safe by the WHO. The teams view, supported by the agency that did most to encourage the massive well-driving programme since the 1970s (UNICEF), is that the only realistic solution is a return to rainwater harvesting and purification.

See also: Ball, P. 2005. Arsenic-free water still a pipedream. Nature, v. 436, p. 313.

Legendary events at the Gibraltar Straits

Everyone has heard of Atlantis, but few would care either to point to its former position, or to accept its existence without a shed-full of salt. Nevertheless, no lesser an authority than Plato first described the legend of Atlantis in the 4^th century BC, following verbal accounts that originated in pharaonic Egypt. In the last decade a number of legends, if not their religious connotations, have received scientific support. Foremost among these is that of the biblical Flood, which Ryan and Pitman pursued relentlessly, using the Epic of Gilgamesh as a geographic and chronological guide. They discovered that the Black Sea had catastrophically filled through the Bosphorus once global sea level topped the level of its floor, following glacial melting. Their evidence now includes numerous examples of habitations now inundated by the Black Sea.

As with Ryan and Pitman’s work, one key to resolving a real basis for a legend is carefully puzzling out clues in the most detailed accounts of it. In the case of Atlantis, the clues come from Plato himself (Gutscher, M-A. 2005. Destruction of Atlantis by a great earthquake and tsunami? A geological analysis of the Spartle Bank hypothesis. Geology, v. 33, p. 685-688). Marc-André Gutscher and previous workers focused on Plato’s geographic description of Atlantis, as well as its fate. Plato clearly specified an island in the Atlantic beyond the Straits of Gibraltar, and an earthquake and flood that put paid to the Atlanteans in a single day. Indeed, bathymetry does show well-defined shallows (less than 100 m depth) in such a location, but only about 5 km across. This is the Spartel palaeo-island, on which Gutscher turns his focus. Until the final, decisive rise in sea level after around 12 ka, Spartel would have been a low island. Plato’s account is supported by the existence of a proto subduction zone on the Atlantic sea floor off the Straits of Gibratlar, a major earthquake on which devastated Cadiz in 1755, partly because of a 10 m tsunami. Offshore sediments include turbidites that indicate 8 tsunamis since 12 ka, suggesting a 1500- to 2000-year periodicity of large earthquakes at the entrance to the Mediterranean. Plato’s version of the events includes a rough chronology that suggests a time around 11.6 ka before the present. The thickest of the tsunami-driven turbidites is of roughly that age. Unfortunately for the hypothesis that Spartel was Atlantis, at that time only two tiny islets would have stood above the waves. Seismic destruction of coastal regions by tsunamis is something that might easily become legendary, the more so in the distant past. There is one other possibility that might revive the Spartle hypothesis, demonstrated by the great Indian Ocean tsunami of 26 December 2004. Very powerful earthquakes can also result in massive displacement of the crust, or the order of tens of metres. Spartle might have sunk repeatedly since 11.6 ka, as a result of later events.

Fortunately, the most devastating earthquakes with magnitudes greater than 9 on the Richter Scale occur less than once in a human generation.  Records show that when such strain is released there may be two or more as major faults adjust to the release by the first.  That was the case for the Sumatra-Andaman earthquake (magnitude 9.1 to 9.3) of 24 December 2004 that created the Indian Ocean tsunamis.  On 28 March 2005 it was followed by the magnitude-8.7 Nias earthquake to the south of the movement zone of the earlier event.  Both occurred on the subduction zone that consumes the Indo-Australian plate obliquely, from SW of the Indonesian archipelago through the ocean floor west of the Nicobar and Andaman islands to link with the Himalayan subduction system.  The last seismic event of such magnitude was beneath Alaska in 1964, before modern seismograph development.  How such events propagate could only be guessed at by analogy with lesser earthquakes, so scientific interest in the seismograph records of these two and their analysis has been very high.  The 20 May 2005 issue of Science devotes 22 pages to full accounts of the findings (Hanson, B. 2005.  Learning from natural disasters; and 5 other papers.  Science, v. 308, p. 1125-1146).

The Sumatran-Andaman earthquake involved movements of up to 20 m vertically that lasted about an hour, and thrusting “unzipped” the subduction zone over a length of around 1300 km, proceeding from south to north.  The energy released was equivalent to that of 100 thousand one megaton nuclear explosions, or the energy used in the US in 6 months.  It set up resonances in the entire Earth that are still reverberating, and changed the shape of the crust across a hemisphere by an amount measurable using high-precision GPS monitoring, which has raised global sea level by about 0.1 mm.  Half a globe away, the surface waves from the earthquake triggered several minor shocks in Alaska in exact harmony with their passage.  In social terms, the loss of 300 thousand lives resulted from the displacement of around 30 km³ of sea water by the movement of the faults.  The prolonged event was complex, and one sobering feature is that in the northern part of its propagation it moved slowly, thereby failing to unleash yet more tsunamis: they would have devastated most of the coast of eastern India and the west of Myanmar and Thailand.  Much of what occurred was unpredictable, and quite possibly the lessons learned here may not be directly applicable to future earthquakes of this magnitude, except for one: hazard assessment based on scaling up from lesser events underestimates enormously what actually happens.  What the seismograph data will not do is help warn when similar events will occur elsewhere, with sufficient leeway to take measure that will mitigate effects.

Promising developments for forecasting lesser earthquakes

Although there are many places that are riskier, California is widely regarded as the earthquake capital of the world, mainly because so many people live there with such an economically huge infrastructure.  At any rate, it is indeed the centre for the most advanced seismic forecasting based on far more data that are available for analysis than anywhere else.  Until recently, forecasting was limited to the likely aftershocks following unpredictable large earthquakes.  Seismologists of the US Geological Survey and at ETH in Zurich have developed an advanced modelling system based on the wealth of data (Gerstenberger, M.C. et al. 2005.  Real-time forecasts of tomorrow’s earthquakes in California.  Nature, v. 435, p. 328-331).  Their model allows day-by-day calculation of probabilities for strong shaking (> Mercali Intensity VI), using the way in which seismic events cluster along different faults and monitored lesser movements that might presage a major fault break.  These take the form of extremely graphic maps of hazard across the whole state.  The system has been tested using historic data that preceded historic earthquakes.

The shores of the Indian Ocean and the people who live near them will take years and maybe decades to recover from the awful events of 26 December 2004.  While relief and reconstruction efforts are underway, so too is the scientific analysis of what happened.  Throwing a malevolent shadow is the uncertainty of whether there may yet be more tsunamis so soon after the first in the region for 150 years.  The Sunda trench where the massive earthquake took place had remained stable for a long time.  Stresses built up, eventually to cause the subduction zone to fail catastrophically.  However stress relief in one place redistributes that which remains along other fault lines, and can create space in which new breaks might occur.  Geophysicists from the University of Ulster have analysed the likely disruption of stress in the eastern Indian Ocean (McCloskey, et al. 2005.  Earthquake risk from co-seismic stress.  Nature, v. 434, p. 291) following the distribution of about 20 m displacement on the Sunda subduction zone over a N-S length of around 500 km.  They feared that such a huge perturbation may activate other large faults.  A changed stress field seems to have been the cause of the Izmit earthquake that devastated central Turkey and also set in motion repeated seismicity along the subduction system off Japan in the past. McCloskey and colleagues foresaw two worrying possibilities for the Sunda subduction system: stress localised just to the south of the Boxing Day event could migrate southwards to trigger release again on the subduction zone; a large strike-slip fault that runs down the centre of Sumatra, itself linked to subduction, may fail soon. fear that the second is the more likely.  Since modern seismology emerged, so few earthquakes have occurred in the area compared with other large subduction settings that prediction is difficult.  The Ulster scientists were correct, very soon after their prediction was published.  On 28 March 2005, a magnitude 8.7 earthquake occurred on the subduction zone about 150 km south-west of that on Boxing Day 2004.  Its motion involved vertical displacement, so it was feared to trigger yet more tsunamis and sirens sounded throughout the previously devastated areas.  The warnings were heeded.  Apart from some panic that cause two deaths in Sri Lanka, people moved quickly to safe ground.  Thankfully, perhaps miraculously considering an energy release not far short of that at the end of 2004, there were no tsunamis of any consequence.  Yet the places on the nearby Indonesian island of Nias were devastated by the shock waves, killing upwards of a thousand people.  This is a grim warning that McCloskey and colleagues’ interpretation of stresses moving southwards along the main ocean floor fault system is happening.  The risk of further devastation soon is by no means over.

Almost every month there are announcements of yet more areas of the world that face hazards from natural contamination of groundwater by release of arsenic from whichever minerals host it in sediments.  In Bangladesh alone, the WHO estimates that tens of million people are at risk.  Although large tracts of the US and other rich countries do have arsenic levels in groundwater that are above the maximum recommended for safety, the crisis is one that most severely affects some of the world’s poorest and most populous countries. To help solve this massive public health problem, the National Academy of Engineering is offering the Grainger Challenge Prize for Sustainability, a sum of US$1 million, to the individual or individuals who design and create a workable and cheap water treatment system that anyone can use for arsenic-contaminated groundwater in Bangladesh, India, Nepal, and other developing countries.  The most likely cheap remedy lies in the use of iron hydroxide as a means of absorbing dissolved arsenic, but several other candidates, including coal fly ash and limestone, together with biological precipitation, have recently begun tests.

Incidentally, the action in the UK against the Natural Environmental Research Council, for negligence in failing to analyse for arsenic in Bangladesh groundwater in the early 1990s, on behalf of 400 Bangladeshis affected by arsenic poisoning, recieved the legal go ahead to appeal against an earlier decision by a British court to throw out their case.  My thanks to John McArthur of University College London for this news.

Drilling into the San Andreas Fault?

It seems that in order to really get a feel for the physical and chemical processes involved in faulting, drilling into an active one is a good idea, or at least that seems to be the driving motive behind the SAFOD (San Andreas Fault Observatory at Depth) project of the US Geological Survey (Cohen, P. 2005.  Journey to the centre of a quake.  New Scientist, 5^th  February 2005 issue, p. 42-45).  It might make sense, because pressures of pore fluids near active faults seem likely to exert some influence over whether a fault segment moves or not.  Overpressured fluids can serve to lubricate the otherwise sticky fault surface.  In the case of the San Andreas, activity is fragmented.  Detailed monitoring of microseismicity near Parkfield, California revealed that a mere 100 x 100 metre patch on the fault plane was responsible for much of the activity.  It lies about 3 km down, just within reach of oil-drilling technology.  In fact the Parkfield segment is one of the shallowest active zones on the whole fault..  There are already holes in place, drilled to 2 km to host monitoring instruments, and new drilling methods eventually will allow sideways puncturing of the fault plane so as to install more.  But even sophisticated drilling is still largely a blind operation, which inevitably hits snags, and there have been several in the SAFOD project.  One severed communications with existing instruments.  The general idea behind SAFOD is that fault displacements propagate from small “nucleation” sites.  The length of the fault that undergoes displacement during one movement is generally correlated with the magnitude of the resulting earthquake.  Parkfield seems to be such a nucleation site, but since the earthquakes associated with it are of small magnitude chances are that interfering with it will not accidentally release a large one.  The benefits, set against the risks and undoubtedly high costs, are mainly that even the tiniest motions can be monitored.  Surface monitoring of course cannot investigate pore fluids and other phenomena, and nor can it detect events less than magnitude 0.5, whose energy is absorbed by rock before it can reach the surface.  By monitoring what happens in events with a range of small magnitudes, it ought to be possible to develop earthquake theory to the point where at least the role of fluid pressures, the feedback between earth vibrations set off by one event and movements on a later one, and the effects of mineralogy on friction that resists movement can be assessed.  Whatever, once in place, the wait for useful results to accumulate could be a long one, so SAFOD is planned for a 15 year lifetime

More information on SAFOD is available at http://www.earthscope.org/safod/index.shtml

The main aftermath of Boxing Day is of course the millions of survivors, deeply traumatised, without their homes and possessions, short of food and clean water, and threatened by a host of diseases.  Second comes the spontaneous generosity of millions of ordinary, but more fortunate people, who within days deeply embarrassed mean-spirited politicians across the globe.  Then there are the aid agencies who responded to the unprecedented magnitude and breadth of the disaster.  How successful they will have been remains to be seen in the months ahead.  Finally, in the public arena, the media has effectively dropped the topic, and the death toll seems to have been capped at “more than 150 000”.  It will have been far, far greater than that, judging by the proportion of those reported missing to those whose death is confirmed, particularly for foreign tourists in the affected areas.  There comes a point, when the actual number becomes meaningless because of its size, as in the case of the Holocaust; 6 million Jews, maybe 20 million Russians.  There is of course an irresistible case for concentrating on the living and the future.  That is within the geoscientific sphere. 

That a tsunamis warning system failed to be established for the Indian Ocean when it was mooted can only be condemned in retrospect.  It is dreadful to contemplate the fact that Boxing Day did a lot of the work needed for risk assessment. It left kilometres-wide scars along all the affected coastlines, which geoscientists are already looking at to assess the mechanisms that either enhanced the power of the waves or, in a few cases, diminished them.  Geophysicists knew beforehand that submarine earthquakes of high magnitude affecting the Indian Ocean will likely occur only along the Sunda arc, so any future tsunamis will revisit the places already devastated this time.  There are environmental lessons too.  Coastlines stripped of their original mangrove swamps, for developments such as prawn farming, lost any protection.  Oddly, many environmentalists are decrying the destruction of habitats and pressuring for rehabilitation.  But this was a purely natural disaster, which over millennia will have happened again and again, before being restored to a temporary ecological balance.

So, it seems likely that measures to predict future Indian Ocean tsunamis will be put in place, with Thailand as the most likely centre.  Yet, seismologists fear that since the Sunda subduction system has failed once, after more than a century of muted activity, there may soon be further high-magnitude earthquakes.  Let us hope not.  As well as more rapid assessment of seismic magnitude, a warning system requires sea-floor pressure sensors to detect any major disturbance of ocean water, and careful modelling of how that is distributed by bathymetry.  Many fear that warnings that are not followed by actual events will induce the “crying wolf” response, and caution care in making warning.  The head of the Thai Meteorological service issued warnings following the announcement by the Pacific Tsunamis Warning Centre that a tsunamis had been unleashed in 1999.  Although it hit New Guinea and killed several thousand people there, it had no effect on Thailand, so he was dismissed.  He has campaigned for an Indian Ocean warning system since then, and has recently been reinstated.  When millions have been directly affected, and memory of the events of 26/12 will last for decades, it seems unlikely that “crying wolf” will result in much public outcry.

Warning system or not, the most pressing needs are for effective and swift communications in hazardous times, and for widespread education about what the hazards are and what to do when they are imminent.  Throughout the Pacific basin, even school children know what to do – head for high ground, especially if the sea goes down suddenly.  There have been fascinating reports of how the culture of ancient tribal people of the Andamans, probably living there for 20 thousand years or more, saved people.  A little girl saw ants swarming away from the sea on the fateful morning, and shouted to everyone to go inland.  That response may have been inculcated by previous tsunamis.  Communications across the affected region were indeed very poor in this case, largely because geoscientists who understood the risk when the magnitude and location of the earthquake became known did not know whom to contact in the Indian Ocean.  The answer is surely whoever issues weather forecasts, for most rural people have radios and listen to weather forecasts every day.

Sources:  Nature, 6, 20 and 27 January 2005 (see especially Schiermeier, Q. 2005.  On the trail of destruction. Nature, v. 433, p. 350-354.  This gives an outstanding, brief discussion of the processes involved in the disaster); New Scientist, 8 and 15 January 2005; Science, 14 January 2005 all contain substantial reports and some editorials.

A list of web links to maps, satellite images and other data relating to the Indian Ocean tsunamis has been assembled by David Stevens of the UN Office for Outer Space Affairs in Vienna.  After Friday 4^th February, this can be accessed through UNOOSA’s  web page at www.oosa.unvienna.org/SAP/stdm.

World Conference on Disaster Reduction: words or action?

From 17 to 21 January 2005, delegates representing 168 states met to discuss measures to mitigate the effects of major disasters that have natural causes in Kobe, Japan.  The conference declaration designates 10 years for resolving the issues around predicting, warning of and responding to such events (the Hyogo Framework for Action 2005-2015).  A New Scientist editorial (Words will never save us.  New Scientist, 29 January 2005, p. 3) expressed caution about the fine words, because the actions needed are, in many fields, not well established.  Kobe did indeed concretise the intergovernmental pledge to establish not only an Indian Ocean tsunamis warning network, but one that will eventually cover all maritime countries.  It also highlighted the success of the Drought Early Warning service, that has a strong focus on Africa.  Yet time and again, the UN, EU and well heeled governments have been alerted to this long-lived kind of disaster, only to fail to respond in a way that truly mitigates the affects.  Drought-stricken people are kept barely alive by food aid, only to await the next failure of rains without the infrastructure to assist themselves.  New Scientist highlights the common factor in failing to survive natural calamities – poverty.  One thing characterised the response to Boxing Day: ordinary people everywhere took decisive action to help, financially and practically, thereby embarrassing and shaming their own governments, the “great and good” multinational institutions, and many an attendee at conference such as Kobe.

Following the tragic discovery ten years ago that tens of millions of Bangladeshis drink groundwater that is naturally contaminated by arsenic, the lessons learnt there have been applied on a global scale.  That has resulted in further cases with similar causes coming to light.  Remediation is chemically quite simple, and since the US reduced the maximum permissible arsenic level in public water supplies from 50 to 10 parts per billion in 2001 research into methods of removal have increased rapidly.  There are a number of methods that are based on adsorption of arsenic by iron and aluminium hydroxides and are low-cost.  But it seems that biological activity in aquifers can be equally effective (Kirk, M.F. et al. 2004.  Bacterial sulphate reduction limits natural arsenic contamination in groundwater.  Geology, v. 32, p. 953-956).  In the anaerobic conditions that favour the dissolution of iron hydroxide, which is often the most important source of arsenic in sediments, the conditions are also suitable for chemotrophic bacteria.  Among these are species that obtain metabolic energy from the reduction of sulphate ions to sulphide.  Where metal ions are also present, they combine with the sulphur to precipitate sulphide minerals.  In turn, sulphides readily accept arsenic from solution, thereby helping decontaminate potentially dangerous groundwater.  Arsenic-bearing groundwater is also found to have high methane levels, which suggests that methanogenic bacteria dominate its micro-ecosystem when sulphate ions are at low concentrations.  Perhaps it will prove possible to encourage sulphate-reducers to thrive in such waters, by the addition of some sulphate by injection.  That would a cheap remedy to what seems to be a growing risk in areas that extract groundwater from aquifers that are full of organic matter that creates the oxygen-free conditions that release arsenic into solution.

Bacteria in groundwater seem to have another benefit.  Where landfill contaminates subsurface waters with a cocktail of pollutants, the nutrients encourage bacterial colonisation, often in the form of biofilms in pore spaces.  It seems that their metabolism generates electrical currents (Gosline, A. 2004.  Bug “batteries” send out pollution alert.  New Scientist !8 December 2004, p. 17).  These create electrical potentials of several hundred millivolts that are easily detected by passive electrical monitoring.  The voltage highs occur at the margins of pollutant plumes in the groundwater, and can therefore be used to monitor spread of contamination and to indicate safe supplies.

In 1783, the Icelandic fissure volcano Laki erupted.  One in five Icelanders perished, partly because most of their livestock died in the eruption’s aftermath, but also because of direct effects from the geochemistry of the lava.  The effects spread to much of continental Europe, but with less gruesome results.  There are many archival reports of the presence of a bluish-grey haze or “dry fog” and an acrid smell to the air – probably high sulphur dioxide levels.  There was an increase in mortality in Europe too, with 25 % more deaths over and above the annual norm in France, possibly exacerbated by the fog’s coincidence with a scorching summer.  The politician-scientist Benjamin Franklin was the first to make the connection between news of the eruption, atmospheric oddities and spectacular sunsets.  The spread of volcanic emissions far and wide at the surface can be put down to the relatively quiet effusion of lava from Laki; explosive eruptions generally jet gases and ash upwards to reach the stratosphere.  The principal killing agent was the fluorine-rich nature of the gas and ash from Laki, which induced a rapid onset of bone-diseases in humans and livestock alike.  That is something special to Icelandic magmatism, the only significant above-sea level part of a mid-ocean ridge system.  However, fluorine compounds commonly occur in some volcanic ashes, and mortality spread beyond the immediate effects of volcanism is a major threat.  Currently, archaeologists and pathologists are exhuming burials from the time of Laki’s last known killer eruption to seek statistics on the influence of fluorosis in its human victims (Stone, R.  2004.  Iceland’s doomsday scenario?  Science, v. 306, p. 1278-1281).  The signs are bony nodules and spiky fibres that fluorine ingestion, most disastrously from water, produces.  Early results reveal many skeletons with clear malformation.  Fluorosis leads to a hugely painful and lingering death.  Usually it results from a slow build-up of fluorine from contaminated water in areas that are rarely associated with active volcanism.  The clearest sign of its onset is a brownish mottling of children’s teeth, and it is easily remedied by changing the water supply.  Delivered massively and suddenly, as it was in late 18^th century Iceland, gave little chance to its victims.  A recurrence would possible be just as disastrous today.

Almost 35 million people in Bangladesh are probably drinking well water that contains arsenic well over the accepted safe limit.  Why that is so is one of the greatest tragic ironies of our age.  In an attempt to reduce the incidence of gastrointestinal disease from drinking polluted surface water, the government, with assistance from international agencies, sank millions of tube wells from the 1970s onward.  The wells tapped abundant and seemingly clean groundwater from the alluvium beneath the Brahmaputra and Ganges plains.  Health problems dropped dramatically, especially among children.  But by 1983 a Calcutta dermatologist reported skin lesions on patients from neighbouring West Bengal in India that are a sure sign of arsenic poisoning.  Even though the British Geological Survey conducted a pilot survey of water chemistry in some Bangladeshi well waters in 1991, the danger from arsenic remained unknown; BGS did not test for the element, despite routinely analysing it in British groundwater.  Shortly after the report was published, typical symptoms of arsenic poisoning appeared from a wide tract of low-lying Bangladesh.  Dermatological symptoms generally only start to appear about 10 years after individuals are exposed to low, but dangerous levels of arsenic in water.  They are followed by a variety of cancers (of the skin, bladder, liver and kidneys) at around 20 years from the start of exposure.  A number of affected Bangladeshi people have taken legal action against BGS for negligence (see British Geological Survey sued over arsenic in EPN of October 2002).  However, on appeal against a legal decision to put their case to trial, Britain’s Natural Environment Research Council, of which BGS is a part, were judged to be too distant from the villagers to have had a duty of care.  The issue will not go away, and informing as many people as possible about the arsenic tragedy, its causes and possible remedies is vital.  This has been taken a step forward by a clear review article by a Bangladeshi health scientist, Mushtaque Chowdhury who co-chairs the UN Millennium Project’s task force on child and maternal health (Chowdhury, A.M.R. 2004.  Arsenic crisis in Bangladesh.  Scientific American, August 2004, p. 70-75).

Despite the common knowledge of rapidly deteriorating conditions for civilians in Liberia for the last 10 years or so, the Joint Oceanographic Institutions’ drilling vessel Resolution and its predecessors continues to this day to be registered under a Liberian flag of convenience.  Shipping registrations form a major part of Liberia’s foreign earnings, and have been used for purchase of arms that have been used on its population, and quite possibly on that of Sierra Leone.  Flags of convenience allow ship owners to avoid taxation and internationally agreed regulations for the safety and working conditions of its crew.  So, the International Ocean Drilling Program and NSF which funds it are in an awkward position.  The whole venture is privatised, NSF funding JOI, which in turn co-owns the famous vessel with Transocean, the world’s largest offshore drilling company.  ODP, which directs operations claims to have been too busy with that to consider the implications of ship registry….

Source:  Dalton, R. 2003.  Ship row flags up funding of war in Africa.  Nature, v.  426, p. 485.

Wildfires and uplift chronology

The “next big thing” in geomorphological studies has been said to be precisely dating crustal exhumation during erosion and uplift.  Fission tracks produced in some minerals by particles emitted by radioactive isotopes within them are preserved only when temperature is below that at which annealing can take place.  That temperature varies from mineral to mineral.  By counting the tracks it is possible to estimate the time since the containing mineral cooled below its annealing temperature during its rise to the surface.  Analysing surface samples from different topographic elevations in an area can therefore build up a history of uplift, those lowest in the section being the last to pass through the temperature, and vice versa.  Similarly, radiogenic gases only accumulate in a mineral once it cools below a temperature at which the molecular structure blocks diffusion of the gas from the mineral.  One example is radiogenic argon produced by decay of ⁴⁰K.  Ages of potassium minerals, such as micas and feldspars, determined by the Ar-Ar technique relate to the time when the containing samples rose through the blocking temperature.  There are numerous problems with fission track dating, although most users assume that the ages that they get are real.  For Ar-Ar “thermochronology” the blocking temperatures are above 150ºC, which is also problematic, because for a normal continental geothermal gradient of 30ºC km^-1 a sample would have to rise 5 km to reach the surface before yielding an age relevant to uplift and erosion history.  Unless a study area has much higher geothermal heat flow, or has undergone enormous rapid uplift, most ages obtained by such studies are much older than the event of interest.  In the case of helium, the blocking temperatures are lower, about 70ºC in the case of apatite.  So dating the accumulation of helium produced by decay of uranium and thorium in apatite offers a tool that seems near-ideal for studying rapid exhumation of the order of a couple of kilometres, and that seems likely for many mountain belts and continental margins.  It is the apatite U-Th/He dating method that has spurred a flurry of new studies, now that mass spectrometry is capable of precisely measuring the tiny amounts of helium in single apatite grains.  But that has its drawbacks too.  On that is pretty obvious is the effect of heating of the surface in recent times.  Sara Mitchell and Peter Reiners of the universities of Washington and Yale studied the effects of biomass burning on the method (Mitchell, S.G & Reiners, P.W. 2003.  Influence of wildfires on apatite and zircon (U-Th)/He ages.  Geology, v. 31, p. 1025-1028) because modelling suggests that fires can reset apatite ages.  They found that resetting and scrambling of ages does indeed occur, down to depths of 3 cm in surface samples.  That casts doubt on this dating not only on detrital apatites found in soils and sediment, but also in rocks, unless the exposed surfaces are ground away before separating mineral grains.  Fires are not the only means of heating rock surfaces, and high temperatures are experienced daily by many rocks due simply to solar heating at low latitudes.  This affects depths down to as much as 30 cm, especially in rocks with a dark surface.  It is possible to fry eggs on exposed rock in some parts of the world, though they are not very appetizing.

With little hype, a British company (Surrey Satellite Technology Limited, linked to the University of Surrey) is beginning to develop a constellation of remote sensing satellites that aim at monitoring a variety of threatening phenomena across the whole planet.  The Disaster Monitoring Constellation produces images at the same resolution (about 30 metres) as the US Landsat Thematic Mapper, but is unique in two aspects.  The satellites and launching them are cheap, because they are tiny by comparison with the giants normally associated with remote sensing, weighing in at only a few hundred kilograms, and they also use off-the-shelf components including the imaging devices.  Second, the four current DMC satellites fly in concert to cover the whole Earth with images 600 km across (Landsat images cover less than a tenth of the area) every day. No other system is capable of that degree of timeliness, the shortest “revist” time to now having been 16 days.  SSTL does not own the satellites or the data, but builds them on contract for developing countries.  The first to reach orbit, in November 2002, belongs to Algeria.  It was joined on 27 September 2003 by three more, sponsored by Turkey, Nigeria and the UK, which were successfully launched by a Kosmos rocket from Plesetsk in northern Russia, at a total cost of around $85 million.  These will be joined by similar platforms sponsored by China, Thailand and Vietnam in the next few years.  The targets are wildfires, floods, windstorms, volcanic eruptions, erosion and potential landslides, with the added benefit of very detailed information about changes in agriculture and forestry, and baseline mapping of geological and hydrological features.  Perhaps most important, it gives less affluent countries independent access to space imagery, which can only boost the confidence of natural scientists in the third world who are venturing into remote sensing after years of playing second fiddle to North American, Japanese and European specialists.  Organisations, such as Reuters Foundation AlertNet and the International Charter, plus other international disaster relief organisations, can tap in for images at very short notice  Astonishingly, SSTL has launched and is planning imaging satellites that weigh in as little as 7 kg.  The low-key announcement of the launch of the 3 latest members of the DMC (www.sstl.co.uk) coincided with US and British hype-fests centred on the current missions to Mars.  There is little doubt which will provide the most lasting benefits.

The threat of arsenic poisoning from the use of groundwater (see October and December 2002 issues of EPN) is wider that the well-publicised delta of the Ganges-Brahmaputra rivers in Bangladesh (Pearce, F. 2003.  Arsenic’s fatal legacy grows.  New Scientist, 9 August 2003, p. 4-5).  Although springs from rocks that contain arsenic-bearing sulphides, particularly mine drainages, were once the main hazard, increasing use of water from tube wells into alluvium have greatly increased the incidence of arsenic-induced ailments.  This is sadly ironic, because massive investment in well boring since the 1960s aimed at reducing the endemic gastro-intestinal infections and parasites from polluted surface water in many third-world countries.  Arsenic is a cumulative poison, building up to dangerous levels over several years.  So ill-health, including fatal liver cancer, does not immediately appear in populations that are at risk.  Areas in which metals are mined are obvious places where caution is needed in groundwater development, particularly where the ores are sulphides – arsenopyrite is a common waste mineral in gold mining.  However, mines produce relatively small zones of risk.  The alluvium derived from large mountain ranges, in which sulphides occur commonly in sediments and igneous rocks, pose the widest hazards.  That is the case in Bangladesh.  However, reports are emerging of similar problems in the Ganges flood plain in Bihar, India and Nepal, the Mekong Delta in Vietnam, lowland China and the Argentine Pampas, each affecting more than half a million people, together with lesser cases in 11 other countries, including the USA.  Over a billion people world-wide have no access to clean drinking water, and a favoured solution is to develop local groundwater.  The arsenic tragedy is not going to stop that necessary improvement in people’s lives, but rigorous testing for chemical contaminants is now a must.  Also, there are means of cheaply removing arsenic from contaminated water – it is almost totally adsorbed by the iron hydroxides that form rust when conditions are oxidising.  In fact, if wells are driven into zones of oxygen-rich groundwater, dissolved arsenic is rarely apparent – part of the problem in Bangladesh is extraction from levels where groundwater has reducing chemistry.

Senile dementia and copper

The chemical constituents of drinking water vary a lot, according to where you live, and some like arsenic are widely feared.  Having a well drilled into pure silica sand fed with rainwater is not the answer.  Humans get a sizeable proportion of essential elements from the water that they drink, and pure water would result in deficiencies of many elements.  Upper limits for many potentially harmful elements are set legally in some countries, and the World Health Organisation offers useful advice (see http://www.who.int/water_sanitation_health/GDWQ/Summary_tables/Tab2a.htm).  However, little is known about the geochemistry of human health, when it lies within advised limits.  Recent biomedical research reveals a possible link between copper in drinking water and Alzheimer’s Disease (Sparks, D.L. & Schreurs, B.G. 2003.  Trace amounts of copper in water induce {beta}-amyloid plaques and learning deficits in a rabbit model of Alzheimer’s disease. Proceedings of the National Academy of Sciences, 14 August 2003 – online publication).  Two experiments investigating the effects of high-cholesterol intake on rabbits both suggested that beta-amyloid plaques, implicated in human senile dementia, build up with cholesterol intake.  Nothing too surprising in that.  However, the results differed significantly between the two laboratories, one in the USA, the other in New Zealand.  Trying to work out why two labs should get such different results, Larry Sparks of the Sun Health Institute in Arizona discovered that the New Zealand rabbits drank tap water, whereas his were given distilled water.  The US rabbits had significantly less plaque build-up than those studied in New Zealand, so perhaps water chemistry had an input.  Sparks and his colleague varied the copper content of their rabbits’ water, and found that even with one-tenth the maximum safe concentration advised by the WHO, plaque built up 50% faster in the hapless animals.  However, it is early days in this research.  Cells possibly contain numerous mechanisms that fight off accumulation of potentially harmful elements, and perhaps the plaques implicated in Alzheimer’s play such a role.  One line of investigation is to check records of the incidence of Alzheimer’s against local water chemistry, but both kinds of record, even in well-heeled countries like the USA and Britain, are rudimentary to say the least.  If there is a risk, it is likely to be highest among people who use local well water in metal mining areas, or where bedrock includes sediments that contain high copper concentrations, sulphidic shales being a widespread example.

Source: Marx, J. 2003.  Possible role for environmental copper in Alzheimer’s Disease.  Science, v. 301, p. 905