Category: Environmental geology and geohazards

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.