Category: Environmental geology and geohazards

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

In the highlands of central Sri Lanka the sediment suspended in rivers suggest rates of soil loss from agricultural land of the order of up to 7000 tonnes per km² each year.  However, it is difficult to judge how much would be eroded under natural conditions, compared with the probable loss as a result of deforestation and human activities, particularly from very rugged landscapes where seasonal rainfall is high..  Radionuclides produced by cosmic-ray bombardment of minerals exposed to them, such as ¹⁰Be and ²⁶Al, accumulate in soil that is being eroded at a rate that is inversely proportional to the rate of erosion.  The nuclides form in the top 0.6 m of soil, which is the depth within which cosmic rays are normally absorbed.  So erosion rates that can be calculated from the cosmogenic nuclides in minerals, such as quartz, in river sediments apply to the times taken to remove that depth of soil.  Essentially, the rates that are measured represent the long-term erosion within a catchment basin.  Swiss and Sri Lankan geoscientists have applied the technique to rivers in central Sri Lanka, whose catchments have different vegetation cover and land usage (Hewawasam, T. et al. 2003.  Increase of human over natural erosion rates in tropical highlands constrained by cosmogenic nuclides.  Geology, v. 31, p. 597-600), such as forest reserves, rice terraces, tea plantations, areas of slash and burn agriculture, and various levels of degraded land.  The unmodified forest catchments give the lowest long-term erosion rates of 5-11 mm per 100 ka (13-30 tonnes per km² per year) as expected, but this is about a quarter of the rate of erosion measured by the same method throughout the highland region.  That probably reflects the antiquity of erosion induced by agriculture, yet current rates measured from sediments being carried by rivers suggests that soil erosion is now between 10 and 100 times faster than would occur under natural conditions.

Remote signs of earthquakes

All manner of ground-based observations have been tried as means of timely predictors of pending earthquakes, ranging from strange behaviour of wildlife to emissions of radon from wells (see Radon emissions and earthquakes, July 2003 issue of EPN).  So far, none of them have been universally useful, although there have been successful evacuations of threatened populations, principally in China, whose seismologists have focused on a wide range of signals.  Ideally, what is needed is some kind of global monitoring, and as with attempts to predict volcanic eruptions the only realistic means is from satellite surveillance.  Long ago, Doug Shearman of the Royal School of Mines at Imperial College, London introduced me to the peculiar properties of the mineral dolomite, as discovered by the man whose name it takes, Count Deodar de Dolomieu.  If you rub two lumps of dolomite together in a darkened room, they emit a sinister glow, and so do other minerals, such as quartz and even sugar.  Excellent for amusing the kids.  But then I learnt of “earth lights”, which had been photographed by Japanese observers just before earthquakes, in the vicinity of active faults – previously they were supposed to be as mythological as the fire balls during thunder storms (also a proven fact now).  At the time, the Landsat remote sensing satellite captured images during its night-time overpasses, on request.  A nice, if a little “blue skies” research project.  I submitted a brief proposal to my department’s research committee for ranking along with other studentship projects.  Perhaps my wry attitude to what had become somewhat dominated by other disciplines than remote sensing coloured my efforts; it was rejected.  So it was with some glee, a decade later, to find that NASA and the US Federal Emergency Management Agency had been testing the idea using weather satellites and the MODIS instrument carried by the Terra platform since 2000 (Enriquez, A. 2003.  The shining.  New Scientist, 5 July 2003, p. 26-29).  Encouragingly, though not for their victims, the devastating 1999 Izmit and 2001 Gujarat earthquakes were preceded by increased infrared emissions, detected from space, 5 days before the event.  Experiments show that when rock is stressed, emissions build up, and then vanish once the rocks fails, as in an earthquake, so the method looks very promising.

Another seismic phenomenon is changing magnetic fields around the site of failure.  This was first noticed from magnetometer records on the ground before the 1989 Loma Prieta earthquake that damaged large tracts of northern California.  Magnetic field variations too can be monitored from orbit.  The privately funded QuakeSat, launched on 30 June 2003 aims to test this possibility, as will a more ambitious French satellite, due to reach orbit in April next year (Reichhardt, T. 2003.  Satellites aim to shake up quake prediction.  Nature, v. 424, p. 478).

Models abound for predicting earthquakes from past seismicity and detailed tectonic maps, analogous to those suggested for prediction of volcanic hazards.  The Izmit earthquake of 17 August 1999 in Turkey was among the most savage in recent years and killed thousands.  It was as powerful (magnitude 7.8) as the celebrated 1906 San Francisco earthquake, and like it stemmed from movement on a continental-scale strike-slip fault.  The North Anatolian Fault is almost as well studied as the San Andreas line, and seismicity was known to be heading westwards well before the Izmit catastrophe.  Indeed, the Izmit area was predicted to be next on the list, yet no preparation had been made, even by Turkish tectonicians who had been involved in seismic analysis.  Chinese geoscientists take a different approach to seismic prediction than those in the west – over the last few centuries, hundreds of thousand Chinese people have perished in earthquakes.  They are trying to organise local people to monitor possible precursors to earthquakes, such as rises in water levels in wells and strange behaviour of animals.  They have had some notable successes, including preparation for one earthquake in recent years that saved an estimated 80 thousand people in one particularly hazard prone city.  The Geological Survey of Israel has been testing a well known correlation between the times of anomalous radon emissions from the ground and earthquakes along the Aqaba Fault that controls the Dead Sea.  Over a 7-year period, hourly scintillation-counter readings of radon emissions from springs, wells and especially gravels near known active faults allowed a rigorous test of a possible prediction system, because in that time there were almost 800 minor earthquakes (Steinitz, G. et al. 2003.  Statistically significant relation between radon flux and weak earthquakes in the Dead Sea rift valley.  Geology, v. 31, p, 505-508).  For events beneath the Dead Sea rift, there is a good correlation between the start of radon emission increases and earthquakes, which suggests that about 3-days warning could be given, if the monitoring was widely deployed.  The same cannot be said for small tremors with a source outside of the active fault zones.  The success may possibly be because sufficient radon to be easily detected is generated by radioactive decay of uranium in a phosphorite bed that underlies the study area. Radon escape to the surface is possibly eased when microfractures begin to open as strains build before an earthquake.

Unless it is possible to give people who live near dangerous volcanoes sufficient warning that they can escape disaster, eruption prediction might be looked on as a lugubrious topic.  Up to now, there have been very few predictions that have been better than a few hours or days.  Mexico’s Popocatapetl gave two days warning in late 2001, and that was sufficient for a completely successful evacuation of those threatened.  In the case of the eruption of Nyirangongo in eastern Congo, a few months later, warning signs preceded eruption by 5 days, but the people of Goma were not told and 45 people died trying to rescue possessions from the quiet, but relentless movement of a lava stream (see EPN February 2002, Is volcanic eruption predictable?).  In both cases it was abnormal seismicity that presaged the events.  John Murray, of the British Open University, has analysed the statistics of seismic events and eruptions of possibly the world’s most monitored volcano, Etna on Sicily (Murray, J.B. 2003.  Seismicity and time-lagged lava output at Mount Etna: A new method of long-term forecasting at a destructive volcano.  Geology, v. 31, p. 443-446).  Energy released during 19-year periods by earthquakes beneath the volcano since 1870 shows a inverse relationship with 9-year lava production, which suggests that seismicity and eruption are widely separated in time over long periods.  However, by examining the correlation of seismic energy with eruption volume for time differences between the two from 0 to 50 years, Murray has been able to show that Etna increases its productivity roughly 25 years after major releases of seismic energy.  Using this as an input to a model that might predict eruption intensity, he has been able to mimic the actual volcanism through the 20^th century with fair accuracy.  In his opinion, the very high eruption rate since 1950, which reached a peak in the 1990s, is only likely to decline a quarter of a century after large earthquakes (> magnitude 6) return to Sicily.  So, Sicilians have a difficult choice.  Should they worry about lava flows or earthquake damage?  Sadly, data suitable for broadening Murray’s method are available for very few volcanoes, all in quite prosperous countries.

Modelling the duration and extent of mining contaminants

Release of high concentrations of heavy metals and other pollutants to drainages is a natural consequence of geochemical anomalies associated with mineralization.  However, these have come to balance with the rest of the environment over periods measured in thousands of years or even longer.  The pose perpetual hazards, some of which are known, some not.  Environmental disturbance by mining and associated activities scales up releases of pollutants many times over those of natural origin.  Even with modern means of waste containment, escapes occur, sometimes of very large magnitude, such as the breaching of tailings dams or landslips in spoil heaps.  Of course, these hit the news when they happen, but assessing how long the pollution dwells in downstream areas and how it moves is not easy.  It requires some kind of model of the hydrology, erosion and sediment-transport characteristics of the affected drainage basins, that takes into account catchment topography and the size-distribution and density of escaped wastes.  Such a modelling tool is now available, having been developed at the University of Wales in Aberystwyth (Coulthard, T.J. & Macklin, M.G. 2003.  Modelling long-term contamination in river systems from historical metal mining.  Geology, v. 31, p. 451-454).  It is complex, because it combines the 3-D shape of basins with water discharge and depth, vegetation cover, depth to bedrock and the properties of released materials. In a simulation of hydrological dynamics.  TRACER is able to take account not just of the fate of grains that enter drainages, but how they are deposited in alluvium and then reworked by later changes in hydrology.  Coulthard and Macklin apply the model to the base-metal mining district of Swaledale in North Yorkshire, England, where production began in 1700 and ended 200 years later.  Swaledale was a minor producer of lead and zinc in modern terms, and the miners paid scant attention to environmental protection.  Results suggest that contamination spread downstream to the flat land of the Vale of York in only 10 years after mining started, but the pollution lingers, and seems likely to stay above safe limits until well after the start of the 22^nd century.  When possible increases in rainfall through global warming are factored in, the simulation remains much the same for 10 to 25 % rises, and only moves towards clean-up with 50 to 100 % increases in precipitation, when clean sediments should dilute the pollutants.  As well as predicting the general effects of contaminant releases, TRACER is able to highlight parts of a drainage basin that are particularly at risk due to trapping of sediments.  Mining in Swaledale produced, at most, only about 600 thousand cubic metres of metal-rich waste, fine enough to be transported by water.  Recent escapes from tailings dams and landslipped spoil heaps, as in Spain and OK Tedi in Papua New Guinea, were orders of magnitude larger.

Unlike some natural catastrophes, there is no stopping a volcanic eruption.  The best that can be done is to give people who live in the danger zones sufficient warning that they can escape disaster.  Many volcanic areas are densely populated, largely because soils derived from lavas and ash are extremely fertile, and high volcanoes create decent rainfall because of their orographic effect.  Naturally, nobody likes to up sticks, whatever the dangers, least of all if there are false alarms.  As with seismic prediction, volcanologists do not have a good track record of foretelling big eruptions, even though a great many geologists cluster on and around volcanoes.  Most of them flock to areas with active lavas, pyroclastic flows and other lugubrious after effects of major activity.  However some do the painstaking work of trying to monitor the plumbing of volcanoes, to get a handle on which parameters are most likely to be authentic warnings of impending doom.  It is no longer a matter of experienced volcano watchers and their instinctive feel for when one is about to blow its top, but one of ever more sophisticated instruments and software to analyse data and model volcanoes’ inner workings.  The 28 March 2003 issue of Science (p. 2015-2030) devotes 16 pages to a review of volcano monitoring.  While advances are being made, there is still a long way to go before they can pay dividends by reducing the loss of life.  What is not going to go away, even in the best of all possible scientific worlds, is the economic devastation that follows any geohazard.

The April 2001 issue of Earth Pages News (Taming Lake Nyos, Cameroon) announced attempts to release CO₂-rich water from the bottom of the notorious Lake Nyos, by setting in motion a sort of soda siphon.  A massive discharge of gas from Lake Nyos in 1986 killed 1700 local people, possibly after a small earthquake and landslide disturbed the bottom water.  Nearby Lake Monoun had already asphyxiated 37 people two years previously.  Both lakes are stagnant, and carbon dioxide released by exhalation from deep magma chambers dissolves under pressure in their deepest levels.  If the water rises, then it belches out dissolved gas, with potentially disastrous results.  Taming these killer lakes by bringing gas-rich water up pipes works because as the gas bubbles out of solution it rushes up the pipe dragging water with it, to create a fountain.  This is slowly relieving the danger of Lake Nyos, and there have been no problems caused by disturbing the deep water by the pipe’s presence, so far.  A French team from the University of Savoie is now installing a similar device in Lake Monoun, which poses a greater threat than Nyos, because the gas-rich water is only 60 metres down.  Potentially far more dangerous are the lakes of the East African Rift system, where magma exhalation is far more widespread and seismicity more common.  Lake Kivu, near Goma on the border between Rwanda and the Democratic Republic of Congo, threatens far more people with a massively greater threat, which also includes huge volumes of buried methane.  Luckily, the lava flow there during early 2002 did not reach the gas-rich level.  The experience from Cameroon promises an eventually easing of the dangers elsewhere.

Source: Krajick, K. 2003.  Efforts to tame second African “killer lake” begin.  Science, v. 299, p. 805.