Australia: The Land Where Time Began
Expected future climate change
It is suggested by new evidence from the last interglacial period that the sensitivity of the polar ice sheets to even a small degree of global warming is much greater than previously believed. In a paper in Nature in 2009 by Robert Kopp, a climate scientist at Princeton and others from Harvard they suggest that during the Eemian temperatures at high latitudes were 3-5o C warmer than at the present and there was a 95 % probability the global sea levels were at least 6.6 m higher than at the present and a 67 % chance they were 8 m higher. An estimate of the likely rate of sea level rise as the climate warmed in the Eemian was a rage of 5.6-9.2 per thousand years. This is an average of 56-92 cm per 100 years, and this is close to the numbers arrived at by some models for the sea level rise of this century, and also fits with some of the most recent observations of the polar ice cap melting.
The author1 suggest that the rate of temperature increase, melting of the ice sheets, and the rate of sea level rise may be comparable with those in the post-glacial period, making it likely that there may be a response from the Earth's crust, making it likely that the scale and extent of these reactions would broadly keep in step with the rising temperatures, though he suggests this may be a dangerous simplification. The response of the geosphere may occur in sudden bursts followed by quiescent phases as thresholds are crossed and tipping points are passed, instead of the steady linear increase that might be expected by some. According to the author1 there will obviously be differences when compared with the post-glacial period, such as a much more subdued response to a future loss of the Vatnajökull Ice Cap than occurred in post-glacial times when there were extraordinary eruptions resulting from the wholesale melting of the vast mass of ice that capped Iceland in the last glacial period.
The overall picture may be the same, if the speed and scale of the future anthropogenic climate change are large enough, the most obvious regions of geological response occurring in the places where ice sheets and glaciers are melting, sea levels are rising, and with the most pronounced increase of precipitation. These include all those places where evidence from the past of responses to climate changes that are rapid: ocean margins, glaciated regions, both at the poles and at high altitudes and elevated topography, volcanic and non-volcanic. According to the author1 the knowledge that has accumulated concerning the post-glacial period leads to the conclusion that the transformation of the world at that time involved an all-pervasive, severe and rapid climate change that mobilised the entire planet. The Earth system is so complex and entangled that in the future there is no aspect of the world that should be regarded as immune from the influence of anthropogenic warming, and he suggests the first signs are already being seen of the response of the geosphere to changes brought about by rising temperatures, and it is indicated by ongoing research that the changes are far from complete.
As was indicated by the evidence presented by the author1 for increasing earthquake activity occurring in southern Alaska as unloading results from the melting of ice over wide areas, Alaska in this case acting as the 'canary in the mine', as it has a lot of ice in a geologically dynamic setting which provides the conditions for the interaction between the 2 as the climate in the area is warming considerably faster than the overall temperature of the Earth. It has been predicted that Alaska would be affected by climate change more than other state in the US. What is happening in Alaska at the present has been suggested to be providing some indication of what is in store for other comparable parts of the world, with more landslides as well as more earthquakes. As large ice masses such as the Bagley Ice Field melt, reducing the pressure that has kept any underlying faults locked they are expected to become progressively more active as the ice shrinks and loss of permafrost and ice from mountains the rock faces will be destabilised and promote the formation of giant landslides.
There are a number of impressive peaks, volcanic and non-volcanic, in Alaska, of which Mt Bona rises to more than 5,000 m and the 6198 m high Mt McKinley, the tallest mountain in the US. It is common for many large landslides to occur as a result of the combination of very high, steep terrain in an environment that is tectonically active, but landslides appear to have been happening more frequently than they used to. Huge avalanches of rock and ice with volumes of 10-30 million m3 previously occurred about once every decade, though in the past 15 years this frequency has increased to 1 every 3-5 years. It is not likely to only appear to have increased the frequency of landslides as others have been doing the same. A 50 million m3 landslide resulted from the detachment of the glacier that capped the 3,200 m high Mt Stellar in Southern Alaska in 2005. It has been estimated that the avalanche may have reached a speed of 100 m/sec (360 kph), and possibly even faster, the debris travelling 9 km and eventually stopping on the Bering Glacier. The seismic shock was measured on seismometers around the world.
Studies have been carried out on the recent landslide activity in Alaska by Christian Huggel of the Eidgenössische Technische (ETH), Zurich, Switzerland (Zurich Technical University) and Jacqueline Caplan-Auerbach, Western Washington University, as well as others. It is suggested by their studies that at Iliamna volcanic heat is probably the driving force of repeated landslides that have occurred on it, by providing an efficient means of melting the base of the glacier that is attached to it, and promoting the collapses that happen periodically. They have pointed out that the glacier is continually replenished after collapses by the climate, snow falling on the peak reforming the glacier. The volcano receives 10 m of snow annually. The author1 suggests that it could be speculated that more rapid replenishing of the glacier, possibly as a result of increased precipitation associated with climate change could result in more frequent failure. There have been increases of precipitation in Alaska of up to 33 % measured across most of Alaska between the late 1960s and the early 1990s.
The giant 2005 avalanche on Mt Stellar cannot be blamed on volcanic heat, and the author1 suggests there seems to be a more explicit role for climate change in this case. At the height of the summit of Mt Stellar temperatures have increased by 0.3-0.4o C per decade according to Huggel & Caplan-Auerbach et al., as a result of global warming. A possibly more significant observation by them is that during both 2004 and 2005 the summer temperatures in the vicinity of the mountain were higher than usual, reinforcing the year-to-year rise in temperature, the avalanche occurring in 2005. The scientists carrying out the studies suggest such a combination of glacier melting and the thawing of mountain permafrost could have triggered the failure and formation of the avalanche.
Very large landslides have also occurred in mountainous terrain in many other parts of the world in recent decades, and there has been an apparent increased frequency of landslides around the world that the author1 suggests may be the beginning of the global scale response of the geosphere to anthropogenic climate change. The largest ice and rock avalanche that has been observed occurred in 2002 in the Caucasus Mountains in Russia, situated east of the Black Sea and west of the Caspian Sea. The avalanche originated on the summit of Dzhimarai-khohk and had a volume of 10-20 million tonnes of rock and ice that landed on the Kolka Glacier chopping off most of the glacier, the chopped off part being incorporated into the avalanche. A mass of rock and ice that has been estimated to have totaled 100 million m3 dropped into the Genaldon Valley, crashing into the Karmadon Depression, a small, sheltered valley between 2 ridges. All 120 people living in the farming communities in the depression were killed and are still beneath the avalanche debris. After travelling for 19 km most of the material was stopped by the Gates of Karmadon, a narrow defile where the massive boulders comprising part of the avalanche became wedged to form a large natural dam. The watery residue of the landslide forced its way through the dam wall the fed a torrent of muddy water that continued on for 15 km, and stopped just before it reached Gisel, that was a much larger town. Since the 1990s the glaciers in the Caucasus Mountains increased their rapid rate of retreat, indicating a general warming that is continuing. The author1 suggests it is reasonable to assume that this warming had some part in triggering this massive avalanche.
In other parts of the world there are also mountain faces that have endured for long periods of time are now becoming unstable and failing. Since the 1990s there have been many avalanches of rock and ice that have occurred that originated on the peak of Monte Rosa in the Italian Alps. In 2005 the culmination came in the form of a million m3 or more of rock and debris falling from the east face. Major avalanches of about 1 million m3 have also occurred at other places in the Alps, such as at Monte Bianco (Mont Blanc), 1997, and Punte Thurwieser, 2004, both of which are in Italy, and at Dents du Midi and Dents Blanches, 2006, both in Switzerland. Other large landslides and avalanches have occurred in Canada and the New Zealand Alps.
As the Earth continues to warm an increase in the number of large, potentially catastrophic landslides that are expected to continue while there is any ice or permafrost. There is also the possibility that landslides could continue even then as indicated by Mt Stellar in Alaska where landslides occur either in unusually warm years or the year following an unusually warm year, and this would result in a threat that is more erratic. Studies have been carried out by Christian Hugel and others that have found clear links between the occurrences of major rock and ice avalanches that have occurred recently and heat waves. They studied landslides at Mt Cook in the Southern Alps of New Zealand, 1997; Mt Stellar, Alaska, 2005, 2008; Mt Miller, Alaska, 2008; and Monte Rosa, 2007. In ever case the collapse was preceded by weather that was unusually warm. As the atmosphere warms the land areas warm faster than the oceans, and in the polar regions the temperatures are rising faster than elsewhere on globe. There is also the expectation that periods of extreme temperature are predicted to rise at double the rate of increase of average temperatures, and the episodes of extreme temperatures are expected to last longer than they have in the past, with heat waves becoming more common.
The author1 suggests the same pattern is probably present in other parts of the world such as other peaks in Alaska, the Himalayas, the Andes and other parts of the Southern Alps, the trend being reinforced by longer, hotter heat waves leading to increasingly unstable mountain faces and glaciers driven by a general year-to-year warming.
The Caucasus event is the only one of the recent major landslides and avalanches to strike an inhabited area. In places where mountain glaciers are melting rapidly large landslides that block streams in valleys can cause another risk for people downstream by forming dams of rock and ice that can accumulate huge volumes of water before eventually failing, either by breaching or by tsunamis caused by further landslides pushing water over the top of the dam. When this occurs it can lead to catastrophic flooding of areas downstream, such torrents in some cases being capable of continuing for up to hundreds of kilometres.
In February 1911a moderate earthquake triggered a giant landslide in Tajikistan, a Central Asian Republic, with an estimated volume of 2.2 km3 from the side of a steep-sided valley in which flowed the Murghab River, burying all but 4 of the population of about 300 in the village of Usoi, and blocking the valley by a dam 5 km long and 567 m high, the tallest natural dam in the world, named the Usoi Dam after the village buried beneath it. As the river steadily rose behind the dam it eventually inundated the neighbouring village of Sarez. By the present the dam has backed up 55 km and contains 16 km3 of water. The densely populated areas downstream became concerned in 1968 when a small landslide triggered a low tsunami in the lake. A larger collapse in 1987 caused more worry when it generated a 6 m tsunami in the dam. It is now an increasing worry as it continues to accumulate water, a collapse of the dam would now be a catastrophic event that would cause a massive amount of death and destruction downstream.
There are considered to be 2 possible scenarios about the future of the dam. One involves a collapse of a large mass of rock that could be triggered by a large earthquake that generated tsunamis that overtop the dam and possibly erode it and eventually releasing the water into the valley network below that are home to about 5 million people. The other scenario involves an earthquake centred on the dam wall that causes it to allow the water to break through. A number of studies have been carried out on this scenario but have arrived at conflicting conclusions concerning the dam stability and a probable future collapse. As there are about 900 glaciers on the surrounding peaks supplying an increasing amount of water to the lake as they melt it is continuing to grow. Seepage through the dam has been increasing, and there is always the threat of earthquakes, both of which could lead to the triggering of further landslides capable of destabilising and breaching the dam. A 1998 model that was developed by the US Army Corps of Engineers has predicted that even after rushing through the maze of valleys the water would still be the height of a 2 story building after it travelled 1,400 km to the town of Termiz on the Uzbekistan-Afghanistan border.
There are many such natural dams in mountainous areas, especially in the Himalayas and the Andes, that are rapidly increasing in volume as the increasingly warmer temperatures melt the many glaciers and ice caps. Since the 1940s there have been more than 30 glacial outburst floods (GLOFs) in the Peruvian section of the Andes. An avalanche of rock and ice originating in the Hualcán Glacier dropped into a lake in Peru triggering a 25 m high tsunami that flooded 4 towns destroying 50 houses. The ice fields of Patagonia constitute the 3rd largest ice mass on Earth and are melting to form ever-increasing glacial meltwater lakes, and their number is increasing as the ice in the high Andes melts at an increasingly rapid rate. More than 200 glacial lakes have been identified by the International Centre for Mountain Development in India, China, Pakistan, Nepal and Bhutan that could potentially burst through dams of rock and debris that are a threat to populations in the valleys below.
The rising water levels in these glacial meltwater lakes will promote slow cracking, the same process involved in the collapse of Mount Toc's north face into the Vajont Reservoir in 1963. Movement of adjacent faults may be encouraged by pressurisation of pore water, increasing the possibility that at least the largest lakes may promote local earthquakes, and this could result in catastrophic flooding if the dams were caused to collapse. In the Himalayas where there are about half a dozen earthquakes due that are tectonics driven, as well as in the Andes that are seismically active, the destruction of the dams may be achieved more effectively.
As a result of anthropogenic climate change there will be many parts of the world that will get wetter as the temperature rises, and this has probably already begun as indicated by observational evidence. It is being predicted that there will be more intense rainfall events and these can be expected to cause increased formation of debris flows, and also saturating slopes leading to the promotion of landslides and the pressurisation of pore water. Unconsolidated surface material such as bare surfaces recently exposed by retreating glaciers, the ash-covered volcano slopes and steep slopes that have been deforested, are all especially susceptible to mobilisation.
The collapse of the Casita Volcano in Nicaragua in 1998 as a result of torrential rainfall across Central America produced by Hurricane Mitch gives some indication of what is to come, mudslides caused by the extreme rainfall killed 2,000 people. In the same year at Sarno in southern Italy more than 160 people were killed and 600 houses were damaged or destroyed by fast flowing torrents of mud and debris resulting from torrential rain on loose volcanic soil, another example of the sort of extreme events that are predicted to increase in frequency as the global temperature increases. The Aare Valley in the Swiss Alps through which the Aare River flows was blocked by a missive debris flow in 2005, initiated by heavy rain that fell on loose rock pulverized by the Holman Glacier that is retreating in the mountains above the valley, temporarily blocking the river but it eventually broke through the dam and caused serious flooding. The flow, the largest to affect the Alps for about 20 years, had a volume of about 500,000 m3 . In 2010 40 landslides were triggered by heavy rainfall blocking all routes that linked to Machu Picchu in Peru. According to the author1 as tropical cyclones are predicted to become wetter and intense downpours to become more common it seems likely such large land movements would occur more frequently.
As the conditions of the earth are expected to become increasingly similar to those that existed in the post-glacial time following the close of the ice age, with ice mass loss, rising temperatures and sea levels, it seems not unreasonable to expect that the reaction of the deep Earth processes, earthquakes and volcanic eruptions, will be similar, though on a smaller scale, to the geological response to the changing climatic conditions that occurred in post-glacial times.
There is little time left to avoid the catastrophic loss of polar ice and rising sea levels. At the present the Greenland glaciers are retreating, the glacial meltwater being dumped into the Arctic Ocean at the rate of hundreds of billions of tonnes per year which accounts for 25 % of the sea level rise that has already occurred. There is a lag between rising temperatures and melting of glaciers around the world, so even if the temperature rise was stopped now the melting would continue. More than half of the Greenland Ice Sheet experienced melting in 2010, and it doesn't seem likely to survive the rising temperatures. Sebastian Mernild's team at the Los Alamos National Laboratory in New Mexico have developed a model that predicts that the measures being taken to save the Greenland Ice Sheet are insufficient to prevent the loss of this ice sheet. The continuing population rise and economic growth will doom the ice sheet, even if renewable technologies are adopted, according to the model and a tipping point will be reached in about 30 years from now, after which the ice loss will pass the point of no return.
Based on predictions such as this and with the lack of serious attempts to cut greenhouse gas emissions to the extent that the science indicates is necessary it can only be assumed that temperatures will continue their rise throughout the 21st century and beyond, ice sheets and glaciers will continue to be lost and sea levels will continue their rise, probably at rates comparable to those in post-glacial times. According to the author1 it would be surprising if there wasn't a response from the crust of the Earth that could be measured. A number of studies have begun in the areas where signs of a crustal response to changing environmental conditions are likely to be observable first, such as Alaska, where melting glaciers have already invoked a seismic reaction.
Iceland is another place being studied as it is where there was a spectacular volcanic response to the changing conditions in post-glacial times. The studies in Iceland are concentrated on the remaining glaciated areas, especially the largest, the Vatnajökull Ice Cap, beneath which is the volcano responsible for the Lakagigar eruption in 1783 that was so devastating. Freysteinn Sigmundsson and his team of volcanologists have studied the possible significance of the eventual loss of the Vatnajökull Ice Cap in connection with the volcanoes beneath it. The ice cap is about 8,000 km2 in area and in places up to 1 km thick, though between 1890 and 2003 it lost about 10 % of its mass, or about 40 billion m3 , and is currently losing about 0.5 m of its thickness every year, and the crust is rebounding accordingly over much of the extent of the ice cap. As the lithosphere rises the pressure it applies to the asthenosphere is decreasing, and as the upper layer of the asthenosphere melts, because at the temperature of the asthenosphere it is the pressure that has been applied to it that has been keeping it in a less liquid state. It is currently believed to be very unlikely that a revival of volcanic activity would be on the same scale as occurred in the post-glacial times, when the production of magma increased by up to 30-fold or possibly even more. Sigmundsson et al. do expect to see some degree of volcanic activity as the ice cap disintegrates, based on their calculations. They estimated that 1.5 billion m3 of magma would be produced per century, that would be enough to support a moderate eruption about every 30 years, though they suggest it could possibly be a few centuries before the magma reaches the surface. They suggest that a mechanism that could lead to an increase in the frequency of volcanic eruptions could be if some volcanoes that have already accumulated magma and are close to erupting may be triggered sooner as the progressive reduction of pressure on the underground plumbing systems of the volcanoes results from the melting of the ice. An impression of the effect in the long term of volcanic eruptions in Iceland can be gained from the Lakagigar event of 1783 and its global climatic knock-on effects which could possibly have been involved in a loss of life running to the millions around the world.
There are also a number of other places, such as Alaska and the west coast of the US, the Kamchatka Peninsula in Russia as well as long the length of the Andes, where a warmer climate could possibly induce a volcanic response, the potential for more violent blasts increasing as the increasing temperatures lead to the loss of glaciers from these volcanoes. Hugh Tuffen, a volcanologist at the University of Lancaster, suggests that as the ice thins, as well as driving more explosive eruptions as the pressure on the magma chambers is reduced allow the contents to become more liquid, it could also lead to the loss of mechanical support of the volcano flanks by their permanent ice cover making them more likely to collapse laterally which could cause a violent eruption from the side of the volcano. As the ice progressively melts it would expose more ash and loose debris that would be a ready supply for debris flows that could result either from meltwater or intense bouts of rainfall. It could be expected that as the ice thins and weakens it would become easier for the volcanic heat to dislodge the remainder of the ice, and there could be glacial outburst floods resulting from the catastrophic release of meltwater by the overtopping or or the breaching of crater lakes or depressions, especially at places where crumbly ash and debris have impounded water. In 2007 just such a event occurred in New Zealand when 500,000 m3 of water and mud cascaded down the flanks of the Mt Ruapehu volcano when a debris dam breached. At some point in the future volcanoes at lower latitudes or lower altitudes, that have never had an ice cap, but which have been forecast to be subject to a wetter climate, could be expected to respond with eruptions. It has also been predicted that in places such as the Caribbean, Europe, Indonesia, the Philippines and Japan, wetter hurricanes and typhoons would be linked to rainfall events that are more intense with the result there could be more debris flows that have the potential to be destructive, and the promoting of more landslides. The author1 suggests the Casita event could reasonably be seen as a forerunner of such events that could become more frequent in the future.
As the temperatures of the world increase and the present evidence suggests an apparent tendency for volcano flanks to collapse when the local climate is warm and wet it is very likely there will be an increase of such collapses, the problem being that these can often trigger lateral eruptions from volcanoes that are already charged with magma. When the upper levels of a volcano become saturated, either by meltwater of by a wetter climate, the pore water pressure increases, which then increasing the chances that the sliding will take place along existing planes of weakness. This appears to have happened on Mt Etna, Sicily, Italy in the Early Holocene when the soggy volcano was intruded by fresh magma also provides a means of causing flank collapse and possibly an eruption. It is suggested that another factor that could be involved in slope collapse is rising sea levels, that are expected to rise by several metres over the next few centuries, the resulting crustal bending in coastal areas where volcanoes are present promoting instability of seaward flanks, and also makes the rise magma at shallow depths into the volcano easier, and then the eruption of this magma. As exemplified by the Pavlof volcano in Alaska, this latter behaviour raises the question of the likely scale and extent of a volcanic response, in the future, to planetary warming, will it be limited to volcanoes that were previously ice capped and those with significantly wetter local climates; or as there are 800 active, or potentially active, volcanoes that either form islands or are located in coastal areas, will changes of stress and strain conditions in the crust, resulting from large, rapidly rising sea levels, drive a response that it much more widespread?
It has been estimated that land-based volcanic activity rose rapidly by 4-6 times between 12,000 and 6,000 years ago. At the present there are about 50 volcanoes erupting in a year, and this 50 is made up of volcanoes that erupt frequently, some that lie dormant for long periods before erupting and some that slowly erupt continuously. If this number increased by between 100 and 300 it could not go unnoticed. An argument against this possibility is that any increase in volcanic activity in Iceland will be at a much lower level than the volcanic response of the volcanoes of Iceland at the beginning of the post-glacial period. And at high and mid latitudes that had much thicker ice mantles in the Late Pleistocene than they do now, so any response in these volcanoes would also be on a much smaller scale than following the close of the last glacial period. According to the author1 it is unlikely that coastal or island volcanoes would be triggered to erupt by even a 10 m sea level rise on the same scale they did to a 130 m rise, though it is demonstrated by Pavlof that if a volcano is primed it only takes a miniscule sea level change to trigger an eruption. It has also been demonstrated by the annual movement of water around the Earth that many volcanoes can be extremely sensitive to negligible changes in their environment. There is also evidence that the activity of individual volcanoes can be influenced by storms, heavy rain or the increases and decreases of atmospheric pressure.
A rise of the global sea level of 1-2 m during the 21st century would be only 20-40 % of the catastrophic rise that occurred 15,000-7,000 years ago, a time at which the volcanic response was at its highest. The diminishing ice cover on Iceland, as well as on other volcanic regions, still in the process of melting at this time, would have contributed to sea levels that are suggested to have been rising at this time by evidence from research in the Mediterranean, the higher sea levels driving, in part, the peak of volcanic activity. The author1 suggests that if a sea level rise was anywhere near a comparable rise to that in the post-glacial times it would be surprising if the consequent loading of the crust by the encroaching ocean didn't lead to at least some increase in the degree of volcanic activity at some point, either in this century or further into the future.
It has been suggested by research published in 2011 that sea levels can be expected to rise much more rapidly than they are predicted to rise in the IPCC's Fourth Assessment Report, as it indicates an astonishing acceleration over the last few years of melting at both poles. It has been found by research carried out by Eric Rignot et al., from the University of California, Irvine, that the ice sheets on Greenland and Antarctica combined are losing an additional mass of 36 billion tonnes to the oceans annually. These same ice sheets are estimated to have lost half a trillion tonnes in 2008. It has been forecast by Rignot et al. that if the rate of ice melt continues at the present rate that global sea level will rise by 1/3 of a metre by 2050 and by 2100 at the same rate of melting it should reach more than 0.5 m. When the volume increase resulting by thermal expansion and the contributions from all other ice sources, such as the thousands of glaciers that are retreating, the total rise could be more than 1 m, though there is always the chance that the ice mass at the poles will increase, possibly dramatically, because the temperatures at the poles are rising much faster than the global average. If this does eventuate it is anybody's guess how high the global sea level will rise by 2100.
The author1 suggests that a caveat needs to be attached if rising sea levels provoke a noticeable volcanic response at some time in the future, as new magma production deep in the asthenosphere does not necessarily occur if more magma is erupted at the surface. According to the author1 the annual volcano season can only be explained if changing environmental conditions modulate the timing of eruptions in volcanoes that are already primed so that the inevitable eruption is merely brought forward, the favourable conditions for eruptions occurring at specific times of the year, resulting in the clustering of eruptions instead of a random distribution of eruptions throughout the year. If variations of stress and strain caused by rising sea levels in coastal and island volcanoes lead to a response in the future it would be in a similar manner to that occurring in the volcano season, the timing of various volcanoes being brought into line by external forcing, with the result that in a given time period the level of volcanic activity can be observed as an increase.
While providing some indication of what to expect from volcanoes as anthropogenic warming increases, it also raises some key questions, such as will the number of erupting volcanoes be enough to become apparent above the background rate, or will an increase in eruptions be small enough to be missed in the statistical noise? Another question is if there is an increase in eruption numbers that is linear, with more occurring progressively from decade to decade, or will it increase in surges as thresholds are crossed? A question suggested by the author¹ to probably be the most important is whether any response to rising sea levels in the future would occur only in volcanoes that are especially sensitive producing small to moderate eruptions easily and frequently or will volcanoes that produce explosive blasts that are much larger? The importance of this question lies not only in this type of eruption having the potential to be far more destructive, but also as in the case of the Tambora eruption of 1815 that can put volcanic dust and gases high enough in the atmosphere to have a cooling effect on the climate. If there are no blasts on the scale of the Toba blast, that occurred in prehistoric times, the author1 suggests anthropogenic climate change will not be affected by volcanic eruptions. He also suggests that the warming could be slowed if there were 1 or 2 Tambora scale blasts it might do the trick, cooling the Earth for a couple of years.
Active faults in a warming world
Another possibility in a warmer world of the future is increasing numbers of earthquakes. There continues to be talk about the recent bout of powerful earthquakes possibly being connected with the changing climate. There has been 7 earthquakes of magnitude 8.8 or higher on the Moment Magnitude Scale since 1900, one of which occurred in the first half of the 20th century, striking Ecuador in 1906. There were 3 of this magnitude in the second half of the 20th century - 1 on the Kamchatka Peninsula, Russia in 1952, 1 off the coast of Alaska in 1964, and in 1960 an earthquake of magnitude 9.5, the biggest ever recorded, ripped open the Peru-Chile Subduction Zone. There have already been 3 earthquakes of magnitude 8.8 or higher in the 21st century, covering a total of less than 6.5 years. Though this could merely be a fluke, clustering being possible. It has been suggested that there may be some underlying mechanism that hasn't been found so far that leads to the clustering of quakes in a short time period. Stress transfer is a process known to occur which can cause an earthquake to occur earlier than it otherwise would by an earthquake occurring on part of a fault putting pressure on the part of the fault that then ruptures, and so on to the end of the fault. This process operates on the North Anatolian Fault that ruptures from the west to the east over about a century, a series of earthquakes being triggered in succession. It has been suggested that the Sumatran earthquake of 2004 was responsible for triggering aftershocks represented by the Chilean earthquake of 2010 and Japan earthquake of 2011. In the case of the earthquake off the coast of japan in 2011 the author1 suggests that as the fault would have been critically poised and ready to rupture after being quiescent for more than 1,000 years it probably needed no more than a tiny stress to trigger it, possibly provided by another massive earthquake several years earlier and thousands of kilometres away. It has been suggested by John McCloskey from University of Ulster, Northern Island, that the 'pressure of a handshake' is all that is required to trigger a major earthquake under some circumstances. As with volcanoes, earthquake faults that are poised to rupture require very little to do so.
The author1 suggests this leads naturally to the potential increase of earthquake activity in a warmer world where the stresses acting on some active faults, at least, by glaciers that are melting and the rise of the sea levels. In Alaska more earthquakes are occurring as the glaciers melt, and there are other places in the world where a seismic reaction could be expected to become apparent as ice melts, such as the Andes, the Himalayas, the Southern Alps of New Zealand and beneath the Vatnajökull Ice Cap in Iceland. Earthquakes could arise in such regions consequent on the load reduction on active faults, the movements of which are impeded by the pressure of the overlying ice, as is the case in Alaska at the present. Increased pore water near active faults that result from the expansion and deepening of meltwater lakes, as well as by the catastrophic draining of such meltwater lakes.
Any possibility of climate change contributing to the triggering of really large earthquakes is of interest to scientists, regardless of whether or not it can be justifiably implicated in the large seismic catastrophes that have occurred over the past 7 years. According to the author1 rising sea level is the only climate change factor that is believed to possibly be implicated in influencing the recent cluster of catastrophic earthquakes, though he says the current rate of rise is small, and rising sea level tends to stabilise subduction zone faults offshore where the biggest earthquakes are located. This effectively disallows any anthropogenic climate change from triggering these exceptionally large seismic events such as those of the past several years, though doesn't rule out the possibility that there may be a higher level of seismic activity in a warmer world. The work of Luttrell and Sandwell, that was mentioned previously, indicates that the seismic focus at marine subduction zones may be shifted landwards, with deeper earthquakes being promoted inland. A migration such as this would lessen the chance of tsunamis, though it is likely to make the earthquakes that occur more destructive, as their epicentres would then be closer to coastal towns and cities. Transform faults that move laterally, such as the San Andreas Fault and the Haitian Fault, that killed 250,000 people in 2010, may be able to more easily generate earthquakes as the rising ocean promotes their unclamping by bending the lithosphere at the point where the ocean meets the land.
In the context of the Earth's seismic future the Greenland and West Antarctica ice sheets is one of the big unknowns, the loading on the crust beneath them being greater than anywhere else and they are the places where the melting is happening more rapidly than anywhere else. It is unknown if and to what extent seismic activity will increase as the ice melts. At the present they are seismically quiescent. The Vatnajökull Ice Cap in Greenland is rapidly rebounding and, according to a study by Tim Dixon of the University of Miami, and others, Greenland is rising at an accelerating rate as the ice is melting rapidly. Dixon and his colleagues have shown that in places, the rebound is occurring at as much as a couple of centimetres per year, based on GPS data from Greenland, Iceland, and elsewhere, and suggest that by 2025 the rebound rate could have doubled. The author1 suggests it is astonishing that there is any uplift at the present as it is so early in the climate change process and gives some indication of just how fast the Greenland ice is melting. He suggests the uplift observed at the present is the forerunner of future uplift that will be far greater and more widespread, and a long way still remains. At 3,700 m the highest point on the island is contributed to by some areas having an ice cover that is up to 2 km thick. The centre of Greenland is a basin 300 m below sea level as a result of the loading on the crust due to the ice cover.
It has been suggested by Andrea Hampel of Ruhr University Bochum and colleagues that any faults in Antarctica and Greenland are being locked by the massive weight of ice above them. Hampel and colleagues suggest there will be an increasing frequency of earthquakes in these regions as the ice continues to melt and they speculate that the first signs of this seismic activity could begin within decades. If large earthquakes are generated in these areas in the future they could possibly send catastrophic tsunamis to heavily populated areas, especially from Greenland where tsunamis could impact on coastlines of the North Atlantic.
Major submarine faults of the type that triggered the devastating tsunamis that caused so much damage in 2004 and 2011 are not known of around Greenland's margins. The Mid-Atlantic Ridge that runs parallel to the east coast, and not very far from Greenland, is a constructive plate margin at which new crust is produced, and associated earthquakes are small to middling. The Storegga Slide that occurred 8,000 years ago was triggered by the collapse of a vast volume of sediment that was dislodged by the Scandinavian rebound after the ice sheets of the last ice age, that had a maximum thickness of 3 km, had melted. Spectacular faults that have been found in Lapland indicate that there were very large earthquakes of magnitude 8 of more that were triggered by post-glacial rebound. The author1 suggests that if the Greenland Ice Sheet is completely lost the rebound that would occur has the potential to trigger giant submarine landslides if the necessary amount of sediment is available at the time, and at the present not enough is known about the offshore zone around the island. He suggests that this situation will change when the hydrocarbon companies begin surveys of the sea floor and the putative treasure beneath. It appears likely that seismic activity will likely occur as the ice on Greenland continues to melt and if it is found that there are large sediment deposits around the island then it is likely tsunamis could be generated by their destabilisation and collapse.
According to the author1 there is also another potential threat posed by the accelerating rebound of Greenland. He also suggests that even as the melting Greenland ice contributes to sea level rise, Greenland could rise up even faster, and at the present some parts of the Greenland coast are rising 6 times faster than the oceans are rising. If this trend continues the pressure exerted by the ocean on the offshore sediments will progressively decrease, this could lead to the dissociation of the any gas hydrates in the sediments, allowing the release of methane to the atmosphere and destabilising the sediment in the process, and if landslides are triggered by the escaping methane these slides could cause the generation of tsunamis into the North Atlantic. It is not certain that higher temperatures in the ocean will promote a worldwide increase of submarine landslides as a result of the instability of the gas hydrates with the associated threat of tsunamis. At the present the general consensus appears to be that sea level rise will act to stabilise most gas-hydrates as they are situated deep in the sediments of the sea floor and therefore it would be centuries, at least, for the increased temperatures of the warming oceans to reach them and trigger their dissociation.
Greenland and other places in the polar regions are believed to be where any problems arising from marine gas hydrate breakdown will most likely occur as the global temperatures rise, and these are the places where the temperature rise is occurring much faster than any other part of the world and where the cold conditions have allowed the gas hydrates to form much closer to the surface of the sediment deposits. The author1 suggests these gas hydrate deposits may already be in a precarious position with a submarine permafrost layer, that is not likely to survive for long, being all the prevents warmer water temperatures reaching them and causing their dissociation. It has been suggested by Russian scientists that have been monitoring the region that the submarine permafrost is already beginning to break up in some places which has allowed millions of tonnes of methane to escape into the atmosphere above the Arctic Ocean. It is suspected that up to 1.4 trillion tonnes of gas hydrate and methane gas are trapped beneath this submarine permafrost. Something that is particularly worrying to the scientists is that they have observed up to 10 % of the area is now being punctured by taliks, areas where thawed permafrost provides an escape route for methane from the breakdown of gas hydrates and the entry of warmer water that increases the amount of breakdown of the gas hydrates, the author1 suggesting 'this is a recipe for climate catastrophe'. It has been suggested by Natalia Shakova of the International Arctic Research Centre, University of Alaska, and her colleagues that up to 50 billion tonnes of methane could possibly be released abruptly and with no warning into the atmosphere from the Arctic sediments. Such a massive release would increase the atmospheric methane concentrations by 12-fold virtually overnight which would drive cataclysmic warming. As the warming reached further in the submarine sediments it would lead to further dissociation of submarine gas hydrates and thawing of land-based permafrost would rapidly release the methane stored beneath them and wet land production of methane that is already high could produce even more.
'In the course of drawing together and evaluating all the evidence, I have been persuaded that it would be remarkable if unmitigated anthropogenic climate change failed to elicit a conspicuous and salient response from the surface and the interior of our planet, even if it does not fully, as it were, 'reawaken the giant'', Bill McGuire in his book Waking the Giant1. He also says that adding to his conviction is the accumulating evidence that a variety of potentially hazardous geological phenomena are extremely sensitive to the smallest changes in their environment.
Earlier in his book he has described a number of phenomena that can be triggered by tiny changes in the environment:
Volcanic eruptions - triggered by rainfall, triggered or modulated by tidal stresses, extremely small changes of local sea level, and very small variations in the shape of the Earth over the course of a year
Earthquakes - that can be induced by variations in the rate of spin of the Earth that are infinitesimally small. If a fault is critically poised it could be triggered to rupture by the pressure of a handshake. In Taiwan, falls in air pressure associated with typhoons crossing the island have been shown to be all that is required to induce movement in faults. In parts of Japan loading and subsequent unloading by snowfall in winter. On the Cascadia Subduction Zone small-scale slips and tremors have been correlated with ocean tides. In Germany, the timing of small earthquakes is controlled by rainfall changes. In Colorado daily atmospheric pressure variations modulate the amount of slip on the Slumgullion landslide. The suggestion that many geological systems that are potentially hazardous may be on the verge of becoming unstable is supported by this evidence, a tiny nudge being all that is required to move the system from stabile to unstable.
|Author: M.H.Monroe Email: email@example.com Sources & Further reading|