At first glance, there doesn't seem like there could be any connection between global warming and seismic activity. After all, why would the earth become less stable just because it's a little warmer?
Well, connected they are. The earth's crust is a lot more sensitive than you might think. There are well documented cases of even the load of water in a new dam triggering earthquakes in the local area.
A number of geologists say glacial melting, in particular, will unleash pent-up pressures in the Earth's crust, causing extreme geological events such as earthquakes, tsunamis and volcanic eruptions.
Consider this: a cubic meter of ice weighs nearly a ton and some glaciers are kilometers thick. This prodigious weight acts to suppress tectonic movements in the underlying crust, and plug cracks where volcanic magma might otherwise escape to the surface. When the weight is removed through melting, the suppressed strains and stresses of the underlying rock are free to come to life.
As reported only this year, Harvard seismologist Göran Ekström has found a striking increase in the frequency of glacial quakes, particularly in Greenland, but also in Alaska and Antarctica.
Greenland quakes have risen from 6 to 15 a year between 1993 and 2002, to 30 in 2003, 23 in 2004 and 32 in the first 10 months of 2005, closely matching the rise in Greenland's temperatures over the same period. Their source was traced to surges and slips within ice sheets, where rapid melting is causing water to collect under glaciers, making them glide faster into the sea, triggering quakes.
Similarly, retreating glaciers in southern Alaska are likely to open the way for future earthquake activity.
Accelerated melting of glacial ice decreases the load on the Earth's crust, thereby decreasing the pressure holding volcanic conduits closed. Already, we are seeing evidence of new volcanic activity in Antarctica. A new, previously unknown volcano has appeared on the sea bottom in waters off the Antarctic Peninsula, in an area with no previous record of volcanic activity. Investigations into a large area of surface slumping on the West Antarctic Ice Sheet revealed a huge accumulation of water underneath that has now been shown to be due to an active volcano erupting under the sheet.
Glacial melting has a less direct but just as unsettling additional impact on global seismic activity. The reliquified water released raises sea levels and increases the weight on the ocean floor, unbalancing tectonic forces deep below the surface. Underwater quakes and therefore tsunamis could thus become more frequent. Though they get little attention, glacial melting of the Antarctic ice is already causing earthquakes and underwater landslides.
Other hotspots at high risk of submarine earthslides – similar to the one that set off the disastrous tsunami in Indonesia in 2004 – include seaward of the mouths of the Ganges, Nile and Amazon rivers, as well as much of the Atlantic and US coast (E. G. Nisbet, 2004.)
Even the shape of the Earth appears to have been significantly influenced by climate events due to changes in the mass of water stored in oceans, continents and atmosphere. Satellite data indicate the bulge in Earth's gravity field at the equator is growing, counteracting the long-term shrinking up to 1998 due to post-glacial rebound.
Current estimates of polar ice melting are too small to explain the recent changes in the gravity field. Scientists postulate that global warming-induced redistribution of existing water mass is possibly behind the phenomenon. However, the specific cause still remains a mystery.
Dramatic climate shifts of the past have also been associated with spectacular seismic activity. During the late glacial and early Holocene periods when climate was see-sawing from one extreme to another in the interval known as the Younger Dryas, submarine landslips were widespread. For example, 8,200 years ago an enormous slip in the Norwegian Sea involving over 3000 cubic kilometers of material set off a massive tsunami more than 20 meters high. At about the same time mega-earthquakes ruptured the crust and lifted Scandinavia's mountain backbone by 5 to 15 meters. Could it happen again?
The science suggests that as redistribution of the Earth's mass induced by global warming disturbs the relative equilibrium of its crust, monumental forces in the form of increasing earthquakes, tsunamis and volcanic activity could be unleashed. And the forecasts from some quarters are dramatic - – not only will the earth shake, it will spit fire (Bueckert, 2006).