May 10th, 2012 by James Ayre
There is growing evidence that some of the Earth’s most catastrophic geological events were triggered by changes in the climate.
The melting of ice sheets and changes in sea level served as triggers to some of the world’s largest earthquakes and volcanic eruptions, according to British geologist Bill McGuire.
The best evidence of climatic influence on geology is from around 12,000 years ago, the end of the last ice age. Recent studies of volcanic deposits, have shown that this period of rapid change, as the ice sheets retreated, coincided with an outburst in geological activity.
Volcanic eruptions increased about 50 fold after the ice sheet retreated, and took around 1,500 years to return to the previous level.
McGuire argues that the weight of ice, two kilometers thick over Iceland, kept pressure on the volcanoes and suppressed the eruptions. As the ice sheet retreated, the surface of the ground in some places rose up by hundreds of meters, relieving the pressure.
Freysteinn Sigmundsson of the Nordic Volcanological Center at the University of Iceland in Reykjavik, is quoted as saying “Reduction of pressure enabled mantle rocks to melt, creating a zone of magma upwelling underneath Iceland.”
The production of magma then increased 30 fold, leading to the huge increase in volcanic eruptions.
Similar activity has occurred across the globe, anywhere that retreating ice sheets or glaciers have melted, according to Hugh Tuffen, a volcanologist at the University of Lancaster in England. From Germany, to Chile, to California, to Kamchatka, volcanic activity increased.
The climate has been mostly stable since then and volcanic activity has lessened greatly. McGuire warns that as the climate warms, there could be a large increase again.
“Volcanoes can be incredibly sensitive to tiny changes to their external environment, constantly teetering on the edge of stability,” he says.
Serge Guillas, one of Bill McGuires colleagues at University College London, has found that El Niño cycles in the eastern Pacific regularly trigger seismic events, with more earthquakes there in the months after the cycle lowers the sea level in the area by a few centimeters.
In a 2009 study by the Carnegie Institution, it was found that even just the low atmospheric pressure of a typhoon was enough to trigger earthquakes near Taiwan.
The evidence for volcanoes is even better, according to Oxford University geologists Ben Mason and David Pyle. The Earth has volcanic seasons, with eruptions happening most frequently between November and April in the Northern Hemisphere.
There are many sleeping volcanoes and fault lines under the Antarctic and Greenland ice sheets that could potentially reawaken.
Andrea Hampel, a geologist at Leibniz University, is quoted as saying, “Shrinkage [of the ice] owing to global warming may ultimately lead to an increase in earthquake frequency in these regions. This effect may be important even on timescales of 10 to 100 years.”
The frequency of large earthquakes has seemed to be increasing, but with the limited nature of records on the matter, it’s hard to tell for sure.
There have been seven earthquakes above 8.8 since 1900, with only one recorded from 1900-1950, three between 1950-2000, and another three just in the last seven years. The recorded earthquakes above that magnitude seem to be increasing exponentially. Though it’s still debatable how much of that is due to an actual increase, or increased detection.
In response to critics of his ideas, Bill McGuire is quoted as saying, “people who find the idea [of climate change triggering geological events] flaky don’t appreciate that the link between abrupt climate change and a response from the solid Earth is supported by huge amounts of research.”
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