Ian Bartholomew at Edinburgh University in Scotland said the variability was much stronger than earlier observations of glacier movement in Greenland. The study was published in the journal Nature Geoscience. this behavior was not observed before about the mid 1990s. It was also tat about this time that great icequakes were discovered coming from the Greenland ice sheet.
A paper published in 2007 describes a new icequake that has been found mostly in Greenland. These icequakes are much larger than their traditional icequake brothers, coming in at magnitudes between 4.6 and 5.1 on the Richter scale. They are unlike traditional icequakes in that their magnitude is much large and their times scales are between 35 and 150 seconds. Traditional icequakes have a magnitude of no greater than 2.7 and last only one second or less. These icequakes were discovered in a summary of global seismic data and pinpointed to outlet glaciers in Greenland in 2003. The recent report describes “a dramatic increase in the number of these icequakes since 2002”, and a doubling of their numbers in 2005 above any single year prior to 2003.
These icequakes are probably caused by meltwater draining down to the bottom of the ice sheet through cracks. The ice basically lubricates the ice and lets it flow more quickly. Satellite observations have shown the ice actually rising – floating on this film of water, up to two feet during the highest melt periods. This allows the ice to unstick from the bedrock and slip frictionlessly downhill. When the ice grinds to a halt against the bedrock it creates the icequakes.
Khan, et. al., Spread of ice mass loss into northwest Greenland observed, Goephysical Research Letters March, 2010.