Seismic slippage

doi:doi:10.1038/climate.2008.36

Nature Reports Climate Change
Published online: 24 April 2008 | doi:10.1038/climate.2008.36

Seismic slippage

Anna Barnett

Science doi: 10.1126/science.1153360 (2008)

Science doi: doi:10.1126/science.1153288 (2008)

IAN JOUGHIN, UW POLAR SCIENCE CENTER

Summer meltwater draining from the surface of the Greenland Ice Sheet down to the bedrock below can cause seismic shifts in the ice. Yet despite the dramatic drainage — in one case exceeding the flow of Niagara Falls — seasonal streams have little effect on the descent of glaciers into the sea, show two new studies.

Both were led by Sarah Das at Woods Hole Oceanographic Institute in Massachusetts and Ian Joughin at the University of Washington. The researchers first monitored a large surface lake that formed near the edge of the Greenland Ice Sheet and drained through deepening cracks. Once the fissures spread down through all 980 metres of the ice sheet, the two-kilometre-wide pool was sucked dry within 90 minutes — moving more water per second than the famous falls, and shifting the sheet by 1.2 metres.

Using radar and GPS measurements across a range of Greenland sites, however, they then found that coastal glaciers dumping icebergs into the ocean are relatively insensitive to such summer meltwater pulses. Inland ice sheets slid up to twice as fast in the melt season, but coastal glaciers increased their speed by less than 15 per cent. The coastal glaciers' remarkable recent acceleration seems instead to result from melting of their front edges, possibly in response to declining sea ice.