Learning More about Role Water Beneath Glaciers Plays in Ice Loss
16.12.2009 - Water & Oceans, Ice & Snow
Researchers led by Dr. Ian Howat, Assistant Professor of Earth Sciences at Ohio State University have been able to gain new insight into how water flowing beneathglaciers contributes to ice loss.
As the ice melts at the surface, water trickles down into the glacierthrough moulins (narrow chutes or crevasses via which water enters aglacier from the surface) of various sizes, eventually forming vastrivers and lakes under the ice. Until now it was believed thatmeltwater that reached the bedrock merely lubricated the ice againstthe bedrock, causing glaciers to flow to the sea faster, and that thissub-glacial water was responsible for sudden increases in the flow rateof outlet glaciers as they made their way to the ocean.
However results of GPS monitoring studies show that most of the time, meltwater at the base of the ice sheet has little influence on ice loss along the coast. In fact meltwater gradually carves out an intricate network of moulins, forming a constantly-changing ‘plumbing system' that regulates where water between the ice and bedrock accumulates at different times of the year. Meltwater increases in summer when ice melts and decreases in winter when water refreezes.
When a sudden massive influx of meltwater arrives at the start of the summer melting season, it overwhelms the subglacial drainage system, and the sudden increase in water pressure lifts the ice off the bedrock and makes it flow faster - as much as 100 meters per year. As the waterways expand to meet the new volume of water, water pressure drops and so does the rate at which the glaciers flow.
Yet with no clear correlation between peak melt in the summer and sudden acceleration measured in outlet glaciers, Dr. Howat and his team turned their attention to where the glaciers meet the sea. Using computer models they determined that friction between the sides of the glacier and the surrounding fjord holds the glacier in place and sudden increases in ocean temperature is what causes the outlet glaciers to accelerate.
The research team did find that meltwater can influence on ice loss along the coast when it expands within cracks to form stress fractures or bubbles out from the base of the ice sheet and agitate warm ocean water, both of which cause huge chunks of the glacier to calve off.
Howat presented his findings at the American Geophysical Union (AGU) meeting in San Francisco, California on 16 December. His project and the related projects being run by the University of Colorado-Boulder / NOAA Cooperative Institute for Research in Environmental Sciences (CIRES) and NASA's Jet Propulsion Laboratory (JPL) can help better understand ice loss elsewhere in the world (including Antarctica) and could ultimately lead to better estimates of future sea level rise due to climate change.
