Click For Photo: https://www.sciencedaily.com/images/2019/03/190322163342_1_540x360.jpg
The ice-cliff research was spurred by a helicopter ride over Jakobshavn and Helheim glaciers on Greenland's eastern coast. Helheim ends abruptly in the ocean, in near-vertical ice-cliffs reaching 30-stories high (100 meters). On the flight, scientists viewed large cracks (called crevasses) on top of the ice that marched towards the end of the glacier.
"Geologists have spent decades -- centuries -- worrying about slumps," says Richard Alley, co-author of the new paper in Geology. A slump occurs when mass of rock or sediment loses some of its strength, breaks away from its neighboring land, and slides down a slope. Typically, slumps are marked by a steep scarp where the material broke away, followed by a block of material moved downslope.
Alley - Research - Team - Features - Helheim
Alley says the research team noted that features on Helheim glacier are typical of what you might see in a slump-prone terrestrial landscape and they wondered if ice might suffer the same fate. "You've got a crevasse that serves as a head scarp and then you've got the stresses [within the ice] maximized down at the water level," he says.
To test if slumping occurs on ice cliffs, the team monitored Helheim glacier during a calving event, using real-aperture terrestrial radar interferometery. They measured speed, position, and motion of the calving ice. The researchers observed an ice-flow acceleration just before an initial slump, followed by a rotating, full ice-thickness calving of the glacier -- including the entire remaining ice-cliff, reaching both above and below the water line.
Weight - Ice - Encourages - Ice - Back
Removing the weight of the upper ice by slumping encourages the underlying ice to pop upward. "Because it's still attached at the back, it's going to rotate a little bit," says Alley. The rotation causes a crack to form at the bottom of the glacier as the ice flexes. In turn, the crack can weaken the ice,...
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