May 12, 2014
Melting Ice Found To Cause Quicker Movement Of The Earth Underneath
Gerard LeBlond for redOrbit.com - Your Universe Online
Antarctica’s ice shelf lays motionless at the surface, but 250 miles below, the Earth is moving at an incredible rate, according to recent research.The new study explains why the upward movement of the Earth’s crust is happening so rapidly in the northern Antarctic Peninsula and was published in this week’s Earth and Planetary Science Letters.
Scientists from Newcastle University in the UK led the research with assistance from international teams from DTU, Denmark; University of Tasmania, Australia; Hamilton College, New York, US; University of Colorado, US; and the University of Toulouse, France. Previous studies have shown that the Earth is rebounding from the overlaying ice shelf shrinkage caused by climate change. It was considered to be an instantaneous result from the elastic response followed by a very slow uplift occurring over thousands of years.
However, new GPS data has revealed that, in this region, the land is rising at an incredible rate of .60 inches a year. Also, for the first time, the study revealed how the mantle below the Antarctic Peninsula is moving much faster than originally thought; most likely from the small changes in temperature or chemical make-up. By shrinking, the weight load of the ice shelf is reduced on the mantle causing it to move easier and quicker, thus changing the shape of the land.
“You would expect this rebound to happen over thousands of years and instead we have been able to measure it in just over a decade. You can almost see it happening which is just incredible. Because the mantle is 'runnier' below the Northern Antarctic Peninsula it responds much more quickly to what's happening on the surface. So as the glaciers thin and the load in that localized area reduces, the mantle pushes up the crust. At the moment we have only studied the vertical deformation so the next step is to look at horizontal motion caused by the ice unloading to get more of a 3-D picture of how the Earth is deforming, and to use other geophysical data to understand the mechanism of the flow,” explained lead researcher Grace Nield, a PhD student from Newcastle University, in a recent statement.
Since 1995 there have been several ice shelves in the Northern Antarctic Peninsula that have collapsed triggering ice-mass unloading, which caused the solid Earth to ‘bounce back’.
“Think of it a bit like a stretched piece of elastic,” says Nield, whose project is funded by the Natural Environment Research Council (NERC). “The ice is pressing down on the Earth and as this weight reduces the crust bounces back. But what we found when we compared the ice loss to the uplift was that they didn’t tally – something else had to be happening to be pushing the solid Earth up at such a phenomenal rate.”
The team used seven GPS stations to collect data and found the rebound happened so fast that the viscosity in the upper mantle was ten times lower the previously thought in the region and even lower than the remaining area in Antarctica.
“Seeing this sort of deformation of the earth at such a rate is unprecedented in Antarctica. What is particularly interesting here is that we can actually see the impact that glacier thinning is having on the rocks 250 miles down,” added Peter Clarke, one of the authors of the study and Professor of Geophysical Geodesy at Newcastle University.