How quickly these huge bodies of ice slide off the Antarctic and Greenland land masses into the ocean help determine the speed at which sea levels rise.
The stakes are enormous: an increase measured in tens of centimetres (inches) could wreak havoc for hundreds of millions of people living in low-lying deltas and island nations around the world.
Researchers discovered only recently that inaccessible subglacial lakes in Antarctica periodically shed huge quantities of water.
Data collected by a satellite launched in 2003 -- the Ice, Cloud and Land Elevation Satellite, or ICESat -- revealed a complex network of subglacial plumbing in which water periodically cascades from one hidden reservoir to another.
But the new study, published online in the journal Nature Geoscience, is the first to measure the potential impact of this invisible flooding on sea-bound glaciers.
A trio of scientists led by Leigh Stearns of the Climate Change Institute at the University of Maine matched ICESat da