When melt water leaves an ice sheet, where does it go?
Some of it it quickly flows off the surface of the ice toward the ocean
through underground channels. But some water gets trapped near the top of the ice sheet
in a region of compacted snow which has not yet
been squeezed hard enough to become solid ice.
This region is known as firn and it sits between the fresh snow above and the solid ice below.
In some places, so much water can accumulate in the firn
that it acts as a natural aquifer within an ice sheet or a glacier.
A new NASA study of the massive Helheim Glacier
in eastern Greenland shows that some of the water trapped in the firn
may be reaching the bedrock of the glacier through giant cracks in the ice
called crevasses.
Helheim is criss-crossed by a series of these large crevasses,
and models show that the water flows into these crevasses and descends all the way down to the glacier bed.
From there, the water has a clear path to the ocean.
This study is a step toward understanding how firn aquifer water
contributes to sea level rise.