This incredible image is a radar profile revealing the layering under a particular part of the ice-sheet of East Antarctica.  The ice in this area can be 2 miles thick and overlays the Gamburtsev mountains (depicted by the red line) which are about as large as the European Alps.  These invisible mountains have been known to exist for 50 years,  but the discovery of the huge bulge in the picture was totally unexpected.

What is thought to be happening here is that sub-glacial water at the base of the ice sheet is being forced up the valley sides, as it gains elevation the weight of the overlying ice becomes less and exerts less pressure, because of this the water rapidly turns to ice (this effect is called super-cooling) creating this freeze-on ice bulge.

Water can remain liquid at the base of the ice sheet even when it is below the normal freezing point, this is because of the immense pressure of the overlying ice.  Furthermore, friction at the ice-bed interface can generate heat as well as heat radiating from the underlying rock, this heat is then insulated by the overlying ice.  So again if the water is being forced away from these insulated heat zones or, as mentioned above, experiences a rapid pressure drop as it moves up the valley walls it will turn to ice.

This idea turns our common perception that ice-sheets grow from above, by falling snow layer-upon-layer, upside down.  Apparently about a quarter of the ice thickness in this area is grown from below.

“We usually think of ice sheets like cakes–one layer at a time added from the top. This is like someone injected a layer of frosting at the bottom–a really thick layer” Robin Bell (lead author)

Reporting here from the BBC and here from the New York Times or the press release itself from The Earth Institute, Columbia Univerisity.  The work has been published in Science and can be found here (access required).

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