Magma!
Reported here:
Thwaites Glacier, the large, rapidly changing outlet of the West Antarctic Ice Sheet, is not only being eroded by the ocean, it’s being melted from below by geothermal heat, researchers at the Institute for Geophysics at The University of Texas at Austin (UTIG) report in the current edition of the Proceedings of the National Academy of Sciences. ... Until now, scientists had been unable to measure the strength or location of heat flow under the glacier. Current ice sheet models have assumed that heat flow under the glacier is uniform like a pancake griddle with even heat distribution across the bottom of the ice. The findings of lead author Dusty Schroeder and his colleagues show that the glacier sits on something more like a multi-burner stovetop with burners putting out heat at different levels at different locations.
