Penetrating radar has generated a surface map of Greenland far below all that ice, revealing a canyon over two thousand feet deep in places, hundreds of miles long, a canyon which may still be moving meltwater off the ice fields to the sea. More than four million years ago this was a river valley when Greenland had not drifted so far north. Just under an inch per year of continental drift translates into fifteen miles every million years. That's two or three hundred miles since the last dinosaur died out.
The story, reported at Science Daily News.
Link to current continental drift rates, some estimated by satellites, using relative motions.
A river landscape under the North Sea off Scotland under a mile of mud.
UPDATE: This is also an aquifer covering 27000 sq. miles within a hundred feet of the surface of southern Greenland. Year round water persists in voids in the ice.
UPDATE: An even greater Grand Canyon discovered on the seam between the east and west Antarctic, up to a mile below sea level in spots.