Climate Central: The flat, glistening, white expanse of the Greenland Ice Sheet, stretching out across hundreds of thousands of square miles, appears placid, unchanging ... boring even. But this tranquil surface belies the turmoil taking place below, at the base of the ice sheet. There, scientists have discovered sections of ice up to a kilometer thick and tens of kilometers long where meltwater has refrozen to the base of the ice sheet, setting off a dynamic process that causes the layers of ice to build up over...