“The mapping uncovered widespread deep valleys below the ice sheet, many of which lie below sea level. Many valleys also originate far inland and end at the sea. Out of 123 marine-terminating glaciers, “60 drain 88 percent of the ice sheet in area and are grounded below 300m depth at their termini, meaning they are deep enough to interact with subsurface warm Atlantic waters and undergo massive rates of subaqueous melting.”32 Under the right conditions, this could lead to a rapid meltdown that would affect a substantial portion of Greenland.”