Picture a meltwater flood moving half a billion to a billion cubic feet per second. On his tours out west, Randall takes people to the top of Steptoe Butte in southeastern Washington, above the rolling Palouse landscape about 1,400 feet below. At one point that whole landscape was submerged by a gigantic meltwater river carrying huge icebergs.
Anyone who survived on top of the butte would see only a sea of mud in every direction. They would have no way of knowing whether anyone survived 50 or 100 miles away. From that perspective, it would be rational to conclude the whole world had been destroyed.