The repeated collapse of the ice dam holding back Glacial Lake Missoula, at the end of the last Ice Age, unleashed floods that were utterly disproportionate to the scale of the landscape, in the depth and speed of the water. (It’s been suggested it’s analogous to dumping a bucket of water onto a tabletop model.) The floods carved the Channeled Scablands of eastern Washington, including the Grand Coulee. Dry Falls, which separates the upper and lower Grand Coulee, is a nick point where the floods were eroding upstream; the falls’…
