Today's idle clicking through Wikipedia...

...introduced me, as I am introducing you now, to the Missoula Floods, a series of cataclysmic floods resulting from the periodic rupture of the ice dam at the end of the glacial Lake Missoula in Washington State during the Ice Age. The ice dam regularly gave way because (to simplify slightly) as water built up behind the dam, the increased pressure at the foot of the dam lowered the water's freezing point, melting the dam. The result was Dry Falls (satellite view), the largest known waterfall ever, ten times the size of Niagara, and a peak flow of the floods of 80 mph. Woo!