Lake Missoula and the Scablands,Washington, USA

Gigantic floods that, for just a few days, had flow rates many times greater than the combined flows of all the other rivers of the world put together. Sounds ridiculous, and it's almost inconceivable, but it's real, and it all happened at the end of the last Ice Age. The water came from Lake Missoula, which exists no more, but the effects are still to be seen in the landscapes, most notably in the vast scablands of eastern Washington.