NOVA had a show the other day about what happened in Washington State about 15,000 years ago, how glaciers from Canada created a huge dam ( Glacial Lake Missoul ) with trillions of gallons of water or 500 cubic miles of water estimated. When the dam broke it created the Scablands about 200 miles east of Seattle. The interesting was part was how the scientest discovered the process by which water (which is supercooled, below 32 C) interacts with the ice breaking the glacier apart which then creates deluge of water and ice. The process was discovered I think they said Greenland; in 1993 there was a glacier/water flood on a smallar scale but it was discovered that water under tremendous pressure water will not freeze, it then becomes "supercooled" and then starts running through fissures in the glacier, this in turn starts to weaken the structure of the glacier which then results in the water and ice creating a flood. This is what happened in the Scablands, but on a much larger scale it created valleys a 1000 feet deep, a waterfall 5 times wider then Niagara Falls and the evidence seems to point that is all happened over a 48 hour period. Interesting show.