[bert]

I saw remnants of such an impoundment from Polychrome in Denali National Park in Alaska. There is clear evidence of areas swept by rushing water, very large and worn boulders in odd places, large scour holes made by these big rocks being roiled around in the same place.

The scale is extremely large,ie miles, but the same phenomena are visible in small streams.

[Sawdring]

They run a couple of shows on the Science channel that claim the Scablands in Washington were created when a glacial damn repeatedly burst and formed over hundreds of years. The forming of the Scablands might be a good one to look up and watch in God's Video Store when one gets there.