On 30 Nov 97 at 21:08, Glenn Morton wrote:
> Geology accepts catastrophic glacial dams failing, but they don't scoop out
> canyons like the Grand Canyon.
The Grand Canyon of Yellowstone National Park is one canyon created by
glacial dam failure.
There are a host of factors to consider here - the geological work done by
surging floodwaters can generate a diverse variety of morphologies.
Regarding the Mt St Helens canyon, Glenn writes:
> Remember that volcanic ash is very soft and of ONE lithology. The Grand
> Canyon has many different lithologies. The situation at Spirit Lake is quite
> different from the Grand Canyon.
This is a relevant observation - and it has some bearing on the
Yellowstone River Canyon also. It is worth asking: what other factors
are relevant to Grand Canyon? Fault control of erosion? Ongoing high run-
off? In the case of Grand Canyon, it is necessary also to explain the
incised meanders - features which suggest that the present is not the key
to the past.
Best wishes,
David J. Tyler.