[Da_Shrimp]

but the former gives clues how a canyon could form very very quickly.

The channels at Mount St Helens are cut through unconsolidated ash. How can this be compared to the situation at the Grand Canyon?

[DittoJed2]

Grand Canyon was rapidly formed when a dam broke. That little River did not carve that great big canyon. If you have ever seen flooding, it can do a lot of damage rather rapidly.

[DittoJed2]

How is granite formed? By the cooling of magma. What is going to happen to the ash and lava flows of M.S.H. in a few hundred years? How about the trees that are in Spirit Lake? There are upright petrified trees all over the world that cut straight through the sacred geological column. If that column formed over millions and millions of years, the tree would have rotted and turned to dust. These trees are perfectly preserved. Mt. St. Helens shows how this likely happened.