[Secret Agent Man]

The 1980 eruption of Mt St Helens proves that water carving out these canyons and the hydrological sorting that occurs (leaving layers) occurs in days.

[Paul R.]

Nothing remotely close to the Grand Canyon was carved out @ Mt. St. Helens. That MSH canyon was cut into fresh mud and ash, and is (was) only about 20 meters deep. It's not even all that impressive, really, given the soft substrate it had to work with.