CompuServe Messages

Hi, Kamron– That stretch of the Colorado River I spoke of had nearly completed its first rows of towers. It seems clear the river established a meandering pattern like the Mississippi in the flat plateau, when it _was_ dealing with dirt and sand, but then it cut into the plateau rock enough to fix the meanders in stone. Now locked in a pattern, it just kept cutting. It is obvious that a little more cutting will isolate what will then be towers – the canyon width is almost enough to cut across the meander loops. The river will never have switched sides relative to the tower; on one side of the tower the isolation will have been by collapses of rock the river undercut, not by the river itself. More than this must have happened to form the Grand Canyon, at least partly because of tributaries and maybe weak areas in the bedrock, but this meandering mechanism may have started it out. Once it has cut the first canyon, the river can still change course if dammed, especially if tributaries and such have created a partial route. For example, it might cut into a soft layer, then cut sideways through the soft stuff, causing the overhang to collapse and dam the river. It shifts a bit and resumes undercutting… Say, this presents an alternate theory for the meandering pattern. I suspect this undercutting trick could cause it to generate meanders even after it has cut into the plateau. I prefer the meanders-before-first-cutting theory, but the same asymmetry of speed-ups feeding back to cause stronger asymmetries might work in undercutting mode. –Doug