Erosion not only reason for mountains

Continents slide on moving plates

We have considered erosion a number of times as a means of producing mountains. There also are other considerations.

When the battle was raging about movement of continents, the theory of continental movement was an untried field. Men scornfully flouted the idea of a continent plowing its way through other solid earth.

Once the idea was accepted that continents have no motion of their own but ride on the moving plates of the earth, the idea made some headway.

Hot rock in a fluid form spews up out of great cracks in the crust of the earth and slowly moves outward from the cracks, carrying the material of continents.

When reaching existing continents, there is nowhere to go. So they dive under the existing landmass in an action called subducting. Back into the depths they flow until they get deep enough to melt, a distance measured in more than a hundred miles.

When melted, they start up back to the surface. We saw the results of this at Mount St. Helens in 1980. That was a small emission. In greater activity, mountains are formed.

And once surfaced, there still is motion. We are told that the Cascades are still rising, at a rate of an inch or a little more a year.

It’s a natural movement, but not a particularly neat or orderly one if you consider the mess that was made of and around St. Helens at the time. Since this had happened in earlier centuries, it is possible that it will happen again.

But there had been enough of it in earlier millennia that it built the entire range, with varied shapes and forms and kinds of rock, some of which was reheated, squeezed and subjected to tremendous changes, giving us the wide variety of kinds of rock to be found in the Cascades.

I am much intrigued by a large rock deposit up in the vicinity of Straight Creek in the North Cascades.

For obvious reasons, the younger rock usually is at the top of the pile, but in that particular one, the whole mass has been turned over so the oldest rock is at the bottom of the heap.

The whole pile has been overturned. Can we imagine the turmoil that must have shaken the area while that was going on?

The very name of the creek indicates that something unusual went on, for rocks, creeks, rivers and ridges in the mountains usually are not straight. They have too much other stuff to go over or around.

As for the forces powerful enough to turn over stacks of rocks, I will again quote Dr. Peter Misch, then of the University of Washington geology department. I had said it was hard to understand a force that can do that.

“You can’t,” he answered.

Elizabeth Widel is a columnist for The Chronicle. This is the 2,827th column in a series. She may be reached at 509-826-1110.


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