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Geology of the National Parks

GEOLOGY OF OLYMPIC NATIONAL PARK:
PART I OLYMPIC GEOLOGY

Gravity: The Great Leveler

In the long run, gravity is the force behind all the processes that tend to drag the mountains back to the sea. The spherical earth is a restless creature whose internal troubles keep wrinkling up its skin, but because it is so massive, that thing we call gravity keeps smoothing out the wrinkles, trying to reform the earth into a perfect sphere.

Ridgetop depression formed by deep creep
Fig. 36. Deep creep produced this depression along a ridge top. The fallen trees from a recent fire emphasize the feature.

In the Olympics, gravity often moves soil and rock downhill with only minor help from water or ice. Slow movement is called creep and fast movement, landslide and rockfall. Creep is commonly shallow: the surficial cover of weathered rock, moraine, or soil slides slowly downhill, wrinkling like a rug on a tilted floor. Deep creep

The soft rocks of the Olympics appear to have crept and slid valley-ward most actively right after glacial retreat, when the walls of the deeply carved valley channels were most unstable . But even today a creek or river gnawing into the toe of a slope may remove support from upslope material, causing the whole mass to slide gradually or catastrophically down (fig. 37).

Landslide scar
Fig. 37. Landslide scar above Dosewallips River, west of Constance Pass.

Creep and landslide processes tend to smooth steep and jagged ridges into low, rounded hills. They turn the steep-walled gorges sawed by rivers into V-shaped valleys and destroy the U shape of glacier channels. The smoother and lower the hills get, the slower the descent of rock and debris to the rivers and the slower the removal of the material to the sea by the rivers. But gravity never relents and, given enough time, will smooth even the boldest peaks of the Olympics into low, rolling hills.


Material in this site has been adapted from Guide to the Geology of Olympic National Park by Rowland W. Tabor, of the USGS. It is published by The Northwest Interpretive Association, Seattle.

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