GEOLOGY OF OLYMPIC NATIONAL PARK:
PART I OLYMPIC GEOLOGY
Running
Water: The Persistant Sculptor
Anyone
who has stood at the brink of an Olympic gorge and watched the foaming
river at the bottom knows that running water is king in this land (fig. 28a). From
the very instant that the part of the earth's crust that is now the
Olympics pushed up above the sea, rain and melted snow have been carrying
bits of it back down again. As the land rose and the growing mountains
intercepted more moisture, trickles grew to streams, and streams grew
into rivers.
Fig. 28a.
Elwha River in the gorge at Gobblin's Gate |
The running
water cut deeper and deeper into the rising land mass. Several factors
contribute to a river's ability to cut: the amount of water it carries,
the steepness of its descent, and, very important, the load of silt,
sand, and gravel, which are its cutting tools. For example, an Olympic
river that is laden with silt, sand, and gravel supplied by glaciers
cuts bedrock faster than does a clear river not fed by glaciers.
The radial
drainage pattern of the Olympics results from the domal uplift: as the
Olympic land mass bowed up from the sea, water tended to run off in
all directions. Rivers that had some advantage over their neighbors
in rate of erosion extended headward more rapidly and captured more
drainage area. The Elwha, which appears to breach the very center of
the uplift (fig. 29), may have captured more drainage than the other
rivers because it had a shorter, steeper course to the sea. The eastern
rivers are short today, but they must have had a longer trip to the
sea before the Cordilleran ice sheet carved out Hood Canal.
Fig. 29.
Development of the basic drainage pattern of the Olympics |
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