Thursday, 26 January 2012
TECTONIC FORCES: PACIFIC NORTHWEST
Over vast expanses of time, powerful tectonic forces have massaged the western edge of the continent, smashing together a seemingly endless number of islands to produce what we now know as North America and the Pacific Northwest. Intuition tells us that the earth’s crust is a permanent, fixed outer shell – terra firma.
Aside from the rare event of an earthquake or the eruption of Mount St. Helen’s, our world seems unchanging, the landscape constant. In fact, it has been on the move for billions of years and continues to shift each day.
As the earth’s core began cooling, some 4.5 billion years ago, plates, small bits of continental crust, have become larger and smaller as they are swept up in or swept under their neighboring plates. Large chunks of the ocean floor have been uplifted, shifted and now find themselves thousands of miles in the air, part of mountain chains far from the ocean today or carved by glacial ice into valleys and basins.
Two hundred million years ago, Washington was two large islands, bits of continent on the move westward, eventually bumping up against the North American continent and calling it home. Even with their new fixed address, the shifting continues; the more extreme movement has subsided laterally and continues vertically.
The upthrusting of plates continues to move our mountain ranges skyward – the path of least resistance. This dynamic movement has created the landscape we see today and helped form the fossil record that tells much of the recent history of the Pacific Northwest.