Transcript for Exotic Terrane, segment 10 of 12


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Plate tectonics is still changing the face of western North America. Two crustal plates have collided just offshore of Oregon and Washington. A subduction zone formed which created a great chain of volcanoes a short distance from the coast. These volcanoes like majestic Mount Rainier in Washington have produced some of the most powerful eruptions on Earth.

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Mount Saint Helens released its fury in nineteen eighty. The landscape around the volcano was completely devastated. Terrane features including a dense forest were buried under thick layers of ash. New vegetation is growing on a highly modified land ife ace.

Volcanic lava and ash buried most of the exotic terranes in the Pacific Northwest. Great outpourings of lava called the Columbia River Basalt flooded the region many times for several million years. It may have looked something like this volcanic landscape on the island of Hawaii.

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The Snake River in Idaho was just a minor stream then, running gently over thousands of feet of hardened lava and other rocks, but powerful geologic forces allowed the cutting of Hells Canyon in only two million years. Geologically speaking, the canyon formed rather quickly.

All through the west, geologic activity made dramatic changes in the landscape in the past few million years. The exotic terranes of the Pacific Northwest look nothing like they did when they first formed. Fortunately, enough has been preserved to reveal their fascinating past.