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Posted By:
Hal Brown
Date Posted:
Sep 13, 2008
Description:
The broad expanse of the Columbia River makes an excellent seaplane avenue into the inland. Even the low hills before the Cascades would make for some nervous flying. Though not visually spectacular, the low hills are interesting for their unique composition. The hills are part of a broad area of oceanic crust pushed up onto the continent.
The Willapa Hills were born two miles deep in the ocean at an old oceanic ridge similar to the mid-Atlantic Ridge. This ridge now sits offshore, stretching from Vancouver to California.
The thing about rocks spewed forth from oceanic ridges is that they are heavy. They normally sink into the crust as lighter continental rock float above them. That didn’t happen for the Willapa Hills because there was a micro-continent, the North Cascade subcontinent, that got in the way.
Another oceanic ridge, on the east side of the Cascades, was pushing crust westward. This forced crushed and crumbled the lighter continental crust into a deep trench and shoved it under the Willapa crust. It’s kinda like making a rock raft: the light rocks floated the heavy rocks.
Date Taken:
Sep 13, 2008
Place Taken:
McGowan, WA
Owner:
Dan Nickens
File Name:
46_Heading_for_the_Hills.jpg - Photo HTML
Full size - <img src="/show.php?splash=SZTBE0000h">
Medium - <img src="/show.php?splash=SZTBE0000m">
Thumbnail - <img src="/show.php?splash=SZTBE0000s">
Category:
329, Taking Peli Home
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