Monday, September 19, 2016

Geo 895: Lost Lake

Looking more or less west from its newest "drain hole." The old one is just out of the frame to the right. It's an odd spot, even without the drains: the basin was almost certainly covered in glaciers during the Pleistocene, but more recent volcanic activity blocked the outlet. As I mentioned on Friday, much of this area is covered with very permeable lava flows. Rain and snow melt goes directly into the ground, to re-emerge as springs at Clear Lake and elsewhere along the Upper McKenzie River. Here, apparently, the tephra seen in Fridays post, and the lacustrine sediments visible in the sides of the hole above, create a less permeable cap and impounding the lake's water. I can't say what portion of the lake's summer water loss goes down these holes, and what infiltrates directly through the lake bed and into the underlying bedrock, but I doubt the holes account for all of it. That is, I expect the lake bed isn't entirely impermeable.

Route 20 runs through the notch in the horizon on the left, and along the south side of the lake.

Photo unmodified. September 7, 2016. ZoomEarth location. (Location approximate- can't resolve hole.)

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