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Glacial Erratics at Olmstead Point

Glacial Erratics at Olmstead Point. Yosemite National Park. August 13, 2004. Photo copyright Dan Mitchell
OlmsteadErratics2004|08|13: Glacial Erratics at Olmstead Point. Yosemite National Park. August 13, 2004. Copyright Dan Mitchell.

(For those who may not be familiar with the term, a glacial erratic is a large rock or boulder left in place by a retreating glacier as it melted.)

March 21, 2005 - Posted by | Commentary

2 Comments

  1. They are termed erratics because they often don’t belong within the context of the current environment (such as large chunks of striated granite sitting in the middle of plains in Iowa).

    They aren’t quite so erratic in valley glaciers that formed Yosemite (granite boulders on granite bedrock), but the process is the same. The boulders were carried to that point by the glacier and dropped when it retreated.

    Tom Clifton's avatar Comment by Tom Clifton | March 21, 2005

  2. Thanks, Tom, for the information from a real geologist! I like your description of them being “not quite so erratic” in places like Yosemite where they are pretty much expected.

    Dan Mitchell's avatar Comment by Dan Mitchell | March 21, 2005


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