A fine polishThe bright, reflective surfaces in this photo have been exposed for something like 10,0
A fine polishThe bright, reflective surfaces in this photo have been exposed for something like 10,000 years. This is a shot of a granite slope in California’s Yosemite National Park. 20,000 years ago, massive glaciers sat in the mountains of North America, including what is today Yosemite National park. The Ice Sheet covering the Sierra Nevada Mountains sent long tongues of ice down into the valleys, including an 80 kilometer long ice stream that flowed through what is today Yosemite Valley. The ice at the center of the valley has been estimated to be more than 500 meters thick – high enough that only the tallest peaks of the park today actually poked through at the top.This mass of ice picked up debris from the surrounding rocks and gradually wore down this surface to a fine polish.By 10,000 years ago, the ice sheet and valley glaciers had melted away, leaving behind the polished surface now exposed to rain and the elements. Over time, little bits have eroded away – from this image you can basically tell how much erosion there has been at this site over 10,000 years, which is also a neat observation. Seems like these must be really tough rocks, as only a tiny bit of the exposed granite has been stripped away over the entire Holocene.-JBBImage credit: James St. Johnhttps://flic.kr/p/2jexv64Reference:https://www.nps.gov/yose/learn/nature/tiogaglaciers.htm -- source link
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