Friday Rock Blogging: Glacial Polish

glacial polish in Yosemite Glaciers look regal and calm, or at least, that’s the canonical photograph: blue-tinted light refracted around a majestic pile of ice. And they basically are, but like most regal majesties, glaciers are also cruel oppressors who grind the peasantry under their boots. And by “peasantry” I mean “rocks” and by “boots” I mean “rocks and ice”.

When glaciers retreat, they leave behind a variety of characteristic marks, all of which have funny names: drumlins and eskers and cwms on a large scale, chatter marks and striations and polish* on a smaller scale. There’s nothing special about the process that produces glacial polish; it’s simply dust and grit on the bottom of the glacier acting as a piece of sandpaper as the glacier goes wherever it’s going.

flaking glacial polish in Yosemite

The images here are both from Yosemite, and the second one is supposed to be a particularly accessible outcrop, worth visiting if you’re up there for pedagogical purposes.

*Okay, “polish” isn’t funny.


  1. Modulator wrote:

    Friday Ark
    Cats, Dogs, Spiders and ? every Friday. We’ll post links to sites that have Friday (plus or minus a few days) photos of their chosen animals as I see them (photoshops at our discretion and humans only in supporting roles). Leave a comment or trackback…

  2. loyd wrote:

    There are lots of other fine examples of glaciation within Yosemite National Park. There’s cirques, terminal and lateral moraines, lots of polish and scarring, hanging valleys, and glacial erratics everywhere. The canyon Bridalveil Creek comes down to the precipice it forms the falls over is, in fact, a hanging valley.
    I’m actually more excited by the eastern side of the park and the Mono to Mammoth Lakes region though. No only do you have glaciation but there’s active vulcanism (within the last 10,000 years) taking place. There’s cinder cones, plug domes, lava flows, volcanic glass sheets, ash piles, duft, and the currently active Mammoth Mountain volcano. Not to mention you get to hang out in the Mammoth Caldera where evidence of magma is easily seen in Hot Creek. Mammoth has even had some Co2 pockets make their way to the surface of lakes and kill off trees and wildlife.

  3. yami wrote:

    Definitely! I’m a huge fan of Little Hot Creek. And you forgot to mention the Mono Lake tufa towers! Not glacial, of course, but still fabulous
    But I thought Hot Creek was in the Long Valley Caldera, are you using “Mammoth Caldera” synonymously or are we talking about different places here?
    I do think at *some* point it gets a little silly to keep going to Mammoth/Mono without ever visiting Yosemite National Park proper, which is what I’ve been doing… the next time I’m up there I want to finally visit the canonical bits of Yosemite.

  4. loyd wrote:

    Most people visit Yosemite but never get to the really cool stuff on the other side.

  5. yami wrote:

    And hoorah for that, or all the good hot springs would be crowded!

  6. cowgirl wrote:

    danls 4 the info… glaciers are NOT evil…. glacial polish is pretty…
    omg im sooooo evil!!!!!!! muahhaha!!!
    get a load of this cowboy!

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