Rock Glacier photo, Wrangell St. Elias National Park, Alaska.

Rock Glacier on Soudough Peak, Wrangell St. Elias National Park, Alaska.

Hey Folks,

So what, you’re all asking, is a ‘rock glacier’? I know you’re asking, I can hear it. Well, you’re in luck; I’ll tell you.

Rock glaciers are a mix of ice and rock, usually talus, that flow down a mountainside much like regular glaciers do. One of the main differences is how they’re formed. Regular glaciers tend to be formed simply by the compacting of snow, fallen over the years, into ice, which, as the pack gains weight over the years, starts to flow a mountain. Rock glaciers, dozens of which exist in Wrangell St. Elias National Park, are mostly comprised of rock, such as talus and scree that falls from a steep faced cirque (what’s a cirque? a cirque, also called a cwm (in Wales) or coomb (England), is a large bowl shaped hollow on the top of a mountain). Over the years, rock and scree falls from the steep mountain sides into the base of the cirque, this pile of rock sits on the base of the cirque, forming a big old pile, known as talus. As the years go by, precipitation, be it snow, hail or rain, falls, and the water sits in the gaps and cracks between the pieces of rock or talus. During colder periods, this water freezes and turns to ice. So now we have a big ole pile of rock/talus that is kinda of glued together with ice. Eventually the pile gets so large it starts to slide down out of the cirque and on down the mountain side, as a glacier flows. It’s not a rock slide. It doesn’t fall and it’s not loose pieces moving individually; it flows as one, much like a viscous kind of substance might. generally, they flow relatively slowly, but sometimes they really move quickly, more so than a regular glacier might – I’ve not read, but I presume it’s because they’re found on relatively steep mountain faces.

Only a little is known about rock glaciers, they’re kind hard to study. But — a few years back some bush pilots noticed a rock glacier in Wrangell St. Elias National Park near the Chitina River, Wrangell St. Elias National Park, that the toe had dropped off (the toe is the lower end of a glacier). So a couple of scientists headed out, ASAP, and crawled all over it, measuring and re-measuring and studying the broken face of the glacier to learn what they could. The glacier was a meld of rocks and ice all the way through its thickness, not a bunch of rocks piled on top of ice. They probably learned as much from this one situation as anyone had ever learned about rock glaciers over the years.

What’s interesting to me is that although rock glaciers and ice glaciers are very different features, they’re related; ice glaciers are what form cirques, and it is in these cirques and bowls that rock glaciers then form, many, many years later – so, in a way, they’re siblings!

This rock glacier is just south of McCarthy, near the Nizina River, on a peak called Sourdough Peak. I shot this back in September when I was visiting Wrangell St. Elias National Park with my parents. I was having a few issues with my stupid camera, and I only managed 2 photos that werenot out of focus; this one posted above and a vertical composition as well. I can’t wait until next fall to get some more photos of this way cool rock glacier.



3 thoughts on “Rock Glacier photo, Wrangell St. Elias National Park, Alaska.

  1. Neil Donohue

    Hi Carl,

    Now I know what I was looking at back in September. I found your information on rock glaciers very interesting. I must admit all I could see at the time was a pile of grey,drab- looking mud. Your info on how they are formed and the difference between rock glaciers and ice glaciers gave me a much better perspective.By the way, talus is a latin word meaning hook or claw, thus the word talon, and it also refers to the ankle. So maybe you have a toe and an ankle in a rock glacier.
    Just thought I’d toss that in.

    Cheers, Dad

  2. Carl Donohue

    Hey Dad

    Yeah, rock glaciers are very cool. This was the one we flew over right before getting back in to McCarthy, out your window of the plane.

    “Talos” was also a Greek Mythology figure, a giant rock thrower. I’m guessing that’s the root of the word ‘talus’ for rock piles.



  3. Pingback: Porphyry Mountain, Wrangell - St. Elias National Park, Alaska. - Stock Photos - Skolai Images

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