Glacial caves: Kayaking in Alaska

Photo: puttsk/Shutterstock

The glaciers of Earth's ancient past are to thank for some of our most beloved natural landforms, including the Great Lakes, Yosemite Valley and even the kettle pond that inspired one of America's greatest writers. While it's interesting to see what a glacier can do to rocky terrain, it's also fascinating to observe how crevasses, ridges and caves dramatically develop under the pressure and stress of these ever-moving chunks of dense ice.

In particular, glacier caves form when liquid water — typically melt water from the surface — runs underneath or through a glacier. They can also be formed by subterranean geothermal vents or hot springs, which are common in places with volcanic landscapes such as Iceland.

Glacial caves: Mount Hood cave

Photo: Andy Best/500px

While these caves are certainly beautiful, they are also often unstable and dangerous to explore due to persistent glacial motion and melting. Because of the warming climate, many of them are under threat of collapsing completely. Oregon's famous Sandy Glacier Caves (above) — one of the largest glacier cave systems in the United States — is expected to melt completely within the next decade.

Continue below for a look at just a few of the many striking glacier caves found on Earth:

Glacial caves: Mendenhall glacier in Alaska

Photo: Sean Lema/Shutterstock

Mendenhall glacier cave, Juneau, Alaska

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Glacial caves: Rhone Cave

Photo: Ian Grant/Shutterstock

Rhône glacier cave, Valais, Switzerland

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Glacial caves: Vatnajökull

Photo: Yongyut Kumsri/Shutterstock

Vatnajökull glacier cave, Iceland

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Glacial caves: Near British Columbia

Photo: West Coast Scapes/Shutterstock

Wedgemount glacier cave, British Columbia, Canada

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Glacial caves: Mendenhall

Photo: Yosuke Sano/Shutterstock

Mendenhall glacier cave, Juneau, Alaska

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Glacial caves: Saribung peak, Nepal

Photo: Yongyut Kumsri/Shutterstock

Saribung Peak glacier cave, Mustang, Nepal

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Glacial caves: Kamchatka

Photo: Sergey Krasnoshchokov/Shutterstock

Kamchatka glacier cave, eastern Russia

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Catie Leary is a photo editor at Mother Nature Network. Follow her on Twitter and Google+.