Turquoise tarn in Olympic National Park (WA)
This beautiful tarn sits in a glacially-carved cirque and is still bright turquoise due to the large amounts of fine glacial sediment suspended in its waters (Olympic National Park, Washington)

NPS Photo/Pete Zaidel

Tarns are lakes that form in glacially-carved cirques. They are often dammed by moraines. If they are still associated with moving glaciers, tarns are often full of tiny, glacially-ground sediment that scatter light and can make the water appear colorful. Thus, the color of a glacier's tarn is a good way to diagnose whether or not the ice is still actively moving (crevasses on the glacier surface are another good indication of glacier movement).

To learn more about glaciers, glacier features, and glacial landforms, see the Glaciers & Glacial Landforms Page.

Part of a series of articles titled Glacier Ice Features.

Last updated: February 9, 2018