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).
Last updated: February 9, 2018