Alaska's Bering Glacier ends in Vitus Lake, south of Wrangell-St. Elias National Park, roughly 10 kilometers from the Gulf of Alaska. The flowlines of a surging glacier are often warped and twisted (as seen in the center left of this photo) as the fast motion of a surge disrupts the usual patterns of ice flow. This photograph was taken in 1984 as part of the U.S. Geological Survey Ice and Climate Project Collection. —Credit: Photograph by Austin Post, 1984. Bering Glacier: From the Glacier Photograph Collection. Boulder, Colorado USA: National Snow and Ice Data Center.

In the early summer of 2011, the Medvezhiy Glacier in Tajikistan slid abruptly down its valley and for a greater distance than it has in at least 22 years. The sudden downhill slide of the glacier raised concern among glaciologists and emergency management groups about a potential glacial outburst flood that could flow down into the Vanch River valley. According to satellite imagery and reports from local scientists, the glacier has moved roughly 800 to 1,000 meters (875 to 1,094 yards) since June 2011. The glacier normally moves 200 to 400 meters (219 to 437 yards) in an entire year. Glaciologists describe it as a pulsating glacier with periodic surging; the most recent prior surges were 1989 and 2001. —Credit: NASA.