A large retrogressive thaw slump on the Noatak river; the top of the slump is ~900 feet above river water level. Retrogressive thaw slumps are caused by thawing of ice-rich permafrost and subsequent melting of ground ice on slopes. The National Park Service is currently monitoring 19 active retrogressive thaw slumps in Noatak National Preserve and Gates of the Arctic National Park and Preserve. Extrapolating the growth rate of these retrogressive thaw slumps back in time suggests that these slumps started in the late 1990s or early 2000s.
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