Retrogressive thaw slumps (RTS) are caused by thaw of massive ground ice on slopes and combine subsidence, mass movement, and water erosion. They can expose several hectares of bare soil that is susceptible to erosion into nearby water bodies. In the summers of 2010 and 2011, oblique aerial-photographs of 26 RTS in Noatak National Preserve (NOAT) and Gates of the Arctic National Park and Preserve (GAAR) were taken with a hand-held, 35-mm digital camera. Accurate ground control was obtained at 23 of the slumps by surveying the location of temporary targets that were captured on the aerial photographs and then removed. These photographs were used to create high-resolution three-dimensional topographic models with photographic overlay. Photographs were taken in both years at 18 of the RTS. The current report: 1) documents changes in the slumps that had photographs from both years, and 2) describes a new slump photographed for the first time in 2011.

The newly acquired, nearly complete coverage of ARCN by high-resolution satellite imagery has allowed the NPS to make a comprehensive survey of erosion features caused by permafrost thaw in the Noatak National Preserve (NOAT). The author combined automated mapping methods with visual recognition of geomorphic features to make a comprehensive map of ALD and RTS in NOAT. The purpose of this report is to present the results of mapping in NOAT. Mapping in three other NPS units (Bering Land Bridge National Preserve (BELA), Cape Krusenstern National Monument (CAKR), and Kobuk Valley National Park (KOVA) was reported previously.