Monitoring of permafrost slope failures in Alaska’s arctic national parks: Updates from 2018 satellite images

Swanson, David

Permafrost is an important component of Arctic ecosystems that is monitored by the Arctic Inventory and Monitoring Network (ARCN) of the National Park Service. As a part of ARCN Permafrost Vital Sign, we monitor landforms caused by thaw of permafrost. This monitoring includes 1) mapping over extensive areas of small landslides caused by thaw of ice-rich frozen ground: retrogressive thaw slumps (RTS) and active-layer detachments (ALD); and 2) intensive monitoring of selected high-impact RTS. This report contains results from 2018 satellite high-resolution imagery for both projects. Images from 2018 were available for an area of about 800 km2 in the Maiyumerak Mountains of southwestern Noatak National Preserve. This area was previously mapped on images from 2007-2009. The area of ALD and RTS both declined greatly from 2007-2009 to 2018; the area of bare soil in ALD decreased from 245,796 to 9,060 m2 and bare soil exposed in RTS decreased from 75,151 to 10,455 m2. Most of the ALD present in 2007-2009 had revegetated, and the ALD mapped in 2018 were mostly newly formed in other locations. About half of the RTS in 2018 had developed from ALD mapped in 2007-2009, and the remainder were newly formed or persisted from RTS mapped in 2007-2009. A mass initiation event of ALD and RTS occurred around 2004, just prior to the images used in the previous mapping effort. The results presented here support our informal observations suggesting that as of 2018, no major new ALD and RTS events had occurred in ARCN. An image from 2018 was also available to update intensive monitoring of the Noatak Slump, a large RTS located directly on the Noatak River. This slump had 6 previous measurements from 2008 to 2016, during which time it had grown rapidly. However, from 2016 to 2018 it grew by just 370 m2, which was less than 1% of the 2018 area (42,913 m2 or 4.3 ha). The main escarpment was active only on a small portion of the slump, where it retreated a maximum of about 8 m in the two years. The slump has apparently largely stabilized, though most of it still remained un-vegetated.

Monitoring of permafrost slope failures in Alaska’s arctic national parks: Updates from 2018 satellite images

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