Article

Ice wedges surprisingly stable over the past decade

Permafrost Monitoring Brief, 2022

Map of Arctic parks.
The National Park Service’s Arctic Inventory & Monitoring Network parks.

The NPS Arctic Inventory and Monitoring Network (ARCN) monitors permafrost in the five National Park units of northern Alaska. We monitor ground temperatures at remote stations and permafrost landforms with satellite images and aerial photographs. Ecologist Dave Swanson recently re-examined the condition of ice wedges at three study areas in ARCN. Ice wedges are responsible for much of the unique polygonal patterned ground in the Arctic. Ice wedges are masses of nearly pure ice near the surface. They are quite susceptible to thaw and thus can be an early warning of permafrost loss. Ice-wedge thaw also creates new ponds and drainage pathways that can cause rapid lake drainage.

Aerial image of ice wege polygons in Arctic tundra.
An aerial photograph from our Bering Land Bridge National Preserve study area with numerous ice-wedge polygons.

NPS/Matt Nolan

Key Findings

  • Recent satellite images (from 2019 and 2020) showed little new subsidence due to melting ice wedges since our previous images from 2006-2009.
  • This was surprising given the record warm temperatures in the region during the period 2014-2019, and the significant degradation of ice wedges that occurred during the previous sampling interval (between the early 1950s and 2006-2009, in Kobuk Valley National Park).
  • A lingering effect of earlier ice-wedge degradation was continued formation of new drainage channels by the linking up of small ponds from earlier ice-wedge degradation. These can lead to the rapid drainage of lakes.
  • We will continue to monitor the condition of ice wedges in case climate change or unusual weather causes us to cross a threshold that makes ice wedges unstable again.
A three-panel image of changes over time of ice wedge polygons in Arctic tundra/permafrost.
Most of the ice wedges between these lakes in the Noatak National Preserve didn’t change a lot from 2007 to 2019. But previous degradation in the form of small pits and ponds provided a path for this lake to drain, once growth of the lake opened up a path around the higher ground on its west side.
Small channels of water formed by melted ice wedges.
An example of a small pond formed by ice-wedge degradation in the KOVA study area. Elongated ponds formed over degraded ice wedges; these ponds are about 3 feet wide.

NPS/Dave Swanson

How We Monitor Ice Wedges

When ice wedges melt, ponds can form around the margins of the ice-wedge polygons. We use aerial photographs and satellite images to make maps of the distribution of ponds around ice-wedge polygons in three study areas, one each in Bering Land Bridge National Preserve, Kobuk Valley National Park, and Noatak National Preserve. We use these maps to locate areas of degrading ice wedges.

Management Implications

  • The fact that we didn’t see a lot of ice-wedge degradation in the past decade is good news. The ice wedge degradation that we observed prior to 2009 - and associated impacts on the landscape - appear to have slowed down for the moment.
  • This finding reinforces our recent study of landslides caused by permafrost thaw in ARCN: there have not been many in recent years, in spite of the record warm temperatures.
  • However, local effects of ice-wedge degradation can be dramatic. The pits from previously degraded ice wedges can link up to form new drainage channels, and these can result in rapid lake drainage.

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Last updated: December 14, 2023