Permafrost Photo of the Month

March 13, 2017
By Jessica Rohde

Each month, our new Permafrost Collaboration Team (PCT) shares a photo with the 1000+ Arctic researchers on our member space. The “Permafrost Photo of the Month” series not only supplies the community with a new piece of media for use in presentations, but also provides an opportunity for education on permafrost and other Arctic science topics. Please enjoy the March photo below. To view future photos, please request an account on our member space and join the PCT.

An ice wedge polygon photographed from underneath within the advancing headwall of a retrogressive thaw slump in the Wulik River basin, northwest Alaska. Melting of ice wedges and relict glacial ice within thawing permafrost often drives retrogressive thaw slump expansion, as the high gravimetric water percentage promotes instability and soil structural failure. Photo by Andrew Balser (2010).

Retrogressive thaw slumping is a prominent mode of permafrost degradation in upland and hill slope settings where permafrost is ice-rich throughout the Arctic.  Melting of massive ice bodies within thawing permafrost, to include ice wedges and relict glacial ice, can drive rapid growth and result in very large, deep, single retrogressive thaw slump features (Siberian Mega Slump, Slump Morphology & Growth). 

While thaw slumps have been a continuing feature of Holocene warming (Holocene Slump Episodes), recent work has shown an acceleration in retrogressive thaw slump activity (Thaw Slump Activity), and in the frequency of feature distribution across Arctic regions (Permafrost Remote Sensing, Landsat Analysis for Thaw Slumps). 

A retrogressive thaw slump ('mega slump') which is over 300m wide, over 200m wide, and about 25m deep. This is a polycyclic slump, which was small and briefly active during the 1980s, went dormant, then re-activated in response to an anomalous combination of warm temperatures and heavy rainfall in May 2004. Ground ice driving this slump is roughly 30% late-Pleistocene glacial ice, and 70% late-Pleistocene ice wedges. Photo by Andrew Balser (2011).

Generalized climate warming has been linked with increased thaw slumping, possibly due to a pre-conditioning effect.  However, shifting patterns in weather and seasonality may be more important than general warming for triggering individual slump features (Timing Thaw Slump Initiation).  The impacts of retrogressive thaw slumps in context of climate variability and permafrost carbon are likely associated with complex combinations of terrain properties and shifting seasonality and weather patterns.

Posted by Jessica Rohde on behalf of Andrew Balser, Cold Regions Research and Engineering Lab

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