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Volume 10, issue 3 | Copyright

Special issue: The evolution of permafrost in mountain regions

The Cryosphere, 10, 977-993, 2016
https://doi.org/10.5194/tc-10-977-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 12 May 2016

Research article | 12 May 2016

Frozen debris lobe morphology and movement: an overview of eight dynamic features, southern Brooks Range, Alaska

Margaret M. Darrow1, Nora L. Gyswyt1, Jocelyn M. Simpson1, Ronald P. Daanen2, and Trent D. Hubbard2 Margaret M. Darrow et al.
  • 1Department of Mining and Geological Engineering, University of Alaska Fairbanks, Fairbanks, Alaska 99775, USA
  • 2Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska 99709, USA

Abstract. Frozen debris lobes (FDLs) are elongated, lobate permafrost features that mostly move through shear in zones near their bases. We present a comprehensive overview of eight FDLs within the Dalton Highway corridor (southern Brooks Range, Alaska), including their catchment geology and rock strengths, lobe soil characteristics, surface movement measurements collected between 2012 and 2015, and analysis of historic and modern imagery from 1955 to 2014. Field mapping and rock strength data indicate that the metasedimentary and metavolcanic bedrock forming the majority of the lobe catchments has very low to medium strength and is heavily fractured, thus easily contributing to FDL formation. The eight investigated FDLs consist of platy rocks typical of their catchments, organic debris, and an ice-poor soil matrix; massive ice, however, is present within FDLs as infiltration ice, concentrated within cracks open to the surface. Exposure of infiltration ice in retrogressive thaw slumps (RTSs) and associated debris flows leads to increased movement and various stages of destabilization, resulting in morphological differences among the lobes. Analysis of historic imagery indicates that movement of the eight investigated FDLs has been asynchronous over the study period, and since 1955, there has been an overall increase in movement rates of the investigated FDLs. The formation of surface features, such as cracks, scarps, and RTSs, suggests that the increased movement rates correlate to general instability, and even at their current distances, FDLs are impacting infrastructure through increased sediment mobilization. FDL-A is the largest of the investigated FDLs. As of August 2015, FDL-A was 39.2m from the toe of the Dalton Highway embankment. Based on its current distance and rate of movement, we predict that FDL-A will reach the Dalton Highway alignment by 2023.

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Frozen debris lobes (FDLs) are slow-moving landslides in permafrost. Several FDLs are located adjacent to the Dalton Highway in Alaska's Brooks Range, and may pose a risk to adjacent infrastructure as their rates of movement increase. Through a comprehensive overview of eight FDLs, we found that FDL movement is asynchronous, surface features suggest that increased movement rates correlate to general instability, and the closest FDL will reach the current Dalton Highway alignment by 2023.
Frozen debris lobes (FDLs) are slow-moving landslides in permafrost. Several FDLs are located...
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