Project Update

December 4, 2015

Frozen Debris Lobes 2014-1B

Filed under: Project Update,report — billy.connor

Frozen debris lobes (FDLs) are slow-moving landslides in permafrost, many of which are present along the Dalton Highway in the Brooks Range.  While twenty-three FDLs are within a mile uphill of the highway, the closest, FDL-A at MP219, is less than 190 ft from the highway shoulder as of August 2013.  In 2010, FDL-A was 65-ft high and 560-ft wide at the toe.  Using some estimated values for cross-sectional shape, unit weight of the soil, and the historic rate of movement, in 2010 FDL-A was moving about 60 tons of debris towards the highway every day.  Measurements indicate that FDL-A started moving faster in recent years, and is beginning to demonstrate characteristics of further instability.  A few years ago, similar signs of instability were present in FDL-D, another frozen debris lobe three miles to the south.  In essence, FDL-D “detached” from its catchment area and moved 380 ft in three years (between 2010 and 2013).  Should FDL-A follow a similar trend, it could cover the distance to the highway in about a year, and be almost half way to the Trans Alaska Pipeline System (TAPS) in three years.  While a Phase 1 study provided a preliminary characterization of the internal structure of FDL-A, additional study is needed to define further the movement mechanism/s of the FDL and to characterize better its internal makeup.  This information is necessary to identify the best mitigation technique/s for implementation.

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FDL arial photo

Picture by M. Darrow


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