Spatial distribution of thermokarst landforms across Arctic Alaska
L.Farquharson1, G.Grosse2, V. Romanovsky2, B.Jones3, C. Arp4, A. D. McGuire5
1. Department of Geology, University of Alaska Fairbanks
2. Geophysical Institute, University of Alaska Fairbanks
3. US Geological Survey, Anchorage
4. Institute of Northern Engineering, University of Alaska Fairbanks
5. U.S. Geological Survey, AKCFWRU, University of Alaska Fairbanks
Arctic Alaska is characterized by widespread past and present thaw of ice rich permafrost and
subsequent thermokarst development. Variations in ice content and distribution, and topography across
Arctic Alaska result in thermokarst landform diversity. Thermokarst causes a number of
biogeochemical and ecological shifts that include changes in soil carbon dynamics, nutrient cycling,
vegetation composition, wildlife habitat, and fresh water availability. Ongoing climate change may
lead to an increase in thermokarst landscape features. Thus, a better understanding of the current
temporal and spatial dynamics of thermokarst is needed in order to project its future dynamics.
Understanding how vulnerable the Arctic Alaska is to future thermokarst development is critical for
resource management, industry development, and subsistence hunting.
We focused on the distribution of thermokarst landforms among ten study sites aligned with the
NSF CALON (Towards a Circum-Arctic Lakes Observation Network) project in Arctic Alaska.
Sites represent diverse substrates including eolian silt, eolian sand, marine sand, deltaic, and
marine silt. We conducted thermokarst landform mapping and spatial and morphometric analyses
using high-resolution aerial photography, an interferometric synthetic aperture radar derived
digital elevation model (IfSAR DEM), and hydrographic layers from the National Land Cover
Database derived from Landsat-7. Non-lake thermokarst landforms were visually mapped and
hand digitized using aerial photographs and the IfSAR DEM.
Initial results show thermokarst forms are most prevalent in marine silt areas with up to 99% of
study areas affected by thermokarst activity. Eolian sand areas are the least thermokarst affected
(mean of 57%). Drained thermokarst lake basins, thermokarst lakes, and areas affected by
thermokarst pit formation were the dominant thermokarst landforms, covering up to 70%, 54%
and 8%, of the landscape. The number of overlapping lake and basin generations was used as a
proxy for landscape dynamics over the Holocene. Thermokarst was most advanced in marine silt
and marine sand, where up to five overlapping generations of thermokarst lake basins were
identified. We also used depth of drained thermokarst lake basins relative to adjacent uplands as a
proxy for maximum subsidence and an indicator for average ground ice content. Subsidence is
greatest within areas of eolian silt (mean of 20 m). In contrast, marine silts exhibit a mean
subsidence of 4.5 m. This difference can be attributed in part to the large size and depth of
syngenetic ice wedges in eolian silt, compared to shallower epigenetic ice wedges in marine silts.
Our preliminary data show that thermokarst landform distribution, the extent of thermokarst
activity and the depth of maximum subsidence vary across Arctic Alaska and that surficial
geology is an important controlling factor. We plan to use these data to parameterize and validate
the Alaska Thermokarst Model currently being developed as a component of the Integrated
Ecosystem Model for Alaska and Northwest Canada.