Using a combination of aerial imagery and ~1m resolution airborne lidar (collected July, 2009), we use manual visual inspection of the two datasets to identify point locations of over 7000 thermal erosion features (thermokarst) of varying maturity. For each feature we report its x,y position, the facing direction of the feature, the local topographic setting, the geologic unit it occurs on, the relative age of the feature and the specific type of thermal erosion feature.
Data set ID:
EML revision ID:
Methods and Notes:
Data were collected by Master of Geology student Kacy Krieger during his work at Idaho State University. Features were observed visually typically using a slope map derived from the 1m DOT Umiat LiDAR DEM. Features were visually categorized for the local topographic setting, the relative age of the feature and the specific type of thermal erosion feature. Automated techniques were used to add the x,y position of each feature, the aspect and underlying geologic unit. All work was completed in ArcGIS v10.0 and data were organized within a geodatabase.
Description of variables:
All reported positions are based on the following projection system used by the LiDAR contractor for the Umiat project.
Linear Unit: Foot (0.3048)
Geographic Coordinate System: GCS_North_American_1983
Angular Unit: Degree (0.0174532925199433)
Prime Meridian: Greenwich (0.0)
Semimajor Axis: 6378137.0
Semiminor Axis: 6356752.314140356
Inverse Flattening: 298.257222101
This is the downslope direction (in degrees) that the feature faces. This was calculated as a derivative from the DEM and averaged using a neighborhood around the feature.
This category was used to describe the setting of the feature to explore whether certain features occurred within or created a particular type of landform. The categories used were Conv (Convergent), Planar (no significant curvature) and Margin (feature is close to or on a break in slope, typically the edge of a river or lake).
These categories and codes are consistent with the surficial geology map units described by Hamilton 1978 and 1979. They typically describe the glacial age of the landform but may simply describe the type of material present at or near the surface e.g. 'c' for undifferentiated colluvium. Note that some features are off Hamilton's maps and are thus not assigned an age. The full references for the publications are:
Hamilton, T. D. (1978). Surficial geologic map of the Philip Smith Mountains Quadrangle, Alaska. United States, U. S. Geological Survey: Reston, VA, United States.
Hamilton, T. D. (1979). Surficial geologic map of the Chandler Lake Quadrangle, Alaska. United States, U. S. Geological Survey : Reston, VA, United States.
We classified each feature into one of three relative maturity classes: sharp (1), degrading (2), and diffuse (3) based on the condition of the head scarp, lateral walls, and depositional lobes. Sharp features have the steepest headwalls and best defined erosion and depositional zones. Degrading features have moderate relief on the headwall, a relaxed headwall slope and the change in boundary with the surrounding topography and headwall is diffused. Diffuse features have smooth, rounded headwall and depositional zones that make them difficult to distinguish from the surrounding topography.
Feature Type (or class):
We classified individual features based on morphology into three classes; active layer detachment, gully thermokarst and retrogressive thaw slumps (Jorgenson and Osterkamp, 2005; Jorgenson, 2008; Osterkamp et al., 2000). Active layer detachments (ALD) form when the active layer becomes saturated causing the active layer to slide or flow over the frozen substrate. These features are linear to curvilinear, narrow and generally much longer than wide. Retrogressive thaw slumps (RTS) form when exposed permafrost soils are exposed and experience rapid transport downslope resulting in a steep arc-shaped headwalls that retrogressively move upslope as thawed materials flow downslope and are deposited. Thermal erosion gullies or gully thermokarsts (GTK) form narrow, long channels along degraded ice wedges, bifurcated along those patterns and occur where surface water is concentrated.
Version 2 renamed directory Jim L 13Dec13
Download a comma delimited (csv) or Excel file (includes metadata and data sheets).
Use of the data requires acceptance of the data use policy --> Arctic LTER Data Use Policy
To cite this data set see the citation example on the LTER Network Data Portal page for this data set.