Thermokarst in pingos and adjacent collapse scar bogs in interior Alaska

A region of discontinuous permafrost 50 kilometers southeast of Fairbanks, Alaska exhibits rapid thermokarst and landscape change. The area contains a dozen pingos (hydrolaccoliths), mounds of ice covered by earth material typically 100 meters across and 20 meters above the surrounding ground surface. The pingos have sunken craters in their centers formed through melting and collapse of an inner ice lens core. Adjacent to the pingos are collapse scar bogs in various states of formation and ice wedge terrain undergoing thaw subsidence to polygons and thermokarst mounds (baydzherakhs). With a mean annual temperature of -1 degree C the area contains warm ecosystem-protected permafrost vulnerable to thaw. We analyzed historical imagery to the 1970s to track water features in a subset of pingos. The craters have expanded over the past few decades suggesting melting and collapse of the ice cored center and potential permafrost degradation along pingo margins. Collapse scar bogs in adjacent low-elevation terrain are roughly the same size as the pingos but have little vertical elevation gradient compared to the surrounding terrain. Electrical resistivity tomography (ERT) measurements, high resolution GPS surveys, SIPRE coring, and thaw depth probing were focused along nine 400 meter transects across three of the pingos to identify relationships between geophysical properties, permafrost composition, seasonal thaw, and ecological state. A large ( 40 meters across and 20 meters thick) lens shaped region of thawed permafrost is evident in the ERT results about 10 meters below the ground surface in the center of one pingo we surveyed in detail. This is believed to be the original ice cored region of the pingo that has melted. A thin (1-5 meters thick) layer of permafrost is present above this thawed region while the rampart margins surrounding the pingo are underlain by thick (10-30 m) permafrost. The pingo and thermokarst features reside in a location where rapid permafrost thaw in response to warming or changing hydrology could provide a hot spot for landscape change, particularly given a projected climate warming of 5 degrees C over the next 80 years in the area. Their future thermal, geomorphological, and ecological states may be a harbinger for how discontinuous permafrost in the region responds to projected climate warming.