Geomorphological characteristics of Yedoma terrains in the northern part of Seward Peninsula, Alaska

Yedoma (Ice Complex) is a Late Pleistocene periglacial formation of syngenetic permafrost with large ice wedges. These extremely ice-rich stratigraphic sequences have been widely observed and studied in northern Siberia. However, very few studies have focused on Yedoma terrain in Northern America. Occurrence of Yedoma landscape has a great significance for paleoenvironmental reconstructions because the regions where Yedoma can be observed remained unglaciated during the late Pleistocene. Understanding the dynamics of Yedoma landscape and the geotechnical properties of this permafrost unit is necessary for modeling the evolution of the periglacial landscape in the context of climate change. Degradation of Yedoma terrain triggers several geomorphological processes such as thaw settlement due to deepening of the active layer, development of thermokarst lakes, thermo-erosion gullies, and active layer detachment slides. Degradation of yedoma terrain also releases greenhouse gases (e.g. methane, CO2), water from melting ice, and various types of mineral and organic sediments which need to be accounted for in climate warming scenarios. Yedoma terrains in their contemporary state can be identified by the presence of typical geomorphological features such as erosional remnants with specific shape, baidjarakhs (ground mounds formed as a result of wedge-ice thawing), abundance of thermokarst lakes, drained lakes basins, low-gradient streams and erosion-thermokarst valleys (alas valleys) with occasional pingos. We have studied and characterized in the field the metrics of two Yedoma sites at the northern part of Seward Peninsula. Geomorphic sub-units such as drained lake basins and Yedoma remnants have been characterized in detail via optical leveling surveys. Bathymetry of thermokarst lakes was measured by lake-based sonar and GPS surveys. Drilling was conducted in several locations along the survey transects. The cores retrieved were described in the field in terms of cryostructures and sedimentary assemblages. In the laboratory, we measured the ice and organic matter content of the permafrost cores and conducted grain-size distribution analysis. We present here the metrics and typical permafrost properties of geomorphological sub-units forming Yedoma terrains.