Quantifying recent thermokarst changes in the Northwest Territories, Canada and Alaska, USA using ArcticDEM

Abstract

Due to Arctic amplification, impacts of surface warming are significantly observed at higher latitudes. Positive feedbacks between periglacial environments and climate have increased thermokarst extent and associated landforms. Subsidence rates depend on active layer sensitivity which controls the geothermal heat balance between the Earth’s surface and interior. Carbon release is important, both gradually as the active layer seasonally thaws and deepens, and more notably as abrupt thaw mobilises deep soil organic carbon (SOC). Hillslope processes responsible for abrupt thaw are less well studied using remote sensing due to detection difficulties. Using high-resolution elevation data, this study increases understandings of relationships between topographic settings and climatic forcings by quantifying rates and magnitudes of geomorphic change for features identified within previous studies. Digital elevation model (DEM) differencing techniques are applied to ice wedges at three sites on Garry Island (Canadian High Arctic), where research has historically been limited to in-situ measurement. The aim is to assess the capabilities of ArcticDEM. Results detected rates of vertical change comparable to field studies. Patterns of positive elevation change were explored through hydrological network analysis and snowblow modelling. The differencing method is applied to mass movements (active layer detachment slides (ALDS) and retrogressive thaw slumps (RTS)) at four sites in the Alaskan Brooks Range. Abrupt thaw events on north facing slopes increased in magnitude, with length exhibiting the most significant rate of change in both features. Semi-automated delineation techniques developed using ArcGIS Model Builder, aided the mapping of five previously undetected features and facilitated carbon release estimates. As the Arctic warms, permafrost will continue to thaw, and hillslopes will become more unstable, impacting spatial extents of periglacial landforms. This thesis uses repeat elevation data at high resolutions in a method which could be implemented across the High Arctic to provide contributions to studies of periglacial environments.