Rock glaciers in the low Arctic of Greenland: surface and subsurface structure, permafrost conditions, long-term evolution, and present kinematics of a large rock glacier system at Bjørneø Island, SW Greenland

Abstract

<p>Active rock glaciers in Greenland have been studied since the 1980s focusing on two regions (Disko Island and Zackenberg) located north of 69°13’N. As judged from permafrost models, widespread existence of permafrost and thus active rock glaciers are also possible south of this latitude. Therefore, research on a large rock glacier on the island of Bjørneø (size: 1 km²; elevation 250-600 m a.s.l.; NNW-exposed) at 64°30’N was initiated in 2016. Research focused until 2020 on repeated differential GPS measurements at several fixed ground control points, on the analysis of the bottom temperature of the winter snow cover, and on the assessment of high-resolution orthophotos and digital terrain models based on UAV campaigns. Results up to 2020 indicate that permafrost influences a large part of the rock glacier and surface displacement takes place in the order of cm per year particularly in the central part.</p><p>Within an INTERACT research project we continued and expanded research at this rock glacier in 2021 applying two types of geophysics (electrical resistivity tomography, ground penetrating radar), differential GPS, relative surface dating, geomorphic mapping, clast form analysis, and monitoring of ground, air, and water temperatures. We find that widespread permafrost is likely along the measured geophysical profiles, that ground and water temperatures generally support the assumption of present permafrost conditions, and that the rock glacier evolved over a period of several thousand years, starting to form soon after the recession of the Greenland Ice Sheet from the coast some 10.4 to 11.4 ka BP.</p><p>In addition to fieldwork, different types of remote sensing- and modelling based research at this rock glacier were accomplished. Clast size distribution was semi-automatically quantified using a high-resolution digital terrain model. Results reveal distinct clast size-differences along a longitudinal profile of the rock glacier. Analyses of time-series of Sentinel-1 differential SAR interferograms for the period 2016 to 2021 showed minor motion in the uppermost part of the landform during a period of two months, distinct compressive flow (few cm) of two lobes of the landform after several months, and landform-wide movement over a period of 3 years. The terrain surface before the formation of the rock glacier, and thus the rock glacier volume, were reconstructed on the basis of field observations and terrain data. The volume of material relocated due to rock glacier activity was approx. 10 million m³. Finally, the present rock glacier extent and morphology were numerically reproduced as a steadily evolving and slowly moving viscous mass using a model implemented in the GIS-based open-source mass flow simulation framework r.avaflow.</p><p>Our chosen multidisciplinary approach is a significant step forward in understanding the long-term evolution and present conditions of large rock glacier systems in the low Arctic region of Greenland.</p>