Articles | Volume 12, issue 2
The Cryosphere, 12, 549–564, 2018
The Cryosphere, 12, 549–564, 2018

Research article 14 Feb 2018

Research article | 14 Feb 2018

Sub-seasonal thaw slump mass wasting is not consistently energy limited at the landscape scale

Simon Zwieback1,2, Steven V. Kokelj3, Frank Günther4, Julia Boike4, Guido Grosse4,5, and Irena Hajnsek2,6 Simon Zwieback et al.
  • 1Department of Geography, University of Guelph, Guelph, Canada
  • 2Department of Environmental Engineering, ETH Zurich, Zurich, Switzerland
  • 3Northwest Territories Geological Survey, Government of Northwest Territories, Yellowknife, Canada
  • 4Periglacial Research, Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Potsdam, Germany
  • 5Institute for Earth and Environmental Science, University of Potsdam, Potsdam, Germany
  • 6Microwaves and Radar Institute, German Aerospace Center (DLR), Wessling, Germany

Abstract. Predicting future thaw slump activity requires a sound understanding of the atmospheric drivers and geomorphic controls on mass wasting across a range of timescales. On sub-seasonal timescales, sparse measurements indicate that mass wasting at active slumps is often limited by the energy available for melting ground ice, but other factors such as rainfall or the formation of an insulating veneer may also be relevant. To study the sub-seasonal drivers, we derive topographic changes from single-pass radar interferometric data acquired by the TanDEM-X satellites. The estimated elevation changes at 12 m resolution complement the commonly observed planimetric retreat rates by providing information on volume losses. Their high vertical precision (around 30 cm), frequent observations (11 days) and large coverage (5000 km2) allow us to track mass wasting as drivers such as the available energy change during the summer of 2015 in two study regions. We find that thaw slumps in the Tuktoyaktuk coastlands, Canada, are not energy limited in June, as they undergo limited mass wasting (height loss of around 0 cm day−1) despite the ample available energy, suggesting the widespread presence of early season insulating snow or debris veneer. Later in summer, height losses generally increase (around 3 cm day−1), but they do so in distinct ways. For many slumps, mass wasting tracks the available energy, a temporal pattern that is also observed at coastal yedoma cliffs on the Bykovsky Peninsula, Russia. However, the other two common temporal trajectories are asynchronous with the available energy, as they track strong precipitation events or show a sudden speed-up in late August respectively. The observed temporal patterns are poorly related to slump characteristics like the headwall height. The contrasting temporal behaviour of nearby thaw slumps highlights the importance of complex local and temporally varying controls on mass wasting.

Short summary
We analyse elevation losses at thaw slumps, at which icy sediments are exposed. As ice requires a large amount of energy to melt, one would expect that mass wasting is governed by the available energy. However, we observe very little mass wasting in June, despite the ample energy supply. Also, in summer, mass wasting is not always energy limited. This highlights the importance of other processes, such as the formation of a protective veneer, in shaping mass wasting at sub-seasonal scales.