Monitoring Rock Glacier Kinematics with Satellite Synthetic Aperture Radar

Abstract

Active rock glaciers represent the best visual expression of mountain permafrost that can be mapped and monitored directly using remotely sensed data. Active rock glaciers are bodies that consist of a perennially frozen ice/rock mixture and express a distinct flow-like morphology indicating downslope permafrost creep movement. Annual rates of motion have ranged from a few millimeters to several meters per year, varying within the annual cycle, from year to year, as well as at the decennial time scale. During the last decade, in situ observations in the European Alps have shown that active rock glaciers are responding almost synchronously to inter-annual and decennial changes in ground temperature, suggesting that the relative changes of their kinematics are a general indicator of the evolution of mountain permafrost conditions. Here, we used satellite radar interferometry (InSAR) to monitor the rate of motion of various active rock glaciers in the Swiss Alps, Qeqertarsuaq (Western Greenland), and the semiarid Andes of South America. Velocity time series computed with Sentinel-1 SAR images, regularly acquired since 2014, every six days over Europe and Greenland and every 12 days over the Andes, show annual fluctuations, with higher velocities at the end of the summer. A JERS-1 image pair of 1996 and stacks of very high-resolution SAR images from TerraSAR-X and Cosmo-SkyMed from 2008 to 2017 were analyzed using InSAR and offset tracking over the Western Swiss Alps in order to extend the main observation period of our study. A quantitative assessment of the accuracy of InSAR and offset tracking was performed by comparison with in situ methods. Our results for the three different study regions demonstrate that Sentinel-1 InSAR can complement worldwide in situ measurements of active rock glacier kinematics.

InSAR time series analysis of seasonal surface displacement dynamics on the Tibetan Plateau

“…However, neither study could analyze the seasonal displacement patterns of rock glaciers due to large temporal baselines of their interferograms. Strozzi et al (2020) observe rock glacier velocities of approximately 1.5 to 2 m yr −1 in the Argentinian Andes, 2 to 4 m yr −1 in western Greenland and 1 to 2 m yr −1 in the Swiss Alps. The former two show a velocity increase of 30 % to 50 % and the latter around 100 % between winter and late summer.…”

“…Many of those pixels are close to streams and water bod-ies. Approximately 30 % in the Niyaqu basin and 60 % in the Qugaqie basin fall into permafrost regions (Zou et al, 2017;Tian et al, 2009). This makes permafrost degradation a potential driver of this subsidence, as a thinning permafrost layer would result in meltwater escaping from the thawing soil.…”

Insights into a remote cryosphere: a multi-method approach to assess permafrost occurrence at the Qugaqie basin, western Nyainqêntanglha Range, Tibetan Plateau

“…Nevertheless, the current results should be compared with a permafrost model of the study area in order to make a prognosis and zonation of the permafrost distribution. We also follow the suggestion by Strozzi et al (2020) to include rock glaciers and the monitoring of rock glacier velocities as an essential climate variable in the Global Climate Observing System (GCOS) of the World Meteorological Organization due to the essential contribution of the results as climate-sensitive parameters. As a next step, we plan to provide a rock glacier inventory for the western Nyainqêntanglha Range based on InSAR data as a status quo to understand the sensitivity and the vulnerability of the highmountain cryosphere in reference to climate warming.…”

“…The periglacial landforms in this study show lower creeping rates than similar landforms of other regions. Other studies employing InSAR techniques observe creeping rates from centimetres to several metres per year for rock glaciers in the western Swiss Alps (Strozzi et al, 2020), in western Greenland (Strozzi et al, 2020) and in the Argentinian Andes (Villarroel et al, 2018;Strozzi et al, 2020). Furthermore, all of them clearly indicate seasonal variations in the rock glacier movement, with faster rates in summer and reduced creeping rates in winter months (Cicoira et al, 2019;Delaloye et al, 2008Delaloye et al, , 2010.…”

“…The lack of seasonality and the lower creeping rates compared to rock glaciers in the Alps (Cicoira et al, 2019;Kenner et al, 2017;Wirz et al, 2016) and the semiarid Andes (Strozzi et al, 2020) might be related to the semiarid climate conditions (lack of moisture) and the short time span of 3 months with positive air temperatures in the Qugaqie basin (Zhang et al, 2013). Strozzi et al (2020) figured out that their highest rock glacier "Dos Lenguas" (4300 m a.s.l.) in the Andes is characterized by "less amplitude variations of the annual cycle than observed for the Swiss Alps".…”