Measurement of rock glacier surface change over different timescales using terrestrial laser scanning point clouds
2021
Abstract. Topographic change at a given location usually results
from multiple processes operating over different timescales. However,
interpretations of surface change are often based upon single values of
movement, measured over a specified time period or in a single direction.
This work presents a method to help separate surface change types that occur
at different timescales related to the deformation of an active rock
glacier, drawing on terrestrial lidar monitoring at sub-monthly intervals.
To this end, we derive 3D topographic changes across the Auseres Hochebenkar rock glacier in
the Otztal Alps. These changes are presented as the relative
contribution of surface change during a 3-week period (2018) to the
annual surface change (2017–2018). They are also separated according to the
spatially variable direction perpendicular to the local rock glacier surface
(using point cloud distance computation) and a single main direction of rock
glacier flow, indicated by movement of individual boulders. In a
1500 m 2 sample area in the lower tongue section of the rock
glacier, the contribution of the 3-week period to the annual change
perpendicular to the surface is 20 %, compared with 6 % in the direction
of rock glacier flow. Viewing change in this way, our approach provides
estimates of surface change in different directions that are dominant at
different times of the year. Our results demonstrate the benefit of more
frequent lidar monitoring and, critically, the requirement for novel
approaches to quantifying and disaggregating surface change, as a step
towards rock glacier observation networks focusing on the analysis of 3D
surface change over time.
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