Controls on spatial and temporal patterns of slope deformation in a
paraglacial environment
Abstract
A comprehensive surface displacement monitoring system installed in the
recently deglaciated bedrock slopes of the Aletsch Valley shows
systematic reversible motions at the annual scale. We explore potential
drivers for this deformation signal and demonstrate that the main driver
is pore pressure changes of phreatic groundwater in fractured granitic
mountain slopes. The spatial pattern of these reversible annual
deformations shows similar magnitudes and orientations for adjacent
monitoring points, leading to the hypothesis that the annually
reversible deformation is caused by slope-scale groundwater elevation
changes and rock mass properties. Conversely, we show that the ground
reaction to infiltration from snowmelt and summer rainstorms can be
highly heterogeneous at local scale, and that brittle-ductile fault
zones are key features for the groundwater pressure-related rock mass
deformations. We also observe irreversible long-term trends (over the
6.5 yr dataset) of deformation in the Aletsch valley composed of a
larger uplift than observed at our reference GNSS station in the Rhone
valley, and horizontal displacements of the slopes towards the valley.
These observations can be attributed respectively to the elastic bedrock
rebound in response to current glacier mass downwasting of the Great
Aletsch Glacier and gravitational slope deformations enabled by cyclic
groundwater pressure-related rock mass fatigue in the fractured rock
slopes.