Rock slope temperature evolution and micrometer-scale deformation at a
retreating glacier margin
Abstract
In deglaciating environments, rock mass weakening and potential
formation of rock slope instabilities is driven by long-term and
seasonal changes in thermal- and hydraulic boundary conditions, combined
with unloading due to ice melting. However, in-situ observations are
rare. In this study, we present new monitoring data from three highly
instrumented boreholes, and numerical simulations to investigate rock
slope temperature evolution and micrometer-scale deformation during
deglaciation. Our results show that the subsurface temperatures are
adjusting to a new, warmer surface temperature following ice retreat.
Heat conduction is identified as the dominant heat transfer process at
sites with intact rock. Observed non-conductive processes are related to
groundwater exchange with cold subglacial water, snowmelt infiltration,
or creek water infiltration. Our strain data shows that annual surface
temperature cycles cause thermoelastic deformation that dominate the
strain signals in the shallow thermally active layer at our stable rock
slope locations. At deeper sensors, reversible strain signals
correlating with pore pressure fluctuations dominate. Irreversible
deformation, which we relate with progressive rock mass damage, occurs
as short-term (hours to weeks) strain events and as slower, continuous
strain trends. The majority of the short-term irreversible strain events
coincides with precipitation events or pore pressure changes.
Longer-term trends in the strain time series and a minority of
short-term strain events cannot directly be related to any of the
investigated drivers. We propose that the observed increased damage
accumulation close to the glacier margin can significantly contribute to
the long-term formation of paraglacial rock slope instabilities during
multiple glacial cycles.