Glacier and permafrost risks in a changing climate

Abstract/Description

Global glacier mass loss can have adverse effects on slope stability due to the thermodynamic, mechanical, and hydrological changes occurring in the subsurface during and following glacier disappearance. In Alaska, glacier mass loss is particularly rapid and the close proximity of unstable slopes to the termini of rapidly retreating marine- or lake-terminating glaciers means that some landslides pose a tsunami risk. One such case is at Portage Glacier, Southcentral Alaska, where two large, active landslides border a rapidly thinning and retreating glacier adjacent to a deep lake. At this site, we seek to understand the factors controlling slope motion at weekly to seasonal time scales, and how those controls evolve over time.
We conducted measurements over the course of three years, installing geophones, GNSS receivers, and a time-lapse camera to monitor the landslides, as well as ablation stakes on the glacier. A nearby weather station provides meteorological measurements at up to hourly resolution. These data are supplemented by high-resolution DEMs and satellite imagery. We localize rockfall events using the seismic data and compare this to movement hotspots using feature tracking of the time-lapse imagery, which we put into context with slope velocities from the GNSS, local precipitation events, as well as periods of higher melt rates or faster glacier velocities.
The combined datasets provide a holistic picture of the various ongoing processes within these landslides, allowing us to disentangle destabilization mechanisms related to debuttressing, glacial erosion, pore water pressure variations, and seismic activity.

Abstract/Description

The frequency of high-elevation rockfalls in the Alps has increased significantly over the past two decades, regularly making headlines in the media. Numerous studies have shown that this increase is largely attributed to the ongoing climate crisis and associated permafrost degradation. However, the temporal and spatial variability of erosion rates in these environments remains insufficiently constrained. We aim to understand the dynamics of erosion and rockfalls in the Mont-Blanc massif (French Alps) by quantifying erosion rates and identifying links between the climate crisis and the frequency of these processes. We propose an original approach combining two complementary methods: analysis of cosmogenic nuclides (10Be) concentration in supraglacial clasts for long-term estimates (centuries) and terrestrial laser scanning (TLS) for short-term erosion rates (years). By integrating these complementary datasets, we assess both sustained and recent changes in high-alpine erosion dynamics.

Our results reveal significant differences in erosion dynamics between the massif’s NW side, including the Mer de Glace catchment area, and SE side, which includes the Brouillard and Frêney glacier catchment areas. Long-term erosion rates reach 1.3 ± 0.7 mm per year on the former (elevations below 3950 m a.s.l.) and 0.2 ± 0.1 mm per year on the latter (southeast-facing slopes and elevations above 3,950 m a.s.l.). Regarding the TLS data, we documented over 750 rockfalls (1–15,500 m³, 2005–2022). The TLS indicates a notable acceleration in erosion rates, especially in the past decade. On the NW side, rates increased from 4.0 mm per year (2005 2011) to 26.7 mm per year (2011 2018), stabilizing at 23.4 mm per year (2018 2022). On the SE side, while erosion rates were initially lower, they have risen significantly, from 0.7 mm per year (2005 2011) to 15.9 mm per year (2018 2022), indicating a growing sensitivity to recent thermal fluctuations.

These findings underscore the intensification of high-altitude erosion in response to the climate crisis, particularly through glacier retreat and permafrost degradation. The observed acceleration in rockfalls has significant implications for hazard assessment and risk management in high-alpine environments and the long-term stability of high-mountain environments.

Abstract/Description

The current climatic phase is significantly affecting the global cryosphere, resulted in the incipient small glacial lakes, expansion of existing glacial lake areas and volumes, a decline in permafrost coverage. This study aims to quantify glacial lake dynamics in the Lachung Basin of Sikkim, Eastern Himalaya, with a particular focus on potentially dangerous glacial lakes (PDGLs). Using satellite imagery and aerial photographs from 1974 to 2023 (area of >0.001 km²), an updated inventory of glacial lakes was compiled. In 2023, a total of 99 lakes were identified, covering an area of 4.570 ± 0.29 km². Between 1974 and 2023, both the number (from 46 to 99) and total area (from 2.986 ± 0.10 km² to 4.570 ± 0.29 km²) of glacial lakes grew substantially. A strong correlation was observed between glacial lake expansion and the accelerated rate of deglaciation from 2001 to 2014, with the highest recorded lake area expansion rate of 0.057 km²/y in this basin. The expansion rate varied by lake type, with supraglacial lakes showing the lowest rate at 0.013 km² per/y (1988–2001), while proglacial lakes expanded at a higher rate of 0.037 km²/y over the same period. The supraglacial lake at Tenbawa glacier has a history of Glacial Lake Outburst Floods (GLOFs) in 1998, and rapidly expanding afterwards, likely due to climatic changes. Furthermore, other supraglacial lakes on Illibu Khangse glacier were identified as high-risk for GLOF events. Field mapping documented an unreported breach of a small moraine-dammed lake on August 2, 2023, and later quantified through satellite imagery. To evaluate the outburst risk of PDGLs, 22 key determinants were analyzed using the Analytical Hierarchy Process (AHP), categorizing 24 identified PDGLs into three risk levels: 9 lakes were classified as very high risk, 12 as medium risk, and 3 as low risk. With nearly 88% of lakes falling into the medium to high-risk categories, urgent and precise bathymetric and geophysical assessments, permafrost evaluations and continuous monitoring, are essential for risk mitigation. It is crucial not to underestimate even small glacial lakes, as their potential breaches could lead to catastrophic cascading effects downstream.