Avalanche maps of the Alps, Himalayas and Karakorum : variability and impact on glaciers

Snow and ice avalanches are events that contribute to the accumulation of snow on the surface of mountain glaciers. They are therefore important elements to consider when modeling the evolution of glacier mass balance, which is a metric for glacier health. On the other hand, data on avalanches in remote glaciated massifs of the Alps and Himalayas are almost non-existent or highly biased spatially or temporally, which limits our understanding of these phenomena and their link with glacier dynamics.

In a new study recently published in The Cryosphere, a team from the Institut des Géosciences de l’Environnement (IGE) and the Centre d’Etudes de la Neige (CEN), proposes a new approach to mapping avalanche deposits using radar images taken by Sentinel-1 satellites. By applying this approach to the Mt Blanc (Alps), Everest (Himalayas) and Hispar (Karakorum) massifs, it has enabled the development of an unprecedented database of over 16,000 avalanches in glaciated areas, and highlighted the spatial and temporal variability of these events.

Mapping of avalanche deposits

The method developed for mapping the avalanche deposits is based on the detection of changes in surface roughness caused by avalanches, visible in consecutive radar images taken by Sentinel-1 satellites. The advantages of these Sentinel-1 data is that the signal is not influenced by clouds, and that these images have been acquired at regular time intervals (6 days in the Alps, 12 in the Asian massifs) since 2016. This has enabled the systematic mapping of 16,302 events, avoiding spatial and temporal biases, over the period 2016-2022 and in the three study regions.

Figure 1 : The same avalanche deposit in the Mt. Blanc massif visible in a very high-resolution optical image from the Pléiades satellite (left, mapped in blue, © CNES, distribution AIRBUS DS) and in a pair of Sentinel-1 radar images (right, mapped in red).

 

Spatio-temporal variability

This unprecedented inventory of avalanche deposits has enabled us to identify the areas and glaciers most affected by avalanches, and more generally to quantify for the first time the spatial and temporal variability of such events in these massifs. Unsurprisingly, avalanche activity is strongly conditioned by snowfall and changes in the rain-snow transition line, with avalanche activity being highest during the monsoon season (June-September) in the Everest region. The Hispar region, on the other hand, is very regularly affected by avalanches, due to its high rainfall and low temperatures throughout the year.

Figure 2 : Evolution of the total size (a) and number (b) of avalanche deposits in the Everest region as a function of time and altitude, as obtained from Sentinel-1 images at 12-day intervals. (c) Temperature and precipitation trends over the same period.

 

Link with glacier mass balance

These event maps provide crucial information on the occurrence and size of avalanche deposits, but do not directly quantify the total mass of snow and ice redistributed on the glacier surface. On the other hand, they do offer the possibility of constraining existing avalanche models with a view to representing these phenomena in glacier evolution models. This avalanche inventory is therefore a crucial step in taking these phenomena into account for the mass balance of mountain glaciers.

Figure 3 : Avalanche deposits mapped in the Western Combe of Everest (a), on Argentière Glacier (b) and on Talèfre Glacier (c) in the Mt. Blanc massif. The colors correspond to the number of deposits mapped over a five-year period with the ascending (red) or descending (blue) orbits of the Sentinel-1 satellites.

 

Scientific contact : Marin Kneib

Reférence :
Kneib, M., Dehecq, A., Brun, F., Karbou, F., Charrier, L., Leinss, S., Wagnon, P., and Maussion, F. : Mapping and characterization of avalanches on mountain glaciers with Sentinel-1 satellite imagery, The Cryosphere, 18, 2809–2830, https://doi.org/10.5194/tc-18-2809-2024, 2024.