Distribution and Evolution of Ice Aprons in a Changing Climate in the Mont-Blanc Massif (Western European Alps)

Abstract

Abstract. Ice Apron (IA) is a poorly studied ice feature, commonly existing in all the world’s major mountain regions. This study aims to map the locations of the IAs in the Mont Blanc massif (MBM), making use of the very high-resolution optical satellite images from 2001, 2012 and 2019. 423 IAs were identified and accurately delineated in the MBM on the images from 2019, and their topographic characteristics were studied. We generated our own Digital Elevation Model (DEM) at 4 m resolution since the freely available products predominantly suffer from significant inconsistencies, especially in steep mountain areas. Results show that most IAs exist at elevations above the regional Equilibrium Line Altitude (ELA), on steep slopes, on concave surfaces, on northern and southern aspects and on the most rugged terrains. They are also commonly associated with steep slope glaciers as 85% of them occur on these glaciers’ headwalls. A comparison between 2001 and 2019 shows that IAs have lost around 29% of their area over a period of 18 years. This is significant and the rate of area loss is very alarming in comparison with the larger glacier bodies. We also studied the effect of topographic parameters on the area loss. We found that topographic factors like slope, aspect, curvature, elevation and Terrain Ruggedness Index (TRI) strongly influence the rate of area loss of IAs.

Effects of topographic and meteorological parameters on the surface area loss of ice aprons in the Mont Blanc massif (European Alps)

“…Thus, it is likely that underlying permafrost conditions aid the sustainability of IAs in the long term, and an increase in rock surface temperatures around IAs could result in IAs losing mass more rapidly. Kaushik et al (2021) further showed that most IAs exist in extremely rugged terrains: 51 % of the total IAs mapped exist in the TRI's high and very high ruggedness class, while only 8 % exist in the low ruggedness. Thus, comparing the terrain ruggedness to the area loss of IAs makes sense since the topography around the snow/ice bodies can critically influence their stability (Deline et al, 2015).…”

“…A precisely co-registered, high- resolution, robust 4 m DEM was obtained at the end of the processing steps. More detailed information about the processing parameters for DEM generation and co-registration can be found in Kaushik et al (2021). We used this DEM to compute topographic parameters like slope, aspect, curvature, elevation, TRI, mean annual rock surface temperature (MARST) and direct solar radiation.…”

“…Both coarse and fine co-registration procedures were performed, and the co-registration process was stopped when the RMSE values achieved were less than half the pixel resolution of the warped image based on the recommendations of Han and Oh (2018). A more detailed description of the co-registration process was discussed in Kaushik et al (2021).…”

“…It also highlights the importance of high-resolution images because of the small dimensions of our studied ice bodies. However, these data are not always available in the best quality for the past periods as we could only very accurately map 200 IAs (out of the total 423 IAs reported in Kaushik et al, 2021) for all the periods. These 200 IAs were selected carefully after a detailed visual inspection and considering issues related to shadow and illumination.…”

Analysis of the Temporal Evolution of Ice Aprons in the Mont-Blanc Massif Using X and C-Band SAR Images

“…IAs are very small ice bodies located on very steep slopes. The slant range acquisition geometry of SAR images is always associated with geometric distortions, which can create geometrical artefacts (GA): strong foreshortening, layover (active and passive) and shadow (active and passive) (Kaushik et al, 2021a). To study the temporal evolution of backscattering response from IAs, it is necessary to find areas free from these artefacts.…”