Ice Aprons in the Mont Blanc Massif (Western European Alps): Topographic Characteristics and Relations with Glaciers and Other Types of Perennial Surface Ice Features

Abstract

Ice aprons are poorly studied and not well-defined thin ice bodies adhering to high altitude steep rock faces, but are present in most Alpine-type high mountain environments worldwide. This study aims to precisely define ice aprons based on a detailed analysis of their topographical characteristics in the Mont Blanc massif (western European Alps). For this, we accurately identified and precisely mapped 423 ice aprons using a combination of high-resolution optical satellite images from 2019. To better understand their relationship with other types of glaciers, especially the steep slope glaciers and other surface ice bodies, we built a detailed inventory at the scale of the massif that incorporates nine different types of perennial surface ice bodies. In addition, an analysis using different topographic factors helped us to better understand the preferred locations of the ice aprons. We show that they predominantly occur on west-oriented steep and topographically rugged rock slopes above the local Equilibrium Line Altitude (~3200 m a.s.l.), with concave profile curvatures around them that facilitate snow accumulation. They are also found in areas underlain by permafrost. The extensive inventory also helped us to identify different types of ice aprons based on their relationships with glaciers/ice bodies. The analysis shows that ice aprons existing at the headwall of large glaciers above a bergschrund are the most dominant ice apron type in the study area, with ~82% of the total.

Ice aprons on steep high-alpine slopes: insights from the Mont-Blanc massif, Western Alps

“…Given the slope of the IAs which is unfavourable to thick accumulations of snow, it should be noted that the formation of ice does not occur by compressive firnification metamorphosis but more likely by refreezing of meltwater in snow in the same way as superimposed ice in perennial ice patches (Davesne and others, 2022). The study of Kaushik and others (2022 a ) carried out at the scale of the whole MBM made it possible to specify the spatial distribution of IAs, resulting in a better understanding of their location within the high-mountain slopes as well as their relations with the other types of glaciers.…”

“…A combination of very high-spatial resolution images like the orthophotos available from (0.4 m resolution), panchromatic images from SPOT 6 (1.5 m resolution) and the high-resolution images available from Google Earth were accurately used in order to manually digitize IAs in the MBM under a GIS environment (Kaushik and others, 2021, 2022 a ). Since IAs have a slope >40° (slope angle regularly used as a minimum value to define rock walls), they might be confused with avalanching glaciers but they do not have a vertical front from which blocks of ice (‘séracs’) break off, nor do they have crevasses.…”

“…A total of 423 IAs were identified by Kaushik and others (2022 a ) (Fig. 3), corresponding to a total of 4.21 km 2 which is ~0.8% of the massif surface area and ~2.6% of the total surface area covered by ice (162.4 km 2 according to Kaushik and others, 2022 a ).…”

“…A total of 423 IAs were identified by Kaushik and others (2022 a ) (Fig. 3), corresponding to a total of 4.21 km 2 which is ~0.8% of the massif surface area and ~2.6% of the total surface area covered by ice (162.4 km 2 according to Kaushik and others, 2022 a ). Regarding the surface area of IAs, the statement of Guillet and Ravanel (2020) defining IA <0.1 km 2 is confirmed since the values in the MMB are from 0.001 to 0.05 km 2 .…”

“…1g) have a surface area ~0.1 km 2 . Problems associated with the lack of coverage over the entire MBM, presence of cloud cover, illumination and shadow area issues, which make visual interpretation difficult and the presence of seasonal snow cover were all overcome using images acquired through different modes (Kaushik and others, 2022 a ).…”