A glacial interpretation for the origin and formation of the marinet rock glacier, alpes maritimes, france

Abstract

Rock glaciers of the Southern French Alps, specifically the Marinet Rock Glacier, are commonly thought to have a ‘permafrost origin’. However, there are other rock glaciers in the Southern French Alps found in association with small corrie glaciers, suggesting that glacier ice has a role to play in their formation. At the Marinet Rock Glacier, results from ground surveys, relationships between debris and ice input, lichen dating and historical documentation suggest a glacial rather than a permafrost origin. Rock glacier palaeovelocities, calculated for an ice core within the rock glacier, suggest that it once moved much faster (up to 20 ma‐1) than at present (<0.04 ma‐1). This difference can be accommodated by a glacial explanation with development of the rock glacier over a 300 year period from the beginning of the Little Ice Age (derived from lichenometry). This relatively recent origin, compared to that required for a permafrost origin, accounts for the unstable nature of the rock glacier surface and its lack of vegetation. The very limited rock glacier movement shown at present (< 0.04 ma‐1) is explained by the thinning of the ice core underneath a rock debris cover.