Supranival processes and grèzes litées

Abstract

Article in French.

TYTUŁ ORYGINALNY: Processus supranivaux et grèzes litées

In his remarkable quantitative study of periglacial processes in Spitsbergen, Alfred Jahn¹ describes small gravels (mainly of 1 to 10 mm) deposited on snow and often aligned in streaks down the slope. He then states: “Both the material’s type and its mode of accumulation show a striking resemblance to deposits designated in the French literature as grèzes litées. In reality, the grèzes litées of France are primarily defined by their bedded, stratified appearance in vertical sections; it would be interesting to see whether the supranival deposits of Spitsbergen display similar features in vertical cross-section. The material in Spitsbergen is not entirely identical; Alfred Jahn describes it as “cubique” (p. 21); in the grèzes litées of France, by contrast, it is usually strongly flattened, at least in the 10- to 20-mm size range. It is true that certain beds of grèzes litées are, like the supranival deposits of Spitsbergen, devoid of silt or fine particles; however, in other grèze beds, these fine fractions are present. In conclusion, the grèzes litées of France and the supranival deposits of Spitsbergen exhibit some analogies, but also differences. The hypothesis previously put forward² for the grèzes litées of France and Belgium (sliding over an icy or frost-coated surface) seems to me just as defensible as that of supranival deposition accompanied by runoff. Alfred Jahn’s observations provide highly valuable new details on this latter type, for which he deserves the warmest of thanks.