The early formational stage of present-day stone rings in the Alps, near Sallanches

Abstract

Article in French.

ORIGINAL TITLE: Amorce de roses de pierre actuelles dans les Alpes, pres de Sallanches

The paper describes the observation of modern stone rings (structures in which smaller stones arrange themselves around a larger central pebble) forming in the Arve River valley, near Sallanches in the Alps. The phenomenon developed within alluvial deposits left by a flood in 1960, which cover a grass layer, thereby forming an impermeable substrate. During the winter of 1960/61, the repeated freezing and thawing of fine, moist sandy and silty material caused the stones to rise, tilt and stand upright, forming the beginnings of stone ring structures. This process was observed after about forty freeze–thaw cycles. The favourable conditions included constant humidity, fine-grained sediment suitable for ice segregation, high daily temperature variations, and the absence of rain that might have otherwise erased surface cracks. The author emphasises that periglacial microforms can develop very rapidly, even within a single winter season, when conditions are exceptionally favourable. This case also shows that, in reconstructing Quaternary palaeoclimate, researchers should not rely on isolated observations but rather on the frequency and recurrence of such phenomena.