Cryonival phenomena in the Andes near Santiago (Chile)

Abstract

Article in French.

ORIGINAL TITLE: Phénomènes cryonivaux dans les Andes de Santiago (Chili)

Observations carried out by the author throughout all seasons were conducted in the region of the La Disputada mine (45 km north-east of Santiago, Chile), at altitudes ranging from 3400 to 4300 metres above sea level. In this region, winter precipitation occurs exclusively in the form of snow, amounting to the equivalent of approximately one metre of water, whereas the summer season is completely dry. The 0 °C isotherm is situated at around 4000 metres, and the glacier equilibrium line lies near 4800 metres, although it can descend to 3800 metres during abnormally wet years. Nevertheless, at around 4000 metres elevation, only one fifth of the terrain is glaciated. The remaining four fifths are predominantly occupied by either young or old, more or less developed rock glaciers, with no vegetation present.

This is an area where stripes are abundant, and the author classifies them into four subgroups. These forms are explained as resulting from the eluviation of fine particles at the end of the snowmelt period, whereas a layer of frozen soil from the winter persists at depth. The stone rows act as drainage channels, whose efficiency increases progressively. The spacing between these rows depends on the depth of thawing during mid-afternoon, which is significantly greater between the rows than beneath them.

Stripes tend to evolve into stone fields, which represent a stable form. However, sheet-like mudflows that occur during exceptionally wet springs may locally renew the surface of the terrain. The repetition of such cycles leads to the formation of stratified slope deposits.