Deformation of loess cylinders surrounded by gravel under the effect of freeze/thaw cycles. Experiments on the origin of cryoturbations

Abstract

Article in French.

ORIGINAL TITLE: Déformations de cylindres de limon entourés de graviers sous l'action d'alternances gel/dégel. Expériences sur l'origine des cryoturbations

Cylinders, composed of coloured and uncoloured layers of. aeolian loess and surrounded by gravel, were placed in wooden containers and subjected to cycles of slow freezing and rapid thaw in a cold chamber. When the temperature was above 0°C, the gravel was filled up with water. This water was removed before the beginning of the freezing.

Two kinds of experiments were made giving considerable deformation of the cylinders.

In the first one, the water was removed several hours before the freezing and the small stones were uncemented when the container was frozen. The main deformation was an uplift of the coloured beds at their contacts with the gravel (Fig. 3). This movement probably resulted from the adherence of this material to gravel at the moment of thaw.

The uplift of the coloured layers in polygonal soils at Chambeyron (Fig. 1) probably results from the same action of relapse of fine materials uplifted by the frost.

In the second one, the water was removed just before the freezing. Enough water was left to cement with ice the small stones. Not only the coloured beds were deformed at their contacts with the gravel but, in the same time, the diameter of the cylinder, at the surface, progressively decreased, while the centres of the cylinders sank (Fig. 4). These movements result from the fact that gravel and loess were cemented by ice when dilatation of the cylinders occurred.

This experiment shows: (1) that considerable deformation can be progressively produced (Fig. 5) in the course of freezing, without the material being liquified; (2) that the fine material tends to be displaced in the direction of advance of the freezing front.