Sir, Rate of Movement of Surface Debris in Solifluction Processes

Little is known of the rate of development of polygonal or “solifluidal” soil patterns or of their rate of down-hill movement—subjects which are of significance to the geomorphologist and to the ecologist interested in the stability of the cover of vegetation.

In 1947, with M. Jean Michaud, I made some experimental studies at Chambeyron near Barcelonnette in the French Basses-Alpes at an altitude of 2700 metres. Selected stones were distinguished by painting them. Two years later some of the stones remained undisturbed, but others revealed clear evidence of movement. The front of the largest “rock glacier” investigated had moved a few decimeters. In another case the increase in the rate of movement from sides to centre was beautifully displayed, being very small at the sides and reaching a maximum of several centimetres at the centre.

In an experiment with polygonal soils in 1947 we intentionally destroyed the surface pattern of some small polygons (20 cm. broad). The pattern had been completely reformed into polygons by 1949. In another case painted stones were placed half-way between the centre and the side of a polygon. After two years it was found that they had moved, mainly outwards, a distance of 1–3 cm.

These experiments are being continued by Jean Michaud.

Laboratoire de Geomorphologie, Ecole Pratique des Hautes Etudes, St-Maur (Seine).

[It would be valuable if comparable experiments were made, preferably by local observers, at localities in Britain, notably the Lake District, North Wales and Scotland on the one hand and under more severe climatic conditions, such as Spitsbergen, on the other.—Ed.]