structural periglacial grounds; Chambeyron; field experience; High Mountains; sols structuraux périglaciaires; sol structural périglaciaire; expériences de terrain; Haute montagne
Résumé :
[en] ln the Chambeyron massif, between 2800 and 3000 m above sea level, reference marks have thrown light on geomorphological processes which operate in the formation and evolution of periglacial patterned ground.
I. Polygones of several decimeters diameter
The observed processes are:
1. The formation of a polygonal net of contraction cracks which persisted for years but opened and closed (fig.1et3);
2. the appearance on the surface of pebbles uplifted by frost (fig. 2);
3. the movement of the pebbles on the surface to the stony borders (fig.1, 2 et 3);
4. the presence of mass movement in the center of the polygones (fig. 4 et 5).
II. Polygones of almost a meter diameter
Painted stones buried in these polygones appeared rapidly on the surface.
Painted stones placed on the surface move quickly to the borders of small secundary polygones where some have moved clown to a depth of several centimeters in 5 years.
III. Stripes of several decimeters width
Painted stones buried in the fine bands appeared rapidly on the surface and then moved to the stony band. lt is not clear if the rate of movement downslope is greater in the stony bands
than in the fine bands.
IV. Stripes of almost one meter width .
Ten years obserbations of painted lines have shown that the fine bands move downslope more quickly than the stony bands (fig. 7). Vertical bands of coloured fine matérial showed that this movement was rapid only very close to the surface (fig. 8).
