PEAT SOIL FLOWS IN BAHIA-DEL-BUEN-SUCESO, TIERRA-DEL-FUEGO (ARGENTINA)

On the southeastern edge of Tierra del Fuego, a mountainous area with a cold humid oceanic climate, peat soils cover not only flat areas but also steep hillslopes under an evergreen Nothofagus betuloides forest. Peat flows in the form of chutes are very frequent on these hillslopes. Some data were gathered on the field for 11 of these movements and from aerial photographs for 21 of them. The results suggest that peat soils become unstable when thickness exceeds a critical value which depends on the slope. This critical slope depends on the altitude and aspect regardless of soil thickness. A temporal analysis carried out by tree-ring counting demonstrated that the occurrence of these movements is not random though there are some periods of higher hazard, the probable triggering mechanisms being heavy snowfalls or earthquakes.