SEDIMENT YIELD DURING LATE-GLACIAL AND HOLOCENE PERIODS IN THE LAC-CHAMBON WATERSHED, MASSIF-CENTRAL, FRANCE

A sediment budget for the Late Glacial and Holocene periods was calcul ated for the Lac Chambon watershed which is located in a formerly glac iated temperate crystalline mountain area. It appears that over 15 500 years: (1) 69 per cent of eroded particles have been displaced by gra vity processes and then stored within the watershed, compared to 31 pe r cent that have been displaced by running water and evacuated outward ; (2) the mean mechanical erosion due to gravity processes on the slop es amounted to 16.1+/-6m and only developed on a quarter of the waters hed surface, whereas the mean mechanical erosion due to running water amounted 1.24+/-0.37m and involved the whole watershed surface. The me an sediment yields due to gravity processes on slopes were 2300+/-1360 , 1770+/-960 and 380+/-100 m(3) km(-3) a(-1), respectively, for basalt s, and basic and acidic trachyandesites. Values of sediment yield due to running water were 49+/-15, 120+/-36 and 79+/-24m(3) km(-2) a(-1), respectively during the Bolling-Allerod, the Younger Dryas and the Pre -Boreal-Boreal periods. They were 56+/-17 and 166+/-50m(3) km(-2) a(-1 ) during the Sub-Atlantic period before and after 1360 a BP, respectiv ely. These values reflect variations in the natural environment and th e impact of human-induced deforestation. (C) 1997 by John Wiley & Sons , Ltd.