High mountain basins in nothern Chile: water balance problems in an arid volcanic area

In, the arid volcanic area of northem Chile, over 3,100 m, the overflow layer is very high and shows little variation in time. During dry years, it may exceed the precipitation layer and it seerns independent frorn rainfails. The natural overload is very scarce and the resources that actuaily are developed could be considerated as fossil groundwaters. To explain these anornalous vaiues of the water balance, the most likely hypotheses are three: 1 - rnissestirnation of actual precipitations (infiltration of snow cover); 2 - existence of extemai contribution (drainage frorn the east below the volcanic range); 3 - discharge of powerfulaquifers (lst, the clirnatic conditions in the Holocene have been rnuch wetter than previously considered; 2nd, thick detritic formations are interstratificated in the volcanic cornplex)