ABSTRACTThe hydraulic geometry, runoff and sediment transport processes were studied during the 1991 summer season in two small pyroclastic drainage basins on Deception Island, South Shetland Islands. Daily discharge measurements were conducted in two channels draining 0.65 km2and 0.12 km2.The empirical relationship between the depth, velocity and width exponents- f>m>b in channels with non-cohesive material is valid for the studied area. Width is relatively conservative during increase of water discharge. Runoff was almost continuous for about 40 days, showing a strong association between streamflow and temperature. Two main periods are distinguished in the annual hydrological regime: 1. Runoff during a short melting period of snow and glaciers. 2. Snow cover and frozen period of the entire drainage area. Temperature is the main factor affecting the hydrological regime of the rivers and snow availability during the summer season determines discharge water volumes in the non-glaciated basin. The specific discharge value was 3.42 1/sec/km2.Fluvial sediment transport for the 1991 season was 46 ton/ km2yr, one order of magnitude less than values for Arctic rivers, but similar to average yearly sediment yield values of pyroclastic basins in middle latitude areas.