CHARACTERISTICS OF TIDE-WATER CALVING AT GLACIAR SAN-RAFAEL, CHILE

Glacial calving is a poorly understood process. This study tests the i nfluence of local environmental variables on the magnitude and frequen cy distributions of calving behaviour at Glaciar San Rafael, Chile. Ne ar the terminus of the glacier, surface speeds average 17 m d(-1) in s ummer and calving is profuse and continual. The size, location and cha racteristics of over 7000 calving events were recorded during 32 d in 1991 and 1992, together with meteorological, bathymetric and oceanogra phic data. Mean daily calving exceeds 400 events per day and the mean calving flux is more than 2 M m(3) d(-1). Mean annual calving speed an d calving flux are about 4500 m a(-1) and 2.0 km(3) a(-1), respectivel y. This calving speed is higher than that predicted by the established empirical relationship between tide-water calving speed and water dep th. This is surprising, given the low salinity of Laguna San Rafael an d chat fresh-water calving speeds are commonly much lower than those i n tide water. Daily patterns of calving frequency and flux correlate p oorly or not at all with meteorological variables, but tidal stage may have some control over the timing of large submarine calving events. Submarine calving produced the largest bergs. However, the relatively small total flux recorded from the submerged part of the ice cliff may imply unusually rapid melt rates.