Abstract

Pio XI (or Brtiggen) Glacier is probably the only glacier in the world currently at its Neoglacial maximum. Its recent fluctuations provide a striking example of non-climatic glacier behaviour. A rapid 3 km advance in the \920s was followed by retreat in the 1930s. Between 1945 and 1983 the glacier advanced 10 km at a mean rate of 263 m a- , since when it has oscillated around a quasi-stable position. In 1992 the terminus was advancing over large accumulations of proglacial sediment and the western margin was advancing into mature forest composed of southern beech (Nothofagus spp.) and Pilgerodendron uviferum. The pro glacial delta has aggraded to sea level along two thirds of the front and the PD[LPXPwater depth is 22 m, pennitting on! y small-scale ea! ving. The advance has blocked a tributary valley, forming a 240 km ice-dammed lake into which large-scale, frequent calving is taking place. This pattern of behaviour cannot be explained with reference to climate alone. A simple descriptive model combining calving dynamics, sediment budget, fjord topography and climate explains the main features of recent behaviour. Many other Patagonian calving glaciers have also responded indirectly to climate this century. Since the established Late Glacial and Holocene chronology ofPatagonian glacier oscillations is largely based on records from si