Calving rates in fresh water: new data from southern Patagonia

Data relating to calving dynamics in fresh water are scarce, especially for deep-water sites. A linear dependence of calving velocity (V-c) on water depth (H-w) is commonly accepted for both tidewater and fresh-water calving glaciers. Here we use recent data from temperate Patagonian glaciers to propose a revised relationship for calving in fresh water. The new ratio is derived front glaciers calving rapidly into deep water, documented using sequential satellite images and depth soundings. The main data source is a detailed remotely sensed dataset of the rapidly retreating Glaciar Upsala, complemented with global positioning system field Surveys and precise ice-proximal bathymetric surveys. The area-integrated mean water depth between glacier positions in 1996 and 2000 is 490 in, with a maximum recorded depth of > 700 m. In the same period, image analysis reveals surface area loss of 1.37 km(2) a(-1) (4.8 km(2) ) and an average calving rate of 1880 in a(-1). The resulting V-c/H-w ratio is of a similar order of magnitude to that recently derived for nearby Glaciar Moreno, but is well above the range of values commonly reported for lacustrine calving.