Ice‐front variations and speed changes of calving glaciers in the Southern Patagonia Icefield from 1984 to 2011

Abstract

AbstractPatagonian icefields are losing volume, and their loss is due partly to rapid changes in their outlet glaciers that terminate in lakes or the ocean. Despite this key influence from outlet glaciers, relatively few of these calving glaciers have had high‐frequency measurements on their frontal variations and ice speed changes. We describe here recent frontal variations and ice speed changes of all 28 major calving glaciers in the Southern Patagonia Icefield (SPI), including ice speed maps covering approximately half of the entire icefield. The analysis is based on satellite data from 1984 to 2011. Over this period, only the two termini of Glaciar Pío XI advanced. Of the remaining glacial fronts, 12 changed less than ±0.5 km, but 17 retreated at least 0.5 km. In the latter group, three glacial fronts (Glaciar Jorge Montt, HPS12, and Upsala) retreated over 6 km. Averaged over all 31 glacial fronts of the calving glaciers, the front positions retreated 1.56 km (median is 0.71 km). Along the flowline within 20 km of the front, the ice speeds up to 5900 ± 200 m a−1. Except for regions showing large acceleration or deceleration, the mean speed over the measured area decreased by 30 m a−1 from 1984 to 2011. The three most rapidly retreating glaciers showed much larger acceleration near the calving front, suggesting that ice dynamics drive their rapid retreat. Thus, we see retreat as a long‐term trend for the calving glaciers in the SPI, with behavior that implies a dynamically controlled rapid recession that may explain the recently reported volume change of the SPI.