[ACC39-02] Changes in ice-front position and surface elevation of Pío XI Glacier, an advancing calving glacier in the Southern Patagonia Icefield, in 2000–2018
キーワード：氷河、人工衛星画像、パタゴニア、写真測量
Glaciar Pío XI, the largest glacier in the Southern Patagonia Icefield (SPI), has advanced over the last several decades in contrast to a shrinking trend of other glaciers in the SPI. The mechanism of the unique behavior is unclear due to lack of detailed observations. To investigate the mechanism of the recent advance of Glaciar Pío XI, we measured ice-front position and glacier surface elevation by using satellite data from 2000 to 2018. Ice-fronts of all separated termini showed advancing trend. The largest advance of 1400 m was observed at the southern main front. Glacier surface elevation increased by 35 m as a mean over the ablation area during the study period, and the rate of elevation change increased by 240% from Period 1 (2000–2007) to Period 2 (2007–2017/18). The rate of elevation change was non-uniformly distributed over time and space; i.e. rapid thickening (~20 m a−1) was observed in a limited area during Period 1, whereas only slightly positive rate (~2.4 m a−1) was observed over the entire region during Period 2. Previous studies reported ice speed deceleration near the southern main front, suggesting decrease in frontal ablation over the study period. Based on satellite image observations from 2000 to 2018, we attribute the deceleration to deposition of sediment and formation of shoal in front of the glacier. In the accumulation area, increase in snow accumulation is reported for a period from 1980 to 2015. Therefore, we propose the reduction in frontal ablation and increase in accumulation as possible mechanisms of the recent advancing and thickening trend of Glaciar Pío XI. Our data illustrate details of advancing despite a retreating trend in adjacent glaciers in Patagonia.