Seasonal changes in ice velocity and terminus positions of Pio XI Glacier, Southern Patagonia Icefield, Chile

The Southern Patagonian Icefield (SPI) is the largest temperate ice mass in the southern hemisphere. 96% of the outlet glaciers in the SPI are calving into lakes or the ocean. The glaciers in the SPI showed retreat and thinning over the last several decades, causing rapid mass loss of the SPI. Contrary to this trend, Pio XI glacier is gaining mass. Pio XI glacier is the largest glacier in the SPI located in the west of the icefield. The glacier has two termini, one calves into a lake to the north and the second one into fjord to the south. The both termini have been advancing and thickening since 1945. The glacier showed a surge-like rapid velocity change, which is not commonly observed in other Patagonian glaciers. Optical satellite observation is a powerful tool to study these features of Pio XI glacier, but western SPI is often covered with clouds. Synthetic aperture radar (SAR) is not influenced by clouds, but repeat cycles are too long to detect short-term velocity variations.

In this research, we used high frequency optical and SAR satellite data to investigate seasonal changes in surface velocity and terminus positions of Pio XI glacier in 2014-2017. Throughout the observation period, ice velocity showed large seasonal variations, between 2.0 and 5.6 m/d at 7.5 km from the termini, and between 1.0 and 4.7 m/d near the northern glacier front. In 2015 and 2016, ice speed largely accelerated in July-September, with a maximum speed of 2.3 times greater than the mean velocity. The glacier front positions showed only small fluctuations between 2014-2017, 0.3 km advance in the northern front and nearly stable at the southern terminus. The advance of the northern terminus occurred after the winter speed up in 2016. In the presentation, we discuss the role of the velocity change in the advance of PioXI glacier.