Pio XI glacier: The exception to the deglaciation trend in Patagonia

Abstract

The Pío XI glacier also called Brüggen (49º13'S  74ºW), the largest glacial basin of the Southern Patagonian Ice Field (SPI), has experienced a net increase in area of 126 km² since 1945 due to an almost permanent state of advance with rates of 150 m/a and a thickening of 2 m/a between 1975 and 2013. This behaviour is an anomaly in Patagonia, since it is the only glacier with a net advance throughout the SPI. Most of the rest of the glaciers of the SPI have lost mass at high rates, highlighting the losses of Jorge Montt and O’Higgins among many others. Several hypotheses have been proposed to explain the anomalous behaviour of Pío XI, particularly the presence of surging events that have occurred in several occasions, but so far there is no certainty of the causes that explain its complex behaviour. However, it is estimated that the topographic features of the glacier, in particular the presence in the accumulation zone of the active volcán Lautaro, the highest peak of the SPI, and a little more to the south the presence of the Cordón Mariano Moreno, the second highest mountain of the SPI, are a formidable barrier of about 55 km north-south for the prevailing westerly winds, generating the largest amounts of solid precipitation of all the CHS. The process of glacial advance has repressed lateral valleys generating numerous proglacial lakes, and in its term, it is forming a frontal moraine due to the high sedimentation rates, significantly reducing the calving area.