A Record of Rapid Change
The Upsala Glacier is one of the primary outlet glaciers of the Southern Patagonian Ice Field, the second-largest contiguous extrapolar ice field in the world. This massive glacier, with an area of around 765 square kilometers, terminates in the northern arm of Lago Argentino. Its retreat has been one of the most dramatic in the region. Between 1986 and 2014, the glacier's terminus pulled back 7.2 kilometers, an average rate of about 260 meters per year.
The process of retreat is not uniform. Analysis of satellite imagery shows a significant acceleration that began around 2008. From 2000 to early 2008, the glacier retreated approximately 670 meters. However, from January 2008 to May 2011, it receded a further 2.9 kilometers. This rapid phase was accompanied by an increase in ice velocity of 20–50% and substantial thinning, with the ice surface lowering at rates up to 39 meters per year near the terminus between 2006 and 2010. The primary mechanism for this ice loss is calving, the breaking off of large icebergs into Lago Argentino, driven by the glacier thinning and lifting off its bed, which reduces friction and allows it to flow faster.
This retreat has had visible consequences on the landscape. By 2021, the main trunk of the Upsala Glacier had almost completely separated from a major tributary, the Bertacchi Glacier. For centuries, the two glaciers were joined, providing a stabilizing, buttressing effect on each other. Their separation is a significant structural change in the glacier system.
Reading the Ice
Scientists use a combination of methods to track the changes at Upsala Glacier. Satellite imagery from programs like Landsat and Sentinel provides a continuous visual record of the terminus position, allowing for precise measurement of its retreat over decades. These satellites can also be used to calculate ice flow velocity by tracking the movement of surface features like crevasses between images taken on different dates.
In addition to tracking its length, researchers measure changes in the glacier's mass and volume. This is done by comparing digital elevation models (DEMs) created from satellite data over time, which reveals how much the ice surface has lowered. Between 2006 and 2010, the glacier lost an estimated 5.9 cubic kilometers of ice from a 129 square kilometer area near its terminus.
The behavior of Upsala contrasts with some other glaciers in the park. Perito Moreno Glacier, for example, is famously stable, maintaining a state of equilibrium where it advances and retreats in cycles without a significant net loss. This difference local factors, such as the depth of the lake it terminates in and the geometry of the valley, affect a glacier's response to regional climate warming.