An Advancing River of Ice
The Perito Moreno Glacier is an ice formation covering 250 square kilometers (97 square miles) in Argentina's Los Glaciares National Park. It is 30 kilometers (19 miles) long and has a terminus, or front wall, that is 5 kilometers (3 miles) wide. This front wall rises an average of 74 meters (240 feet) above the surface of Lago Argentino. The total ice depth reaches 170 meters (558 feet).
This glacier is one of 48 fed by the Southern Patagonian Ice Field, the world's third-largest reserve of fresh water. For much of the 20th and early 21st centuries, it was notable for maintaining a state of equilibrium, meaning it accumulated mass at a rate similar to its loss. It advances at a rate of about 2 meters (6.6 feet) per day. Since 2018, scientists have observed an accelerated retreat and thinning at its northern front, ending its long period of stability.
The Rupture Cycle
The glacier's forward movement causes it to press against the Península de Magallanes, a landmass on the far side of a channel of Lago Argentino. This advance creates an ice dam that separates a southern arm of the lake, called the Brazo Rico, from the main body. With its outlet blocked, meltwater causes the water level in the Brazo Rico to rise by as much as 30 meters (100 feet) above the main lake.
The immense pressure exerted by the rising water eventually becomes too great for the ice dam to withstand. Water begins to filter through a subglacial channel, which rapidly enlarges. This process culminates in a catastrophic rupture event where the ice arch collapses. These ruptures do not happen on a regular schedule, but have occurred every few years. The first recorded event was in 1917, with others happening in years like 2004, 2012, 2016, and 2018.
Scientists use modern techniques to study the glacier's behavior. Integrating time-lapse cameras with seismic data helps monitor and identify calving events with high temporal resolution. Studies have also used hydrophones to analyze the underwater acoustic signals generated by calving ice, which helps detect individual events and understand the mechanics of ice fracture.