Perito Moreno Glacier

Lore & Background

The glacier was first sighted by non-indigenous people in 1879 by British Chilean Navy captain Juan Tomás Rogers, who named it Francisco Gormaz. Later, Rudolph Hauthal named it Bismarck. In 1899, Lieutenant Iglesias named it Perito Moreno in homage to explorer Francisco Moreno, who studied the region in the 19th century and played a major role in the 1902 Arbitral award of the Andes between Argentina and Chile.

The glacier advances between June and December and recedes between December and April. Its terminus is 5 km wide and averages 74 m above the water of Argentino Lake, with a total ice depth of 170 m.

Since 2020, the glacier has been retreating on its northern front, possibly due to climate change. It was previously one of the few glaciers that maintained equilibrium during the late 20th and early 21st centuries, accumulating mass at a rate similar to its loss. The reason for this stability remains debated by glaciologists.

Reader's Guide

The Perito Moreno Glacier is significant for its dynamic and visually spectacular rupture cycle, where the advancing glacier dams the Brazo Rico arm of Lake Argentino, causing water levels to rise up to 30 meters before breaking through in a massive discharge. This natural dam–ice-bridge–rupture cycle recurs irregularly, from once a year to less than once a decade, and has been recorded since 1917. The ruptures are classified as sudden, progressive, or minor, with sudden events reaching discharge peaks of up to 8000 m³ per second. The glacier's stability until recent years made it an unusual subject of study for glaciologists, who debate the reasons for its long equilibrium. Its location in Los Glaciares National Park and proximity to El Calafate make it a major tourist attraction, drawing thousands of visitors to witness the rupture events. The glacier also holds historical importance in the boundary disputes between Argentina and Chile, resolved through treaties and agreements in 1881 and 1998.

Did You Know?

• The glacier is one of 48 glaciers fed by the Southern Patagonian Ice Field, the world's third largest fresh water reserve.
• The first recorded rupture of the ice dam occurred in 1917, after the glacier front began moving toward the opposite bank at the end of the 19th century.
• In the 2004 rupture event, an estimated 10,000 tourists watched the discharge.
• The glacier was named after Francisco Moreno, a pioneer who studied the region in the 19th century and defended Argentina's position in the 1902 boundary arbitration.

Geography & Physical Scale

The Perito Moreno Glacier is a 30-kilometer-long ice formation covering roughly 250 square kilometers, and it ranks among 48 glaciers nourished by the Southern Patagonian Ice Field in the Andes. That ice field, which straddles the border shared with Chile, constitutes the world's third-largest reserve of fresh water. At its terminus, the glacier spans five kilometers in width and towers an average of 74 meters above the surface of Lake Argentino, with a total ice depth of 170 meters. Situated 78 kilometers from El Calafate in Santa Cruz Province, it lies within Los Glaciares National Park. A small portion of its origins extends into Chile's Magallanes Region, falling inside Bernardo O'Higgins National Park, while the bulk of the glacier and the lake it feeds remain under Argentine sovereignty. The glacier drains into Lake Argentino, which sits east of the Andean range. Today it draws enormous numbers of visitors and stands as one of the premier tourist attractions in Argentine Patagonia.

The Dam-and-Rupture Cycle

The glacier's most dramatic feature is its periodic dam-and-rupture cycle. As the ice slowly advances across the inner fjord of Lake Argentino, it reaches the coast of Península de Magallanes, effectively bisecting the lake between Brazo Rico and the Canal de los Témpanos. With no outlet, water on the Brazo Rico side can climb as high as 30 meters above the main lake level. Eventually, the pressure of the dammed water shatters the ice barrier, unleashing a torrential outpouring into the main body of Lake Argentino and downstream into the Santa Cruz River. The exposed shoreline afterward bears visible scoring marks that record the height of the buildup. This cycle recurs naturally anywhere from once a year to less than once per decade. Discharge events are classified as sudden, progressive, or minor burst; sudden events can peak at 8,000 cubic meters per second, while smaller ones evacuate as little as 123 cubic meters. The glacier advances from June through December and recedes from December to April, with a complex feedback mechanism between ice and lake governing the oscillations of the front.

Naming & Border Disputes

The glacier's identity reflects decades of geopolitical tension between Argentina and Chile. In 1879, British-Chilean Navy captain Juan Tomás Rogers became the first non-indigenous person to sight it, naming it Francisco Gormaz after the Director of the Chilean Navy's Hydrographic Office, which sponsored the expedition. Years later, Rudolph Hauthal, attached to the Argentine Boundary Commission, renamed it Bismarck in honor of the Prussian Chancellor. The 1881 Boundary Treaty eventually defined the Andean border up to the 52nd parallel, placing the glacier east of the range and within Argentine territory, though the area had previously been contested during the East Patagonia, Tierra del Fuego and Strait of Magellan Dispute. In 1899, Lieutenant Iglesias of the Argentine Hydrographic Institute, after years of research and surveys, bestowed the name Perito Moreno, honoring the 19th-century explorer Francisco Moreno, who had studied the region and later played a pivotal role in defending Argentina's position in the 1902 Arbitral Award. The glacier's origin remained disputed until a 1998 agreement drew a boundary line leaving a small portion in Chile and the remainder in Argentina.

Stability & Modern Retreat

For much of the late 20th and early 21st centuries, the Perito Moreno Glacier occupied a rare position among Patagonian glaciers: it maintained a state of dynamic equilibrium, accumulating mass at roughly the same rate it lost it. This unusual longevity of stability has puzzled glaciologists, who continue to debate the underlying reasons. The glacier's seasonal rhythm, advancing between June and December and retreating between December and April, was governed by a feedback mechanism between the ice and the lake that kept the front's oscillations fairly stable. However, since 2020, the glacier has begun retreating on its northern front, a shift possibly linked to climate change. This marks a departure from the long period of balance that had made the glacier a distinctive case study. The recorded rupture events, spanning from 1917 through 2019, document the glacier's active behavior over more than a century, with intervals ranging from back-to-back events in 1952 and 1953 to gaps of several years, and even two separate ruptures in 2013 alone.