Perito Moreno Glacier

High in the mountains, lots of snow falls and piles up.

The snow gets pressed into ice. The heavy ice slowly slides downhill. It moves all the way to the lake.

A glacier forms where more snow falls each year than melts. The snow piles up, gets squeezed into ice, and the weight pushes the ice slowly downhill. The park explains that Perito Moreno moves because of the push of all that piled-up snow.

Perito Moreno is fed by the Southern Patagonian Ice Field, about 12,500 square kilometers of ice. Scientists measured the ice moving around 800 meters a year along the middle of the glacier, and almost 900 meters a year near the front (2021–2023). That is more than two meters a day. Ice ages long ago covered this land with even more ice, and the glaciers carved the valleys that now hold big lakes.

The Southern Patagonian Ice Field, about 12,500 km² and shared by Argentina and Chile, is the remnant of glacial expansions from the late Miocene to the late Pleistocene (IUGS). Snow accumulating above the equilibrium line, at about 1,200 m on Perito Moreno, drives the flow down the valley.

The 2025 study measured ice up to about 700 m thick at a narrowing of the valley, and a trough near the front 200 m below sea level. Surface speeds were around 800 m a year in mid-glacier and almost 900 m a year near the front in 2021–2023. The IUGS describes the glacier as temperate, its base staying in contact with the rock where it enters the lake. As past glaciers advanced and retreated, they carved basins that filled with meltwater, forming large lakes such as Lake Argentino, 160 km long (UNESCO).

Sometimes the glacier pushes across the lake to the other shore.

Then it blocks the water like a wall. The water rises on one side. Later the water digs through the ice and breaks the wall.

In front of the glacier is a rocky point of land called the Magallanes Peninsula. Now and then the glacier pushes forward until it touches the peninsula. That cuts one arm of the lake, Brazo Rico, off from the rest, like a dam.

Cut off by the ice, Brazo Rico's water level rises. The water presses on the ice, wears a tunnel through it and drains away, until the ice dam breaks. The park calls this rupture a natural show that is impossible to predict.

The glacier's front pushes against the western tip of the Magallanes Peninsula during brief advances, damming Brazo Rico. Water then builds stresses at the front and drains into the main lake through a tunnel cut in the ice, until the dam ruptures (IUGS). The park's walkway map shows the steps: the glacier advances to the shore, blocks the water and raises Brazo Rico, then the water erodes the ice and the rupture begins; it calls the event impossible to predict.

During particularly strong advances in 2003–2004 and 2011–2012, the dam raised Brazo Rico by more than 9 m, according to the 2025 study, whose lake survey found a moraine marking those front positions in the Canal de los Témpanos. UNESCO calls the ruptures regular and thunderous, and the study notes that these calving and lake-damming events made the glacier a tourist attraction.

For a long time this glacier stayed about the same size.

Now scientists see it getting thinner. Its front has moved back in some places.

Many glaciers in Patagonia have been shrinking, but Perito Moreno was known for staying about the same. From 1999 to 2013 its front moved back and forth by no more than 50 meters.

A team of scientists from Germany and Argentina flew radar over the ice in 2022 and measured the lake bottom in 2023. In a study published in 2025, they report that the ice near the front has been getting thinner much faster since 2019. On one side the front moved back 800 meters in about four years.

Earlier studies described Perito Moreno as relatively stable compared with other large Patagonian glaciers; the IUGS site page cites work from 2010 saying it had not retreated in the previous 50 years. Koch and colleagues (2025) combined helicopter radar (March 2022), a lake-bed survey (March 2023) and satellite elevation and speed data from 2000 to 2024.

They found frontal surface lowering rising from 0.34 m a year (2000–2019) to 5.5 m a year (2019–2024), faster flow, and a retreat of 800 m in about four years after 2020 on the north-western shore of the Canal de los Témpanos. The front rests on a ridge of bedrock under the ice, an extension of the Magallanes Peninsula. Their simple model suggests that if thinning continues, the glacier could retreat on a large scale once it pulls back past that ridge, though the authors make no prediction of when.

Near the glacier there are forests with trees called lenga.

Great condors soar in the sky. A shy deer called the huemul hides in the forest.

Los Glaciares National Park has ice, but also forests, lakes and dry grassland called steppe. Its forests are mostly southern beech trees called lenga, ñire and guindo. The calafate bush and the notro, with bright red flowers, grow lower down.

Andean condors, with wings about 3 meters across, glide on rising air. Giant woodpeckers, torrent ducks and pumas live in the park too. The park also protects Argentina's southernmost huemul deer, an endangered species.

Almost half of Los Glaciares National Park is ice; the rest is Andean-Patagonian forest, lakes and Patagonian steppe. The forests are mainly Nothofagus: lenga (N. pumilio, the most common), ñire (N. antarctica) and guindo (N. betuloides, the only evergreen), with calafate and the red-flowered notro lower down, visited by hummingbirds and insects.

The park leaflet's emblematic species include the Andean condor (wingspan about 3 m), the giant woodpecker (Campephilus magellanicus), the torrent duck (Merganetta armata), a sign of healthy mountain streams, and the puma, the region's top predator. The huemul (Hippocamelus bisulcus), an endangered deer found only in Argentina and Chile, was declared a National Natural Monument in 1996; the park protects Argentina's southernmost population and monitors it every year.

Visitors watch the glacier from wooden walkways.

Stay behind the railings. Hold the handrail on the steps. Ice that falls can send pieces flying far.

Visitors look at the glacier from a circuit of walkways and balconies, with trails from very easy to challenging. The park asks everyone to stay behind the railings: when ice breaks off the front, chips of ice can fly dozens of meters.

Keep your hands free, hold the handrail on the steps, and walk carefully when it is rainy, icy or snowy. Grown-ups are asked to keep children close so they don't run off or fall.

Argentina's national parks service runs a walkway circuit with several balconies facing the glacier, from a 150 m Icebergs trail (very easy) to a 1,100 m lower trail (challenging). Its accident-prevention rules: walk with your hands free, hold the handrail on steps, check each trail's length because every step down must be climbed back, take short firm steps when wet or icy, protect children from falls and getting lost, and never climb or cross the railings, because calving throws ice chips dozens of meters.

The park leaflet adds general rules: no pets, fishing only with a permit, fire only in permitted places, and no damaging cultural remains. Visitor numbers are large: the 2025 study reports almost 800,000 park tickets sold in 2023, with nearly 90% of visitors to El Calafate going on to the glacier.