Part of Patagonia
- Where
- Los Glaciares National Park
Santa Cruz Province, Argentina - Coordinates
- 50.5000° S
73.1330° W - Biome
- Subpolar glacial ice
- Ice face
- c. 5 km wide, c. 60–74 m
above the lake - Status
- UNESCO World Heritage, 1981
(Los Glaciares) - Best visited
- November–March
The short answer
Perito Moreno is a glacier roughly 30 kilometres long in Los Glaciares National Park, Santa Cruz Province, Argentina, fed by the Southern Patagonian Ice Field and terminating in Lago Argentino about 80 kilometres from the town of El Calafate. Its front is around five kilometres wide. It is best known for a repeating cycle in which the advancing ice reaches the Magallanes Peninsula, seals off the Brazo Rico arm of the lake, and holds back water that can rise as much as 30 metres above the main lake before bursting through. The last confirmed rupture was on 28 December 2019.
Why it's worth knowing
Two things, and the second is the one that gets misreported constantly.
The first is accessibility. Most outlet glaciers of the Southern Patagonian Ice Field require boats, small aircraft or multi-day approaches. Perito Moreno's front sits across a narrow arm of the lake from a road, a car park and a system of steel boardwalks. You can stand on dry land a few hundred metres from a five-kilometre wall of ice and watch pieces of it fall off, several times a day.
The second is the rupture cycle, and here the popular account is wrong. It is widely said that Perito Moreno ruptures every four years, or every two to four. It does not. Ruptures were recorded in 1917 and repeatedly through the twentieth century, then nothing at all between 1988 and 2004 — sixteen years in which people reasonably concluded the phenomenon had ended. It resumed in 2004 and has recurred irregularly since, at intervals from under a year to a decade.
The field notes
How the dam works
The glacier advances at roughly two metres a day along its centre line, fed by exceptionally heavy precipitation on the Southern Patagonian Ice Field. When the front reaches the Magallanes Peninsula it closes the Canal de los Témpanos and cuts the Brazo Rico and Brazo Sur arms off from the rest of Lago Argentino.
Those arms keep receiving meltwater and rivers, with nowhere to drain. The level rises — historically as much as 30 metres above the main lake, with 23 to 28 metres reached in earlier events, though the March 2018 rupture, the largest of the twenty-first century, peaked at around 14.4 metres.
The failure is not a snap. Water works into the base of the ice and opens a subglacial channel; the channel widens as its walls melt and slabs fall from its roof; eventually a tunnel becomes an arch, the arch spans the water, and it comes down. The whole process can run over two or three days.
The actual record
Recorded ruptures: 1917, 1935, 1940, 1942, 1947, 1952, 1953, 1956, 1960, 1963, 1966, 1970, 1972, 1975, 1977, 1980, 1984, 1988 — then a sixteen-year gap — 2004, 2006, 2008, 2012, 2013 (twice), 2016, March 2018 and 28 December 2019.
The 2008 event happened in July, in the middle of the southern winter, which had not occurred before. Minor events, where the ice slows the water without fully damming it, are not counted in that list.
The anomaly, and whether it is ending
For most of the twentieth century Perito Moreno held roughly steady while neighbours in the same ice field — the Upsala Glacier most dramatically — retreated by kilometres. Why is not fully settled; proposed factors include the glacier's width, the slope of its bed, its accumulation pattern, and a bedrock threshold beneath the snout that resists calving-driven collapse.
That stability may be ending. Satellite and altimetry work through the 2020s has reported thinning along the terminus and lateral margins. Whether the glacier has passed a geometric threshold, and whether the damming cycle will continue at all, is an open question.
The report before the fall. A crack like distant artillery arrives across the water, then a low groan, and then a slab of blue-white ice several storeys tall peels off the face and goes into Lago Argentino. Sound outruns attention: most people hear it, then look, then see the water still closing over whatever it was.
Getting there
Fly to Comandante Armando Tola International Airport at El Calafate, served from Buenos Aires. The glacier is roughly 80 kilometres west on Provincial Route 11, about an hour and a half by rental car, scheduled tourist bus or private transfer; there is no public bus. The boardwalk system is covered by the Los Glaciares National Park entry fee, payable at the gate.
Ice trekking on the glacier — sold as Minitrekking and Big Ice — is booked separately, requires a licensed guide and a boat crossing, and is subject to age and fitness limits that vary by operator and change; check before booking. Boat trips run close to the ice face as an alternative. November to March gives the longest daylight and most stable conditions.
Common questions
How often does the Perito Moreno Glacier rupture?
Irregularly, and not on the four-year cycle often claimed. Ruptures were recorded repeatedly through the twentieth century, then not at all between 1988 and 2004 — a sixteen-year gap. They resumed in 2004 and have recurred at intervals from under a year to a decade. The last confirmed rupture was 28 December 2019.
What causes the Perito Moreno ice dam to break?
When the glacier advances into the Magallanes Peninsula it seals the Brazo Rico arm off from the rest of Lago Argentino. That arm keeps filling with no outlet, and the water level rises. Water then works into the base of the ice and opens a subglacial channel, which widens until the remaining ice forms an arch that collapses.
How high does the water rise behind the Perito Moreno Glacier?
Historically as much as 30 metres above the level of the main lake, with 23 to 28 metres recorded in earlier events. More recent ruptures have been smaller: the March 2018 event, the largest of the twenty-first century, peaked at around 14.4 metres.
Can you walk on the Perito Moreno Glacier?
Yes, on guided excursions sold as Minitrekking or Big Ice, which include a boat crossing, fitted crampons and a licensed mountain guide. Independent glacier walking is not permitted. Visitors who prefer to stay off the ice get close views from the steel boardwalk system.
Why doesn't the Perito Moreno Glacier retreat like other glaciers?
Perito Moreno held roughly stable through the twentieth century while neighbouring glaciers in the same ice field retreated by kilometres, and the reason is not fully settled. Proposed factors include its width, bed slope, accumulation pattern and a bedrock threshold beneath the snout. Recent surveys have reported thinning, so the anomaly may be ending.
How far is Perito Moreno Glacier from El Calafate?
About 80 kilometres, roughly an hour and a half by road on Provincial Route 11. There is no scheduled public bus; visitors travel by tour bus, private transfer or rental car. The boardwalks are included in the Los Glaciares National Park entrance fee.
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