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
Stood on a boardwalk built for waiting, in front of a wall of ice several storeys high, and waited, professionally. The ice announced itself before showing itself: a crack, a pause, applause of water, a sound rather than a sight. The glacier looked as though it had its eye on the far shore, and the lake as though it knew. I did not take sides. I brought a sandwich.
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 ice front 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. Accounts of the most recent rupture differ: some record one on 28 December 2019, while reporting from 2025 names March 2018 as the last full ice-dam collapse. No rupture has been documented since. And the glacier long famous for holding its ground is now losing it: a study published in August 2025 reported that its front, almost unchanged between 2000 and 2019, has since thinned sharply and begun to retreat.
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 ice flows forward 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 by some accounts 28 December 2019 — though 2025 reporting treats March 2018 as the last full collapse.
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 its 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 has ended. A study published on 7 August 2025 in Communications Earth & Environment, drawing on helicopter-borne radar, surveys of the lake bed and time series of the ice surface, reported that the rate at which the glacier’s front was lowering rose from about 0.34 metres a year (2000–2019) to 5.5 metres a year (2019–2024), and that the ice was flowing faster and retreating. The authors identified a ridge in the bed beneath the snout that probably held the glacier in place, and warned that once the front thins back beyond it, the glacier could retreat quickly into deeper water. Whether the damming cycle will happen again is an open question.
The glacier from the International Space Station, February 2012: its front ends in Lago Argentino, where the ice dam forms.
Satellite image: NASA (ISS030-E-091253) · Public domain
A slab of ice falls from the front, December 2015.
Photograph: Murray Foubister · A quick visit to Perito Moreno Glacier - of course everyone is hoping to get some spectacular calving shots - (25160864746) · CC BY-SA 2.0
February 2013: the gap where the ice bridge broke, between the glacier and the shore.
Photograph: Gustavo Muñoz Clos · Aquí rompió el puente del Perito Moreno, hay que esperar que avance y vuelva a apoyarse - panoramio · CC BY-SA 3.0 · cropped
The boardwalks facing the ice front, May 2014.
Photograph: LuigiStudio · CC BY-SA 4.0
Seracs of blue ice in the front wall under a heavy sky, February 2014.
Photograph: Shamil Valeev · Blue Ice — Glaciar Perito Moreno - panoramio · CC BY-SA 3.0
- Walk every tier of the boardwalk before choosing a favourite.
- Wait for a calving without once checking the clock. (Checked the list instead, a great many times. It had nothing new to say either.)
- Applaud inwardly. (Outwardly acceptable here, I am told.)
- Take the boat for the low angle and feel correctly small.
- Ask a ranger how things stand between the ice and the lake, and take the long answer.
The steel boardwalks. Some seven kilometres of walkway run along the Magallanes Peninsula opposite the ice face, built in tiers so that visitors can stand a few hundred metres from a five-kilometre wall of glacier on dry land. Reporting from the site describes a deep cracking sound preceding each calving; the walkways exist because enough of it happens, often enough, that people come to wait for it.
Tally, in the marginTiers of steel walkway, every face on them turned the same way. When the crack came we all flinched together, like one very long audience, and then pretended we had not.
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.
Mark this place
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. Sources differ on the most recent event: some record a rupture on 28 December 2019, while 2025 reporting names March 2018 as the last full collapse.
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.
Is the Perito Moreno Glacier retreating?
Yes, according to a study published in August 2025 in Communications Earth & Environment. Perito Moreno held roughly stable for decades while neighbouring glaciers in the same ice field retreated by kilometres, and it barely retreated between 2000 and 2019. Since 2019 its front has been thinning much faster, from about 0.34 to 5.5 metres a year, and the ice has sped up and pulled back. The authors link its earlier stability to a ridge in the bed beneath the snout, and warn that retreat could become rapid once the front thins back beyond it.
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.
Know somewhere that belongs here?
The Field Guide grows by recommendation. If there is a place you love — somewhere strange, overlooked, or simply worth the trip — tell us about it and why it matters. Good suggestions get researched, written up, and credited to the person who sent them in.
Suggest a place →