Aletsch Glacier: The River of Ice Switzerland Once Prayed to Stop

In 1678, the people of Fiesch, a village at the foot of the Aletsch Glacier, made a promise to God. The ice above them was growing. A lake trapped by the glacier kept bursting and flooding their valley. So they vowed to live virtuously and to pray, year after year, that the glacier would stop advancing.

More than three centuries later, their descendants went to Rome with the opposite request. They wanted to pray that the glacier would stop melting.

That reversal tells you almost everything about the Aletsch Glacier. It’s the largest glacier in the Alps, a river of ice about 20 kilometres long that flows from the snowfields of the Jungfrau down towards the Rhône valley. It’s also one of the best-measured glaciers on earth, and its records read like a diary of a changing climate. This guide covers both sides: the beauty you can see from the viewpoints, and the stories and data hidden in the ice.

The Aletsch Glacier at a glance

The Great Aletsch Glacier, Grosser Aletschgletscher in German, lies in the canton of Valais, on the southern side of the Bernese Alps. It begins high in the Jungfrau region, close to Jungfraujoch, and ends above the Massa gorge near Riederalp and Belalp. Along the way, it passes some of the most dramatic scenery in Switzerland.

In 2001, the glacier and its surroundings became the heart of the Swiss Alps Jungfrau-Aletsch World Heritage Site, the first natural World Heritage Site in the Alps. UNESCO extended it in 2007, and it now covers about 824 square kilometres of peaks, ice and valleys. For the country’s cultural World Heritage Sites, from Bern’s Old Town to the castles of Bellinzona, see our guide to the cultural treasures of Switzerland.

How the Aletsch Glacier works

A glacier looks frozen in place, but it never stops moving. Think of the Aletsch Glacier as a slow conveyor belt. Snow falls high up in the mountains, gets buried and squeezed into ice, then creeps downhill under its own weight. At the bottom, it melts away.

Konkordiaplatz: where four rivers of ice meet

The engine room is Konkordiaplatz, a vast plain of ice below the Jungfrau. Here, four large ice streams flow together and form the main glacier. The ice at Konkordiaplatz is about 800 metres thick. That's roughly the height of the world's tallest skyscraper, buried under a frozen surface.

The dark stripes

From any viewpoint, you'll notice long dark stripes running down the middle of the glacier. These are medial moraines: rock debris carried along where two ice streams merge. They make the Aletsch Glacier look like a motorway with lanes, and they show you exactly where each stream came from.

A very slow journey

How slow is the conveyor belt? Researchers once calculated that ice near the upper glacier travelled about 10.5 kilometres in 86 years, at an average of around 122 metres a year. We know this because of a sad story you'll read below.

A glacier that came and went

It's tempting to think the Aletsch Glacier was always huge until recent warming. The real history is more interesting. Research summarised by the World Heritage organisation shows that in the Late Bronze Age, about 3,300 years ago, the glacier was several hundred metres shorter than today. Around 800 to 950 AD, it was roughly the size it is now.

Then the climate cooled. During the Little Ice Age, the Aletsch Glacier advanced several times: shortly after 1369, around 1678 and around 1860. Notice that middle date. The year of the Fiesch vow was a year when the ice was pushing forward.

So glaciers have always grown and shrunk. What makes today different is the speed. The Aletsch Glacier is now losing ice far faster than at any time in its long recorded history, and the cause is human-made warming.

The prayer that worked too well

Back to Fiesch. In the 17th century, life below the Aletsch Glacier was frightening. Avalanches were common, and the Märjelensee, a lake dammed by the glacier's edge, often broke through its wall of ice. Swissinfo reports that nearby glacial lakes overflowed 35 times in a hundred years, sending floods down the valley.

The vow

In 1678, the villagers of Fiesch and Fieschertal turned to faith. They promised to live virtuously and to pray against the growth of the glacier and the flooding of the lake. According to Swissinfo, an annual procession has taken place since 1862, on 31 July, the feast of Saint Ignatius. It leads to the Ernerwald chapel and lasts about five hours.

The engineers' answer

Prayer wasn't the only answer. Between 1889 and 1894, engineers drilled a drainage tunnel to stop the Märjelensee from rising too high. It worked. The tunnel carried water only once, in 1896, and the lake never rose that high again.

Reversing the vow

Then the climate turned. By the 21st century, the danger was no longer too much ice, but too little. In September 2009, Herbert Volken, a mountain guide and a descendant of the priest behind the original vow, handed Pope Benedict XVI the parish's request to change it. In 2010, the Holy See gave its approval. Today, the procession prays for the preservation of the glacier. As Volken put it: "Ice is water and water is life."

The Märjelensee itself tells the same story. Compare the two pictures below.

Then and now: the Märjelensee

The same ice-dammed lake beside the glacier, more than a century apart.

1890s2009

1890s: Photoglob Zürich, Photochrom Print Collection, Library of Congress (public domain). 2009: Addvisor, Wikimedia Commons (CC BY-SA 4.0). The two photos were taken from different viewpoints.

What the ice gives back

On 4 March 1926, four young men, three of them brothers, set out across the Aletsch Glacier. They were most likely caught by a storm, and they never came home. For decades, the glacier kept their story to itself.

Then, in summer 2012, mountaineers came across human bones, clothing and old equipment on the glacier. Among them were wooden ski poles, an old pair of binoculars and coins from the 1920s. They were the remains of the three brothers. The fourth man has never been found.

Scientists later used a computer model of the ice flow to reconstruct their journey. The bodies had travelled about 10.5 kilometres inside the glacier. In 1980, they were probably buried about 250 metres below the surface, under enormous pressure. Only as the ice thinned did the glacier finally give them back.

It's a haunting reminder that a glacier is also an archive. As the Aletsch Glacier melts, it returns what it has kept for decades, and sometimes for centuries.

The Aletsch Glacier in numbers: a 150-year record

Few glaciers anywhere are measured as carefully as this one. Swiss glaciologists, today organised in the GLAMOS network, have tracked the position of its tongue since 1870 and calculated its annual ice balance back to 1915. The charts below use their official data. Switch between the two records and drag the slider.

What the data shows

Three things stand out. First, the Aletsch Glacier has lost about 3.4 kilometres of length since 1870. Second, the losses have sped up. In the 2023–24 season alone, the tongue retreated by 64 metres.

Third, look at the year 1984. It was the last clear gain. Since the mid-1980s, the glacier has lost ice almost every year, and the worst years have come very recently. In 2022, after a dry winter and a hot summer, only about 11% of the glacier's area kept its winter snow, and the glacier lost the equivalent of about three metres of water across its entire surface.

Then came 2026. In September, GLAMOS reported that the 2025/26 season had been even worse for the Great Aletsch: a new record loss of more than three metres of water equivalent. The tongue was already free of snow in mid-April, and at the lowest measuring point, about 13 metres of ice melted in a single year. That figure is too new to appear in the chart above, which runs to 2025.

When the mountains start to move

A shrinking glacier doesn't just change the view. It changes the mountains around it.

The Moosfluh landslide

For thousands of years, the Aletsch Glacier pressed against the valley walls like a buttress. As the ice thinned, that support disappeared. Above the glacier, near Riederalp, a whole mountainside at the Moosfluh began to creep downhill. In autumn 2016, parts of it moved up to 80 centimetres a day. According to the monitoring firm Geopraevent, the unstable area covers about one square kilometre and at least 150 million cubic metres of rock. Several hiking trails were closed for good.

The stairs that keep growing

Further up, the Konkordia Hut tells the same story in a more personal way. When the first hut was built in 1877, it stood about 50 metres above the ice. Today, guests have to climb more than 450 steps of metal stairs from the glacier to the hut, and the staircase has to be extended every few years.

What happens next?

In 2019, the glaciologists Guillaume Jouvet and Matthias Huss at ETH Zurich modelled the future of the Aletsch Glacier. The results are sobering. Even if the world kept warming below 2 °C, as the Paris Agreement aims, the glacier would still lose more than half its volume and length by 2100. With high emissions, only small patches of ice would remain, and Konkordiaplatz, today buried under 800 metres of ice, would be completely ice-free. The record losses of 2022 and 2026 suggest the glacier is already following the darker path.

The Swiss have started to respond in their own way. In June 2023, 59% of voters approved a new climate law. Parliament had drawn it up as a counter-proposal to a popular initiative known as the Glacier Initiative, whose backers agreed to withdraw it if the law passed. It's a typical example of Swiss direct democracy, in which citizens push an issue onto the national agenda.

The Aletsch forest: an ancient forest on young ground

Right beside the glacier, above Riederalp, grows one of the most remarkable forests in the Alps. The Aletsch forest covers about 400 hectares of larches and Swiss stone pines. Some of the stone pines are around 1,000 years old. They have watched the glacier grow and shrink for a millennium.

In 1933, the forest became a nature reserve, under the protection of the conservation group now known as Pro Natura. Its centre sits in Villa Cassel on the Riederfurka, a grand summer house built in the early 1900s for the British banker Sir Ernest Cassel. Today, it runs exhibitions and guided walks about the glacier and the forest.

Walk through the forest in autumn, when the larches turn gold, and you'll understand why so many people fall in love with the Aletsch Glacier. You'll also see something rare: young trees and plants moving onto ground the ice left only a few decades ago.

Where to see the Aletsch Glacier

The good news is that you don't need to be a mountaineer to see the Aletsch Glacier. The easiest viewpoints are just a cable car ride away. Tap through the options below.

Tips for your visit

• Base yourself in the Aletsch Arena. The car-free villages of Riederalp and Bettmeralp, reached by cable car from Mörel and Betten, sit right on the glacier's doorstep. Fiesch is the gateway to the Eggishorn.
• Go between June and October. Most hiking trails are open then. In winter, the viewpoints are still reachable, but many paths are not.
• Never step onto the ice alone. Hidden crevasses are deadly. Join a guided glacier hike if you want to walk on the Aletsch Glacier itself.
• Check the weather. Clouds can hide the glacier completely, so keep a flexible day in your plan.
• Combine it with Jungfraujoch. From the Bernese Oberland, the Jungfrau Railway shows you the glacier's source. It opened in 1912, a feat of Alpine engineering in the same spirit as the tunnels in our story about the Gotthard Base Tunnel.

For more ideas, see our list of the best places to visit in Switzerland. If you're driving, our guide to scenic drives in Switzerland covers the mountain passes nearby. And while you're in the Valais, try a raclette or a slice of cholera pie from our guide to traditional Swiss food.

The Aletsch Glacier through history

From the Bronze Age to the record melt of 2026, tap through the key moments in the life of the Aletsch Glacier.

Quiz: true or false?

How well do you know the Aletsch Glacier now? Six quick questions will tell.

Why the Aletsch Glacier matters

It's easy to see the Aletsch Glacier as a postcard: white ice, blue sky, a famous peak in the distance. But it's much more than that. It's a water tower that feeds rivers and hydropower plants, a source of electricity in a country that, as our story of why Switzerland is so rich shows, built its prosperity partly on water. It's an archive that keeps lost lives and old climates. And it's a measuring stick for the warming of the planet.

Above all, it's a place that changes how you feel about time. Stand on the Eggishorn and look down at the ice. The snow that fell on the Jungfrau when your grandparents were young may be melting below you right now.

The people of Fiesch understood the glacier's power in 1678, when they prayed for it to shrink. Their descendants understand it today, when they pray for it to stay. Go and see it while it still fills the valley.

FAQ: the Aletsch Glacier