Grosser Aletschgletscher is by far the longest glacier in the Alps. From head to toe it measures 22 km. The glacier descends from the summits of Jungfrau and Mönch to only 1700 m above sea level.
Grosser Aletschgletscher comprises of three different glaciers at its top. Grosser Aletschfirn is coming from the southwest, Jungfraufirn from the northwest and Ewigschneefäld from the north. They merge at Konkordiaplatz, an enormous ice field at 2700 m. There, the ice is an impressive 800 m thick, more than anywhere in the Alps.
All three glaciers scrape the valley sides. Falling rocks land on the sides of the glacier and are transported down. Where the glaciers converge, their sides become the middle part. Suddenly, the rocks on top of the glacier are no longer at the edge, but form a trail of debris at the seam. These lines of rocks are called medial moraines and run all the way to the glacier’s snout, as conveyor belts. At Grosser Aletschgletscher, the ice moves at 150 m per year.
From Konkordiaplatz downwards, the Grosser Aletschgletscher changes its direction from southeast to southwest. At its outer bend stand mountains of 3000 m high and one of them is accessible by cable car. A short hike brings you to the top of Eggishorn, from where you can see the entire Grosser Aletschgletscher.
The chain of mountains along Grosser Aletschgletscher’s outer bend is interrupted by the Märjela valley. Back in the days, when Aletschgletscher was much thicker, the ice dammed this valley. Water couldn’t escape Märjela and formed an ice-dammed lake. Ice bergs calved into it, making it a popular destination.
Grosser Aletschgletscher is shrinking since 1870. It receded by 3.5 km and its surface has lowered by hundreds of meters. Over the course of this 150 year period the melt rates have increased considerably. While the glacier used to lose 10 to 20 meters annually, it now recedes at least 50 meters every year.
Grosser Aletschgletscher in 1942 (left) and 2020. Photograph 1942: Leo Wehrli, Library ETH Zürich Dia_247-13519.
View over Konkordiaplatz from the Konkordiahütte in 2015 (left) and 2023. Source: fotowebcam.eu.
By melting so much, Grosser Aletschgletscher lost its connection with Oberalteschgletscher and Mittelaletschgletscher (upper and middle Aletschgletscher) already a long time ago. Glacial thinning also makes glacier hikes increasingly difficult, because accessing the glacier gets harder. This is best illustrated at the Konkordiahütte, a mountain hut right above Konkordiaplatz. When the hut was built, it was almost at the same level as the glacier. But nowadays, the gap in elevation is bridged by a long series of ladders. Every few years a new one has to be added, until the valley floor is reached.
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