Grosser Aletschgletscher
Great Aletsch Glacier
Past extents come from the Swiss Glacier Inventories of 1850, 1931, 1973 and 2016. Future extents are illustrative: each glacier’s projected area (OGGM, median of CMIP6 climate models) is removed from its lowest ice upward. About the scenarios.
The largest glacier in the Alps and the centre of a UNESCO World Heritage site. At Concordiaplatz, where three ice streams meet, the ice is almost 800 m thick. In 2022 six metres of ice melted there in a single summer. Without climate protection it could disappear completely within 75 years; with strong protection, parts of its three ice streams would survive. In 2026 it recorded its most negative year ever measured, worse even than 2022.
Grosser Aletschgletscher is the 1st-largest glacier in Switzerland, covering 78.49 km² in the canton of Valais. Its ice spans 1,605 to 4,120 m and faces south-east. Its meltwater drains to the Rhône and on to the Mediterranean. In 1850 it was part of a larger ice body of 105.6 km², which has since split into 6 glaciers covering 85.9 km² in 2016 (−19%). Its tongue has been measured 133 times since 1870. In total it has retreated 3,387 m, about 22.0 m a year. Its mass balance has been measured since 1915: on average −0.60 m of water equivalent per year, with the most negative year in 2022 (−2.87 m). Between 1927 and 2023 its surface dropped by 66 m on average. With strong climate protection (SSP1-2.6), about 30% of its 2020 ice would remain in 2100. With very high emissions (SSP5-8.5) it would be gone around 2085. Its meltwater is projected to peak around 2037.
Then and now
What remains in 2100
Meltwater
Million m³ of water per year, 11-year mean
The record
Length change since 1870
Position of the glacier tongue, measured in the field almost every year. Hover for each measurement.
Mass balance 1915–2025
Ice gained (blue) or lost (red) over the whole glacier each year, in metres of water equivalent. Measured with stakes drilled into the ice.
Thinning since 1927
Average change in surface height, from comparing elevation models made from maps, aerial images and laser scans.
Facts
Area over time
Past areas are the ice body this glacier belonged to at the time. Projections: OGGM median, SSP2-4.5.
- SGI id
- B36-26
- Canton
- Valais
- River
- Rhône → Mediterranean
- Basin
- Lötschental–Aletsch
- Location
- 46.5040° N, 8.0320° E · swisstopo map
- Elevation
- 1,605–4,120 m, median 3,148 m
- Slope, aspect
- 16°, south-east
- Debris cover
- 4.71 km² (6% of the area)
- Inventory image
- 2017
- Ice volume (model)
- ≈ 9.62 km³ in 2020 (OGGM)
- RGI ids
- RGI60-11.01450, RGI60-11.01451, RGI60-11.01458, RGI60-11.01467, RGI60-11.01484, RGI60-11.01551 …
- In 1850 joined with
- Mittelaletschgletscher, Kleines Dreieckhorn E, Kleines Dreieckhorn NE, Grünhörnli, Unnamed glacier B36-58
Events here
Moosfluh starts to slide
When the Aletsch Glacier thinned below a critical level, the valley flank it had been holding up accelerated to 80 cm a day.
The second-worst year
The hottest summer on record: Swiss glaciers lost 5.5% of their ice in one year, second only to 2022.
More in the Lötschental–Aletsch basin
- Oberaletschgletscher17.05 km²
- Langgletscher8.01 km²
- Mittelaletschgletscher6.61 km²
- Tellingletscher5.13 km²
- Üssre Baltschiedergletscher3.56 km²
- Driestgletscher1.80 km²
- Innre Baltschiedergletscher1.68 km²
- Jegigletscher NE1.33 km²
- Joligletscher0.86 km²
- Zenbächengletscher0.82 km²
- Dischliggletscher0.64 km²
- Unnamed glacier B36-590.64 km²
Sources
- Linsbauer et al. (2021). The new Swiss Glacier Inventory SGI2016. Frontiers in Earth Science 9. doi.org/10.3389/feart.2021.704189
- Mannerfelt et al. (2022). Halving of Swiss glacier volume since 1931 observed from terrestrial image photogrammetry. The Cryosphere 16. doi.org/10.5194/tc-16-3249-2022
- GLAMOS – Glacier Monitoring Switzerland. www.glamos.ch
- Zekollari et al. (2024). Twenty-first century global glacier evolution under CMIP6 scenarios and the role of glacier-specific observations. The Cryosphere 18 (OGGM v1.6 projections). tc.copernicus.org/articles/18/5045/2024/
- Huss, Linsbauer & Naegeli (2025). Swiss Glaciers. State, projections and significance. Swiss Academies Factsheets 20(2). doi.org/10.5281/zenodo.14866776
- GLAMOS (2026). Annual mass balance of Swiss glaciers in 2025/2026. doi.glamos.ch/pubs/annualrep/annualrep_2026.pdf
- Kos et al. (2016). Contemporary glacier retreat triggers a rapid landslide response, Great Aletsch Glacier. Geophysical Research Letters. agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016GL071708
Relief: swisstopo swissALTIRegio. 1850 and 1973 outlines: Maisch et al. (2000), Müller et al. (1976), Paul (2004). Length, mass balance and volume change: GLAMOS releases 2025. All sources and methods.