On 19 September 2025, we made the following observations at the Unteraar Glacier:
Front of the Unteraar Glacier on 19 September 2025
The front is still approximately 30 metres high at its highest point (yellow dot). Since July 2024, the front has continued to move westwards as a result of
glacier melt. The Triftbach stream already flows approximately 20 metres east of the front into the young Aare river.
The surface of the ice was covered with a lot of sand and/or debris. The front of the Unteraar Glacier presented a sad sight again this year.
Murky meltwater flows from the Unteraar Glacier. Photo taken on 19 September 2025.
The discharge volumes were lower than on
25.7.2024.
This is due to the following reasons, among others:
- By mid-September, the snow has mostly melted after a winter with little snowfall.
- By mid-September, the days are already shorter than in July and temperatures are usually lower.
The drainage of the glacier will take place on 19 September 2025, mainly via the central glacier gate.
Glacier gates of the Unteraar Glacier on 19 September 2025.
At S1, no meltwater left the glacier.
It was not clear whether meltwater flowed from the glacier at S2. If so, then certainly not much.
At M (= middle glacier gate), approximately 100% of the meltwater left the glacier.
No water flowed from the northern glacier gate (N).
It is conceivable that, in the event of a larger meltwater runoff, water would also flow out of glacier gates S1, S2 and possibly also N.
Middle glacier snout of the Unteraar Glacier on 19 September 2025.
At M, a considerable amount of meltwater flows out of the Unteraar Glacier.
The majority of the water flows through 1.
The greater the volume of water flowing out, the more water flows through 2.
Middle glacier snout of the Unteraar Glacier on 19 September 2025.
Middle glacier snout of the Unteraar Glacier on 19 September 2025.
The meltwater flows through the ice and debris at the yellow dot into the glacier stream. At the orange dot, an ice cone covered with boulders and debris can be seen.
Front of the Unteraar Glacier on 19 September 2025.
North of the central glacier gate is the approximately 30-metre-high front.
Northern glacier snout of the Unteraar Glacier and Triftbach stream on 19 September 2025.
The northern glacier snout is located at
N.
The Triftbach (
T) already flows more than 20 metres east of the glacier portal. At
24.06.2023, the stream still flowed a short distance through the Unteraar Glacier.
Northern glacier snout of the Unteraar Glacier on 19 September 2025.
Cliffs in the southern part of the Unteraar Glacier on 19 September 2025.
The dead ice at the foot of the northern flank of the Desortstock has melted further and large cliffs have formed. The large areas exposed to warm air promote the melting of the ice.
Detail of a cliff in the southern part of the Unteraar Glacier on 19 September 2025.
The photo shows the surface of the dead ice exposed to warm air. Above it is the layer of debris, rubble and sand covering the dead ice above the cliff.
What is special is that the protective layer protrudes 1-2 metres outwards like a roof. On 19 September 2025, small pieces of this overhang repeatedly broke off and fell into the depths.
The photos below show the surface of the Unteraar Glacier near its terminus. The photos reveal the poor condition of the central section of the Unteraar Glacier in the longitudinal direction.
Birds-eye view of the front of the Unteraar Glacier on 19 September 2025.
Birds-eye view of the front of the Unteraar Glacier on 19 September 2025.
Signs of disintegration in the Unteraar Glacier on 19 September 2025.
Signs of disintegration in the Unteraar Glacier on 19 September 2025.
Signs of disintegration in the Unteraar Glacier on 19 September 2025.
Yellow dot: Within a year, the circular edge has expanded further northwards (to the right in the photograph).
Signs of disintegration in the Unteraar Glacier on 19 September 2025.
The signs of decay are not limited to the area at the end of the glacier. As far as the eye can see, signs of decay can be seen on the ice stream, which is covered with a lot of debris.
Vegetation in the forefield of the Unteraar Glacier, seen from a bird
A few years after the retreat of the glacier, pioneer plants establish themselves in the glacier forefield. The photo shows the lower part of the glacier forefield, which is still flooded once or several times a year (snow/glacier melt, heavy rain, etc.). The upper part shows the area that has been ice-free for about 7 years.
Vegetation in the forefield of the Unteraar Glacier on 19 September 2025.
In addition to pioneer plants (flowers and grasses), the first shrubs (willows and alders) were able to take root.
It is always fascinating to see the speed with which glacier forefields are colonised by flora and fauna shortly after the glaciers have receded.
People should use this strength, determination and pace as a benchmark for protecting the climate, biodiversity, soil and water.
Temperatures: 22° (25° near the ground) around 200 metres before the glacier (1940 metres above sea level) at 2 p.m.
Zero degree limit: 4500 metres above sea level (forecast by MeteoSwiss)
Over the previous seven days, the zero degree line lay between 2700 and 4500 metres above sea level, averaging 3250 metres above sea level.