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Snow of Tomorrow | Permafrost in Climate Change

It's thawing: the Alps are crumbling!

by Tobias Hipp • 02/28/2022

Active rock glacier in the Hochebenkar above Obergurgl, Ötztal Alps. The rock glacier creeps downhill at an average of 2-3 meters per year, its front lies at around 2,300 m — Active rock glacier in the Hochebenkar above Obergurgl, Ötztal Alps. The rock glacier creeps downhill on average 2-3 meters per year, its front lies at around 2,300 m

Tobias Hipp

Permafrost - permanently and continuously frozen ground. Direct associations: the vast expanses of tundra in Siberia, where houses stand on "stilts" because of this, the northern Canadian wilderness or the freezing cold Arctic - all really far away. But what the Kitzsteinhorn, Zugspitze, Gemsstock or Aiguille du Midi have to do with it and why a 40° steep north-facing slope is not just about tour planning and avalanche conditions, you can find out in this issue of "Snow of Tomorrow".

Invisible climate indicator

The retreating glacier tongues are clear signs, visible to the naked eye, that the climate in the Alps is warming far too quickly - more than +2 °C since the end of the 19th century. Another significant climate indicator is (alpine) permafrost: it hides inconspicuously beneath the earth's surface in soils, debris or rock faces - but its significance and, above all, the effects when it thaws are anything but inconspicuous.

If soil or rock material remains permanently below 0 °C for at least two years in a row, it is referred to as permafrost - i.e. permanently frozen material, regardless of whether ice is present or not. The top layer of soil thaws every summer to a certain depth, the so-called thaw layer, but below this layer the soil or rock temperature never exceeds the freezing point - and this has been the case for more than 10,000 years since the end of the last ice age.

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Schematic temperature profile in permafrost. In the thawing layer, the temperature fluctuates from frozen (winter) to thawed (summer). Below this, the temperature remains permanently below zero: the permafrost body. Due to the heat from the earth's interior, the ground temperature exceeds 0° again at a certain depth.

Nötzli & Gruber, 2005: Jahrbuch des Vereins zum Schutz der Bergwelt, München

Icy patchwork

Permafrost can form in climatic regions where the average annual temperature is in the range of -6 to -8 °C or below. In the Arctic (Siberia, Canada), for example, the ground is frozen over thousands of square kilometers to depths of 900 m or more - this is known as continuous permafrost. In the Alps and all the high mountains of the world, the picture is different: the higher we go up, the closer we are to the climatic conditions of the Arctic (annual average Zugspitze, 2962 m: -4 °C) and northern slopes are significantly colder than southern slopes. This is why permafrost is found in the Alps above around 2,500 m in shady exposures and north-facing rock faces, while the lower limit of permafrost is significantly higher on the south side.

And there is another phenomenon that favors alpine permafrost: larger debris surfaces or slopes virtually trap the cold air from winter in the spaces between them and cool the ground by up to 4 °C compared to the surrounding air temperature. Permafrost can therefore persist below such debris and moraine surfaces even at much lower altitudes. The best example of this - and also the only form of permafrost that can be seen with the naked eye - are rock glaciers: a mass of blocks, debris and ice that slowly creeps downhill.

The existence of permafrost in the Alps therefore depends on significantly more factors than in the Arctic, in particular altitude, slope exposure, slope steepness and surface characteristics. The Alpine permafrost distribution is therefore more like a patchwork quilt - we speak of discontinuous or sporadic permafrost. Nevertheless, permafrost can be found on a good 5% of Switzerland's land area, for example.

It's thawing underground

The last decade was the warmest globally in the Earth's history, and the last few years have all been record years in terms of air temperature. It takes a little more time for the warm air temperatures to penetrate the ground or the rock face than with gel ice. The effect of a warm year or summer is therefore not immediate, as is the case with glacier melt, but only becomes apparent with a time lag of up to several seasons. However, the trend has now clearly arrived: never before have such high soil/rock temperatures been measured in the permafrost as last summer and the speed of the warming is alarming. At a depth of 20 meters, for example, the permafrost in Switzerland has warmed by 0.8 - 1.0 °C in the last 20 years; in lower soil layers it is significantly more. Since 1850, the lower limit of the permafrost has risen by around 150 meters. With a further warming of 1.5 °C, the permafrost boundary would rise by a further 200-750 m.

Permafrost map of Switzerland

Bundesamt für Umwelt, Schweiz (BAFU)

Glue of the Alps is becoming brittle

In the high mountains, the stability of entire mountain flanks, scree and moraine slopes and even rock faces can be directly dependent on permafrost. The colder the mixture of rock and ice, the more stable the whole thing is: cold permafrost is the glue in the Alps. And it doesn't even matter whether the permafrost actually goes beyond the 0-degree limit and disappears permanently: simply warming the material to between -2 and -4 °C is enough to make the mass soften and creep. The deeper the heat penetrates into the mountain and the thicker the thawing layer becomes, the more material can be mobilized and the higher the probability that stabilizing ice will thaw in the frozen fissures and crevices in the rock. In combination with the steepness of the Alps, the consequences are obvious: slopes can creep downhill, rockfall from rock faces increases and previously stable hut and cable car foundations collapse. Thawing permafrost can even be increasingly identified as the main culprit for triggering large rockfalls and landslides.

Mountain sports facing changing conditions

In short, the dangers in the high mountains are changing, increasing in area and presenting us mountain sports enthusiasts with new challenges. For decades, stable cold permafrost kept alpine dangers, especially rockfall and rock avalanches, halfway at bay along many classic normal routes or on north faces in the high mountains of the Alps; the risk was more calculable. Today, the windows of opportunity for safe ascents are getting shorter and shorter and some routes are even inaccessible.

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From practice 1: The small permafrost lens between Tyrol and Bavaria

You don't have to travel to the Arctic to find permafrost: in the Eastern Alps there is widespread permafrost along the main Alpine ridge, but permafrost can also occur in the lower foothills of the Alps, such as in the Karwendel or the Berchtesgaden Alps. Measurements along a tunnel within the Zugspitze have revealed a small permafrost zone between Bavaria and Tyrol. If the current warming trend in air and ground temperatures continues as it is at present, the Bavarian-Tyrolean permafrost lens will probably have disappeared by 2040.

From the field 2: A hut falls into disrepair

For more than 120 years, the DAV's Hochwildehaus at 2,883 m altitude stood stably on the edge of the Gurgler Ferner in the Ötztal Alps. For decades, small ice lenses were stored under the hut, permanently frozen in the supposedly eternal permafrost. The ice lenses have now thawed and the floor has sunk together with the hut, making it dilapidated. The mountain station of the cable car to the Gemsstock at around 3,000 m near Andermatt also has to contend with this and now has to be secured at great technical expense. These examples will not remain isolated cases: many huts, cable car foundations or mountain stations in the Alps are still standing on permafrost, but are precisely in the altitude range where the lower limit of the permafrost is currently shifting upwards and thus the greatest changes are occurring.

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Permafrost distribution on the Zugspitze: The dark purple areas indicate a high probability of permafrost. Characteristic is a high probability of permafrost in the north face and in the larger north-facing debris flows on the Zugspitze plateau — Permafrost distribution on the Zugspitze: The dark purple areas indicate a high probability of permafrost. Characteristic is a high probability of permafrost in the north face and in the larger north-facing debris flows on the Zugspitzplatt

LFU

From the field 3: constant bombardment on Mont Blanc

On average, more than 21,000 climbers per season, or 300 per day, make their way to the highest peak in the Alps, Mont Blanc, via the Refuge Tête Rousse and Refuge du Goûter. And every year, almost predictably, serious accidents occur here due to falling rocks from the Couloir du Goûter (affectionately known in English as the "Death Couloir"). The warm air temperatures of recent record summers have warmed the permafrost in the upper part of the couloir considerably and a recent study has shown an increase in rockfall incidents.

From practice 4: Major landslides on well-known mountains

It is usually difficult to identify thawing permafrost as the sole cause of major landslides, as too many other parameters contribute to such a major event, such as small, imperceptible earthquakes, heavy rain and extreme weather events, or melting glaciers at the base of the wall. In the past decade, however, the number of events has increased and the correlation between temperature rise, shift in the permafrost base line and rockfall events has become stronger. In Switzerland alone, at least 12 major rockfalls from permafrost areas have been observed, including, for example, on Piz Cengalo in Bergell (1.5 million m³ in 2013; more than 3 million m³ in 2017), on Birghorn (500,000 m³, 2011) or on Piz Kesch in Engadin (150,000 m³, winter 2014). Meanwhile, major rockfalls on the granite peaks in the Mont Blanc massif occur regularly, especially on the Aiguille du Dru.

Unstable foundations and dilapidated high-wilderness house due to thawing permafrost — Instable foundations and dilapidated high-rise building due to thawing permafrost

DAV

Global excursion: thawing permafrost as a climate time bomb

Permafrost exists on around a quarter of the land surface of the northern hemisphere. While permafrost in the Alps is relevant for the stability of our mountains, Arctic permafrost still fulfills a central function as a carbon store and is a ticking climate time bomb.

Organic material (e.g. plants) and therefore large amounts of carbon have been stored in permafrost over thousands of years and stored permanently. Specifically, this amounts to around 1,500 gigatons (1 gigaton = 1 billion tons) of carbon, about twice as much as is currently in the atmosphere. At the same time, the Arctic is warming twice as much as the global average and permafrost soils are thawing over large areas. This creates swamp-like landscapes and lakes in which the organic material is broken down and released into the atmosphere as methane. Methane is a greenhouse gas four times more potent than CO₂. Due to warming, permafrost will therefore change from a carbon sink (carbon is removed from the atmosphere and stored) to a carbon source (permafrost releases more carbon into the atmosphere than can be stored).

Is this "tipping point" (there was also an issue of Snow of Tomorrow) is reached, permafrost will accelerate global warming to a still uncertain but alarming extent and become one of the largest sources of greenhouse gases.

Further information and maps on permafrost in the Alps:

Dr. Tobias Hipp is a physical geographer and completed his doctorate in Norway at the University of Oslo on the effects of climate change on alpine permafrost in the mountains of Norway. His main job is at the German Alpine Association in the nature conservation and cartography department.

Landslide on the Grand Dru, Mont Blanc Massif — Mountainslide on the Grand Dru, Mont Blanc Massif

Ludovic Ravanel

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This article has been automatically translated by DeepL with subsequent editing. If you notice any spelling or grammatical errors or if the translation has lost its meaning, please write an e-mail to the editors.

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