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Nachrichten, Termine, Experten
Nachrichten, Termine, Experten
SLF researcher Samuel Weber explains his new method for determining how quickly heat penetrates deep into permafrost. This will help to detect changes in mountain regions at an early stage and make it easier to assess instabilities and rockslides.
Mr Weber, you've been investigating how quickly heat spreads in permafrost. Is that important?
It certainly is. We determine how well the rock conducts heat, which is a material-specific property. If we understand how quickly temperature changes penetrate deep into permafrost, we can produce much more reliable estimates and better models of how the permafrost will develop in the face of climate change. That's important because this knowledge will ultimately also help to identify changes in high-alpine regions and possible effects on natural hazards at an early stage.
What's special about your work?
Until now, values derived from the literature and a few laboratory results were all that was available for thermal diffusivity in permafrost. There were no values from the field measured directly in the permafrost. What's special about our method is that we don't have to laboriously collect and analyse rock samples in order to determine density, heat capacity or thermal conductivity. Instead, the temperature profiles in boreholes in the permafrost over depth and time are enough. From these, we can directly work out the thermal diffusivity of the material using a physical equation, the heat conduction equation, and its solution. We determined this for all depths of the 29 boreholes in the Swiss Permafrost Monitoring Network PERMOS and, in the process, identified differences between landforms such as rock glaciers, talus slopes and rock faces.
That sounds complicated!
Think of it like a spoon in a teacup. If the spoon is made of metal, it becomes noticeably hot after a few seconds. One made of wood takes much longer, maybe several minutes. Each material absorbs and transfers the heat at different rates. A similar thing happens in rock. Granite typically conducts heat around twice as fast as slate.
What does that mean?
In granite, the heat penetrates to depth much more quickly. This process also happens in slate, but a lot more slowly. This means that there are differences in how quickly climatic changes reach deep into the substrate.
So granite rock faces are likely to collapse sooner than slate ones?
That's too simplistic a way of putting it. Heat is only one factor in these processes. However, our findings are now being incorporated into models, and based on these, more precise statements can be made – both about heat transport in the rock and about the properties of the material present.
Why is that?
In physical terms, thermal diffusivity describes the relationship between temperature change with time and with depth. We then compare the modelled temperatures based on the determined diffusivity with the measured values. In doing this, we've also detected anomalies. These are important because they indicate additional effects. This is because permafrost contains not only rock, but often also air, ice and water. From the anomalies, we can detect, for example, when water reaches deep into the permafrost, as the infiltrated water transports heat much faster.
It's also interesting to note that heat spreads more slowly in talus slopes than in rock. Talus slopes contain much more air, water and ice between the rocks. There's a clear relationship between these three components.
In what way?
The ratio between them determines the speed at which heat propagates in a mixture of these three components and rock (see diagram). Air has a high thermal diffusivity and accelerates the process, while water and ice slow it down. If thermal diffusivity changes over time, this can provide an indication of what combination of the three components is present in the cavity.
Samuel Weber
samuel.weber@slf.ch
+41 81 4170 376
https://doi.org/10.5194/tc-19-6727-2025
https://www.slf.ch/en/news/like-a-spoon-in-a-teacup/ to slf
https://www.permos.ch/ Swiss Permafrost Monitoring Network
Borehole at the foot of the Hörnligrat ridge on the Matterhorn. The graphic shows a cross section of ...
Copyright: Jeannette Nötzli/Samuel Weber/SLF
An illustration of thermal diffusivity. A cold spoon is placed in a cup of hot tea. As time passes, ...
Copyright: Samuel Weber/SLF
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Environment / ecology, Oceanology / climate
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