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PowderPeople | Dr. Benjamin Walter

In conversation with Christiane Eggert from 26th January 2024

by Christiane Eggert • 02/03/2024

Measurements on the snow profile with the SnowImager.

Bruno Augsburger / SLF

Measurements on the snow profile with the SnowImager.

Bruno Augsburger / SLF
Dr. Benjamin Walter is a physicist by profession. He works at the SLF (Institute for Snow and Avalanche Research) in Davos and is primarily concerned with snow physics, specifically the changes to snow crystals caused by wind transport and the resulting risks to the snowpack structure. Christiane Eggert interviewed him for us.

We start with a short introduction. Please complete the following sentences:

...I had my first contact with snow: I grew up on a farm in the Black Forest, where there was often snow in winter. My favourite childhood memory in the snow is tobogganing down the slopes with inflated lorry inner tubes.

...my favourite thing to do after work: (laughs) what was after work with two small children again? Joking aside: if time allows, I like to be outside after a day at the office and get some exercise, for example on a night ski tour or playing ice hockey with friends.

...Ski or snowboard: It depends on the conditions. In spring and hard conditions, I tend to use skis, but on powder days I prefer the snowboard.

..Skiing/snowboarding for me means:  Fun with family and friends. Freeing my mind from everyday life.

...this should not be missing on a tour with the snowboard:  skins! Seriously: it happens more often than you think.

..after a day in the snow, there's nothing better than: a sauna and a Hefeweizen.

..I can do without that: Capitalism and raspberry seeds in the gap between my teeth.

...I secretly dream of:  living off-the-grid in a little cabin in the Yukon.  

...I prefer to spend my holidays in:Italy or Scandinavia. I tend to seek the peace and quiet on holiday and enjoy spending time with family and friends.

...this meal makes me weak in the knees: Kaspressknödel from Knödel- Walter.

...this is my favourite music to listen to:  I'm part of a surf rock band and I also enjoy listening to this music in my private life. My current favourite album is the new album by "The Hives", a really good rock'n'roll album.

...I am afraid of global warming and the resulting consequences. I hope that our children will still be able to spend their lives on an earth worth living on. My work in the field of environmental science gives me a good insight into climate change and its consequences. I now fear that the climate is changing even faster than previously assumed.

..in 10 years I'll be: hopefully healthy and skiing!

Dr. Benjamin Walter in an interview:

Name: Benjamin Walter

Age: 41

Born and raised: In a small town in the Black Forest Wolfach/ Welschensteinach (DE)

Profession: Physicist

Dr. Benjamin Walter in an interview:

Name: Benjamin Walter

Age: 41

Born and raised: In a small town in the Black Forest Wolfach/ Welschensteinach (DE)

Profession: Physicist

PG: Thank you for the introduction. Let's start with the question. You are a snow physicist. Why don't you tell us how that came about? What was your professional career like?

As a "farm kid", I grew up surrounded by nature. I was always fascinated by forests and snow. I had a good physics teacher at school and he managed to get me interested in physics and maths. I actually always wanted to become a forester or forestry worker, but when a forestry worker advised me against it because my back was "broken" at the age of 40, I decided to study physics in Karlsruhe. During my studies, I specialised mainly in the field of renewable energies, photovoltaics and wind power. I came to the SLF (WSL Institute for Snow and Avalanche Research) through my doctoral thesis in the wind tunnel on the topic of snow transport by wind, where I also worked on the topic of "water flow through snow".

I then worked for 5 years at the Physikalisch Metrologisches Observatorium Davos (PMOD) as a research assistant in the field of solar radiation measurement. There I was involved in two major projects: the development of a cryogenic radiometer, which serves as a worldwide reference for solar radiation measurements on Earth, and a space radiometer, which measures solar radiation in space on a Norwegian satellite.  

I've been back at the SLF since 2019 and initially worked in the Snow Processes group for a year, where I used a RADAR device to measure snow plumes on a mountain ridge, before moving to the Snow Physics group in 2020. In the snow physics group, I have so far been researching the formation of cornices, how wind changes the snow microstructure, and helped develop an optical measuring device that can be used to measure the grain size and density in a snow profile.

 

PG: Have you always been interested in snow? What fascinates you about the subject?

Yes, even as a small child I used to press my nose against the window when it snowed outside. Snow can completely change the landscape within hours. I like the fact that snow makes everything quieter and calmer. Snow is such a diverse and complex material, and its properties never cease to fascinate me.

 

PG: You played a key role in the development of the ring wind tunnel. A brief summary for our readers: What exactly is a wind tunnel?

A wind tunnel is best known from the automotive industry for measuring the air resistance of vehicles. In our case, we use the wind tunnel to investigate the transport of snow by wind. The idea of a ring wind tunnel was born back in 2012, but until 2017 there were only linear wind tunnels in the world that were used to analyse snow. The problem with a linear wind tunnel is that only very short distances and moments of snow transport can be investigated, as the snow is blown out of the tunnel again after a few metres. In a ring wind tunnel, we can theoretically simulate "infinitely" long snow transport. About three years ago, we then brought the ring wind tunnel into the cold laboratory, which enables us, for example, to investigate the fragmentation of snow crystals during transport or the formation of cornices under laboratory conditions.

PG: For the laymen among us: What do you mean by fragmentation?

How the snow cover thickens through the fragmentation of snow crystals. New snow crystals usually have a hexagonal structure with fine, fragile knots. When transported by the wind, these structures can break when the crystals hit the ground. The resulting smaller crystal pieces can thus arrange themselves more densely when they are deposited. This means less pore space and a higher snow density of wind-transported snow. There are also more contact points between the individual crystals, which makes the snow layer harder. Fragmentation is just one of the many processes that take place during wind drifting, which we investigate in the ring wind tunnel.

PG: Thanks to your work, the dynamics of the snow cover can be researched very precisely and simulated in the wind tunnel. What does your work mean for the research/(snow) world?

The results on fragmentation from the wind tunnel help to simulate the snow cover structure more precisely using computer models. In our specific case: how the snow density and grain size change depending on wind speed and temperature. In our group, however, we generally deal with snow as a material and its physical (mechanical and optical) properties. We use a wide variety of measurement techniques for our research. For example, as in the hospital, we use computer tomography to measure the snow microstructure in 3D and investigate changes in the structure due to temperature or pressure loads. A particular focus here is on the formation of weak layers such as deep or surface rime, which can lead to critical avalanche situations in a snowpack. We are also developing new measurement techniques and methods to analyse the snow microstructure and its physical properties in the field or laboratory.

Digging a snow profile on Pischa to test the new SnowImager measuring device

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Bruno Augsburger / SLF

Digging a snow profile on Pischa to test the new SnowImager measuring device

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Bruno Augsburger / SLF

PG: What conclusions from your research are incorporated into risk prediction?

Our findings on weak layers, wind transport and cornice formation will be increasingly incorporated into risk prediction in the future by means of computer modelling. Wind, for example, is generally recognised as the master builder of avalanches, as it causes snow to be deposited on mountain sides, gullies or hollows facing away from the wind. Where these deposits take place and what density the snow will have influences the risk of slab avalanches and is therefore an important component for avalanche warnings.

 

 

PG: Your research and findings are used in practice. What are your next goals or what are you currently working on?

We are currently working on a new optical measuring device called "SnowImager", which we are developing together with a local company. The SnowImager is a black box that can be used to illuminate a snow profile with near-infrared light and photograph the reflected light with a special camera. With this instrument it is possible to determine the density and grain size of the different layers in a snow profile. We are also in the process of publishing a research paper in which we were able to proof, for the first time, that snow crystals not only fragment when transported by the wind, but that they can even grow and take on more rounded shapes due to the evaporation and re-evaporation of water molecules on the surface of the snow crystals.

PG: Is climate change also an issue in your research group?

Definitely. We have more and more projects in the polar regions. Unfortunately, climate change is most evident there. I was once on an expedition to Greenland and was able to see the drastic decline in the ice for myself. We want to better understand how the snow cover is changing in these regions. If, for example, there are larger snow grains or more fine dust on the snow surface in the future, this will reduce the reflection of solar radiation. This, together with a generally strong decrease in snow cover in the polar regions, is a major issue. In a nutshell: Fewer snow surfaces on Earth means more solar radiation is absorbed, which therefore drives global warming even more. This is called a positive climate effect, even if it is not "positive = good" for the Earth's climate.

 

PG: With powderguide.com, we are a site for winter sports. Let's talk a bit more about you personally. You don't exactly look like a nerd. Do you spend a lot of time travelling in the mountains yourself?

But I can be quite nerdy sometimes, just ask my colleagues (laughs). I don't think being a nerd is generally negative, for me it also means putting your heart and soul into your work or being very interested in something. Of course, I also enjoy travelling in the mountains, but with two small children I simply have less time for it. Fortunately, I live in Davos and have the mountains on my doorstep, so sometimes it's just a two-hour trip.

 

PG: Where can you be found? On or off piste?

Both. But now I'm not so keen on big crowds anymore, so I prefer off-piste, preferably deep and untracked (laughs).

 

PG: What are your "tools" for the snow? What equipment do you always take with you?

Over the years, you develop a few "quirks". For example, I am an absolute advocate of soft boots with normal laces. I also always have gaffa tape, cable ties and a Buff scarf with me.

 

PG: Do your profession and knowledge of snow make you more of a defensive traveller?

I would say yes. I always see the snowpack structure with "professional" eyes. You can no longer separate the two.

 

PG: How do you behave in a group when touring? Are you expected to judge the conditions?

Since I no longer spend as much time on the mountain as I used to, I now classify myself as a moderately experienced ski tourer. Over the last few years, I've simply not developed a feel for the conditions. That's why I tend to hold back in the group when it comes to recommendations if there are more experienced colleagues in the group.

 

PG: Have you ever experienced avalanches yourself?

Yes, I've already encountered smaller snow slabs, but I've never been buried. Unfortunately, I once had to dig out a colleague who was swept along with some sluff in a narrow gully when he fell awkwardly over a rock. Fortunately, his skis were still sticking out. But it took 10 long minutes to get to him and dig him out. Everything went well, but it was a tough and instructive experience.

 

PG: Benni, thank you very much for talking to us.

Sawing a smooth surface of the snow profile to be able to examine the different layers of snow

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Bruno Augsburger / SLF

Sawing a smooth surface of the snow profile to be able to examine the different layers of snow

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Bruno Augsburger / SLF

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