Snow avalanches in Longyearbyen

Snow avalanches in Longyearbyen

Avalanche season is getting closer. What dangers and what factors do you need to take into consideration when you travel by snowmobiles or by ski around Longyearbyen? New UNIS research can now give you some answers.

Text: UNIS PhD student Markus Eckerstorfer and UNIS Professor Hanne H. Christiansen
6 December 2011

For the first time, snow avalanches have been closely observed for more than three years in the Longyearbyen area. These new observations are timely and crucial to advance our understanding of how snow affects the high Arctic landscape here in Svalbard. In the last ten years alone, snow avalanches have caused five fatalities.

The majority of the results of the Norklima CRYOSLOPE Svalbard research project (2006–2009) are now published in 4 scientific journal papers. The project was initiated with the aim to observe cold mountain slope processes in the Longyearbyen area and their effects on traffic and infrastructure, to use this knowledge to assess their response to future climate change predictions.

Snow avalanche observations were carried out in the about 17 km2 large area around Longyearbyen, around the most used snowmobile route “Little round” here in central Svalbard (Fig. 1).

Map showing avalanches around Longyearbyen.

Fig. 1: The furthest runout location of all 423 avalanches indicated by the points along “The Little Round” snowmobile track. The colors of the points distinguish avalanche types.

Besides an advance in snow avalanche science and particularly for the high Arctic, our findings have also practical implications for Longyearbyen’s inhabitants and students’ visiting UNIS:

Which types of snow avalanches do we have to watch out for?
A unique feature of the snow avalanche regime in the Longyearbyen area is that almost half of all snow avalanches are cornice fall avalanches (Fig. 2).

Due to the large plateau mountains, huge snowdrifts, so-called cornices, build up along the top of the plateau lee sides. These cornices can break down and their impact on the slope beneath triggers an avalanche. We therefore recommend staying away from slopes that have cornices situated on the top, such as the Gruvefjellet slope above Nybyen (Fig. 2).

When is the most dangerous time of the winter?
The timing of snow avalanche activity differs in Svalbard also from other places at more southern latitudes. The snow cover builds only up very slowly, due the small amount of precipitation that Svalbard generally receives. It thus takes sometime into the winter, before a homogenous snowpack is established at the slopes, enabling a snow avalanche to be released. We therefore observed most avalanche activity from March until June.

This is also due to the extreme differences in light conditions. Once the sun returns with 24 hours daylight after the polar night, snow avalanche activity starts. During those very cold and stable high-pressure periods in spring, snow avalanche activity is again at a minimum. Under cold conditions, snow does not deform as rapidly as during warmer conditions. Thus direct insolation is increasing snow avalanche release.

Cornice falls, Gruvefjellet, Longyearbyen.

Fig. 2: Natural cornice fall avalanche (right one) from Gruvefjellet, released 1 April 2009. It ran across the road to Nybyen and destroyed the coal transport system, which had been preserved as cultural heritage on the slope. The left cornice fall avalanche was artificially released when deploying explosives to detach the cornice. Photo: Markus Eckerstorfer/UNIS

Are we safe driving snowmobiles around in the landscape during excursions?
For most of the time yes, unless your excursion group stops for a prolonged period in a narrow valley or gully, as this would be typical snow avalanche terrain. So stick to higher located ground, where you have overview of the surroundings. The view is traditionally also much better from such locations.

Most snowmobile routes follow flat terrain in the valley bottoms, and we observed the majority of snow avalanches to stop at a slope angle of 25 °. Still, during two extreme slush avalanche events in January 2010 and March 2011, we recorded these wet snow avalanches to run down to the valley bottoms at several places. The snowmobile track through Todalen was buried at three locations (Fig. 3), in one site with up to 12 m of hard packed avalanche snow. Both extreme events happened because of very slow passing low-pressure systems, resulting in positive air temperatures for some days, and a 100-year record of rain. Good that on such days, UNIS does not carry out snowmobile excursions.

Slush avalanches in Todalen, Svalbard.

Fig. 3: Slush avalanches that were released on 18 March 2011 in Todalen. Three avalanches crossed the snowmobile track, the furthest one buried the snow mobile track with about 12 m of compact avalanche snow. Photo: Markus Eckerstorfer/UNIS

How does the weather effect snow avalanche activity in Svalbard?
Again it is the low-pressure systems that bring life to our winter landscape here. Low pressures induce snowstorms, which resulted in 19 major snow avalanche periods between 2006–2009, in which 80% of all observed snow avalanches were released. Those periods had a minimum of five releases and lasted between one and 12 days. So especially after these snowstorms, the skiing conditions might be good, but the snow avalanche conditions are rather hazardous.

During or right after such snowstorms, you might also see a number of natural slab avalanches. Slab avalanches get released due to the increase in snow loading on a weak snow layer, which consequently fractures. So it is an especially interesting type of snow avalanche, as it tells us about weaknesses in the snowpack and the meteorological cause that increases the load, or the weight. If one would aim to forecast these natural slab avalanches, we now know from statistics that it would definitely be necessary to study the amounts of snowdrift and precipitation 24, 48 and 72 hours prior to a release.

What do we have to look out for on ski trips?
The landscape around Longyearbyen is generally very dry with not much more than 200 mm of precipitation every year. But still, when maximum snow depths are reached in April, in some parts of the landscape there are several meters of snow. This is due to the wind redistribution of snow, which plays quite an important role in the spatial variability of snow depth, but also snow stability. Again weak layers account for unstable conditions that favour snow avalanche release. The further down such a weak snow layer is buried in the snow, or in other words covered by wind accumulated snow, the harder it is to trigger a fracture in it when skiing.

It needs to be pointed out though that snowmobiles, due to their weight, are able to affect deeper parts of the snowpack, and thus can more easily release a snow avalanche on a deeply buried week layer. On a snowmobile, one travels also through much more terrain in a shorter time, which makes it more likely to hit a weak spot in the snowpack.

With a changing climate, are there going be more or less snow avalanches?
We have examined the almost 100 year long meteorological record for Longyearbyen for similar meteorological conditions as occurred during both extreme events in January 2010 and March 2011. We found four periods with similar conditions, all clustering in the early 1990s. These events are clearly determined by extreme meteorological conditions, and not by rising mean annual air temperatures. The frequency and duration of low-pressure system passages of Svalbard are therefore of more interest.

Surprisingly, Zahn and von Storch (2010) modeled a decrease of North Atlantic polar lows, associated with future climate warming. So we can expect less low-pressure systems arriving in Svalbard, and therefore fewer snowstorms, and consequently less snow avalanche cycles.

Still, we do not know how strong these fewer low-pressures will be in magnitude. What we can conclude though is that with a decreasing number of meteorologically triggered snow avalanches, cornice fall avalanches will become even more dominant.

We wish all of you an enjoyable, accident-free winter season here in Svalbard. If you want to study our findings, here are the links to our scientific journal papers covering the topics of this small article:

Eckerstorfer, M., Christiansen, H.H., 2011a. The “High Arctic Maritime Snow Climate” in Central Svalbard. Arctic, Antarctic, and Alpine Research, 43(1), 11–21.

Eckerstorfer, M., Christiansen, H.H., 2011b. Relating meteorological variables to the natural slab avalanche regime in High Arctic Svalbard. Cold Regions Science and Technology, 69, 184–193.

Eckerstorfer, M., Christiansen, H.H., 2011c. Topography and meteorological control on snow avalanching in the Longyearbyen area, central Svalbard 2006-2009. Geomorphology, 134(3–4), 186–196.

Eckerstorfer, M., Christiansen, H.H., in press. Meteorology, topography and snowpack conditions causing extreme mid-winter slush and wet slab avalanches in High Arctic maritime Svalbard. Permafrost and Periglacial Processes.

Additional reading:
Zahn, M., von Storch, H., 2010. Decreased frequency of North Atlantic polar lows associated with future climate warming. Nature, 467(7313), 309–312.

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