Svalbard Snow Avalanche Advice

Ole Humlum, UNIS, Department of Geology, Svalbard, Norway

Click here for general information about the physical environment in Svalbard

Click here to see a modeling approach to assess snow avalanche risk in Nordenskiöldland, central Spitsbergen.

Photo above show 200 m slab slide below Bingtoppen in upper Fardalen, central Spitsbergen, 24. April 2003.

Field indications of avalanche risk, safety advice

The condition of snow stability is most readily inferred from direct examinations of snow cover structure. The techniques of such observations have been highly developed over the past thirty years, particularly in Switzerland and Norway. The standard techniques of snow pit investigation and the use of instruments as the ram penetrometer have served as the basis for avalanche risk studies. Today their application to avalanche forecasting, the original reason for their development, is also widespread. However, even without doing instrumental investigations, just by observing the certain features in the landscape, and following the meteorological situation, it is possible to avoid many potential avalanche risk situations. A number of field indications and general advice is listed below. Many of the field indications of avalanche danger require that you are able to make good visual observations of the landscape. Today, GPS makes it perfectly possible to navigate in weather with bad visibility. In such weather conditions, however, it might be difficult or even impossible to make the visual observations necessary to ensure avalanche safety.

Previous and recent avalanche activity on slopes represents a major clue to avalanche risk, but is nevertheless often overlooked.

Slopes with an inclination of 30-45 degrees should be avoided as the avalanche risk is especially high on such slopes, if covered by snow. On steeper slopes accumulation of a thick snow layer is usually impossible because of the steepness of the terrain. When traveling across slopes with smaller gradient than 30 degrees you should be aware that avalanches released from steeper slopes higher up could continue down to lower altitudes, affecting slopes of much smaller inclination. The actual avalanche run-out distance depends on terrain, snow parameters, avalanche size, etc.   

Terrain model showing potential snow avalanche risk zones around Longyearbyen, viewed towards SW. This model only indicate potential release zones and potential run-out zones are not shown. In general, however, all areas below potential release zones should be considered as potential run-out zones. The diagram only shows large-scale terrain features and even small slope segments with a height difference of only 5 m (not shown in the diagram) may represent potential avalanche risk zones. The daily avalanche risk will depend upon recent and past wind direction, -strength and precipitation. Especially downwind (lee) slopes will be prone to increased snow avalanche risk. Following the onset of thaw, all steep slopes with a thick snow cover may rapidly become exposed to high avalanche risk.

Warm periods with temperatures at or above freezing  happens several times each winter in Svalbard, and is a normal meteorological event, caused by advection of warm air from south. During such warm periods the avalanche risk increases. There is, however, also a more lasting effect which easily might be overlooked. The presence of permafrost will usually inhibit widespread snow melting during these warm events, but a smooth melting crust may be formed at the top surface of the snow cover, acting as a potential sliding surface for snow accumulated later in the winter. As an example, if the air temperature at sea level during one of these warm events reaches  2^oC, you should expect such a melting crust to form up to about 300 m above sea level, using a standard vertical temperature gradient of 0.65^oC/100m. Melting crusts are often quite persistent, and may represent a potential sliding layer for avalanches for the remaining part of the winter. So pay close attention to the current meteorological situation and seek information on the past development.

Solid precipitation at high temperature.  Weak internal layers may also be produced during events with  solid precipitation at or above ca. -4C. At such temperatures, snow particles often attain a simple, round form (se picture below), giving rise to a snow deposit with little internal strength. Special care to avoid slopes with such snow should therefore be taken following solid precipitation at rather high temperatures. Follow the local weather forecast carefully and look out for the snow crystal form during precipitation events.

Rounded snow particles sampled in Longyearbyen 8. December 2002 following solid precipitation at -2C. Such snow have limited internal friction and may form weak layers in a thicker snow deposit.

Wind erosional surface forms 'sastrugi' in itself does not represent an avalanche danger. On the other hand, they indicate recent  wind erosion of the snow cover, and that some of the snow removed will have been deposited in lee locations. By this, avalanche risk may increase on such lee slopes during periods with clear weather, if the wind speed is sufficient to erode exposed snow surfaces. Snow drifting often begins at relatively low wind speeds, from about 4 m/s.

Sastrugi formed by wind from left, April 2003.

Snow dunes are the visual indication of recent snow accumulation on certain slopes during periods with high wind activity (see above). Slopes with many snow dunes (see photo below and photo at the top of this page) have recently been heavily loaded with new snow, and should be considered as potential avalanche risk zones, especially if the slope approaches the critical range from 30 to 45 degrees.

Snow dunes (wavelike pattern) formed by wind from SE in Vandledningsdalen near Longyearbyen, 18. March 2004. 

Recent wind activity. Pillows or dunes of freshly-deposited snow are often obvious in the winter landscape and their stability is very sensitive to various triggers. Take note of the wind direction during situations with significant snow drifting and consider lee-side slopes as risk zones for especially the first days to follow. It should, however, be observed that topography by channeling effects may exercise considerable influence on the local wind direction.

Avalanche from 10 m high slope at entrance to Helvetikadalen, central Spitsbergen, 30. March 2004. Even low slopes may release avalanches, so consider closely where to take shelter for the wind.

Collapse and whoomp sound. Often, the combined weight of snow and people walking on a snowpack with an internal weak layer such as depth hoar (German: Schwimmschnee) or light density snow will cause the weakness to collapse, dropping the upper layer of snow a few centimeters. The resulting collapse sound ' "whoomp' may sound like  distant cannon fire. Sometimes, a person will actually be able to see or feel the surface of the snow layer drop several inches. If this happens to you on a steep slope you are entering an extreme danger zone and may easily release a slab slide (see photo below). Such a weak snow layer may form gradually over several days or weeks due to the temperature difference between the upper and lower surface of the snow cover.

Slab avalanches released on slopes above western moraine at Kokbreen, Reindalen, central Spitsbergen, 24. April 2003. The innermost slide measures about 300 across.

Hollow sounds. The wind can move huge quantities of snow, accumulating it into drifts and creating slabs. These deposits can be either soft or so hard that they can carry your weight. However, although the slab itself is very strong, it may be sitting on top of a weak layer deeper in the snow. Sometimes a poorly supported hard slab will make a hollow sound like a drum when you walk on it. Also in this case, you are entering a high risk zone.

Shooting cracks. If the snow layer is exposed to strong surface tension, it may fracture as a person walk across. These "shooting cracks" that spread out from your toes are not a problem in gently sloping terrain, but indicate that steeper slopes presumably are suspect. The deeper and longer the cracks, the greater the potential instability.

Snow surfaces without penetrating objects. Snow covered slopes without penetrating bedrock, boulders or trees are potentially dangerous, as such penetrating objects tend to lock the snow cover to the slope by locally increased surface roughness. Plan your route from 'safe area' to 'safe area', minimizing the distance traveled across areas without visible roughness objects. 

Snow surfaces with penetrating objects. Even snow covered surfaces with protruding boulders or rock outcrops may prove dangerous. This happens when pockets of depth hoar (German: Schwimmschnee) develops around boulders due to the special thermal conditions in the snow pack around such penetrating objects.

Loose snow present in trees or on steep surfaces. Avalanche hazard is usually greatest during the first 24-48 hours following a storm or blizzard. The layer of snow will tend to adjust to the weight of new snow with time. If trees (not especially relevant for Svalbard) or other steep surfaces (houses, rock steps, boulders, etc.) are still holding much loose snow after a storm, presumably the snow on the ground has not compacted and settled, either.

Cornice formed in upper Vandledningsdalen, late June 2000. The snow accumulated by snow drift across the mountain plateau by prevalent SE winter winds. The height from the valley bottom to the mountain plateau above is about 70 m.

Cornices. These features form on the lee side of ridges or along plateau rims and indicate that winds have been moving great quantities of snow. Much deeper snow should be expected -- and consequently, increased avalanche hazard -- below a cornice than on the upwind, scoured side of the ridge or mountain plateau.

Mouth and confluence areas of valleys and ravines. If possible, areas immediately below the mouth or confluence of  valleys or ravines should be avoided or hastily crossed. Most avalanches follow such shallow valleys down the mountain slope (see photo below). In addition, avalanches often release simultaneously in neighboring valleys and therefore will merge with each other in the confluence area of two or more valleys, and suddenly achieve huge proportions. This is definitely not the place to pause for lunch, even though such places often represent pleasant areas with shelter against wind. The wind shelter is exactly why snow accumulates here. 

Avalanche in valley on southern slope of Aasgaardfjellet in upper Reindalen, central Spitsbergen, 24. April 2003.

Convex part of slope. A shoulder-like convex part of a slope usually is an area of increased tensional stresses in the snow pack and should be traversed with the outmost care only. Avalanches will often begin at or shortly below such a convex shoulder. If you can not avoid crossing such a snow covered slope, this should preferentially be attempted shortly above the convex shoulder. 

Melting avalanche snow near Larsbreen, July 2000. Rock debris is released on the snow surface by melting, resulting in a high frequency of delicately balanced, perched boulders and stones.

Perched rock fragments. Avalanche snow often contains a lot of debris and rock fragments. As the snow melts during summer, this sediment is released and dumped upon the ground below. During summer time, winter-time avalanche risk areas therefore may be identified by mapping the distribution of such debris (see figure above).

Avalanche boulder tongue in Endalen, Spitsbergen, Svalbard, August 2000. The avalanche track is seen as a light-colored deposit of debris, extending from the small valley in the upper right to the lower left corner of the photograph. The mountain rises to about 580 m asl., while the valley bottom is at about 200 m asl. This avalanche track extents all the way to the river plain, signaling even the valley bottom beyond to be within the avalanche risk zone during winter.

Avalanche boulder tongues. At sites where snow avalanches are frequent, a tongue-shaped deposits of loose, angular debris may accumulate through time (see figure above and below). Such large-scale landform may - at summer time - assist in mapping the extent of areas exposed to increased avalanche risk. Avalanche boulder tongues and associated landforms usually are the result of avalanche activity during long time spans and their internal stratigraphy may yield important palaeoclimatic information relating to past and present wind activity, dominant wind direction and precipitation.

Three avalanche boulder tongues along the eastern valley slope below Larsbreen, near Longyearbyen, Svalbard. Part of the glaciers right lateral moraine from the Little Ice Age maximum extent is seen in the lower right part of the photo. Note the slightly fluted or striated surface appearance of the individual avalanche boulder tongues, testifying to modern avalanche activity. The top of the mountain is at about 500 m asl., while the foot of the mountain slope is at about 300 m asl. Seen towards ENE, August 1999.

Latest update: 19. December 2005.