February 15, 2022/ Posted by Marmot Mountain Europe GmbH
When the first snowflakes fall in the high mountain regions in autumn, the ground begins to transform into a glittering world and the landscape slowly prepares for the upcoming winter. However, the white beauty not only brings a new accent to the color spectrum of the mountains, beneath the white surface hides a constantly changing structure of ice, water, air and water vapor. The snowpack is in constant transformation and this is also the main reason why the study of snowpack is so diverse and challenging, especially when it comes to assessing the avalanche danger to be derived from it.
The danger between the layers of snow
The influences on the snowpack due to constantly changing weather conditions such as wind, temperature, humidity, radiation, etc. determine the transformation processes of the snow. When new snow falls, a new layer is formed over the old one and thus the various snow layers are formed in the course of the winter, similar to the annual rings of a tree. For winter athletes the bond between these snow layers is very interesting. This is determined by the crystal properties at the time of binding, or often a long time later. Layers with poor bonding to each other are critical for the avalanche situation. Flat, and harder layers often have a weak bonding to the layers above. These layers can be formed by warm periods in which the snow melts on the surface and later remains in the snowpack as ice or a hard slush layer, or by longer cold periods in which frost forms on the snow surface and remains hidden as a mini-ice layer when snowing in. Snow covered surface frost is often the hidden cause of avalanches.
The insulating nature of the snow also provides a certain form of transformation. Due to the constant flow of geothermal heat from the ground and the snow as an insulator, there are extreme temperature differences between the ground (usually around 0°C) and the snow surface in winter. The ground acts like a hot plate and vaporizes the lowest layer of snow. The vapor rises to the top and freezes at higher, colder crystals. Cup crystals form and bring with them a hidden danger of triggering avalanches, because this so-called floating snow no longer has a bond with other snow layers – it looks like large crystal sugar.
Determine the snow profile
So how do you find such weak layers in the terrain? You need a shovel and the right place for a snow profile. Dig a profile through the snow layers which allows you to get an overview of the layers, the hardness of the snow and the grain shapes. In a rough overview, one distinguishes between two fundamentally different shades of snow crystals. If the snow crystals are clearly white, it is new snow (soft, large crystals), grainy old snow (medium hardness, small crystals) or wind crust (hard, small crystals). If gray shades are found as the color of the crystals, then it is melt-freeze crust (hard, large crystals), ice (hard, small crystals) or floating snow (soft, large crystals without binding). Surface frost can also be recognized in a faint gray shimmer.
How to simulate an avalanche?
Avalanches are mainly caused by three factors: sufficient steepness of the slope (over 30 degrees), bound snow (crystals transformed by wind) and a weak layer (surface rime, ice, snow crust or floating snow, etc.). In a snow profile, you can run a small avalanche simulation. To do this, expose a block 30 by 90 cm (also cut off the back), place the shovel on one side of the block, and load the block with blows from the wrist (light blow), elbow (medium blow), or shoulder (hard blow) – 10 times each – in an attempt to simulate an avalanche release. This test is called ECT (extended column test). If the block on a flat layer breaks continuously over the entire block with a low number of blows, the snowpack is unstable at this point and an avalanche triggering is possible with a low additional load.
The overall picture is key
When looking at snow profiles and the associated assessment of avalanche danger, it is important to understand that a snow profile is always a point observation and can never be transferred 1:1 to other locations, since the snowpack is locally quite inhomogeneous in structure. Each change in exposure, see level or ground brings about a different type of snowpack buildup. Therefore, the snow profile cannot serve for the single slope assessment, but in any case it provides a piece of the mosaic for the formation of an overall picture.
Text & Photos:
Mag. Albert Leichtfried