Measuring the thermal balance of a snow avalanche

Avalanches can exhibit many different flow regimes from powder clouds to slush flows. Flow regimes are largely controlled by the properties of the snow released and entrained along the path. Recent investigations showed the temperature of the moving snow to be one of the most important factors controlling the granulometry and thus the mobility of the flow. The temperature of an avalanche is mainly determined by the temperature of the released and entrained snow but also increases by frictional and collisional processes with time. The aim of this study is to calculate the thermal balance of an avalanche using infrared thermography technology. For this work an avalanche was artificially released at the Flüelapass (2383 m.a.s.l.) close to Davos, Switzerland. A thermal imaging camera was used to assess the temperature before, during and just after the avalanche with a high spatial resolution. Snow profiles along the avalanche track and terrestrial laser scans, conducted before and after the avalanche, allowed to quantify the temperature of the eroded snow layers. This data set allows for the first time to calculate an entire thermal balance, from release to deposition, of an avalanche. The comparison between the measured temperature of the entrained snow layers and the temperature of the deposition allowed to draw conclusions whether the main contribution to the warming of the snow in the avalanche arose from friction or entrainment of relatively warmer snow. Our results allow for a more comprehensive understanding of snow temperatures in avalanche flow and their consequence on flow regimes. This information can directly be used to enhance the performance of avalanche dynamics models and are thus of great interest for practitioners. We further discuss advantages and limitations of the presented method and the technologies.

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Michael Lehning, Tobias Jonas, Betty Sovilla, Walter Steinkogler
2013
Poster talk

Abstract

Official source

https://infoscience.epfl.ch/record/197623?ln=en

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Related concepts (3)

Avalanche

An avalanche is a rapid flow of snow down a slope, such as a hill or mountain. Avalanches can be set off spontaneously, by factors such as increased precipitation or snowpack weakening, or by external means such as humans, animals, and earthquakes. Primarily composed of flowing snow and air, large avalanches have the capability to capture and move ice, rocks, and trees. Avalanches occur in two general forms, or combinations thereof: slab avalanches made of tightly packed snow, triggered by a collapse of an underlying weak snow layer, and loose snow avalanches made of looser snow.

Snow

Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water throughout its life cycle, starting when, under suitable conditions, the ice crystals form in the atmosphere, increase to millimeter size, precipitate and accumulate on surfaces, then metamorphose in place, and ultimately melt, slide or sublimate away.

Temperature

Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied on various reference points and thermometric substances for definition. The most common scales are the Celsius scale with the unit symbol °C (formerly called centigrade), the Fahrenheit scale (°F), and the Kelvin scale (K), the latter being used predominantly for scientific purposes.