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SnowFlurry

SnowFlurry 2 2019/20 | Introduction and overview

What does a snow profile say?

by Stefanie Höpperger • 11/30/2019
This week, our newly acquired snow rummager repeats the confusion of symbols, abbreviations and numbers that can be found in a typical snow profile. If you know how, you can read all sorts of things from such a graphic and you don't always have to dig yourself to get an overview of the snow cover at a particular location. There's also a new profile from the Sellrain, so you can put your new knowledge into practice right away!

Hardness specifications

Penetrable with...

  • 1: fist

  • 2: four fingers

  • 3: one finger

  • 4: pencil

  • 5: knife

  • 6: ice, compact

Moisture

  • 1: dry - snow below 0°C

  • 2: slightly moist - snow 0°C

  • 3: moist - water detectable

  • 4: wet - squeeze out water

  • 5: very wet - water soaked

Tests

ECT - Extended Column Test

The ECT is the most widely used test and can be carried out quickly. It enables a good estimation of fracture initiation and fracture propagation (spreading) to a depth of approx. 1m. For this purpose, a 90 x 30 cm block of snow is shoveled free at the front and sides down to the ground. The rear side is cut off with a cord or "sliding block cord". It is best to watch the block while cutting! The shovel blade is then placed on the side edge and gradually loaded by tapping. Ideally, one person should carry out the test while another observes the block for possible fractures and their propagation.

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Stages of stress:

  • Fracture when digging or cutting 0

  • Fracture when stressed from the wrist Stroke 1-10

  • Fracture when stressed from the elbow Stroke 11-20

  • Fracture when stressed from the shoulder Stroke 21-30

  • No fracture Stroke 31

Types of fracture:

Sudden fracture (P) Whole block. Fracture propagates through the entire block on strike X.

Partial fracture (N) A partial fracture occurs on strike X. This simply means that the fracture does not propagate through the entire block.

RB - Sliding block test

The best, but also the most complex test to determine the stability of the snow cover. For this purpose, a block with a width of 2 m and a depth of 1.5 m is exposed on a significant slope (approx. 35° steepness). RB 2 @ ... break on the 2nd or 3rd jump with skis into the upper third
RB 2 @ ... break on the jump into the upper third without skis
RB 7 No break.

As with the ECT, the RB distinguishes between sudden breakage (P) and partial breakage (N).

Continue to the example profile on the next page -->

Reading a snow profile using an example

I took this profile on 16.11.19 at 12:30 pm in Kühtai at the Grieskogelscharte.

Altitude: 2589m

Exposure: East (the slope faces east)

Snow depth: 95cm

Layers from bottom to top:

0 cm - 36 cm ..... Edged-rounded crystals. Transformation process from angular back to round grain, (degradative transformation). With a size of 0.5 - 1 mm and a hardness of 1-2, no longer quite so easy to penetrate with a fist, but still too soft for 4 fingers.

36 cm - 38 cm ..... Angular-rounded crystals mixed with angular crystals. The grain shape that is more dominant in the layer is always named first.

With a size of 0.5 mm and a hardness of 1, penetrable with a fist.

This layer forms the weak layer for the ECTP28! A very soft layer with poorly bonded crystals. As you can see, the temperature gradient (large temperature difference in a small area) is high in this area, which promotes the build-up transformation. This will no longer be a major problem with the snowfall of 17.11.19.

The layers of 0 cm - approx. 38 cm are from the snowfall up to 10.11.19 (see profile of 10.11.19 in SnowFlurry 1) You can see here how the crystals, which were still angular at that time, are changing for the better due to the snow load and the additional snow depth and the low temperature gradient in the layers closer to the ground. Here, the process of degradative transformation is underway again - the angular crystals are becoming rounder again.

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38 cm - 52 cm ..... Point with point with a size of 0.5 and a hardness of 1, can be penetrated with a fist.

52 cm - 55 cm ..... Edged with point with a size of 0.5 and a hardness of 1-2, no longer quite as easy to penetrate with a fist, but still too soft for 4 fingers.

55 cm - 76 cm ..... Dot with a size of 0.5 cm and a hardness of 3-4, no longer easy to penetrate with a finger, but still a little too soft for a pencil.

Ca. 38 cm - 76 cm precipitation from 12.11. to 13.11.19

76 cm - 78 cm ..... Felt with angular crystals with a size of 0.5 - 1 mm and a hardness of 2, can be penetrated with 4 fingers.

Angular crystals (building up transformation) formed on 14.11. due to a clear night and very low dew point (down to approx. -30°C). As a result, the snow surface cooled down considerably, which favored the build-up transformation. In this layer, only partial breakage occurred.

78 cm - 94 cm ..... Fresh snow with felt with a size of 1 and a hardness of 1

94 cm - 95 cm ..... Felt with dots with a size of 0.5 - 1 and a hardness of 2. Snow surface slightly influenced by the wind.

Ca. 76 cm - 95 cm of precipitation from 15 - 16.11.19.

The entire snow cover is dry and has a maximum temperature of 0°C (on the ground).

Test results:

An extended column test (ECT) was carried out in each case.

ECTN8 @ 78 cm

A partial break (N) was produced on the eighth wrist strike. A fracture was initiated but could not propagate.

ECTP20 @ 36 cm

On the 20th stroke (tenth stroke from the elbow), a fracture occurred in the weak layer and spread over the entire block. Consequence: The block above the fracture slides towards you

.

Being able to correctly read a snow profile with its layers, grain shapes, hardness and temperatures is a prerequisite for determining the structure of the snowpack on the basis of a profile and getting a feeling for whether it is a compact and stable snowpack with well-connected layers and round-grained crystals, or a rather unstable snowpack with an alternation of crusts and angular crystals. Based on test results, you can get an idea of whether fractures occur at all, whether they spread and whether there are disruptive weak layers.

You don't necessarily have to stand and dig in cold snow holes yourself, because many profiles are publicly viewable. What I still recommend to everyone is to do an ECT from time to time! You don't have to recognize all the layers and write them down in detail, but practice is essential for understanding the process. And an ECT is one of the few methods that allows you to see a fracture live without being in the middle of an avalanche. After all, it's a well-known fact that real avalanches are not good for cherries!

Photo gallery

This article has been automatically translated by DeepL with subsequent editing. If you notice any spelling or grammatical errors or if the translation has lost its meaning, please write an e-mail to the editors.

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