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Natural Hazards and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 31 Mar 2020

Submitted as: research article | 31 Mar 2020

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This preprint is currently under review for the journal NHESS.

On the stability interpretation of Extended Column Test results

Frank Techel1,2, Kurt Winkler1, Matthias Walcher1,3, Alec van Herwijnen1, and Jürg Schweizer1 Frank Techel et al.
  • 1WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland
  • 2University of Zurich, Department of Geography, Zurich, Switzerland
  • 3currently independent researcher

Abstract. Snow instability tests provide valuable information regarding the stability of the snowpack. Test results are key data used to prepare public avalanche forecasts. However, to include them into the operational procedures, a quantitative interpretation scheme is needed. Whereas the interpretation of the Rutschblock test is well established, a similar detailed classification for the Extended Column Test (ECT) is lacking. Therefore, we develop a 4-class stability interpretation scheme. Exploring a large data set of 1719 ECTs observed at 1226 sites, often performed together with a Rutschblock (RB) in the same snow pit, and corresponding slope stability information, we revisit the existing stability interpretations, explore the potential of a more detailed classification, and specifically consider the interpretation of cases when two ECTs were performed in the same snow pit. Our findings confirm previous research, namely that the crack propagation propensity is the most relevant result and that the loading step required to initiate a crack is of secondary importance for stability assessment. The comparison with the RB showed that the ECT classifies slope stability less reliably than the RB. In some situations, performing a second ECT may be helpful, when the first test did neither indicate rather unstable nor stable conditions. Finally, the data clearly show that false-unstable predictions of stability tests outnumber the correct-unstable predictions in an environment where overall unstable locations are rare.

Frank Techel et al.

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Frank Techel et al.

Frank Techel et al.


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Short summary
Snow instability tests, like the Extended Column Test ECT, provide valuable information regarding point snow instability. However, a robust interpretation scheme is needed, and uncertainties related to the tests' result must be considered. Therefore, a large data set of ECT – together with information on slope instability – was explored. The findings clearly show: combining information regarding propagation propensity and fracture initiation provided the best correlation with slope instability.
Snow instability tests, like the Extended Column Test ECT, provide valuable information...