It's easy to underestimate the size of an avalanche from a distance. In this video, Bruce Jamieson outlines a method using on-site estimates of size to calibrate estimates from a distance. March 2022. #avalanchesize #calibration #destructivepotential #size #snow #avalanche

Many experienced backcountry riders believe that fast creep creates tension in the slab, which makes rider triggering easier. However, based on the visco-elastic behaviour of snow, this short video argues that creep is too slow to create elastic energy (including stored tension) in the slab. The elastic energy and tension in the slab are the result of a brittle crack propagating in the weak layer. So, slab tension is negligible BEFORE the rider triggers the crack in the weak layer, which then results in the slab avalanche. For helpful comments on drafts of this short video, I thank Ron Simenhois (Colorado Avalanche Information Center), Karl Birkeland (Birkeland Snow and Avalanche Scientific) and Grant Statham (Parks Canada avalanche forecaster).

Traditionally, convexities were associated with easier triggering of slab avalanches. However, there are two parts to a convex slope: the convexity near the top of the slope and the steeper slope below it. Contrary to traditional teaching, the steeper slope is where riders are more likely to trigger a slab avalanche. The convexity is where the the crown fracture is more likely to occur. But convexities are worthy of our attention when route-finding in avalanche terrain - they are easier to see in poor light and they help us locate steep slopes where triggering is more likely. Bruce Jamieson & Ron Simenhois (CAIC), January 2026 For technical comments and insight, thanks to Alec van Herwijnen, Karl Birkeland and Johan Gaume. #convex #slab #avalanche #trigger #route #crack #propagation #crown #fracture References Trottet, B., R. Simenhois, G. Bobillier, B. Bergfeld, A van Herwijnen, C, Jiang, J. Gaume. 2022. Transition from sub-Rayleigh anticrack to supershear crack propagation in snow avalanches. Nature Physics 18. Gaume, J., T. Gast, J. Teran, A. van Herwijnen, C. Jiang. 2018. Dynamic anticrack propagation in snow. Nature Communications 9, art. 3047. van Herwijnen, A. J. Heierli. 2009. Measurement of crack-face friction in collapsed weak snow layers. Geophysical Research Letters 36, L23502, doi:10.1029/2009GL040389, 2009

The effect of solar radiation on the release of dry slab avalanches is uncertain. This video discusses two situations in which solar radiation may increase the likelihood of dry slab avalanches: 1. Rapid solar warming when there is a persistent slab; 2. First direct sun on fresh dry snow. At 10:03 I said that radiation is less available in quantitative forecasts. However, nowadays radiation is more accessible. In Canada it is in the meteograms for the Mountain Weather Forecast. Bruce Jamieson, Thomas Exner, Bradford White, 2020. Sightly revised 2026 #solar #radiation #dry #slab #avalanche

Hopefully, this will spark discussion on how to classify avalanche size, especially for big avalanches. Based on a 2014 paper at the GeoHazards 6 conference and a corresponding 13 minute video. #avalanche #size #Size5 #SelkirkMountains #D-scale #destructivepotential

This video is about the first estimates of risk from rider triggered avalanches for various levels of avalanche danger. It assumes the skier does NOT use skilled route selection, i.e. the skier "center punches" the avalanche start zones. A presentation based on the paper: B. Jamieson, Schweizer, J., and Shea, C. 2009 Simple calculations of avalanche risk for backcountry skiing, International Snow Science Workshop. Davos, Switzerland. https://arc.lib.montana.edu/snow-science/objects/issw-2009-0336-0340.pdf

This 2011 video for advanced recreationists and practitioners identifies the five types of fracture character and shows the frequency of skier triggering on slopes that exhibited each type of fracture character in compression tests. #fracturecharacter #drops #pops #AlecvanHerwijnen #stabilitytest #snowpacktest #avalancheforecasting #nonplanarbreak #progressivecompression #resistantplanar #suddencollapse #suddenplanar van Herwijnen, A.F.G. and Jamieson, B., Fracture character in compression tests. Cold Regions Science and Technology, vol. 47, no. 1-2, pp. 60-68, 2007.

Case study of the warming period and avalanche cycle, 1-5 Feb, 2012, Purcell Mountains. On Feb 1, the snowpack was a "loaded gun". Many avalanches including deep dry slab avalanches occurred the first two days during which direct short-wave radiation hit the fresh storm snow. A few days later, a similar level of direct short wave radiation did not release avalanches. Thomas Exner prepared this case study. Doug Latimer of Shadow Light Productions shot and edited the video. #solar #short-wave #radiation #avalanche #slab #swarm

A brief how-to for common snowpack tests to locate and assess instabilities within the snowpack, presented by Mike Conlan. #ect #extendedcolumntest #rb #rutschblock #pst #propagationsawtest #compressiontest #ct #handsheartest #deeptaptest #dt #crackpropagation #avalancheforecasting Start times of tests in this video are as follows: 1:32 Compression Test 5:06 Deep Tap Test 7:28 Extended Column Test 10:54 Rutschblock Test 14:48 Propagation Saw Test 18:48 Shovel Shear Test 20:49 Hand Shear Test 22:11 Concluding remarks on initiation, propagation, and limitations. The specifications in this video are based on OGRS (Canadian Avalanche Association 2016). See https://vimeo.com/479569510 for the U.S. interpretation of the ECT, which was adopted in Canada in 2024. Fracture character video: http://vimeo.com/30996756

This video explains why the the PST was developed, shows two demonstrations of the propagation saw test, explains the usual interpretation of test results, and shows how it performed next to real avalanches and whumpfs over four winters. #crackpropagation #ASARC #interpretation #snowpacktest