Item: A MODIFIED EXTENDED COLUMN TEST TO ASSESS THE LIKELIHOOD OF SNOWMOBILE TRIGGERING AND PROPAGATION OF PERSISTENT WEAK LAYERS
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Title: A MODIFIED EXTENDED COLUMN TEST TO ASSESS THE LIKELIHOOD OF SNOWMOBILE TRIGGERING AND PROPAGATION OF PERSISTENT WEAK LAYERS
Proceedings: Proceedings, International Snow Science Workshop, Whistler, BC, Canada, 2026
Authors:
- Iain Stewart-Patterson [ Canadian Motorized Backcountry Guides Association, Revelstoke, BC, Canada ] [ Thompson Rivers University, Kamloops, BC, Canada ]
- Jeremy Hanke [ Canadian Motorized Backcountry Guides Association, Revelstoke, BC, Canada ] [ Soul Rides, Revelstoke, BC, Canada ]
Date: 2026-09-28
Abstract: The Extended Column Test (ECT) is a well-established instability test for evaluating both fracture initiation and propagation propensity within slab avalanche problems. Its utility, however, is largely constrained to weak layers buried at depths of less than approximately one metre. Beyond this threshold, the likelihood of obtaining meaningful results diminishes due to insufficient stress transmission from the applied loading. In these deeper scenarios, skier triggering probability decreases, whereas snowmobile-triggered avalanches remain comparatively more likely. Snowmobiles generate a substantially greater stress field within the snowpack, with an estimated pressure bulb three to five times that of a skier. This increased load facilitates the activation of deeper persistent weak layers (PWLSs), which may otherwise appear unreactive to skier triggering and skier-based instability tests. While Deep Tap tests and Propagation Saw tests can provide insight into fracture propagation characteristics, they do not directly quantify the probability of initiation under dynamic loading conditions typical of motorized use. Of the 140 InfoEx subscribers, only a small subset (approximately five operations) are snowmobile-based. Consequently, machine-triggered avalanche incidents (classified as Ma, Mr, or Mc) are underrepresented in the dataset. This bias is further exacerbated by underreporting within the recreational snowmobiling community, where avalanche involvement is often normalized and not systematically documented. Concurrently, advancements in snowmobile technology and riding techniques, particularly maneuvers such as bow ties and wheelies on short-track, turbocharged machines, result in deeper stress penetration into the snowpack. The Modified Extended Column Test (MECT) is designed to better approximate the increased depth and magnitude of the pressure bulb generated by a snowmobile. To achieve this, surface snow is selectively removed from the test column to a depth corresponding to the measured track penetration of the machine. Excavation is limited to the shovel loading area, while the remaining overburden is left intact to preserve the in situ stress distribution across the column. Loading is then applied following the standard Extended Column Test (ECT) protocol, ensuring consistency in force application and enabling comparison with established ECT results.
Object ID: ISSW2026_P2.58.pdf
DOI: https://doi.org/10.15788/1790099055
Language of Article: English
Presenter(s): Iain Stewart-Patterson
Keywords: Snowmobiling and Motorized Access
Page Number(s): 2210 - 2216
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