STAB ASSESSMENT:
PERSISTENT SLAB HAZARD REPORT
A quick few notes on the reporting standard we are using for this stability hazard.
Assumptions:
You know how to locate and access terrain safely, conduct this assessment, and understand the basic terms and assessment techniques (CT / ECT - Snowform Identification) consistent with your minimum AST2 (Or equivalent) training.
Given our current understanding of the conditions we are looking for signs of a persistent instability. This weakness is well established and documented already in the forecasts. We are trying to establish wether the bridging characteristics of the overlying slab are sufficient to prevent human triggered initiation ( of the persistent weak layer).
If conditions are safe enough to permit and 'Red Flags' observed have been noted and evaluated in the process of running this patrol then we can conduct some pit tests in a suitable (<22˚ incline) aspect. Ideally at an altitude of 1700m or more, although this is not essential.
STEP 1:
Snow Profile & Compression test (CT)
Starting with a simple column test, you will go through the process of isolating any weak layers. Make routine records in your book (CT Scores and Depths), recording the shear quality ( fast/ resistant / stubborn), noting the interface of the weak layer(s) (Crystal forms). Importantly we are interested in the density and cohesive nature of the overlying slab, Finger density scores and the presence of crusts will help establish this.
STEP 2:
Extended Column Test (ECT).
Here in Australia we have a variable and temperate climate, the rate of metamorphosis is relatively high. Our snowpack readily stabilises, establishing its ability to propagate is very important. In the life cycle of a windslab there will be that transitional period in which the slab will be cohesive enough to propagate, and not yet well bonded to the bed surface.
The pit we need for this is very specific for consistent reporting. The task is to isolate a column that is 90cm wide by 30cm from the front to back, and isolated to the depth of the weakness (if on crust), or ideally deeper (on rounds / facets etc).
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TECHNIQUE
Having isolated the block as shown in FIG 1, using the same tapping / loading steps as your Compression Test, tap the loading area and observe closely any propagation across the column. If the column propagation extends the width of the column we report this as ECT:P, or if not report ECT:X.
You can record the loading step as (10), for example ECT:P(10)