the issue of relevance
DESCRIPTION
Ensuring Relevancy and Verification of Snowpack Information. The issue of relevance The task of gathering and interpreting snowpack information should include a process to determine how relevant the information from observations and tests is to snow stability. - PowerPoint PPT PresentationTRANSCRIPT
The issue of relevance
The task of gathering and interpreting snowpack information should include a process to determine how relevant the information from observations and tests is to snow stability.
Ensuring Relevancy and Verification of Snowpack Information
Assessing relevance:
Concept of red flags; weigh certain pieces of information and certain values more than others.
Next – ask,
Where did the information come from, and is it representative of the terrain and snowpack in the start zones?
Ensuring Relevancy and Verification of Snowpack Information
Standardized techniques are important!
• Each snowpack test REQUIRES AN OBJECTIVE prior to commencement.• Practice and experience is required for quality site selection of field test sites.• Tests are skillfully conducted using standardized, practiced techniques. Consistent techniques reduce uncertainty.
Ensuring Relevancy and Verification of Snowpack Information
Checklists to evaluate snow profile
Challenges to the Observer • Choose sites that are “near start zone” in character, but also safe and accessible. • Ensuring conclusions regarding snowpack instability aren’t “premature.” Conclusions should be confirmed by peer review.• Ensuring observations are repeatable and verified by other relevant tests. • Recognizing the possibility of “false stable indicators.”• Understanding the nature and scope of snowpack variation across the slope. • Operational pressures or group dynamics may compromise available manpower or time and not provide the access required to complete tests properly.
Snow profileObs and test structural profiles of spx
Disadvantage: takes time
Yellow flags: points to layer and layer interface with 70-75% accuracy
Ensuring Relevancy and Verification of Snowpack Information
Compression test In combination w/frx character useful for identifying thin, persistent weak layers, and obs the likelihood of frx. initiation. Focus on layer ID, initiation (27-70cm deep) Focus on normal stress Initiation need to record frx character
Fracture character• Sudden planar (SP) V , w/mfc• Sudden collapse (SC) V > 1cm
Ensuring Relevancy and Verification of Snowpack Information
Ensuring Relevancy and Verification of Snowpack Information
Shovel shear testFocus on shear deformationCan use Frx character with only SP, RPGood only for midpack, 30-70 cmObserving layer changes over time in a study plot as block size and (given the same observer) pull force don’t change as the snowpack depth or “load’ increases. More for snow researcher
Deep tap testNot for upper spx layersGood for stiff layer on weak snowBlock always the same sizeAlways use use Frx character
Ensuring Relevancy and Verification of Snowpack Information
Limitations (small column tests)When obs frx character: Progressive compression (Q2) type fracture character is impractical to observe using a shovel shear test.
Sudden collapse (Q1-“drops”) are harder to accurately observe using the ST.
Progressive compression fractures are often associated with new snow or storm snow layers.
Ensuring Relevancy and Verification of Snowpack Information
Ensuring Relevancy and Verification of Snowpack Information
Extended column test Lg column tests offer information about initiation and propensity for further propagation. A 1 m column gives an idea of whether propagation will continue once the fracture has initiated Observing weak layers under “soft slabs” greater than 30 cm thick but =/< 70 cm thick. Similar depth to CT, 27-70 cm False stable with stiff slab (1F) 90 cm long x 30 cm wide Cut to back wall to 100 cm
Propagation saw test Need to indentify layer Useful for observing fracture propensity for propagation. Useful for correlating information gathered from CT & DT tests. END: frx continues uninterrupted to the end of column ARR, propagation arrests within the weak layer before reaching the end of the columnSF,propagation ends at a fracture through the overlying slab
Ensuring Relevancy and Verification of Snowpack Information
Checklists to evaluate snow profile
Layer ID Initiation Propensity further propagation
Propensity propagation - failure
Probing
Shovel tilt
Profiles
Compression
Shovel shear
Deep tap test
ECT
PST
RB
Explosives
Consider all available information prior to making a statement on snowpack instability
• Avalanches: current and past• Snowpack structure: consider history and variability • Weather conditions: season trends, current condition, variation across the range
Ensuring Relevancy and Verification of Snowpack Information
Ensuring Relevancy and Verification of Snowpack Information
Fracture characteristicsSmall column tests + fracture characteristics
w/o frx characteristics, 37% w/ fr characteristics, >97% in >4,000 tests
Checklists to evaluate snow profile
Fracture initiation + fracture propagation = slab releaseIn recent years it has become apparent that snowpack stability tests are better indicators of whether a skier is likely to initiate a fracture in a weak layer than whether ─ once initiated ─ the fracture will propagate.
Learning OutcomesKnow Shear QualityKnow Frx characterKnow the Yellow Flags (e.g., Jamieson and Schweizer, in press)
Unusually clean, planar, smooth and fast shear surface: weak layer may collapse during fracture. The slab typically slides easily into the snow pit after weak layer fracture on slopes steeper than 35° and sometimes on slopes as gentle as 25°. Tests with thick, collapsible weak layers may exhibit a rougher shear surface due to erosion of basal layers as the upper block slides off, but the initial fracture was still fast and mostly planar.
Q1
Shear Quality
Average” shear: shear surface appears mostly smooth, but slab does not slide as readily as Q1. Shear surface may have some small irregularities, but not as irregular as Q3. Shear fracture occurs throughout the whole slab/weak layer interface being tested. The entire slab typically does not slide into the snowpit.
Q2
Shear Quality
Shear surface is non-planar, uneven, irregular and rough. Shear fracture typically does not occur through the whole slab/weak layer interface being tested. After the weak layer fractures, the slab moves a little, or may not move at all, even on slopes steeper than 35°.
Q3
Shear Quality
Checklists to evaluate snow profile
Yellow Flags:
Identifying potential failure layers
There are three layer properties and three interface properties to check.