Ned Bair US Army Corps of Engineers Cold Regions Research and Engineering Laboratory Earth Research Institute UC Santa Barbara AVPRO 910AM 22714 1 Campbell C Spatial variability of slab stability and fracture properties in avalanche starting zones MSc University of ID: 504047
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Slide1
Addressing spatial variability
Ned Bair US Army Corps of Engineers Cold Regions Research and Engineering LaboratoryEarth Research Institute, UC - Santa Barbara
AVPRO9-10AM 2/27/14
1
Campbell
, C.: Spatial variability of slab stability and fracture properties in avalanche starting zones, M.Sc., University of
Calgary
, Calgary, AB., 264 pp., 2004.Slide2
The Weibull
modulus of snow
Materialm
Snow
1-2Freshwater ice
3-5
Concrete
12
Steel
25
Kirchner, H. O., H.
Peterlik
, and G.
Michot
, 2004: Size independence of the strength of snow.
Phys. Rev. E, 69, 011306.
2Slide3
Snow is weak, full of flaws, and unreliable.
The extremely low Weibull modulus means that the failure of snow is highly unpredictable.
Jamieson, B.
Regional Danger Ratings and the Odds of Triggering a Potentially Fatal Avalanche , The Avalanche Review, Vol 28, No. 1, October 2009, p. 15.
“If you are trying to find an avalanche expert, look under the avalanche debris.” – Jim
Kanzler
, 1949-2011
3Slide4
Conway, H., and Abrahamson, J.: Snow stability index, Journal of Glaciology, 30, 321-327, 1984.
Early studies on spatial variability
4Slide5
Weak layer deficit and pinned zones
Conway and Abrahamson (1984) found areas of varying stability (shear strength/shear stress) along crown and flanks of avalanches.They referred to these as deficit (weak) and pinned (strong) zones.
5Slide6
Slab thickness
Slab thickness and its modulus of elasticity (stiffness) affect triggering.For instance, thin spots are known trigger locations.
Crown of fatal avalanche,
Feb 23, 2008 Sunburst Mountain, Turnagain Pass
6Slide7
Stress bulbs
Exner
, T., and B. Jamieson, 2008: The effect of snowpack warming on the stress bulb below a skier. International Snow Science Workshop
.7Slide8
Potential trigger locations
Arapahoe Basin East Headwall 12/26/13
8Slide9
4/17/06 post control, Mammoth Mountain
9Slide10
The top was opened to the public at 1253. The first guests would have skied Climax around 1305.
By the time the post control occurred at 1352, at least 100 skiers had been in the starting zone.
4/
17
/06 timeline
10Slide11
Post holing as trigger? 12/15/08 post control fatality Snowbird, UT
“At 12:24 a group of snowboarders was on the high traverse of Northwest Mt. Baldy and watched the avalanche initiate; the crown face bisected the high traverse. The event occurred as they were crossing the slope but did not involve them. According to witness reports from near the starting zone, as the slide was in motion they spotted a person in the middle of the track who was hiking up the slope to retrieve a
ski…She was not equipped with a beacon or Recco and was located with a probe line at 58 minutes, 3
deep.”-Utah Avalanche Center
11Slide12
Föhn
, P. M. B.: Snowcover stability tests and the areal variability of snow strength, Proc. 1988 Intl. Snow Sci. Workshop, Whistler, B.C. Canada, 1988, 262-273
12Slide13
Föhn
, P. M. B.: Snowcover stability tests and the areal variability of snow strength, Proc. 1988 Intl. Snow Sci. Workshop, Whistler, B.C. Canada, 1988, 262-273,
13Slide14
Simenhois
, R., and Birkeland, K.: The extended column test: test effectiveness, spatial variability, and comparison with the propagation saw test, Cold Regions Science and Technology, 59, 210-216, 10.1016/j.coldregions.2009.04.001, 2009.
14Slide15
Below toe: 3/11/13 16:11 10330 FT, N aspect
20º slope,
ECTP150 22 41cm↓, ECTN300 24 41cm↓PST END 42/140 cm
PST Arr 50/600 cm
3/11/13 15:11 10430 FT
NE aspect, 25º slope
v
arious
ECTN
PST SF
Photo from 3/11/13 16:11
Crown
3/12/13 15:44 10700 FT N aspect, 44º slope
ECTArr163 22, 47 cm↓, PST END 26/127 cm, 51 cm↓Near
left flank:3/12/13 16:30 10550 FT
N aspect, ~38º slopeECTP150 22, 37 cm↓, PST END 25/150 cm, 37 cm↓PST SF 25/600 cm, 37 cm↓
(crack went ~ 2 m)
X
Trigger
15Slide16
Relationship of point to regional stability
Schweizer, J.,
Kronholm, K., and Wiesinger, T.: Verification of regional snowpack stability and avalanche danger, Cold Regions Science and Technology, 37, 277-288, 10.1016/s0165-232x(03)00070-3, 2003.
16Slide17
Quantifying spatial variability
Variograms
17Slide18
Campbell
, C.: Spatial variability of slab stability and fracture properties in avalanche starting zones, M.Sc., University of Calgary, Calgary, AB., 264 pp., 2004
.Campbell, C., and Jamieson, B.: Spatial variability of slab stability and fracture characteristics within avalanche start zones, Cold Regions Science
and Technology, 47, 134-14 http://dx.doi.org/10.1016/j.coldregions.2006.08.015, 2007.
18Slide19
Snow Micropenetrometer
(SMP) studies
www.slf.ch
www.fsavalanche.org
19Slide20
Mapping weak layers and slabs
Schweizer, J.,
Kronholm, K., Jamieson, J. B., and Birkeland, K. W.: Review of spatial variability of snowpack properties and its importance for avalanche formation, Cold Regions Science and Technology, 51, 253-272, 10.1016/j.coldregions.2007.04.009, 2008.
Buried surface hoar
Wind slab
20Slide21
How do we deal with spatial variability?
Carpet bombingUsually effective, but inefficientExplosive testingEffectiveness depends on how good your indicator slope isTracking weak strength for targeted control work
Very difficultFor storm snow avalanches, waiting one day is very effective.
21Slide22
Waiting one day
Bair, E.: Forecasting artificially-triggered avalanches in storm snow at a large ski area, Cold Regions Science and Technology, 85, 261-269, 10.1016/j.coldregions.2012.10.003, 2013.
Fig. 8. Effect of new snow on avalanche activity and explosive yield for selected avalanche paths. B
ox plots are : (a) number of avalanches, (b) sum of R-sizes, and (c) explosive yield, grouped by snow in the past day. The “no new snow” group had no new snow in the last 24 h, but snow prior. The “new snow group” had snow within the last 24 h. N = 132 days for “no new snow” and N = 904 days for “new snow”.
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