1 / 25

4/17/2006 Climax Post Control Avalanche

Monday 4/18/2011 Ned Bair Mammoth Mountain Ski Patrol Ph.D. Candidate, Donald Bren School of Environmental Science and Management, UC – Santa Barbara US Army Corps of Engineers Cold Regions Research and Engineering Laboratory. 4/17/2006 Climax Post Control Avalanche.

shana-berry
Download Presentation

4/17/2006 Climax Post Control Avalanche

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Monday 4/18/2011 Ned BairMammoth Mountain Ski Patrol Ph.D. Candidate, Donald Bren School of Environmental Science and Management, UC – Santa Barbara US Army Corps of Engineers Cold Regions Research and Engineering Laboratory 4/17/2006 Climax Post Control Avalanche

  2. Video shot by guest 4/17/07 @ 1352 hrs • Climax post control

  3. Avalanche summary • R4D2 • Average crown depth: 28”, maximum: 48”. • 755 ft wide, ran 710 vertical ft. • Bed surface: 1F melt freeze clusters 0.5-1mm. • Slab: 0.1-0.3mm wind slab, broken particles, mostly rounded forms (typical) • Step down failure (atypical) • 2nd post control of the 05-06 season on Climax. On 12/29/2005 a cornice collapsed and caught 6 people in an R3D2 hard slab. 5 skis lost, no injuries.

  4. Victim summary • 8 people caught, 1 skied out, 5 dug themselves out • 2 partially buried • 2 non-critical injuries, none went to hospital • 1 patient found from a glove sticking out of debris. She was face down and was resuscitated with rescue breathing. • The other patient had a minor knee injury.

  5. Weather Summary • 9” inches of new snow, 1.23” SWE, 14% water. • Base depth 210” @ 1400 hrs on day of incident • Temperature change from low of 12°F @ 0600hrs on 4/17 to 28° F @ 1400 hrs at Sesame Street Snow Plot (el 9000 ft.). • Time of accident 1352 hrs. • Temperature change from low of 6°F @ 0600 hrs on 4/17 to 11°F @ 1400hrs at the Top Weather Station (el. 11,052 ft.).

  6. 4/17/2006 control work summary • The top had not been open to the public since 4/13. • Climax was ski cut on 4/14, but not opened to the public. • Guns 1 and 2 blind fired that morning. • Climax was shot with 4 1kg hand charges and ski cut, then ski cut on a 2nd lap. Only a small R1D1 (4” crown, ran 75 ft) was recorded. • 32 other avalanches. • Max. class size R4D3, max. crown size 60“(Dave’s Run). 400’path width, 1000’ path length. Triggered by Gun 2 and cleaned up with hand charges. • 5 avalanches that were class 3 and above with ≥ 30” crown sizes.

  7. 4/17 timeline • 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.

  8. Alex finding CT 11 Q 1 @ the Hump the next day

  9. Why did this avalanche happen after the slope had been open for several hours and skied by hundreds of skiers? • Climax cannot be shot by the 105mm Howitzer. Hand charges were likely not a powerful enough control measure. • It is possible that solar radiation destabilized the slope. • Low thermal conductivity of snow makes it unlikely that a small increase (6-11°F) in air temperature affected the weak layer. • It is also possible that hand charging and ski cutting left the slope in a weakened state, but this explanation suggests the avalanche would have been triggered soon after opening.

  10. Radiation effects on slabproperties • Warming effects generally destabilize slopes in the short term and increase stability over longer timescales (McClung and Schweizer, 1996): Short term: • Decreased slab stiffness (elastic modulus).Deeper and shallower stress bulb. • Increased strain rate (deformation). Faster glide and settlement. • Increased energy release rate. The propagating collapse wave can travel more easily. Long term: • Increased rate of bond growth. Weak layer and slab bonding. • Increased settlement causes densfication and strengthening. • Decreased temperature gradient McClung, D. and J. Schweizer 1996. Effects of snow temperatures on skier triggering of dry slab avalanches. International Snow Science Workshop, Banff, Alberta, Canada, 113-117.

  11. Conclusions • A classic non-persistent weak weak layer. It had healed by the time I did a crown face profile less than 24 hours later. • Climax is always a problem because it cannot be shot with the gun (blind or direct). Hand charging with surface shots and ski cutting are probably not always adequate control measures. • It is not possible to leave Climax closed and open the rest of the top. Opening the top easily doubles the amount of skiable terrain, so there is pressure to get it open. • Since this incident, we have been more conservative in opening the top and more proactive with shooting Climax, including hand charging during during storms and throwing hand charges from a gondola cabin to reach further down into the path.

More Related