NORTH EAST VIC: RECENT OBSERVATIONS
Updated: July 12th 2017
REPORT CONFIDENCE: STRONG
This just goes to show, how varied the conditions can be, From observations at Hotham and Falls, we had no indicator that Bogong was ready to let rip. Biggest triggered slide ever? Thanks to Matt O'Keefe, Falls Creek Ski Patrol Director, for the timely update. A real case of 'suck it and see' conditions observations. Good thing these guys knew what they were doing.
RECENT OBSERVATIONS
BOGONG AVALANCHE
Incident Report for Avalanche in Tombstone Gully on Mt Bogong on 10th of July 2017
Date: Monday 10th of July 2017
Time: Approx. 2pm
Overview A large, potentially deadly skier-triggered avalanche occurred near the top of Tombstone Gully on Mt Bogong at around 2pm on Monday 10th of July 2017. No one was caught in the avalanche or injured.
Details Location: Very top of Tombstone ski run, approx. 200m SE of Mt Bogong Summit. 36 o 44’ 5.49” S, 147o 18‘ 24.95“ E
Avalanche type: Hard slab
Avalanche size: R4 (large avalanche relative to path), D2 (could bury, injure or kill a person)
Trigger type: Skier
Slope: 45o, just below rollover from approx. 15o
Aspect: SE
Elevation: 1960m
Terrain: Above treeline, large gully
Crown height: 180cm
Avalanche width: 100m
Avalanche length: 500m
Bed surface: Melt freeze crust
Weak layer: Interface between wind slab and melt freeze crust. No facets, surface hoar or grapple observed
Weather conditions at time of avalanche: Overcast, lightly snowing, winds approx. 30 km/hr NW
Comments
We considered the hazard evaluation for the day as considerable on the lee aspects of slopes due to the wind and snowfall of the previous week. Our assessment of the possible avalanche problem that day was wind slabs.
This avalanche occurred on our third run for the day. The first two runs were in other gullies located SE of Mt Bogong’s summit.
On our third run, our first skier entered on the skier’s left of Tombstone Gully, a large SE facing gully, starting at a slope angle of approx. 15o and quickly rolling over to approx. 45o. The skier performed a ski cut heading towards the right side of the gully, and during this the avalanche broke approx. 5-10m above and to the skier’s right of him. The skier immediately noticed the avalanche and quickly turned and skied hard left to a safe area and stopped. The avalanche propagated right across the gully, and ran for approx. 500m in length and approx. 120m vertical, and stopped mid track before the gully opens up to its apron above Cairn Creek.
The avalanche started at a crown height of 30cm on skier’s left, then progressed to a crown height of 180cm and propagated for approx. 100m varying in crown height around to the skier’s right. It did not cross over into the next gully. The avalanche was a hard slab, possibly caused from the wind and precipitation over the last week often from a NW direction.
The bed surface was a melt-freeze layer approx. 15cm thick. There did not appear to be any faceting, grapple or surface hoar present at the interface of old and new snow. The slab density of the crown at 180cm in height was “four finger” hardness for 40cm, then “one finger” hardness for the remaining height of the crown.
Snowpack Assessments
The schedule for stability assessment reports will be Thursdays and Mondays. The locations chosen are purposefully 'wind loaded' so that the exaggerated results are easier to asses. Locations are on or above tree-line and generally South East aspect, although this is conditions dependent. These assessments are the average of multiple put tests to give you a more comprehensive view of the snowpack.
