Vancouver Island Avalanche Bulletin

Summary:

Large natural avalanche (likely about size 3) on NW through W aspect in the Able Bowl in the Mount Cain area on Friday 18 March, 2011. No humans involved.

Details:

A large avalanche of note occurred in the Mount Cain area on Friday 18 March with details having come in only Tuesday 22 March, 2011. The slide took place some time in the afternoon on that day with an estimated 700-900m wide fracture line that spanned from NW through to W aspects in the Able Bowl below the true and false summits of Mount Able. The fracture line was about 200m below ridge line and was estimated to be between one metre and four metres in height. The avalanche ran the full path to fill the bottom of the bowl with deep debris and almost spilled over into the main east bowl drainage below the east bowl. One local described it as the largest avalanche he had seen in the Cain area in twenty years of skiing the area. The cornice above the slope was said by a number of observers to remain in tact meaning a cornice trigger was not the cause. Wind loading which had been happening for many days previously and continued on Friday is the probable trigger. The failure may have been wind loaded snow on the previous surface, or the failure may have been on our February crust layer deeper down. Further investigation is required.

This avalanche bulletin had the hazard in the alpine at CONSIDERABLE on that day. The part of the definition of this hazard rating under the "Likelihood of Avalanches" heading is that "natural avalanches are possible and human triggered avalanches are likely". This incident is a very good illustration of why it is so important to also make careful note of the "Avalanche Size and Distribution" descriptors in the Avalanche Danger Scale.  At a CONSIDERABLE rating this definition reads "small avalanches in many areas or large avalanches in specific areas or very large avalanches in isolated areas". Clearly there was a very large avalanche in an isolated area on this day. I mention this because it is important for users of the bulletin to recognise that even when hazard is dropping because natural avalanches are less likely and larger triggers may be required to start avalanches, large avalanches are still possible. It is important to read and understand all of the aspects of the hazard definitions (Likelihood of avalanches as well as size and distribution) and to read all of the details in the text of the avalanche bulletin and to apply them correctly to the terrain. We must not become complacent as hazard ratings drop.

It is also interesting to note that this forecaster departed from the Mount Cain area on that day likely within hours of the event, with a feeling of trepidation for what might happen at the mountain that week end. The wind had been blowing hard for most of the previous five days and slabs were fat and well primed for triggering while the wind continued to load. Additionally the wind was forecast to drop with a possibility for improvement in the weather and a big group of spring break skiers was arriving. This is the stuff that we forecasters can lose sleep over!

Reported by VIACS forecaster Jan Neuspiel with information from Cain local Cyril Douglas and observer Jim Stepan. Photos and further details to follow.

Skier triggered slab in the north bowl at Mount Cain.

The slab pulled out on a NNE aspect at about 1600m when the skier was two or three turns into skiing the line. The skier narrowly missed being swept over cliffs and lost equipment which was later recovered. There were no injuries or burials though the skier went for a fairly long ride. The slab was approximately 15-20m wide and perhaps about 30-50cm deep. It ran for about 200m. This avalanche bulletin had the hazard at moderate in the alpine and tree line for that day with a caution about triggerable wind slab. Photographs to follow.

Saturday 27 November, 14:00hrs. Skier triggered avalanche West Bowl Mount Cain, 1500m (tree line), West aspect, size 2.

A group of three skiers in the "Door Number Three" feature in the west bowl of Mount Cain were involved in a size two avalanche which resulted in one injured person and a lost ski.

The avalanche was triggered by a single skier high in the start zone, about 10 metres below ridge line in a soft slab on an unsupported feature. The fracture line was approximately 40 meters wide with a depth of 70 to 130cm. It is speculated that the slab was the result of both cross loading from North winds during our recent cold/clear spell and more recent storm winds. As the avalanche ran down the path a "step down" fracture occurred on a deteriorating crust which sits below all of our new snow since 17 November. This crust became soft and somewhat faceted during our cold, clear spell. The avalanche scoured out snow nearly to ground as it proceeded down the path.

The person triggering the avalanche rode with it the full length of the avalanche path (approximately 400m) hitting small trees as he went. The result was some bad bruising and ligament damage to the victim. The two other skiers were situated on a prominence to the skiers left of the path a short distance below the start zone. One of the two was torn from his stance by moving snow and rode for about 5 to 10 meters before grabbing a tree to stop. This person lost a ski. The other person stayed in their position.

Snowmobilers triggered a size 2 wind slab at 1800 m SE aspect on Jutland Mountain in Strathcona Provincial Park. The Wind slab was 1 meter deep and reported to be 50 meters wide. One machiner was decending onto the slab while a second was climbing up it when it released. The climber mangaged to climb through and on top of it while the descender escaped to the side. No injuries or burial were reported. The avalanche was formed by strong Northerly winds that redistributed cold Northerly and faceted snow into South and South East Aspects.  The slab was quite hard. I measured a slab in a safe place on Mt washington on the same day and it was 35% water content or 350 kilograms per cubic meter. The bed surface would likley have been a pencil hard crust. This was reported to me second hand by cell phone from the site to one of my students and the names and other information were withheld. Submitted by Niko Weis