Wednesday, January 1, 2014

Forsnesvannetrenne Avalanche- mistakes made and lessons learnt

Today’s planned itinerary was a ski tour with Bjarte from Narvik up to 3de Toppen, and then a short descent around the cliff bands before skinning up to the “ramp” and descending down to  Forsnesvannet. From here we would skin up the usual Forsnesvannetrenne before continuing to the summit of Beisfjordtøtta and descending the same way we had come up.

We triggered a moderate sized soft slab while ascending Forsnesvatnrenne and were both taken for a terrifying ride of 200 vertical metres before coming to a stop as a partial burial.

I’m writing this down for myself really, as a learning tool so that I can analyse my decision making process and better understand what mistakes were made.

The planned route for the day

Decision making process before and during the tour

Yesterday (30.12) the mountains around Narvik received around 10cm of low density snow, which fell under relatively calm conditions and was distributed quite evenly over all aspects. At elevations lower than 800 metres the underlying snow was dominated by a rain crust from a mild spell around Dec 27. At higher elevations the underlying snow was primarily wind eroded snow, with isolated pockets of windslab prevalent in sheltered areas.

With no major snow fall in the past two weeks and relatively mild temperatures which have promoted a strengthening of the snowpack, avalanche instability is generally quite good at the moment. There hadn’t been any observed avalanche action in the Narvik region for 10 days. The 10cm of snow which had fallen on Monday did not constitute a significant danger in itself: it was a small snow event of dry snow with a low water equivalent. The avalanche forecast for the day called for a rating of 1, the first day of such a low rating since forecasting began one month ago. The primary avalanche problem on the forecast was for dry slabs above 400 metres on West through North aspects, with the anticipated weak layer being the interface between the old rain crust and wind drifted snow.

Sometime during the evening/ night the wind picked up such that by 10am there was a strong breeze from the SW quarter.

I met up with Bjarte at the base of the ski area, it was the first time we’d been on a ski tour with each other, but we knew each other from frequent encounters on Narvikfjellet where we both regularly do some skimo training. During the skin up to 3de Toppen I was surprised to note that the new snow was still quite evenly distributed around Linken and 2de Toppen. At this elevation of 1000 to 1200 metres the average depth of the new snow was 10cm.

Skinning past Skaret in the early morning twilight

Surface conditions at Linken

Skinning along the ridge between 2de Toppen and 3de Toppen

From the summit of 3de Toppen we skied in a WSW direction for 300 vertical metres to wrap around the cliff bands which mark the start of the Partisanleden. The skiing was superb, with this even distribution of “right side up“ snow perfectly smoothing out all irregularities of the old snow surface. In terms of snow stability it seemed that this aspect was very safe. Ski cuts on steeper roll overs gave no results and no signs of instability were noted.

Skiing the SW facing slopes from 3de Toppen: even distribution of 10cm new snow

We skinned up to the entrance to the “Ramp” a steepish ski line (around 40⁰ in the upper section) which descends 500 vertical metres in a NNE direction to Forsnesvannet at 640m. The closer we got to the ridge the stronger the wind was, coming from the SW at an estimated speed of around 15m/s. I was concerned about windloading on the NE slope which we intended to ski. On closer inspection I saw that the wind drifting was only an issue on the upper few metres, below that the snow surface seemed mainly wind eroded and therefore safer. Some tentative stomping on the rollover cleared the wind drift and I was able to ski the upper section of the Ramp which was mainly wind eroded. Further down there were a few isolated pockets of wind slab which were quite sensitive. A few small, soft slabs (about 5-10 metres wide) released as I was skiing down, but didn’t entrain any further snow. We used safety islands below rock outcrops on the skiers left of the slope to avoid exposure from any snow which the other might release. Once down lower on the slope where the angle was mellow the skiing was great, with about 15cm of evenly distributed fresh snow.

At the top of the "Ramp" with strong winds from the SW building cornices to the lee NE

When we reached Forsnesvannet we discussed the instabilities we had found on the “Ramp”. With the predominant wind direction being from the SW and the small pockets which released on NE aspects I deemed the primary avalanche problem to be isolated pockets of wind slab on North through East aspects, with small avalanches releasing within the newly wind transported snow. Going off the even distribution of snow on West through South aspects which we had encountered on the descent from 3de Toppen I made the decision that the Forsnesvatnetrenne which faces West was relatively safe.

Bjarte descending the "Ramp"

On the lower part of the ascent we encountered a few isolated areas of exposed crust where the wind had stripped the new snow away, but mainly the snow surface was soft, with about 10cm of ski penetration into the new snow. As we gained altitude and entered the gully itself the snow remained soft. As I skinned upwards I noticed that a few isolated sections had a density inversion within the new snow, about 10cm of slightly denser snow on top of approximately 20cm of lighter density. I was concerned about the weak interface between these layers in the wind drifted snow, but these areas of “upside down” snow were isolated and not particularly large. At an altitude of 1000 metres a section of more wind buffed snow with only 1cm of ski penetration made me stop and question aloud whether it would be better to switch over to bootpacking. But up higher the snow looked softer. Bjarte took over the lead and continued breaking trail upwards on skins.

At 12.30pm, when we were at an altitude of 1100metres, Bjarte was about 10 vertical metres above me and 10 metres off to the skinner’s left. I heard a sound which made me look up and I immediately noticed an avalanche had released about 40 metres directly above me and off to the skinners right. My initial instinct was to scream to Bjarte that an avalanche had released, I was halfway through doing so when I looked over and saw that he was already engulfed in a wave of snow. I immediately tried to point my skis downhill and across the fall line in an attempt to ski off to the side of the path. This effort was totally futile as within a second I was myself overrun by the avalanche. The swimming instinct came automatically but gave little result as I tumbled downhill in the snow, completely out of control. After a few seconds I surfaced temporarily, gulped some air and glanced Bjarte a few metres above me. I called out to him and he called back to me. I continued trying to fight the force of the avalanche and attempted to self-arrest, this slowed me down and Bjarte came crashing in to me. Bjarte called out in pain as he crashed in to me, and I inexplicably appologised for the collision. The final period of the slide was marginally more controlled: with my feet facing downhill and my head above the snow I was able to “swim” and maintain this position and realized that a complete burial was not very likely. We came to a stop at an altitude of 900 metres, having been taken by the avalanche 200 vertical metres over what I estimate to have taken about 20-30 seconds. When we stopped both of us were only partially buried up to our thighs in snow that was very soft and still unconsolidated, so it was easy to dig ourselves out. I was about 30 metres uphill from Bjarte. We called out to each other and asked each other if we were injured. Bjarte was uninjured, whilst I had a mildly sprained ankle, with the adrenaline coursing through my veins I didn’t think that my ankle was particularly badly injured though, and I knew that I’d be able to ski out.

Photo taken minutes after the slide, from 900 metres looking up the path.

After a quick bear hug we took stock of our gear. We had both lost one ski each, Bjarte still had one of his ski poles and one of mine had come to a stop just beside him, whilst Bjarte’s other pole had come to rest just beside me. Given that the avalanche had already cleared the slide path and without significant hazard from hangfire above we decided to hike up the debris to try to find our lost skis. We found Bjarte’s ski 20 metres above where I had stopped, and continued up to 1100 masl. without finding any trace of mine. As we were walking back down through the debris I stepped on my completely buried ski by chance. By this stage my ankle was significantly more painful, but still weight bearing. We put our skis on and began skiing back to Narvik via Forsnesvatnet and the usual summer hiking trail.

Mistakes made. Lessons learnt

  •   Effect of localised wind patterns: The predominant SW winds which I had noted throughout the tour blinded me to the fact that the winds in these mountains are obviously highly localized, and wind loading is possible on the same aspects which are not wind affected on neighbouring mountains. In this case the wind loading in the upper extremity of the gully was not so obvious lower down, but I should have taken more note of the what the predominant wind direction had been in the period leading up to the tour, and shown more caution before exposing myself on a slide path which is prone to rapid wind loading from localised wind patterns.

  •  Human factor: A false sense of security on account of familiarity with the terrain. This particular route is one which I follow multiple times each winter, and this familiarity along with all the positive reinforcement inherent in having traveled over a slope in more stable conditions resulted in my having a somewhat blinkered view.

  • Human factor: I was making constant observations of the weather and snow conditions on the outing, and taking note of them in a log book to submit to the avalanche forecasting program. But I was simultaneously concerned with moving quickly and efficiently through the mountains in order to complete the tour in daylight hours. We were both on light weight randonee skis and both share a common passion of “light and fast” travel through the mountains. This has been my standard approach to backcountry skiing for the past few years, and I have always rationalized that covering more terrain on any given outing gives me more feedback about snow and weather conditions across a variety of altitudes and aspects. Indeed I believe that travelling faster and over a larger area means that I get much more clues about potential instabilities than anyone of the “heavy and slow” breed of backcountry skiers who typically make only a single ascent/ descent on a tour. As I sit here now however part of me cannot help but question how much this focus on speed and efficiency might have caused me to neglect a more thorough investigation of the snowpack. To a mild degree I would admit to being a little rushed (in the same way that I am always a little “rushed”, preferring to either be moving, digging a pit or taking notes in my logbook than simply standing around). I guess this human error could be considered a variation of the so called “Lion Syndrome”: a rush for first tracks or summit fever.

  •  Over estimating my ability to deal with the avalanche problem of the day. Having made my observations of recent and current wind loading on a particular aspect and seen small slabs release on that same aspect, I felt that I had successfully nailed my analysis of what were the most dangerous slopes for the day. I was, in a word, over-confident about my cognitive ability in regards to the instabilities of the day.

The entire experience was really a blessing and a curse- a terrifying but necessary reminder for me to practice more humility in the mountains.

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