22 July 2008

This article has two parts. First, it outlines the reported avalanche incidents across all of Japan for the 2007/08 season. Second, it focuses on the evolution of the Hakuba snowpack and details those incidents that occurred in Hakuba.

I am using avalanche incident data from the Japan Avalanche Network as the official source of data in Japan. I am a contributing member and attended their end of year meeting where the indecent summary was reviewed and discussed. Other incidents may have occurred yet remained un-reported.

The data and discussion on Hakuba’s snowpack and avalanche activity is based on my own weather station data, along with my own field observations and observations by guides in Hakuba recorded on the JAN public database.

PART 1: 2007/08 Avalanche Incidents in Japan

There were 15 reported avalanche incident in Japan from between 13 November 2007 and 12 April 2008. I do not have data available to compare to the previous season.

Of the 15 reported incidents:

41 people were caught in an avalanche
9 people sustained injury
15 people died.

It is likely that many more incidents where no injury or death occurred went unreported. I know of some slides that were only mentioned by those involved after the season had ended, particularly incidents that took place during mid-spring.

Mountaineers had a particularly bad year, starting with an unfortunate incident in Hokkaido in November. A senior JAN representative went to Hokkaido to investigate the incident. The high fatality ratio (12 caught, 2 injured, 4 dead) is in part due to the tight spacing between people as they moved through dangerous avalanche terrain.

The second large mountaineering incident happened on New Years Eve when a forecast storm hit the Kita Alps. In Hakuba we received close to 200cm of snow in the valley over 3 days. Further south a group of mountaineers were camping at altitude and died when an avalanche was naturally triggered during the night and struck their tents. The brief Steep Deep Japan report is here.

The Kita Alps season was quite active due to the large number of alpine participants across along a mountain range stretching for 80km. Hokkaido had a reasonably bad year due to one mountaineering incident mentioned above (12 caught, 2 injured, 4 dead). They also had Japan’s only reported snowmobile incident.

The large mountaineering incidents slightly skew the data towards November and December. In Japan backcountry skiing ‘season’ starts in March, so participation rapidly increases over spring, however with it comes relatively better stability. Repeating my above speculation, I believe many spring incidents go un-reported.

PART 2: Hakuba Focus - Weather and Avalanches

There are several very good areas in Japan for good quality backcountry touring, mostly around the Kita Alps. Of these locations, Hakuba has three key ingredients that make it Japan’s true alpine town

1. It has a wide variety of terrain with higher alpine allowing a very long backcountry season (generally Oct/Nov through until May/June).
2. It has a ski resort infrastructure offering access to the wider backcountry terrain and high peaks.
3. It has a permanent and relatively large year-round community of backcountry enthusiasts along with the highest concentration of commercial guiding operations.

Avalanche Incidents in Hakuba.

	Caught	Injured	Died
31 Jan 08	1	1	0
3 Feb 08	4	2	2
21 Feb 08	1	0	0
29 March 08	1	1	0
12 April 08	1	0	1
TOTAL	8	4	3

Comments:

31 Jan 08 - Mixed group including clients and a guide. Victim broke arm and was rescued within 5 minutes after a beacon search, probing and digging. The slide was triggered from above the victim by others in the group.

3 Feb 08 - Victims were inexperienced skiers being escorted by university ski instructors along a closed cat track that passes below high risk avalanche terrain. The slide was naturally triggered from above during an storm and a long period of instability. The skiers took the closed cat track to avoid more difficult terrain during the storm.

21 Feb 08 - Snowboarder (myself) triggered avalanche, partially buried, no rescue required.

29 March 08 - Skier triggered slide during popular 'spring touring' season in a very busy area.

12 April 08 - Skier triggered wet snow avalanche.

In addition to the above I am aware of three other unreported skier/snowboarder triggered avalanche incidents in Hakuba where a person was caught in a slide but no rescue was required nor did the incidents result in injury or death.

Hakuba Weather and Avalanche discussion

I commenced touring and collecting snowpack and weather data in November 2007. A catalogue of my activities and observations are available on this website and the JAN website. These data form the basis for the following season summary.

• Daily field weather and snowpack observations and commentary
• Daily tabulated weather station data and charts
• Snow profile/pit data (I discontinued publishing data as I felt that reporting on different pits across different locations was f no value to those who visited Steep Deep Japan for useful info. Next season I will maintain a permanent profile site and publish weekly data from there, providing a much more valuable temporal picture for a static location)
• Steep Deep Japan reports on observed avalanche activity
• Steep Deep Japan reports on some reported avalanche incidents in the Kita Alps.
• Japan Avalanche Network database. Almost daily reports on snow stability and weather from local guides and other regular backcountry travellers in the Hakuba area such as myself. My English contributions can be found by Ctrl-F to find my name (Damian).

The following charts are based on data that I collected from my weather study plot each morning at 7am. The plot is situated at 860m above sea level near Goryu ski resort in Hakuba.

I have chosen to truncate the data in May as this provides the most useful subset for most backcountry users in Hakuba. Note that early and late season snow depth data is of limited value due to the low altitude of the study plot.  All measurements are metric.

November-December

Snow fell in Hakuba Valley from 21 November 2007 until 8 March 2008. The accumulation season struggled to get going with a few storms and subsequent melts up until mid December, with the first good storm arriving just before Christmas (178cm in 12 days). This was quickly followed by the only really big stork of the season over new years (227cm in 6 days, starting with a brief rain event). This was when 4 mountaineers died in their tents in the southern Kita Alps, 70km from Hakuba. Low altitude temperatures in Hakuba over the November and December period failed to remain below freezing for any 48-hour period. Higher altitudes developed some near-ground freeze thaw crusts that were quickly buried by the end of December.

Observed stability during the months of November December was reasonable with ‘right-way-up’ storms bonding well with the early season rain crusts. By the end of December nearly 300cm had fallen at 860m with almost remaining 200cm on the ground. Snow density at 860m was typically in the range of 60-80kg/m3, with some storms placing very dense snow – almost 100kg/m2.

January

January was slow in terms of snowfall but field observation of the snowpack supported the general consensus that higher alpine was accessible and stable for periods of up to a week, though very few people were hitting it. Early January in particular saw a decrease in snowfall and snow depth, with a reduction of almost 90cm in snow depth due to melting and settling in the valley after the new year storm, after which only 114cm of snow fell for the remainder of the month at 860m. Early to mid January was warm with a period of foen-like winds in the valley. By mid-January the entire north face of Happo was a hard icy area best avoided.

Some naturally triggered windslab avalanches of around size 2 were observed during the middle of the month when strong westerly winds accompanied 12cm of new overnight snow after a prolonged period of relatively mild and sunny weather, crust formation and snowpack bonding. This suddenly cold and windy new snow fell after a brief period of rain to 1600m. During my field trips I found that the rain had broken down some extensive windslab, however had in place left a rain crust that become windloaded in the following days.

Norikura Dake

Unlike the first half of January, the second half brought with it much more poor weather yet no significant snowfall. In terms of lowest daily highs, the second half of January was the coldest all winter with most days remaining below freezing in the valley. Snow density started to fall (42kg/m3 or 4.6% water) and temperatures remained colder for longer periods. Stability in the top 40cm of snowpack started to deteriorate and the rare mid-winter high alpine touring window closed. Despite the moderate snowfalls, we were turning back from lines at 1700m due to a near surface instability.

With the colder temperatures I started looking for faceting around the previous crusts, here is what I wrote at the time:

Besides the top 40cm of pack, the pack was rock solid, in fact I broke my shovel digging pits during late January.  Both rain crusts are visible in this profile chart (29 Dec and 11 Jan). Note the hardness below 30cm.

By the end of January, cumulative snowfall at 860m was only 585cm. With much vaunted and unofficial average snowfalls of 1100cm, Hakuba still had half to go with only one month of real winter remaining.

The end of January saw a day and night of clear weather after which I found protected pockets of surface hoar. At the 1600 – 1900m mark the occasional storm was depositing between 20 and 30cm of new snow on top of the crusts and in places, surface hoar on crust. New snowfall and wind deposited snow was bonding poorly with the crusts from early January and within the new snowfall we were seeing layers of very light low density stellars causing denser new snow in the storm to slide easily. Here is what I wrote at the time (30 Jan 08). Conditions were becoming very poor:

Unfortunately Hakuba had its first very close call the very next day with the quick and successful rescue of a serious burial at about 1400m on the south side of the Goryu area on 31 Jan 08. The victim sustained a broken arm and could very easily have died.

February

Late January set a pretty poor stage for February and for the most, conditions did not improve. The coldest recorded temperatures for the season were in Feb with –10C in the valley being breached several times. Snowfall was light but consistent, seemingly snowing every 12 hours at times. Snow density was not particularly light (80kg/m3, or around 8-9% water). The lightest (3.2%) and heaviest (11.6%) snowfalls of the winter were recorded in the first half of February. Frequency and depth of new storm snow started out low but reached a crescendo in late February, as did the cumulative snow depth at 860m. By month end Hakuba Valley at 860m had 886cm of cumulative snowfall and 250cm on the ground.

For backcountry travel, February was not very safe nor satisfying. The visibility was consistently poor with 19 mornings having more than 50% cloud cover. And of all my observations, I recorded only 5 bluebird days. This bad weather didn’t bring any massive dumps, just consistent top-up of fresh snow of 20-40cm every 48 ours by the end of the month.

Unfortunately, this regular snowfall was not accompanied by reliable stability. After a very unstable end of January, February started with a terrible accident at Tsugaike Ski Resort where 2 inbounds skiers were killed and two injured as they tried to make their way down the hill in a heavy storm, taking a closed cat track that travels below serious avalanche terrain. Besides the instability set-up already discusses during the end of Jan, some very low density snow (3.2% water content) fell during a storm overnight on 2 Feb, followed by denser snow during the day on the 3rd. We were in the back country on a north aspect at 1600m a few km away from the Tsugaike incident and during that afternoon as the storm intensified we began to easily cut size 1 slides and not long after we were having frequent size 1 naturally slides coming down around us. Stability that afternoon had clearly deteriorated and we left the area very quickly. Run closures at nearby Tsugaike Ski Resort were possibly in response to a similar observation of deteriorating conditions. Unfortunately it was not enough to avoid the deaths of two inexperienced young female skiers who probably knew absolutely nothing about avalanches, and why should they? They were at a ski resort and this accident should never have happened.

Further south in Hakuba Valley, snowpack observations on NE facing steep terrain at 1900m around the Goryu area (Kotomiyama and Tenguyama) revealed extensive faceting with depth hoar up to 4mm found in beds 30cm thick. This faceting remained a problem for us well into March. Strangely, I was unable to find the same extensive faceting on similar aspects and altitudes just 10km up the valley in the Tsugaike area. The recent spate of accidents and my own observed instability and some close calls led us to reduce our risk threshold and also put a stop to a lot of touring, thus adding to anxiousness to get back amongst it as the month progressed.

Shooting cracks propagating into size 1 and 2 slides were very common in February.

The period around the 8-12 Feb saw a few high wind days with shooting cracks and easy ski cuts in various locations around the valley. Resorts lifts were periodically being shut due to high wind. Some areas were producing easy compression test results. Feb 13 saw a classic Fuyugata weather event that brings so much deep powder to Hakuba and the Japanese Alps. The storm started out warm and that aided bonding, but windslab was common.

Frequent snowfalls of varying density continued for the middle week of Feb accompanied by breaks in the weather and an unexpected short period of stability. We started to ski some of the more steep and serious middle altitude lines in the valley, with long descents of up to 45-50 degrees being notched up without a single hint of snowpack instability.

Possibly through frustration at being restricted in our touring for 3 weeks followed by a sudden burst of confidence building stability, we ignored the warning signs and set out on a tiring tour in the Obinatayama area, after having already cancelled that morning’s departure on an overnight tour, with much disappointment. The previous day snowfall was very wet and dense at low altitude and some higher lifts had been shut due to winds. We toured to 1900m and found pockets of hard windslab on north aspects due to variable cross-loading. At 1600m I triggered a size 2 slide that carried me for 300m but left me only partially buried and uninjured. We should not have been touring that day and this lucky escape stands as a valuable lesson and a classic example of group dynamics and the physiological factors leading to avalanche incidents/injury/death.

By the end of February we were finding extensive facets in on steep north facing areas near Goryu, windslab on most aspects and near Tsugaike a notably inverted snowpack with a 30cm thick soft layer buried under 60cm of progressively harder pack. An example of the snowpack and stability tests can be found here in English on JAN’s website.

February closed with a few clear and sunny days along with crust formation and some evidence of settlement and bonding. Valley temperatures started to approach 10C during the high of the day.

March

After Feb, March opened with a storm, the second last for the season. In total, 89cm of snow fell over March at 860m, with the second storm coming at the very end of the month. In early March there were reports of slier triggered inbounds avalanche at Hakuba 47 that hit a cat track. The general consensus was that this was almost a non-event, however resort management made a huge fuss about it and leveraged the incident to the fullest extent to avert people form breaking resort rules and skiing off-piste. Some long slide paths were also observed originating in the high alpine, likely due to loose snow sluffing on rocky solar aspects.

On March 3 Hakuba received a dose of Kousa snow, or snow containing yellow dust from a desert in China. It fell wet and heavy at all altitudes and consequently absorbed solar radiation causing new snow above to be warmed. By 9 March another 40cm of cold powder had fallen on the crust layer formed by the Chinese dust. Fortunately it bonded well and some good steeper north aspect riding was possible at tree-line. The Alpine was still variable with obvious windloading on top of the previous dark dusty crust layer.

Mid March saw the instant onset of spring with valley temperatures reaching 15C and remaining consistently above freezing. This resulted in a few natural cornice triggered slides of size 2 and 3 in the alpine, with instability on solar aspects where skiers were frequently triggering single point slides. After a difficult February, March was very disappointing and offered poor touring except for a few isolated periods. Snow pack in the valley at below tree line began to melt rapidly with very no corn cycle to speak of below 1600m

The very end of March was given over to a brief and season closing storm that delivered 25cm of snow at 860m and unstable conditions in the Alpine after so much warm weather and sun crust formation. As the March madness of ‘spring touring season’ continued, so did the near-miss skier avalanches. The worst reported incident in Hakuba came from Norikura Dake on 29 March when a skier was injured after being caught and a slide. I am surprised that there were not more injuries.

April-May

April was excellent in terms of a reliable corn cycle having set up good riding in the alpine. The weather was good and temperatures only a problem on sunny days after 10am below rocky and steep slopes. After a cooler start to the month temperatures reached 25C in the valley and unfortunately this coincided with the busy holiday period resulting in a late season avalanche death on Jiitake just a little south of Hakuba, a popular and rewarding spring touring venue. A well known ski mountaineer and risk taker also died when he fell 200m on Goryu Dake on 23 April.

It snowed a few times in May with 20-30cm of fresh heavy snow at 2700m on 15 May. Touring was generally good, although high temperatures required good timing with cold spells along with early starts. A complete lack of partners meant that I was forced to put aside several riskier itineraries.

The End!

If you read this far then you must care about backcountry touring and avalanche safety in Japan, and specifically around Hakuba in the Japanese Alps. As is my habit, I would like to again promote the free and public information services made available by the Japanese Avalanche Network. Over the 07/08 season JAN members (all trained to the Canadian Avalanche Association Level 1 standard) contributed 419 snowpack and weather observations across Japan. In Hakuba alone guides and regular practitioners such as myself contributed 219 daily observations. In most other countries, professional level field data such as this is not available to the public. This is a valuable and unique resource being developed for the Japanese backcountry community. If you are not using it on a daily basis then you are missing out on important decision making data. Their website: www.nadare-net.jp/

Please contact me if you need assistance in using the JAN website, which besides my field contributions, is understandably all in Japanese.

Damian

steepdeepjapan.com