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AVALANCHE ACTIVITY AND AVALANCHE RISK IN THE ZAILIYSKIY ALATAU RANGE (KAZAKHSTAN)
Viktor Blagovechshenskiy1, Alexander Egorov1, Alexander Kokarev1
The purpose of the investigation is to study main features of avalanche danger and to estimate avalanche risk in the Zailiyskiy Alatau range. Snow avalanches are the most widespread natural hazard in Kazakhstan’s mountains. The territories where avalanche sites amounts more then 0.1 % of the area are considered the avalanche dangerous territories. The total area of these territories is 110 000 km2 in Kazakhstan. The Zailiyskiy Alatau range is one of the most dangerous regions. Avalanches here caught 107 persons from 1951 to 2006. Sixty two persons were killed. In some years, the number of victims amounted 10 people. More than 90
% of victims were tourists and skiers. Avalanches triggered by themselves or their fellow- travels caught about 80 % of victims.
The Zailiyskiy Alatau range concerns to the Northern Tien Shan Mountains. It stretches for 150 km lengthways 43 °N from 76 up to 78 °E. The foothills lay at the 1000 m a.s.l., the altitudes of ridges makes 4000 – 4200. The highest peak Talgar rises up to 4978 m. In the Zailiyskiy Alatau range avalanches usually occur on slopes steeper than 30 °, when the snow height exceeds 70 cm. The lower border of an avalanche dangerous zone passes at the altitude of 1500 m. The maximal avalanche activity is marked in the middle mountain zone: from 2000 up to 3000 m a.s.l. In this zone the height of avalanche sites reaches 1000 m and avalanche starting areas make up to 50 ha. The snow cover height reaches here 200 cm. The winter snowfall sum makes up to 400 mm of the water equivalent. The daily snowfall may reach 70 cm. The maximum of snowfalls occurs in March and April. The avalanching period lasts from December till April. Dry avalanches connected with snowfalls prevail in December and February. When the snow cover height is more than 70 cm 10 cm of new snow is enough to avalanche formation. Dry avalanches prevail in the total avalanche number. The volume of dry avalanches rare exceeds 10 000 m3. Wet avalanches usually fall down in March and April. The main reason of wet avalanches is heavy thaws when maximal day temperatures exceed 15 °C. Wet avalanches prevail in size. The volume on wet avalanches reaches 360 000 m3 and the total wet avalanche volume makes 60 % from annual sum of avalanche volumes.
Avalanche activity varies very strongly in space and time. It depends on snowiness of the year and snow cover distribution on slopes with different aspects. The snow water equivalent at northern slopes exceeds 250 mm In heavy snow year. There are more than 30 days with avalanches in such years. The avalanche volumes exceed 100 000 m3. The snow water equivalent makes less than 100 mm in low snow years. The number of days with avalanches reduced up to 1 – 3 and the maximal avalanche volume – up to 10 000 m3. The years with high avalanche activity repeat on the average one time in 10 years. Such years were 1966, 1975, 1987, 1993, and 2003. In separate avalanche sites avalanche activity varies according to an avalanche starting zone aspect. The total avalanche volume on northern slopes makes 77
%, on eastern and western slopes – 21 % and on southern slopes – only 2 % of the sum of all avalanche volumes.
1 Institute of Geography, Pushkin Str. 99, 050010 Almaty, Kazakhstan (Tel.: 007-727-2911625; Fax: 007-727- 2918102; email: ingeo@mail.kz)
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The individual avalanche risk R can be determined as a death probability for a person constantly staying in winter period on an avalanche dangerous territory. In the Zailiyskiy Alatau range the most typical tourist activity is backcountry skiing. Therefore, we calculated the individual avalanche risk for skiers. It can be calculated as the shear of the average number of avalanche fatalities Nk to the daily number of skiers being on the given territory in winter period Ns: R = Nk ⁄ Ns. The number of skiers killed by avalanches in winter can be estimated using formula:
Nk = Ns · Pa · Pf · Pd,
where: Pf – probability of avalanche formation on avalanche dangerous slopes, Pd - probability of death of skier caught by avalanche. The factor Pa is calculated as the shear of the total area of avalanche dangerous slopes Sa to the area of the territory S: Pa = Sa ⁄S.
Factor Pf can be estimated as the average shear of the years with avalanches Ta to the number of years under investigation T: Pf = Ta ⁄T. Factor Pd is equal to the shear of the number of killed skiers nk to the number of skiers caught by avalanches n: Pd = nk ⁄ n. Using this formula the individual avalanche risk can be written as R = Pa · Pf · Pd. In this case we can estimate R using data on avalanche dangerous area characteristics.
In the Zailiyskiy Alatau range according to data of the long-term investigation of avalanche activity, factor Pa is equal to 0.7, factor Pf = 0.6, and factor Pd = 0.6. Therefore the individual avalanche risk R = 0.25. This value of R characterizes the most dangerous middle mountain zone. In zones, where the coefficient of avalanche hazard or the avalanche frequency is less, the individual avalanche risk is accordingly less. In the low mountain zone R = 0.01, in the high mountain zone R = 0.1. The calculated risk shows the death probability in case when people neglect avalanche danger and there are no protection measures. The avalanche risk can be reduced by avalanche hazard estimation and forecast, avalanche artificial releases and avalanche protection structures. An avalanche warning reduces risk from 25 % to 0.5 %.
Artificial avalanche releases allow eliminating risk to 0.05 %. In the Zailiyskiy Alatau range the real avalanche risk makes 1 death on 1000 skiers per year. It exceeds the acceptable risk for no inhabitant areas in 10 times.
Keywords: avalanche, risk management, skiing tourism
