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NATURAL HAZARDS IN THE ZAILIYSKIY ALATAU RANGE (KAZAKHSTAN)
Viktor Blagovechshenskiy1, Tatyana Kirenskaya1, Akhmetkal Medeu1
The paper is devoted to the results of the long-term investigations of snow avalanches, mudflows, landslides, and rockfalls in the Zailiyskiy Alatau ridge.
The Zailiyskiy Alatau range stretches for 150 km lengthways 43 °N from 76 up to 78 °E. The bottom of the ridge lays at the altitude of 1000 m a.s.l. The altitude of watersheds makes 4000 – 4200 m a.s.l. The highest peak - Talgar rises 4978 m. The most dangerous natural hazards in the Zailiyskiy Alatau are the following: snow avalanches, mudflows, landslides, and rockfalls.
Each of these dangerous processes has the typical values of volume, frequency, and spreading (Tab. 1).
Tab. 1: Typical parameters of dangerous processes
Dangerous process Volume, m3 Frequency, 1/year Spreading, % of hit area
Snow avalanches 102-105 > 1 > 50
Mudflows 103-106 0.1-0.01 10-30
Landslides 103-106 0.1-0.01 10-30
Rockfalls 104-108 0.01-0.001 5-20
Snow avalanches have the highest frequency and spreading. There are three main types of avalanches: the avalanches caused by snowfalls; the avalanches caused by thaws; and the mixed avalanches caused by precipitation and thaws simultaneously. A portion of the avalanches caused by snowfalls is equal to 51 % from the total number of avalanches. The share of the mixed avalanches makes 28 %. The mixed avalanches have the greatest destructive force. Their volumes rises 350 thousand m3, and the path length amounts to 3.5 km. Snowfall avalanches are usually dry. Thaw and mixed avalanches are always wet. Dry avalanches prevail in number. Wet avalanches prevail in size. Winters with big avalanches occur one time in 10 years. They were in 1966, 1975, 1987, 1993, and 2003.
The maximum of avalanche activity is fixed in a middle mountain zone at height of 2000 up to 3000 m a.s.l. Avalanches fall down up here to 5 times in a year, and the total area of avalanche sites makes 0.5-0.8 from the area of the territory. The average volume of avalanches is 10-20 thousand m3. The volume of the maximal avalanches exceeds 100 thousand m3.
More than 450 mudflow events have been registered in the Zailiyskiy Alatau from 1841 to 2006. The most destructive mudflows are formed in basins with modern glaciers, moraine and dammed lakes. In these basins big mudflows of more than 1 million m3 in volume occur on average 1 times in 50 years. The maximal mudflow discharges amount to 10000 m3/s. Such mudflows pass from tops of basins at 3000-3200 m a.s.l. to bottoms of mountains at height of
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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1000 m a.s.l. The travel distance can reach 20-25 km. Mudflows demolish the settlements located on proluvial fans. The most destructive mudflows were observed in the Zailiyskiy Alatau in 1841, 1921, 1963, 1973, 1977, and 1993.
Heavy rains are the main reason for the mudflow formation. The daily sum of precipitation of 40 mm needs usually to the mudflow formation. Rain mudflows make 87 % of total mudflow number. Outbursts of glacial lakes are the second reason of destructive mudflows. The number of glacial mudflows is 11 %. The greatest number of mudflows occurs in May (40 %) and July (36 %). 22 % of mudflows are observed and 2 % - in August.
In the Zailiyskiy Alatau landslides coincide of space with loess and clay grounds in low- and middle mountain zones. Especially large landslides occur during strong earthquakes. Volumes of such landslides can reach several millions m3. Landslides formed by overwetted ground may transform into mudflows. In the spring of 1887 the strong earthquake and heavy rains caused a lot of very big landslides with the total volume more than 200 million m3. Mass of landslide events happened in a low mountain zone of the Zailiyskiy Alatau in the spring of 2004 because of continuous rains. In total, it has been marked more than 100 landslides with volumes up to 100 thousand m3. The number of victims was 31 people.
Rockfalls are the vastest hazardous phenomena. Fortunately, they occur very rare. They are formed in rocky grounds during strong earthquakes only. Rockfalls are marked, as a rule, at tectonic faults in territories with deep valleys. About 20 large rockfalls with volumes up to 200 million m3 were observed in a middle mountain zone of the Zailiyskiy Alatau. The age of these rockfalls is up to 4 000 years. The most resent big rockfalls have taken place during earthquakes in 1887 and 1911.
Keywords: natural hazards, avalanche, mudflow, rockfall, landslide, long-term investigation
