ВІСНИК ЛЬВІВ. УН-ТУ
Серія географічна. 2004. Вип. 31. С. 380–385
VISNYK LVIV UNIV
Ser.Geogr. 2004. №31. Р. 380–385
УДК 551.4
STUDY OF DEBRIS FLOW AND AVALANCHE GEOSYSTEMS OF THE
HIGH MOUNTAIN REGIONS OF THE CENTRAL CAUCASUS
M. Petrushina
Geographical Faculty, Moscow State University,
Vorobjevy Hory, 119992 Moscow, Russia
The structure and dynamics of debris flow and avalanche geosystems, as а specific
vector systems, formed by the lateral flows were studied. Field long-term landscapes
mapping, comparative studies and monitoring, phytoindication and lichenometry were
used. The information of historical maps, maps of forest valuation, repeated air and
theodolite photographs were also taken into account. Some landscape maps as well as maps
of landscape dynamics under the impact of debris flows and avalanches were compiled.
The stop-on zones of debris flows and avalanches with large-scale disturbance, occupied
more than 50% of the bottoms of the valleys, were of a particular interest. Two main types
of debris flows cones with dividing into several subtypes were separated due to the features
of landscape structure and its dynamics. A series of microlandscapes indicating the
frequency and duration of avalanches were revealed in the places of prolonged avalanche
activity. The intensification of landscape change during last decades comes to light.
Key words: avalanche, Caucasus, debris flow, dynamics, landscape structure.
Introduction. As snow avalanches and debris flows are one of the most dangerous
and catastrophic geomorphic processes in the mountain regions, their study is of special
interest. Most studies to date have investigated the physics of flow and initiation,
distribution in space, their relation to climatic fluctuations and general models of avalanche
and debris flow forecasting. Few studies have investigated how avalanches and debris
flows influence vegetation patterns and how we can use them as indicators of their activity
(Turmanina, 1975, 1980; Vlasov et al., 1980 and etc.). And only some researches show the
relationship between landscapes and these processes and their influence on landscape
structure and dynamics (Fedina, 1977; Akifyeva et al.; 1978; Khapayev, 1978; Petrushina,
1999). These studies allows us to characterize them with a view to monitoring avalanche
and debris flow activity in areas or at times when observation is not possible. The debris
flow and avalanche geosystems, combined nature complexes of three zones – zones of
initiation, transit and stop-on (or accumulation), are а specific vector systems, formed by
the lateral flows.
The main goal of our investigation is to reveal the main regularities of landscape
structure of avalanche and debris flows geosystems, as indicators of and mpact and
dynamics with .
Study area and methods. The Elbrus region, the highest part of the Central
Caucasus, has been chosen as the study area. High mountain ridges with altitudes
exceeding 3,5-5,5 km, dissected by balk’s, ravines, deep valleys and steep rocky slopes
results from crystalline bedrock, tectonic movements, modern and palaeoglacial and perigla________________________
© Petrushina M., 2004
STUDY OF DEBRIS FLOW AND AVALANCHE GEOSYSTEMS OF THE HIGH ... 381
cial processes are typical for this region. In contrast the relief of volcanic Elbrus massif has
smoother, round forms and stepped slopes.
The altitudinal landscape zonality, slope-facing vegetation contrasts, especially in
the lower parts of the slopes, the indentation of the zone boundaries, altered by landforms
and intensive geomorphic processes are typical for this region. High mountain glacio-nival,
meadow, forest (with pine [Pinus hamata] and pine-birch [Betula pendula] forests)
landscapes predominate in the Elbrus area (Petrushina, 1992). The ability of avalanche and
debris flows geosystems is the specific feature of the study region.
Most detailed research of avalanche geosystems was carried out in the upper part
of the Baksan valley, characterized by regular and catastrophic avalanches of different
types. Well studied, mainly in the 60th and 70th of XX century (Akifyeva et al., 1978;
Zolotarev, 1980; Troshkina et al, 1980 and etc.) it has been chosen as one of test site for
complex landscape monitoring. It stretches for 5 km along the valley with slopes rising
from 2100 to 3700 m with 19 avalanche tracks reaching the valley floor. The area was
changed strongly by intense avalanching from the late fifties until the end of this century.
During this period near by 2000 avalanches, including catastrophic ones were recorded
there. The last decades are known for particular large avalanches in winters of 1967/68,
1968/69, 1970/71, 1973/74, 1975/76, 1978/79, 1986/87, 1992/93, 1996/97, 2001/02 years.
Several stages of the study were undertaken: 1. landscape mapping,
2. determination of landscape evolution with more detail study of recent decades, 3. study
of snow avalanche and debris flow activity, 4. assessment of landscape changes under the
avalanches and debris flows, detail mapping in the zones of their influence, 5. study of
landscape recovers.
A complex of methods, i. e. field landscape mapping and profiling (1:25000),
comparative studies and monitoring from 1977, dendrocronology and lichenometry were
used. The information of historical maps (since 1871), maps of forest cover, aerial images
(since 1946) and phototheodolite servey were also taken into account. The landscapes with
and without impact of avalanches dispersed on the slopes of different aspects, in different
altitudinal belts and in various zones of avalanching and debris flowing have been
examined in detail with a special interest to the zone of avalanche and debris flow
deposition. Landscape mapping (1:10000 and 1:5000) and practically annual description of
vegetation and soils in the main kinds of microlandscapes within this zone have completed
for the upper part of the Baksan valley. The data were compared with maps of vegetation
patterns by previous investigators (Akifyeva et al, 1970). The study was based on ergodic
and functional-dynamic approaches.
Results and discussion. The study, based on landscape maps, compiled during
field research, shows that the region is characterized by dynamic contrast, mosaic and
metachronic landscape structure, resulting from active natural processes, including snow
avalanches and debris flows, aggravated by different types of human activities.
Snow avalanches and debris flows of different types and frequency cause the
simplification or the complication of landscape structure in different zones of their activity,
which can be regarded as an indicator of the processes activity. The debris flows mainly
destroy the whole complex of low hierarchic levels, while avalanches destroy them or
usually change only vegetation the three main zones of their existence – those of initiation,
transport and deposition with the large-scale disturbance in the last zone. Their position in
different altitude belts causes the complexity of internal landscape structure. Different
landscape spatial patterns are typical for the zones of avalanche and debris flows of
different types and frequency. The complex one is typical for cascade systems.
382
M. Petrushina
It was turned out that geosystems of different ages are forming in the zones of avalanche
and debris flows activity. They exist in various stages of their evolution and form specific
chronoseries.
Two main types of debris flows cones with dividing into several subtypes were
separated due to the features of landscape structure and its dynamics. The landscape
structure of debris flow cones is polytemporal and usually consists of number complexes of
different ages, existing in various stages of evolution. Landscapes of four evolution stages
(initial, formation, quasi-stable and destruction) with different vertical structure and of
different duration were picked out. The majority of complexes have not time for passing all
stages of development. The microlandscapes in initial and second stages of formation
predominate in the study region. It was ascertained that the second stage of evolution is
marked out by the most rapid changes of landscape structure. The study showed that
recurrent debris flow activity maintains the whole landscape structure of the debris flow
cone in a rather stable state.
The avalanche traces are seen most distinctly in this forest belt. The lower part of the
subalpine zone above the forests with more steep slopes is also often appeared to be the
zone of avalanche accumulation. As a result the timberline is usually indented due to the
intense avalanching. It’s characterized by the most contrast structure. In comparison with
the climatic one the real timberline can decrease by 200-300 meters, some times more (500700 m.).
A series of microlandscapes indicating the frequency and duration of avalanches
also appears in the places of their influence. These complexes are regarded as original
spatial models of temporal changes of landscapes. The extreme patterns of dynamic
sequence are microlandscapes with coniferous forests, on the one hand, and with subalpine
meadows, azonal for the valley forest landscape, on the other. Subalpine complexes exist
on the territories with regular avalanching, usually under the action of powder avalanches.
The complexes with sparse subalpine or even alpine meadows and willow stand indicate
also the annual avalanching, but often of wet type. Microlandscapes with birch low elfin
woodland mark the avalanching with the interval of 5-10 years, while those with high birch
forests indicate the avalanching of once in 10-30 years. The complexes with mature birchpine forest indicate the action of avalanches approximately once in 30-50 years and with
pine forests – not more often than once in 50 years or even rare. Our investigation confirms
the results of previous studies (Akifyeva et al, 1971; Turmanina, 1975).
The destruction of landscapes, which rarely been changed before (in
correspondence with the age of pine trees – 150-200 years) is a striking evidence of
avalanche activity during the last 60 years, mainly in the period from the late sixties to the
middle of eighties. The landscape structure of avalanche cones appeared to be more
elementary while in the valley bottom it is more complex as a result of this activity. The
main changes in the upper part of Baksan valley under the avalanches impact of this period
are the following. The lithomorphization of landscapes, that is the increase of avalanche
cones in their size, volume and rock content, as well as the emergence of new rocky plots in
the valley bottom on the opposite bank of the river. The area of rocky complexes increased
by 16%. 2) The reduction of microlandscapes with pine forests (by 75%), birch forests (by
65%) and willow stand, expansion of postforest meadows are indicated. Most part of pine
forests had been destroyed by snow and airwave. The decrease of forest vegetation on the
cones caused the increase of the maximum length of avalance run-out zone. 3) The
destruction of microlandscapes of flood plain and terraces and the change of a river course
are typical for avalanche stop-on zone. 4) The structural changes in the landscape
components, mainly in vegetation, that is the decrease of forest density, the increase of damaged
STUDY OF DEBRIS FLOW AND AVALANCHE GEOSYSTEMS OF THE HIGH ... 383
trees, floristic change and so on, are another important feature of affected avalanche zone.
This zone, usually marked out by the appearance of more mesophilous vegetation, is noted
by opposite trend in vegetation regrowth during last years as a result of expansion of
woodless landscapes, increase of summer temperature and anthropogenic impact. This is
the increase of xerophilous species of grass and scrubs (for example Juniperus depressa,
J. sabina), and the decrease of subalpine species (Rhododendron caucasica) and mesophytes
at whole.
It’s important to mention that the concentric change in vegetation types in the
avalanche stop-on zone, revealed by previous studies (Akiyeva et al., 1970, 1978) is also
typical for landscape structure, but usually to the areas with avalanches of the same
magnitudes. In recent times, this spatial distribution is not so visible, most likely as a result
of several avalanches of different types, magnitudes and frequency.
The study of landscape recovery following the avalanche influence showed up that
single impact, especially accompanied by the airwave, often results in vegetation change
only and relatively rapid recovery of zonal vegetation without soil modification due to
higher stability of soils and longer resumption or the so called "character time". This is
observed most frequently for the avalanche cones along the southern slopes. Vegetation
regrowth near the northern slopes is usually slower and the recover occur through the
succession stages - the formation of birch and birch-pine forests. As a result of prolonged
avalanche influence the zone of landscape changes with increase of landscape and floristic
diversity, existence of different types or subtypes of landscapes in one altitudinal zone
show up. In the forest zone the pine forests can be spatially adjacent to subalpine or even
some times to alpine meadows or birch forests more tolerant to the avalanche impact. There
we can see the process of internal landscape regulation, when the spatial structure changes
in correspondence with the changing in time conditions. While vegetation changes, the soil
begins to reconstruct its structure, physical and chemical properties. The gradual increase of
organic matter, pH, exchange cations, the more intense accumulation of biogenic chemical
elements – P, Mo, Zn, Mn and some other are typical to this process after destruction of
forest vegetation. The period of soil formation is very long (n100-1000 years), that’s why
soils of avalanche zones are often in discordance with the vegetation and there are a lot of
mixed soils. For example, under the birch forest the soils resemble the forest brown soil and
the sod subalpine soil (Petrushina, 1999).
A special map of landscape dynamics under the influence of avalanches and debris
flows was compiled. All microlandscapes, showed on the map were united into 4 main
groups and one of them was subdivided into 4 subgroups according to the character of
landscape structure changes.
Conclucions. The large zones of avalanche and debris flows influence prove the
high scale of mountain landscapes dynamics and relative stability of these processes in
time. The diversity of microlandscapes of different ages, often with the contrast type of
vegetation, with disparity of plants and soils, the recurrent change of their boundaries in
time are marked out to these zones. The character of landscape change depends on the type
of avalanches, their activity, the internal features of the affected landscape. The wet
avalanches usually change the whole elementary landscape, while powder ones change
vegetation only. Microlandscapes with pine forests are more affected than those with birch
forests and meadows. Using series of microlandscapes with different vegetation and soils
we can indicate the frequency and duration of avalanches.
The disturbance of vegetation and soils at the slopes in the zone of avalanche
formation due to the man-induced snow hauling down enhances the avalanche activity and
damage in the valley bottom.
384
M. Petrushina
Landscape structure and its dynamics under the impact of natural and
anthropogenic processes must be taken into account for effective land-use planning and
management in the mountain regions.
The work was supported by Russian Fund for Basic Research (grant 03-0565024).
________________________
1. Akivyeva, K.V., Kravzova V.I., Turmanina V.I. Krupnomasshtabnye
kompleksnye issledovaniya lavinnykh konusov kak ob’ektov deshifrirovaniya na
zvetograficheskikh materialakh (In Russian) // Inform. Sbr. MGG, 15. Moscow,
1970.
2. Akivyeva, K.V., Volodicheva N.A., Troshkina E.S., Turmanina V.I., Tushinsky G.K.
Avalanches of the USSR and their influence on the formation of natural-territory
complexes. // Arct. Alp.Res., 10(2), 1978.
3. Vlasov, V.P., Khanbekov I.I., Chuenkov V.S. Les i snezhnyye laviny. (In Russian)
Moscow, 1980.
4. Zolotarev, A.E. Izuchenie snega i lavin v Prielbrusie fotogrametricheskim
metodom (In Russian) // Laviny Priel’brus’ye. Moscow, 1980.
5. Khapaev S.A. Dynamics of avalanche natural complexes: an example from the
high-mountain Teberda State Reserve, Caucasus Mountains, USSR. Arct.Alp.Res.,
10(2). 1978.
6. Petrushina, M.N. Landshafty basseyna reki Baksan // In Nature Use of the Elbrus
area. Moscow, 1992.
7. Fedina A.E. Dinamika gornykh landshavtov (In Russian) // In Reliev i landshavty. Moscow, 1977.
8. Petrushina M.N. Mnogoletnie sostoyaniya prirodnykh territorialnykh kompleksov v raionakh skhoda selevykh potokov i lavin (In Russian) // Landshaftnya
shkola Moskovskogo universiteta: tradizii, dostizheniya, perspectivy. Moscow,
1999.
9. Troshkina E.S., N.A. Urumbaev. Redkodeistvuschie katastrofisheskie laviny v
Priel’brus’ye [Rare catastrophic avalanches in the Elbrus region]. In Laviny
Prie’lbrus’ye. Moscow, 1980.
10. Turmanina V.I. Opyt sostavleniya fitoindikazionnykh skhem dlya gornykh
raionov (In Russian). // Voprosy sovremennoi biogeografii. Moscow, 1975.
11. Turmanina, V.I. Vliynie na rastitel’nost’ usileniya lavinnoy deyatel’nosti (In
Russian) // Laviny Priel’brus’ye. Moscow, 1980.
STUDY OF DEBRIS FLOW AND AVALANCHE GEOSYSTEMS OF THE HIGH ... 385
ДОСЛІДЖЕННЯ ОСИПНИХ ТА ЛАВИННИХ ГЕОСИСТЕМ
ВИСОКОГІР’Я ЦЕНТРАЛЬНОГО КАВКАЗУ
М. Петрушина
Географічний факультет, Московський державний університет,
Воробйові Гори, 119992 Москва, Росія
Досліджено структуру та динаміку осипних та лавинних геосистем як
специфічних векторних систем, сформованих латеральними потоками. Для цього
використано довготривалі ландшафтні картування, порівняльні та моніторингові
дослідження, фітоіндикація та лікенометрія. Брались до уваги також історичні карти,
карти лісотаксації, аеро- та теодолітні знімки. Складено ландшафтні карти та карти
ландшафтної динаміки, зумовленої осипищами та лавинами. особлива увага
приділена зонам акумуляції осипищ та лавин, які характеризуються масштабними
порушеннями та займають понад 50 % площі днищ долин. За ландшафтною
структурою та динамікою виділено два типи та кілька підтипів осипних конусів
виносу. У місцях тривалої лавинної активності виявлено серію мікроландшафтів, які
індикують частоту та тривалість проходження лавин. Виявлено інтенсифікацію
ландшафтних змін протягом останніх десятиліть.
Ключові слова: лавина, Кавказ, осипище, динаміка, ландшафтна струкутра.
Стаття надійшла до редколегії 28.05.2004
Прийнята до друку 16.06.2004