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Italian Journal of Engineering Geology and Environment - Book © 2011 Casa Editrice Università La Sapienza
DOI: 10.4408/IJEGE.2011-03.B-089
E.V. z
& N.S. k
Sevkavgiprovodhoz Institute - Kirova 78 - Pyatigorsk, Russia - E-mail:
material transport by water torrents, [various] distanc-
es and volumes of deposit transport, which depend on
morphologic conditions along the course of movement.
The length of the period of high temperatures in July-
August, which causes heightened ablation of ice masses
against the background of a lowered general and (or)
filtering stability of natural retaining dams, is most sig-
nificant. At the same time not every close-to-a-glacier
hollow or glacial hollow with the realisation of the out-
burst scenario thereupon is able to initiate a debris flow
process – for that to happen outer slopes of a natural
dam (usually of most recent moraine) should have 30-
35° steepness (~20° steepness is insufficient whereas
within the 20-30° steepness range the possibility of an
avalanche-like increase of conditions for transformation
of a water flood into a debris flow may be realised only
with certain water mass volumes (~ ≥ 80-100 thousand
cubic metres) and relative heights of an eroding slope (~
≥ 80-100m). Herewith every occurred significant debris
flow changes geomorphological preconditions for the
next one. Landslides towards river mouths, wherewith
short-lived blockage-caused water bodies are formed,
are sometimes responsible for secondary waves of de-
bris flows, which have originated from glacial sites (the
Buzulgan landslide on the Gerhozhan-Su river and a
landslide in the Rakyt river valley).
: degradation of glaciers, dammed lake neoforma-
tions, outburst processes, disastrous debris flows, moraine-
ice complex
The negative impact of debris flow processes on
vital facilities is expected to increase as a result of the
forecasted degradation of mountain glaciation, related
to the changes in the climate. In the Caucasus region of
Russia, where debris flows stand out for the frequency
of occurrence in space, time and the power of their en-
ergetic manifestation and are mostly of glacial origin,
that follows from the analysis of the developing situa-
tion, which relies on the knowledge of facts of the last
30 years (events on the Kullumkol-Su, Kaya-Arty-Su,
Genaldon, Gizeldon, Birdzhaly-Su, Bulungu-Su and
Sylyk-Suu rivers). As glacier tongues retreat to higher
true altitudes (~300 m for the last 50 years), massifs
of friable single-grained, primarily moraine, formation
become exposed, periglacial water bodies rapidly (com-
paratively speaking) appear, gradients of tributaries, in
which water torrents may become saturated with friable
detritus, increase. Threats and risks of initiation of re-
gimes of debris flows grow. Most considerable debris
flows, in terms of their destructive effect, are connected
with outbursts of lakes, lying close to glaciers. Dis-
charge of intraglacial hollows more and more frequently
acts as a triggering mechanism for the start and further
development of a debris flow process. In every poten-
tially dangerous debris flow basin of the region, due to
peculiarities of the Quaternary period, there are various
ways of realisation of disaster scenarios for mouth parts
of mountain rivers. Even in the territorially close basins
there may develop various flows of processes of hard
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5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
(in 1983), G
(in 2000), G
(in 2002),
(in 2006), C
(in 2007 and 2010) (Fig 1)
The most significant threats for the Central sector
of the Caucasus come from lake neoformations, form-
ing near glacier tongues behind young frontal moraine.
In practice it is only possible to protect the mouth sec-
tions of debris flow channels from disastrous conse-
quences by organizing the engineered channelling of
the flows into the main receiving river.
The most powerful debris flows on the Ger-
hozhan-Su river in 1960, 1977 and 2009 were con-
nected with outbursts of outwash lakes near glaciers:
Eastern, Central and Western Kaya-Arty, correspond-
ingly (z
, 2002)
A debris flow that originated in the steep front
moraine of the Western Dzhaylyk glacier (in July
1983) was also connected with a rapid discharge of an
outwash lake near the glacier tongue. Having travelled
down the Kulumkol-Su river, it caused disastrous
destruction at a comfortable sport camp (z
, 1985, 2005; b
et alii, 2008).
Flows that have formed in origination sites, located
in the upper reaches of lateral tributaries of main rivers,
and that are caused by rapid discharges of waters, ac-
cumulated in intraglacial hollows (as on the Rakyt river
in 2007) or due to a local discharge of an atmospheric
thunderstorm front (storm rainfall) on these debris flow
origination sites, also turn disastrous for populated river
mouth areas (z
& k
, 2010).
Consequences of a rapid travel of water-snow-
rock-ice masses from the upper reaches of the Genal-
don river (2002, the toll was 125 human lives) have
had vast scientific press coverage (z
2003; P
, G
, 2007 and others). The
years 2006 and 2007 brought new debris flow related
misfortunes to the Central Caucasus suffered – debris
flows went down the b
(2006, a tributary
of the Malka river), b
(2007, a tributary of
the Chegem river) and s
(2010, a tributary of
the Chegem river) rivers (Kabardino-Balkar Republic).
A debris flow on 11 August 2006, which caused
destruction at “Dzhily-Su” spa, repeated the event of
1909 with regard to the consequences and the sce-
Russia tends to be more sensitive to global warm-
ing than the rest of the world: the range of anomalies
in average annual temperatures comes up to 3-4°C
whereas the range of anomalies in average global tem-
peratures only slightly exceeds 1°C. Having started in
the 1910s, the warming continues, now applying to
all seasons of a year. In 2037 against 2007 a global
temperature rise of 1.4±0.3° for the territory of Russia
is expected (G
& R
, 2009)
The high mountains of the Caucasus have been re-
acting to such changes in climate through degradation
of glaciers, which has been especially significant since
after the 1950s. Thus reduction of only two glaciers
on the northern slopes of Elbrus Mount – Birdzhaly-
chiran and Chungurchatchiran – from 1957 to 2007
totalled more than 4 km
et alii, 2009). The
margin of the Birdzhalychiran glacier sad retreated
up to 300m since 1987, and for the period of 1957
to 1987 it retreated 850m in length, and from 3149
to 3320m in absolute height (1957-1997) (z
2009; R
, n
, 2009)..
The rapid reduction of glaciers in the latest dec-
ades has lead to the outcropping of areas of loose
moraine formations and emergence of lake neofor-
mations on territories, freeing from ice – the area of
a group of lakes on the north-eastern slope of Elbrus
increased more than sixfold from 1957 to 2005 (C
et alii, 2009).
With this in view, debris flow dangers sharply in-
crease, their negative impact on vital facilities intensi-
fies (z
, 2007), which for the Northern
Caucasus is substantiated with actual facts of the last
40 years of the 20th century and the first decade of
the 21st century – disasters on the rivers of Kulumkol
Fig. 1 - Study area
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Italian Journal of Engineering Geology and Environment - Book © 2011 Casa Editrice Università La Sapienza
casted an outburst of a lake neoformation (fell ~550
thousand m
) in the Birdzhalychiran ice cup through
overflow of ~400 thousand m
and destruction of an
ice riegel-crossbar, to be accompanied by formation
of a debris flow, capable of reaching the “Dzhyly-Su”
spa. The forecasted scenario became a reality in a
natural manner on 10-11 August 2006. The sweeping
swell reached the outlets of the “Dzhyly-Su” springs
at 4 a.m. on 11 August 2006. Deposits of the debris
flow, that had a sediment-water composition, covered
the area of 9750 m
with a layer of an average thick-
ness of 3.4 m. The volume of hard deposits was 33
thousand m
. Taking into account the material that got
into the Malka river, in the morning of 11 August 2006
the total of ~50 m
was transported to the mouth of the
Birdzhaly-Su river.
The maximum debris flow discharge was instru-
mentally determined based on the marks left at three
non-erodible sections. It turned out to be 125 m
second (see Tab. 1).
Carried out works made it possible to give a fur-
ther forecast of the development of the situation and
propose measures, directed at implementation of en-
gineering protection of the near-the-mouth area of
“Dzhily-Su” and confirm an issued earlier Opinion
letter (negative) on the possibility and problems of
construction of a hydropower station at the mouth of
the Kara-Kaya-Su river
The Bulungu-Su river (basin area of 43.8 square
km) is formed due to confluence of the Koru and Rakyt
rivers and in its mouth part it runs through the skirts of
the village of Bulungu. The latest occurred debris flow
came to the mouth of the Bulungu-Su river on 19 July,
1983, bringing about great destruction. In connection
with the appearance of previously unmarked (on maps
as of 1968) lake neoformations near glaciers on aero-
photography pictures, a survey of the upper reaches of
the Koru river and the glacier of the same name was
carried out in September, 2002. It was established that
nario of the discharge process of waters accumulated
near the marks of tongue parts of the same glacier
(Birdzhalychiran): ~3060 m a.s.l. in 1909 and ~3300
m a.s.l. in 2006 (Fig. 2)
The drive for extending the use of water resources
of the Caucasus, on the one hand, and the intensifica-
tion of the debris flow danger in glacial origination
sites of the region, typical for northern slopes of high
mountains of the Main Caucasus Ridge, on the other
hand, make it necessary to assess the tendency for de-
velopment of a debris flow situation at infrastructure
and spa facilities, at such as, for instance, those locat-
ed on tributaries of the Malka river – the Kara-Kaya
and Birdzhaly-Su rivers (in the mouth of the Kara-
Kaya-Su river a hydro-electric dam is being designed;
in the mouth of the Birdzhaly-Su river a medical and
preventive treatment institution, which operates on the
basis of a complex of mineral springs, is located).
Debris flows on the Kara-Kaya-Su in the historic
period did not reach its mouth (the length of the river
is 9.7km, its average gradient – 0.13). Debris flows
on the Birdzhaly-Su river (length – 8.7 km, average
gradient – 0.116) for the last 100 years have twice
discharged into the receiving river (the Malka river).
On the basis of the developing situation as of July
2006, the Debris Flow Association of Russia fore-
Fig. 2 - 10 September 2009. The state of the breakthrough
passage of the ice crossbar at the Birdzhalychiran
lake at the site ofdischarge of water masses on
10 August 2006. View from the downstream. The
source of the Birdzhaly-Su river
Tab. 1 - Characteristics of the debris flow on 11.08.2006 on the Birdzhaly-Su river w – the area of the cross section, B – the
width of the channel, h – the depth of the flow, i – longitudinal gradient at the site, V – velocity of the flow at the site,
Q – maximum flow discharge
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5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
the Rakyt river’s right source, whose catchment basin
is half as much as that of the central source and ~5
times as less as the basin of the main (left) source;
under the conditions of presence of friable, well wa-
terabsorbing single-grained moraine deposits here,
atmospheric precipitation, that had been there prior to
the debris flow in the form of light rain up to the mark
of ~3200 m a.s.l. (it had been snowing higher), was
not the cause of the debris flow;
– ~900 m down from the debris flow origination
site the discharge of the flow in the concentrated chan-
nel had the value of ~200 cubic metres per second;
lateral debris flow swells appeared already ~200 m be-
neath the modern position of the glacier tongue (at the
mark of ~3300 m in true altitude), at the first fracture
of the relief, after the debris flow groove, uncovering
buried ice here and there;
– the area of the outer western part of the West-
ern glacier under the peak of Rakyt at true altitude of
~3650 m a.s.l. (Fig. 4) was the source of the water
component (water impulse) of the debris flow; there,
apparently, an almost instant discharge of a great vol-
ume of water (~20 thousand cubic metres ± 10 thou-
sand cubic metres), that had been concentrated inside
intraglacial hollow(s), with a further outflow (possi-
bly, a short-time one) and building-up of the outflow
volume, took place;
– beneath the Korgashinlitau ridge and the peak
of Rakyt there are currently three separate glaciers,
that ~50 years ago comprised a single ice massif (ac-
cording to the aerial survey at the end of the 1950s);
tongues of the glaciers have of late years gone up 200
the debris flow danger originated from moraine-ice
masses, that were filling the northern “horseshoe” of
“Dzhosharty” and that the outburst of the water from
the intraglacial hollows would lead to the initiation of
a mud-water-ice flow; and a debris flow of great de-
structive power and of large volumes may come to the
river mouth (the village of Bulungu). The river chan-
nel of the Bulungu river would not let through even a
sediment-water flow under the highway, which leads
to the upper reaches of the Chegem river.
On 3 August, 2007, at 00.15 a.m., a high density
debris flow came down the river channel to the fringes
of the south-western part of the village of Bulungu.
The underbridge span was almost immediately clot-
ted by blocks and drowned wood and the debris flow
mass, “dumped” on the right hand of the course, ~250
m above the bridge, went through residential houses
and adjoining plots of land (Fig. 3).
At that:
– the debris flow (after the “dumping” on
03.08.2007) flatly spread across the village and it only
consisted of a mud mass near the mouth;
– over the remaining stretch, up to the origination
site, the transporting potential of the flow allowed it to
carry boulders weighing up to 40 tons;
– the “high water” level in the first several days
was well pronounced, and boulders and rock blocks
of debris flow swells were mud coated;
– the total volume of deposits along the channel of
movement was calculated to be ~400 thousand cubic
metres; on the territory of the Bulungu village per se
~80 thousand cubic metres of the debris flow material
were deposited;
– the debris flow came from the upper reaches of
Fig. 3. 3 August 2007. The debris flow on the street of the
village of Bulungu
Fig. 4 - 15 July 2008. The western korgashinlitau glacier.
The source of the Rakyt-1 river. 1 – the area of
origination of the 2 August 2007 debris flow and
the path of movement of outburst water masses
from an intraglacial hollow; 2 – the outflow grot-
to, formed in 2008
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Italian Journal of Engineering Geology and Environment - Book © 2011 Casa Editrice Università La Sapienza
bris flow wave at the vertex of the debris fan of the
Bulungu-Su river measured up to 5.8 m.
– the Rakyt and Koru rivers, representative for
consideration of modern debris flow activity tenden-
cies, in connection with the changing glacial situation
due to the warming of the climate, are becoming ex-
tremely debris flow dangerous in the upper reaches;
– the nature of processes, leading to creation of
conditions for a water torrent development according
to the debris flow scenario with disastrous parameters
for the lower reaches of the Bulungu-Su river, is vari-
ous in the basins of its tributaries: steep corrie Rakyt
glaciers retreat while the general stability of the gla-
cial section lowers, the possibility of opening of the
intraglacial hollows increases, as does the role of im-
pacts of collapses on the surface and structure of the
ice massif; the gentler sloping Koru glacier with its
pit lakes and thermokarst lakes advances (due to the
decreasing lateral areal resistance at the “ice-banks”
contacts due to the rapid melting of ice on rocks;
– the intraglacial origination site of the debris
flow of 2007 exhausted its potential for several near-
est debris flow risk periods;
– however, the threat of activation of origination
sites in the upper reaches of the main (left) stream
of the Rakyt and especially Koru rivers is high. The
energy of the debris flow on the latter may surpass
the energy, “discharged” in August, 2007, by several
times; the mouth part, unprotected by engineering
means, within the debris fan area of the Bulungu-Su
river was not able to take in the debris flow, that had
come from the origination site through the Rakyt riv-
er; consequences of the debris flow, having started to
m in true altitude; the surface of the Central and East-
ern glaciers is steep (45-50°), for the latter there are no
conditions in their bed for accumulation of subglacial
and intraglacial waters; in the upper third of the West-
ern glacier such conditions do exist: here, at the break
of the ice relief, there is a cup-like area in the bedrock;
– slopes, surrounding the Western glacier, are
steep and greatly fractured; debris, accumulating on
the surface of the glacier in the form of "fresh" rock
and ice fragments, continuously went down the gla-
cier and the rocks during the week after the main de-
bris flow event (not detected at the glacier tongue);
– the Western glacier was ready for shifting and
for an externally provoked opening of water-filled
– the debris flow of 02-03.08.2007 travelled the
path of ~8.5 km from the site of discharge of water
masses of the glacier to the road bridge across the
Bulungu-Su river at Bulungu village for 1 hour ± 15
– the mouth of the Koru river was not blocked by
the debris flow on the Rakyt river.
Works to establish the debris flow characteris-
tics (with special attention to determination of the
maximum discharge on the basis of marks left in non-
deformable sections) were carried out. Examinations
of cross-section profiles and slopes were executed
instrumentally. Discharges were determined at mouth
reaches (Fig. 5): the Rakyt river (1 profile) and the
Bulungu-Su river (2, 3 profiles). Their peak discharg-
es were 244 m
/s and 302 m
/s, respectively (Tab. 2)
(the starting discharge in the upper reaches 0.9 km
from the origination site was ~200 m
/s according to a
semi-instrumental assessment). The height of the de-
Fig. 5 - Grade profile of the riverbeds
of the Rakyt – Bulungu-Su riv-
ab 2 - Characteristics of the debris flow on 02-03.08.2007 on the Bulungu-Su river.
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5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
originate on the Koru river, will be more significant;
– outbursts of lake neoformations (rapidly in-
creasing their volumes in the last decades) near mo-
raine-ice complexes prevail among other factors of
debris flow formations of the glacial origin.
SYLYK-SU – 2010
On the right bank of the Chegem river, in the
narrow strip of the terrace above the flood-plain
lies the village of Bulungu, whose south-eastern
outskirts suffered from the 2007 debris flow, which
went down the Bulungu-Su river. The centre of the
village is divided by the Sylyk-Su river. The last but
one debris flow on the Sylyk-Su river took place 12
July, 1995, causing casualties and destruction. The
last one happened 20 July 2010 (Fig. 6). It was fore-
cast with an 8-hour earliness.
It had been considered that a debris flow on the
Sylyk-Su river, capable of reaching Bulungu, would
primarily follow the 1995 channel due to more fa-
vourable conditions with regard to the state of ac-
cumulated slope loose debris. Moreover, the upper
reaches and bottom slopes of the main Sylyk-Su val-
ley were “inferior” to those of its right (and its sole)
tributary valley. But the weather – and this is charac-
teristic for mountains - “amended” [the development
of the process]: precipitation of the latter half of the
day of July, 20, 2010 covered only debris flow origi-
nation sites of the main valley, whereas the neigh-
bouring valley’s origination sites remained in the
storm’s “blind spot”, not getting a sufficient water
component for the initiation of the process develop-
ment according to a debris flow scenario. (From the
practical viewpoint of safety assurance for dwellers
of Bulungu village as well as their housing and prop-
erty, the expected location of debris flow origination
sites in the upper reaches has no fundamental impor-
tance, as debris flows come out on to the village area
at one place – out of the gorge on to the vortex of the
debris fan).
The foremost swell of the 20 July 2010 mud-
and-stone flow reached the vortex of the debris fan
at about 8 p.m. The first approximately 100 m of
the river channel did hold the incoming masses, but
downstream the debris flow discharge surpassed the
capabilities of the natural section, overflew onto the
village and through buildings and household plots
reached the receiving river of Chegem (Fig. 7).
The volume of the material deposited within the
village was estimated at 5000 m
There was no erosion
of the natural river channel upstream from the over-
flow site. The peak discharge of the flow determined
at two representative profiles on this reach measured
up to 190 m
/s (Tab. 3). Profiles of the 1995 and 2010
debris flow channels are given in Fig. 8.
The upper reaches of the main valley of the Sylyk
Su river by 20 July 2010 were practically free of snow
patches. 4 origination sites, located beneath the west-
ern spur of the Korgashinglitau ridge at about 3500 m,
were involved in the formation of the debris flow
Debris flows on the Sylyk-Su river may be ex-
pected in the foreseeable future. Without the engineer-
ing channelling of debris flows into the Chegem river
through channels of sufficient clear area (as per esti-
mated flows), such debris flows will time and again
travel through settlements, causing new destruc-
Fig 6 - 27 July 2010. Viev on
the village of Bulungu
(Upper Chegem)
Fig.7 - 26 July 2010The village of Bulungu. A destroyed
house. The household plot is covered with debris
flow deposits
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Italian Journal of Engineering Geology and Environment - Book © 2011 Casa Editrice Università La Sapienza
to a more powerful (second) wave of the flow with
disastrous consequences for the town of Tyrnyauz, the
deepening of the bottom of the river at the landslide
front up to 20m to uncover the bedrock of crystalline
shale and phyllite (Fig. 9). The long-living landslide
massif is composed of strata of a tectonic fragmenta-
tion zone. (z
, 2002; 2003).
The “Bulungu” landslide (limestone, marl) on the
southern flank continuously advances into the chan-
nel at the vertex of the debris fan of the Bulungu-Su
river (Fig. 10). As the opposite bank is composed of
non-erodible hard rock here, the scale of surges may be
such so that the river will not cope with the wash-out of
landslide masses moving into it.
A landslide (of clay slate) in the channel of a
Rakyt river tributary (Fig. 11) was a triggering cause
for a debris flow in the summer of 2008; it reached
the mouth of the Bulungu-Su river and jammed the
underbridge clearance of a motor road.
Debris flows - which are mainly natural - are
in recent history indicative of the variety of causes
and factors of and possible initial impulses for water
masses’ development in a debris flow mode even in
territorially close basins of lateral tributaries of a main
river as a receiver of debris flow deposits. Thus (un-
der otherwise equal conditions, created as a result of
degradation of glaciation on the northern slope of the
Main Caucasus Range):
tion and casualties. Steep slopes of river channels at
the place of their falling into the Chegem river (the last
100 m, the cusp of the high terrace above the flood-
plain) are favourable for the organisation of such chan-
nelling (through debris flow check canals).
Debris flows, originated in proglacial zones, be-
fore they come out to the mouth parts of movement
channels (usually to the vertices of debris fans of simi-
lar processes of previous years), under the conditions
of Central Caucasus region travel over a distance of
up to 10-15 km. The flows re-form, disintegrate or
on the contrary get enriched with hard material: it de-
pends on morphological, engineering and geological
peculiarities of bottoms and slopes of transit valleys.
That’s where they are “surrounded” with dangers of
being blocked by sliding masses, caused by bottom
and lateral erosion. Failure to take into account such
circumstances may lead to an erroneous prediction
of negative consequences and prescription of errone-
ous engineering protection measures. Thus, the dam-
ming of the Gerhozhan-Su river (the undercutting
of the tongue part of the “Buzulgan” landslide 4 km
above the outfall mouth section of the river with the
first wave of the debris flow), the backing and further
breach of the temporary earth dam led at the same time
Tab 3 - Calculation sections of the transit channel of the Sylyk-Su river and results of determination of the peak 20 July
2010 debris flow discharge
Fig.8 - The Sylyk-Su river basin. Profiles of the 1995 and
2010 debris flow channels
Fig. 9 - 31 August 2001. «Buzulgan» landside (left side)
which blocked the debris flow on 19 July 2000
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5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
1. The first warming in the 20th century on the
territory of Russia in 1910-1945 was noticed by
Russian scientists and it was named “the warming
of the Arctic”. The second wave period (after 1976),
lasting up to date, is witnessed not only by the sci-
entific community, but also experienced in every-
day life, especially by mountain climbers: many ice
routes of the beginning of the second half of the 20th
century have now become rock-talus. Our contem-
poraries’ lot is to live in the period of “the warming
of the Caucasus”.
2. At the turn of the 21st century the global
warming tendency has caused reduction of ice-
sheet in the alpine areas of the northern slope of the
Caucasus mountain system. With glacier tongues
retreating to higher true altitudes, massifs of fri-
able singlegrained, primarily moraine, formations
become exposed; peri-glacial water-bodies rapidly
(comparatively speaking) appear, grow and disap-
pear. Threats and risks of emergence of regimes of
debris flows on river channels grow. Most signifi-
– debris flows on the Sylyk-Su river (in 1995
and 2010) are consequences of involvement of loose
single-grained formations of the upper reaches by
streams, caused by passage of storm fronts;
– the debris flow on the Rakyt-2 (in 2008) is a
result of the breach by a surface water stream of a
dammed water-body, created by a landslide dislocation
in the left-side mouth part;
– the debris flow on the Rakyt-3 (in 2007) is linked
to the discharge of water masses from intraglacial hol-
lows (as of now, the sole reliable recorded instance in
the Northern Caucasus region);
– the debris flow on the Birdzhaly-Su river (in
2006) was formed by an outburst discharge through an
ice crossbar of a lake neoformation;
– a potential debris flow danger lurks in the inte-
rior of the so-called “dead ice” in the upper reaches
of the C. Rakyt and Koru rivers. The advance of the
“dead ice” onto the slopes and bottoms of the valleys,
whereas generally there has been a retreat of open ice
surfaces for the last 50 years, is evidenced from the
turn of the century (Figs. 12, 13).
Fig. 10 - 3 August 2007. Active flank part of the “Bulungu”
landslide. The right bank of the Bulungu-Su river
at the debris fannear the village of Upper Chegem
Fig. 11 - 17 July 2009. Landslide in the mouth part of the
Rakyt-2 river at the time of activation, caused by
the bottom and lateral erosion, creates backwater
of surface runoff
Fig. 12 - 17 August 2010. The moraine-ice complex ad-
vancing and blocking the C. Rakyt river valley.
Fig. 13 - 19 August 2010. The upper reaches of the koru
river. A moraine-ice complex advancing on the
foreground and slopes of the valley. -----> direc-
tion of movement.
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Italian Journal of Engineering Geology and Environment - Book © 2011 Casa Editrice Università La Sapienza
tion of conditions for formation of debris flows de-
pends not only and as much on the gradient of tran-
sit channels (the latter always the more significant,
the more minor the tributary) as on peculiarities of
storm atmospheric front discharges: the valley of
a lateral tributary may happen to be in the storm
“blindspot”, while a pinpoint precipitation fallout
in a neighbouring valley of the same tributary will
lead to a debris flood, despite a “softer” profile of
the channel and better morphological conditions for
the flow disintegration, characteristic for the latter.
8. The rapid reduction of glaciation areas leads
to the accumulation of ice masses (moraine-ice com-
plexes), buried under surface moraine in the steep
upper reaches of mountain valleys and losing con-
tact with a mother glacier. With plastic properties
of ice and high feeding with melt waters (from open
glacier surfaces lying above) such complexes (with
bedrock gradients of ≥10° on the C. Rakyt and Koru
rivers) since the beginning of the 21st century have
started advancing upon valley bottoms and slopes,
that have had time to get grass-covered for the previ-
ous decades, in the mode of viscoplastic movement
and block-gliding along the bedrock. With this, there
emerge threats (unpredictable with regard to their
triggering effect) of outflow of gravity water from
buried glacial hollows to be followed by formation
of an outburst debris flood (along transit channels
of effluent seepage from under the foundations of
frontal parts of such complexes).
9. Attempts to stem river mouth high-density
debris flows, the latter characteristic for the North-
ern Caucasus (for example the event in Tyrnyauz in
1999), are doomed. Free channelling of such debris
flows along check canals and free transportation
(without blockages) of material via the main receiv-
ing river should be organized. Parameters of such
facilities (height, target, design parameters) should
be designated with regard to the expected (calcu-
lated) debris flow characteristics. This is a feasible
engineering task.
No reliable and effective ways of artificial “glo-
bal cooling” have been devised so far. Nature is
stronger than man after all. We often forget about it,
but that is the case. Disregard for the past errors is
fraught with numerous losses in the future.
cant (with regard to their destructive power) debris
flows originate from outbursts (discharges) of lake
neoformations, lying close to glaciers, and rapid
outflows of waters from intraglacial hollows.
3. In every potentially dangerous debris flow
basin, due to peculiarities of the Quaternary period,
there are various ways of realization of disaster sce-
narios for mountain rivers’ mouth parts (debris fans)
under economic development. Even in the territo-
rially close basins there may form different devel-
opments of processes of hard material transport by
water torrents, distances and volumes of debris flow
deposits transport, which depend on morphologic
conditions along the debris flow channel.
4. For glacial zones with debris flow origination
sites the length of the period of high temperatures
in July-August, causing heightened ablation of ice
masses against the background of lowered general
and/or filtering stability of natural retaining dams
(not necessarily absolutely watertight), is most sig-
5. Not every water body, lying close to a gla-
cier, or glacial water body at the realization of the
outburst scenario thereupon is able to initiate a de-
bris flow process – for this to happen outer slopes of
the natural dam (most often of most recent moraine)
should have 30-35° steepness; ~20° steepness is
insufficient, and within the 25-30° steepness range
the possibility of an avalanche-like development of
conditions for transformation of a water flood into a
debris flow may be realized only with certain water
mass volumes (~≥ 80-100 thousand cubic metres)
and respective heights of the eroding slope (≥ 80-
100 m). At that every occurred significant debris
flow changes geomorphological preconditions for
the subsequent one.
6. Landslides towards river channels followed
by formation of short-lived dammed water bodies
are sometimes responsible for secondary waves
(including disastrous waves) of debris flows, origi-
nated in glacial sites.
7. On the tributaries of the upper reaches of the
main rivers of the northern slope of the Central Cau-
casus, whose open glacierderived nourishment in
connection with climatic changes has substantially
decreased, or ceased altogether, and where in poten-
tial debris flow origination sites a practically infinite
volume of loose materials is accumulated, the initia-
background image
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