RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 8, ES4004, doi:10.2205/2006ES000207, 2006
Glacial catastrophe of 20 September 2002 in North OsetiaV. N. Drobyshev "Sevosgeologorazvedka" Company, Vladikavkaz, North Osetia, RussiaContents
Abstract[1] The aim of this study was to reconstruct the main parameters of the catastrophe, using the data obtained as a result of instrumental measurements. The parameters of the catastrophe were estimated, and the volumes of the collapsed firn massif and body of the Kolka Glacier were calculated. Also reported in this paper are the results of the topographic monitoring of the glacier barrier in the Karmadon Basin. Using the seismic records available, the speed of the glacier demolition down the Genaldon Ravine was calculated. It is assumed that the main cause that had initiated the beginning of the catastrophic process was the seismic effect resulting in the origin of fumarolic emanations under the firn field in July 2002 (two months before the catastrophe) and its gradual destruction in the course of termocarst development. Introduction[2] The year of 2002 happened to be a disastrous year for North Osetia. In 21 June a catastrophic shower broke down. Thousands of large, huge, and small mud flows produced devastating destructions of the roads, high-voltage electric energy transmission lines, bridges, living houses, and industrial buildings in mountainous regions. The northern part of the Gornaya Osetia territory was paralized for a long period of time. Three months later the echo of the new tragedy in the Genaldon Ravine flied around the world.
[7] As follows from the official data, discovered by 10 November, 2002, were the remains of 18 dead people, 108 people were not found. The dangerous zone included a 24-kilometer segment of the local road. A small relatively new settlement, built at the bank of the Genaldon River in the Karmadon Basin, was obliterated. Two tourist centers, located at the outlet from the canyon, were wiped off by a mud flow. More distant buildings were damaged significantly. It should be noted that during the first weeks after the catastrophe the damaged area grew in size at the expense of the filling of the dammed lake produced by the right tributary of the Genaldon River, which was dammed by ice avalanche. [8] The Kolka Glacier has been of great interest as an unstable natural formation constituting a threat as a potential hazard. The inspection of the catastrophe zone immediately after the event allowed the estimation of its hazard and the first suggestions concerning the mechanism that had caused it and its potential consequences. The Source of the Catastrophe
The Geologic Structure of the Catastrophe Area[11] The upper reaches of the Genaldon Ravine have a complex geologic structure. The close vicinity of the Kazbek Volcano caused the presence of effusive rocks, included stratigraphically into the Tsiklaur Formation (J 1-2 ) represented by siltstones and silty sandstones. The members of sedimentary and volcanic rocks compose the southwestern slope of the Shaukhokh anticline with a diorite body exposed in its core. In the area of the Kolka Glacier, diorite is exposed in the lower part of the left side of the Maili ice fall and in the lower part of the eastern Dzhimarai-Hoh wall, exposed by the glacier descent. [12] The subvolcanic rocks are represented by the numerous diabase dikes feathering the Kazbek volcanic channel, known as the Kazbek Diabase Belt. [13] Kazbek is not ranked as an extinct volcano. In the recent time the peak of its igneous activity is dated 280-180 thousand years ago. The next peak was recorded 50 thousand years ago. Its latest activity was dated 10,000 and 6000 years ago [Rogozhin et al., 2001].
[15] The tectonic structure of the region proves the active geodynamic environment in the crustal block discussed. Numerous faults of different ranks cross the territory discussed, both in the least-west and north-south directions, causing upthrust and overthrust deformations. Climatic Conditions[16] The total glacial zone of the Kolka Glacier resides in the nival zone. The average annual air temperatures are positive up to the elevations of 2000-2300 m, become negative at higher levels, and amount to - 10oC at the height of 4000 m. Precipitation is highly irregular for the basin territory, both in time and space. According to the data reported by K. P. Rototaev, very characteristic is a summer maximum, associated with the reactivation of the cold fronts of the Atlantic cyclones [Rototaev, 1974]. During the anticyclone conditions the bulk of the summer precipitation is provided by the local vertical convection. Most of the days with solid precipitation fall to January. The precipitation amounts are distributed by the seasons in the following way: 500 mm and more in summer, 199-150 mm in autumn, 150-200 mm in winter, and 200 mm and more in spring. Reconstruction of the Catastrophe Preparation Process
[18] This work revealed that on 14 July, 2002, the rock mass of the Dzhimarai-Hoh peak had experienced shaking of intencity 5.2 on the MSK-64 scale. The epicenter of this earthquake was located 8 km west of the Dzhimarai-Hoh peak. In the initial KMV-2002 data sample this earthquake has a number of 244. Its main parameters are: No. 244 (Md = 3.88; K = 9.8; depth = 5.4 km). The same day witnessed two earthquakes more: No. 245 (Md = 3.11, K = 8.3) and No. 246 (Md = 3.20, K = 8.4).
[20] (1) The shaking corresponding to magnitude 5, communicated to the Dzhimarai-Hoh pyramid from the earthquake no. 244, had the following parameters: the acceleration (a) of ~0.28 m sec-2, the displacement rate (v) of ~0.056 m sec -1, the absolute displacement (L) of ~0.04 m. [21] (2) The effect of this intensity on the hanging firn fields of the "Kolka" glacial rock complex (the thickest and steeply dipping in the mountainous area discussed) can increase the momental value of their sliding down force almost by 9%, which will decrease their stability by the same value. Essentially, this effect can cause significant mechanical damages in the ice-firn massif and, eventually, its complete disintegration. [22] Did the Dzhimarai-Hoh Massif experience any more powerful seismic effects during the previous 10-15 years? As follows from the data reported by Savich et al. [1996], the calculated shaking of the Dzhimarai-Hoh Massif from the Racha earthquake (MPSP = 6.6; 29.04.91) and from the Borisakh earthquake (MPSP = 6.6; 23.10.93) was as high as 5.6. No stronger seismic effects were recorded. Reconstruction of the Main Parameters of the Catastrophic Collapse of the Kolka Glacier
[25] (1) the volume of the firn material that collapsed onto the glacier: Vfirn = 22 million m3; [26] (2) the volume of the ice, involved into the catastrophic motion of 20 September 2002 (including the avalanche material): Vice 1 = 137 million m3;
[29] (5) the volume of the ice left along the transit path as selvage and blocks lagging behind: Vice 3 = 22 million m3. [30] The huge avalanche of the Kolka Glacier was recorded by many seismic stations of the Caucasus area. The most complete record (lasting about 16 min) was obtained by the Tsei seismic recording unit, located 44 km west of the catastrophe site. The detailed description of the seismic records, with the beginning and end of each seismograph operation, is provided in the paper of (A. A. Godzikovskaya, in press, 2004). The main result of this study was the discovery of the high variation of all record characteristics in time: [31] 1. 1605:13.0 recording onset (Greenwich time: hour-min-sec). [32] 2. 1605:13.0 - 1609:05.0 noise at the level of the seismograph sensitivity. [33] 3. 1609:05.0 - 1610:21.0 interval of notable amplitude growth. [34] 4. 1610:21.0 - 1615:30.0 interval of substantial amplitude growth. [35] 5. 1615:30.0 - 1621:10.0 interval of notable amplitude reduction. [36] 6. 1621:10.0 end of record.
[39] Taking into account the fact that the description of the process is based on the circumstantial facts, it should be treated as a hypothesis. [40] Proceeding from the data available, it can be noted that: [41] (1) the initial velocity of the active body was equal to zero; [42] (2) no large shock, capable of communicating any significant (additional) acceleration to the glacier body of 137,000,000 tons was recorded by the seismographs; [43] (3) the process of adding new rock material to the glacier rear because of avalanches continued more than two months. The photographs A and B in Figure 9 suggest that the avalanches from the firn fields produced a large and sufficiently thick alluvial fan on the surface of the Kolka Glacier as early as the end of August, 2002. Shear stresses in the glacier body continued to grow until reaching the critical values. The interval No. 2 in the seismic record obtained by the Tsei seismic recording unit (1605:13.0-1609:05.0) can be interpreted as the rapid development of faults in the active glacier body, which produced a large cleavage in the layer of the bottom ice (Figure 13) and, hence, the loss of stability. The amplitudes of seismic waves in this time interval are 10-40 times lower than in the interval No. 3. [44] (4) The value of the seismic effect which stabilized after the date of 1609:05 was high enough to be recorded by the seismographs of the "Alpha-Geon" local network, including the "FIG" seismic station. This fact can be treated as the beginning of the gravitational active glacier body movement.
[46] The acceleration of the active body motion was recorded by the seismographs during the time of 1 min 16 sec (see interval No. 3 in the seismic record obtained by the Tsei seismic station). This time interval is sufficient for an active body to attain a velocity of 220-240 km hour -1 over a distance of about 2 km. At the time interval of 80-90 sec the avalanche front reached the Maili moraine and, having rebounded from it, began its gentle turn to the left at a fairly large angle (up to 50o). In this turn the avalanche flow over the right side rose to a height of 250 m above the thalweg (in the cross-section). The left flank of the avalanche, moving along the thalweg of the Kolka-Don River, left its trace along the left side of the canyon at the height of 30-40 m. This height difference, with same width of its trace (~700 m), can be explained by a significant centrifugal force produced by the high-velocity turn. The sesmographs recorded the first high interaction. This site is marked as point 1 in the topographic map. Shown in the frame of this drawing are several inserts which help to percieve and interpret this information. In the inserted diagram "The time distribution of the total energy vector", the point no. 1 is shown though not in the figure plan, but in the time scale. The arrival time of the "FIG" seismic signal is tied to the time scale of the "Tsei" seismic station and is marked as 1609:05 (Greenwich time). The numbers of the observation sites, shown in the topographic map, and those shown in the diagram correspond to one another. Farther on, the avalanche followed a relatively rectilinear trough with the width varying from 100 m to 150 m, the slopes consisting of loose deposits, varying in steepness from 30o to 40o. The bedrock outcrops have an "island" character and are located mainly at the right side of the valley. The area discussed has a length of 9.5 km, where the avalanche trace resembles the trace of a slalomist. The maximum height of these traces is 180 m, the minimal height being 10-20 m, with the arc length of each turn measuring not less than 1000 m. Of particular interest is Site no. 9 which corresponds to the absolute maximum of seismic energy produced by the moving glacier. Here the avalanche overflow was as high as 248 m. [47] Table 1 shows the results of the computations used to plot the curve of the glacier avalanche speed along the Genaldon Canyon (Figure 19, b-2). The headings of the columns of the calculation table: [48] 1. The name of the object or the number of the trajectory point [49] 2. The distance between the neighbouring sites [50] 3. The distance from Dzhimarai-Hoh Wall [51] 4. Acceleration of an active body at the beginning of its motion [52] 5. The time needed to cover the distance from the previous site [53] 6. Time from the motion onset [54] 7. Time from the seismogram [55] 8. Calculted speed (m sec-1 ) [56] 9. Calculated speed (km hour-1 ) [57] The aim of the calculation was to plot the curve of velocity distribution for the movement of the glacier avalanche from the Dzhimarai-Hoh wall to the Skalistyi Rocky Ridge escarpment. [58] The Greenwich time of 16-15-30 which terminated the time interval no. 4 in the seismic record obtained by the Tsei seismic recording unit did not show any amplitude peak. This proves that there was no significant shock of the glacier on the Karmadon Gate. This was indirectly proved by the morphology of the day surface of the newly formed avalanche: no counter slope was formed (Figure 15). Although the retardation of the avalanche was fairly high over the distance from the Genal settlement to the Karmadon Gate tunnel, yet, there was no shock. The Glacier Body in the Karmadon Basin[59] The ice that filled this basin changed substationally its appearance. The absolutely lifeless territory looked as the piling up of large dirty ice blocks covered by ash-color fine ice crumb. It was notably colder in the basin. During the first two months the ice grew more compact with its individual blocks being frozen together. The ground surface became notably lower, levelled and passable. The surface moraine began to form. [60] The results of the topographic survey of the glacier avalanche (September 2002) were used to calculate its volume (115 million m 3 ) and area (2.1 km 2 ). Because of its forced stopping the avalanche acquired the form of a lying wedge about 3.8 km long with the maximum thickness of about 160 m in the frontal part of the avalanche, and the width varying from 600 m to 900 m. During its retardation, the block material of the avalanche produced a significant promontary which filled the mouth of the right-side ravine damming the Kauridon small river. As to the Genaldon River, which lost its channel in the avalanche area, one week was enough for it to form a channel on the ice surface along the left side of the valley. In the lower part of the avalanche, the water flowed to its internal hollows and was thrown out into the canyon. All of the back-water pools that formed along the Genaldon River were of the flow-through type and disappeared very rapidly.
The Dammed Saniba Lake[62] This lake began to form after the formation of an ice avalanche (Figure 4) in the Karmadon Trough on 20 September 2002. The ice mass blocked the exit from the right lateral canyon damming the channels of two small rivers: the Kauridon R. with the flow rate of 1.2 m3 sec-1 and the Fardon R. with the flow of 0.8 m3 sec-1. This produced a basin of a future lake, which began to be filled with water. The total debit of these two rivers was about 2.0 m3 sec-1, capable of the water accumulation of 170,000 m3 day-1. [63] However, the situation developed much more rapidly. On 24 September 2002, trying to find an exit, the water of the Genaldon R. broke through the right side and flowed to the lake during four days. By the beginning of this break, the lake contained about 0.6 million m 3 of water. On 28 September this break through terminated, yet, the water of the lake rose to the height of 20 m more, its volume being 2.5 million m3. Two small streets were flooded in the Gornaya Saniba Village. On 18 October, 2002, the lake water level ceased to grow, but on October 22 a water channel was formed at the surface of the ice along the right side of the valley. By that time the area of the lake was 260,000 m2, and its volume was 3.5 million m3. No one knew how all of this will end. [64] The inhabitants of the flat land settlements, located along the banks of the Gizeldon R., (the Genaldon R. being its right tributary, see Figure 3), felt a great danger and were ready to abandon their houses in the case of the lake breaking through. Observations of the lake state were carried out during the days and nights. The channel in the ice surface grew notably deeper. The water level in the lake began to decline very rapidly and became 7 m lower during 15 days. The second break of water took place in mid-July 2003, when the water level became 2.5 m lower during 2 days. [65] On 10 and 11 July the lake was inspected by the experts of the Moscow University, and the first topographic survey was carried out. In 10 July, 2003, the lake contained 1.32 million m3 of water. The lake water table was at the level of 1319.63 m.
Mud Flow
[68] By the present time, at the lower stages of the mud flow, the Gizeldon R. flow returns to the initial basis of the bottom erosion with the formation of terraces, the vegetation winning back its lost territories. New roads and bridges are being built in the segments of the demolished roads. No road is planned to be built along the canyon. Transit Zone
Discussion of Results1. The Break Up of the Firn Fields
[71] It cannot be excluded that the reactivation of the fumarole emanations was caused by seismic dislocations during the earthquake no. 244 (KMV-2002 data sample). The vicinity of the Kazbek Volcano explains this phenomenon. The upper reaches of the Genaldon Ravine include a great number of flowing thermal highly mineralized water springs, this being indicative of deep heat vicinity.
[73] Of particular interest is the fact of the rapid cessation of the fumarolic emanations after the catastrophe. It is most likely that another reconstruction of the stress field took place as a huge rock mass vanished from the ground surface. After about a week, no evidence of gas emanation was recorded. 2. The Ice-Rock Body in the Lower Part of the Kolka Glacier Basement, Known as "Rigel"[74] Examining photograph 1 in Figure 13, one can see a transverse ledge in the lower part of the glacier bed. This body, consisting of ice with the high content of a lithogenic material, is geographically inside the paleoboundary of the gone glacier. Its morphology does not agree with the appearance of the post-catastrophe formation. Apparently, this is the terminal part of the glacier, which played the role of a dam which prevented the Kolka Glacier to act as a valley glacier.[75] It was mentioned earlier that a large amount of lithogenic material had been transported to the Kolka Glacier by the firn avalanches. As the ice masses were transported plastically from the rear area to the tongue, the content of lithogenic material increased because of the surface, internal, and bottom melting of the enclosing ice. At the lower levels of the glacier, the content of the lithogenic material attains the level where plastic deformation declines and later vanishes. The ice acquires a rock skeleton. It follows that the glacier locks itself in the zone of predominant nutrition. Under the conditions of normal accumulation (typical of the Kolka Glacier) the glacier stability is controlled by the strength of the dam created by the glacier itself until this strength is sufficient.
Conclusion[78] The Karmadon catastrophe is not a scientific puzzle, in spite of its unique character. The preliminary study of the conditions for the development of a catastrophic process in the Genaldon Gorge was multisided. Each natural factor which might affect the glacier was studied. However, using any combination of the external factors, this avalanche is classified as an exogenic motion of a catastrophic level, that is, as a slope process. Yet, the level of the scientific problems produced was extremely high. To avoid the repetition of any tragedy in future, the Kolka Glacier area must be controlled by several services simultaneously. The meteorologic monitoring should be accompanied by a topographic one. The results of geothermal, meteorologic, and seismic observations should be correlated with the plastic deformation rate of the glacier, determined using high-accuracy instruments. This will enable the calculation of the integral values of the changing physico-mechanical properties of the active body automatically in the field conditions. In the case of the declining glacier stability to a dangerous level, special active measures need be developed to provoke its descent. Acknowledgments[79] I thank I. V. Galushkin (InfoTERRA, Vladikavkaz), L. V. Desinov (Institute of Geography, Russian Academy), G. A. Dolgov (the Respublican Center of North Osetian Geoecologic Monitoring), A. A. V'ukhin (RSO-Alaniya National Park), E. T. Manukyants (Vladikavkaz), S. S. Chernomorets, and O. V. Tutubalina (Moscow University Center of Enginering Geodynamics and Monitoring). ReferencesRogozhin, E. A., L. E. Sobisevich, and Yu. V. Nechaev (2001), The Geodynamics, Seismotectonics, and Volcanism of the North Caucasus Region, edited N. P. Laverov, 335 pp., "Region" (Regional Social Organization of Geoscientists Dealing with the Problems of Applied Geophysics), Moscow. Rototaev, K. P. (1974), The Kolka Glacier: Facts and conclusions, Proc. Glaciological Studies, 24, 3. Savich, A. I., V. G. Vladimirov, A. A. Godzikovskaya, and A. L. Strom (1996), Estimation of Seismic Danger for the Zaromag Hydroelectrostation, RAO "Electric Stations of Russia", Report, vol. 1, Hydroproject Institute Company, Moscow. Teplyakova, A. S. (1984), The main stages of the topographic and recent structural evolution of the Gornaya Osetia territory, Candidate Dissertation, 68 pp., MSU, Moscow. Received 25 February 2006; revised 18 August 2006; accepted 2 September 2006; published 28 November 2006. Keywords: mountain glaciers, firn massifs, avalanches, landslides, earthquakes. Index Terms: 0720 Cryosphere: Glaciers; 1620 Global Change: Climate dynamics; 1621 Global Change: Cryospheric change. ![]() Citation: 2006), Glacial catastrophe of 20 September 2002 in North Osetia, Russ. J. Earth Sci., 8, ES4004, doi:10.2205/2006ES000207. (Copyright 2006 by the Russian Journal of Earth SciencesPowered by TeXWeb (Win32, v.2.0). |