The analysis of the sensed materials for the reconstruction of the glacier Kolka collapse

M. Nikitin - Moscow State University Lomonosov, Russia

Christian Huggel - University of Zurich, Switzerland

Melissa Schwarz - Swiss Federal Research Institute WSL

O. Goncharenko – SRL ”Geologorazvedchik”, Russia

I.V. Galushkin - SRE “InfoTERRA”, Vladikavkaz, Russia

Annotation

The catastrophic collapse of the Glacier Kolka in 2002 aroused scientific interest in the problems of mountain territories, related to the hazardous natural events.

Many Russian and foreign organizations took part in the investigations of the catastrophe, exchanging data, ideas and results. This work is the result of the close cooperation. The authors of the article worked independently, but their results supplemented each other, that showed the correctness of the direction of investigations.

The basis of the work is satellite imagery QuickBird of high resolution, the materials of digital aerial pictures, aerial photographs, made before and after the event, ground investigations and mathematic models of the ice-rock mass transit from the failure zone to the accumulation zone. The results of modeling confirmed the suppositions about the distribution of material during the ice flow transit.

As a result of fulfilled works:

• A scheme of the decoding of accumulations’ complex over the whole region was compiled;
• A version of the interpretation of ice-rock and mud flow formation dynamics, their transit and accumulation, was suggested;
• Preliminary regularities of solid components distribution in the quasi-glacier body, as well as in the transit and discharge zones of the mudflow, were got.

At least three flow fluctuations were revealed:

• Initial “Genal” phase, with the maximal front impact on the slopes and avalanche-like/air uprush of the overlapped debris material. The phase was initiated by the ice-rock mass collapse from the slope Dzhimarai-Khokh;
• Main “Kani” phase, consisting of two sub-phases which filled up the central part and the left board of the depression to the Karmadon gates;
• Final “Saniba” phase, which has a picture of plastic flow with the traces, observed in the near-bottom part of the bed, which are superposed on the previous phases.

Key words

Catastrophic glacier Kolka collapse, decoding of remotely sensed materials, phases of the glacier Kolka collapse.

The analysis of the remotely sensed materials for the reconstruction of the glacier Kolka collapse

Introduction

Many organizations from Russia and foreign countries took part in the investigations of the Kolka catastrophe, exchanging data, ideas and results. This work is the result of the close cooperation. The authors of the article worked independently, but their results supplemented each other, that showed the correctness of the direction of investigations.

The basis of the work is satellite imagery QuickBird of high resolution, the materials of digital aerial pictures, aerial photographs, made before and after the event, ground investigations and mathematic models of the ice-rock mass transit from the failure zone to the accumulation zone. The results of modeling confirmed the suppositions about the distribution of material during the ice flow transit.

The main task for the remote data processing is the analysis of the geological environment conditions in the zone, affected by the Karmadon ice-rock flow after its passage, the structure of accumulated masses formed by the flow, the reconstruction of the event itself.

Methods and equipment

The basis for the work is satellite imagery QuickBird of high resolution. The obtained plane photo-base was quite acceptable for the decoding by its quality and resolution, together with the materials of digital aerial survey.

All the remotely sensed materials were distributed by sections, isolated distinctly from each other. In the limits of every section, all the data were thoroughly visually analyzed, compared with the plane satellite image of the section and transfer to the latter of all the elements of the decoding. Moreover, a stereoscopic decoding of large-scale aero photographs, made during the flights in November 2002, was realized, that allowed detailing considerably the structure of the transit zone and ice-rock accumulations. The availability of pictures of the same object from different angles and with different scale allowed not only to map with a fair degree of reliability, but also to determine its genetic belonging, the particularities of interrelations with other accumulations.

At the second stage, the general analysis, revision and lock-on of the genetic accumulation types to each other in the limits of the adjacent sections were made.

The applied methods of analysis and decoding allowed working out a detailed scheme of positional relationship of the genetic accumulation types formed as a result of the 20 September 2002 event.

The modeling by original procedure allowed confirming the conclusions.

The dynamics of ice-rock and mud-flow formation.

Three phases of the accumulation’s generation were distinguished according to the decoding results and characteristics of the ice body relief structure: Genal, Kani and Saniba.

The presence of phases was observed in the transit zone and was conditioned by the cause, the progress of the event and the particularities of the transit zone. Even if we suppose that the start of the whole mass was a single-phased event and don’t take into consideration a factor of turn on the glacier Maili, the uniform distribution of such a mass is not possible in the valley Genaldon. It is confirmed by the modeling of the collapse, made by the Swiss Federal Research Institute WSL. The model does not take into account the above-mentioned factors, but event without it the flow should be divided into some “portions” (fig. 2).

Three main phases of the process, called by the names of three settlements in the zone of the deposits, are:

• Genal
• Kani
• Saniba

Fig. 1. The traces of phases of the ice-rock mass movement.

Fig. 2. The modeling of the ice-rock mass collapse.

Genal (initial, front) phase of accumulations.

The phase was initiated by the collapse of ice-rock masses from the slope Dzhimarai-Khokh and left a trace on the Kolka’s left board (fig. 3).

Fig. 3. The trace of the collapse of ice-rock masses from the slope Dzhimarai-Khokh.

An imprint has large amplitude and reaches 1 100 m by spread and 300 m by height. At that, the avalanche did not reach its maximal dimensions, as it met with an obstacle in the form of bed rocks, which cut its roof part. The accumulations of the Genal phase were formed by initial, high-speed stage of the flow (which has a rotor type of movement, as I.M. Vaskov pointed to), transporting smoothed ice blocks of different size with smaller quantity of detritus-block filler. The mass contained considerable quantity of air and represented an avalanche-like flow where ice debris was smoothed.

This stage of the flow was the first to reach the depression; it was stopped along the main displacement vector by the left board of the depression near the ruins of the settlement Genal and, continuing to move further along the south-east slope of the Rocky Range, it filled the Kauridon and Genaldon valleys along the right board up to the Karmadon gates. A fragment of its high splash remained directly under the settlement Genal (fig. 4)

Fig. 4. The splash of the first phase of the ice-rock flow.

The traces of the shock wave were observed during the field works on the slope, including the formation of crushed and driven in the slope trees and rock blocks (fig. 5).

Fig 5. The traces of the shock wave.

The Genal accumulation phase along the vector of main flow impact entailed mass subsidence in the detachment cirques. The overlap contact of the following initial sub-phase of the Kani accumulation phase has a linear form and is clearly defined.

The accumulations of this phase were revealed along the right board of the valley Genaldon-Kauridon along south-west slope of the Rocky range in the form of a narrow strip, stretching out to the Karmadon gates. The phase filled up the right, eastern board of the Karmadon depression, leaving the western part free for further filling (fig. 6).

Fig. 6. The deposits of the Genal phase (are marked by brown).

Kani (main, central) accumulation phase.

The accumulations of this phase, second within the limits of the ice body, are situated near the settlement Nizhnee (Lower) Kani, that’s why they are called Kani. They fill up central and western parts of the Karmadon depression and penetrate along its left board to the Karmadon Gates. The Kani phase is mainly formed by large-block ice to 10-30 m in diameter and probably contains basic volume of heterogeneous fragmental material from the Glacier Kolka destruction zone, including the material from the failure zone. To all appearances, it corresponds to the main stage of mass evacuation from the Glacier Kolka bed and overlaps the accumulations of the Genal phase in the Karmadon depression. The contact between Genal and Kani phases of the flow is distinctly observed in the central part of the perspective picture (fig. 7).

Fig. 7. The contact between Genal and Kani flow phases.

Unlike the previous phase, the Kani accumulation phase has sharply defined roughly-uneven ridge relief. The presence of ridges on the surface can be interpreted as a mass “hummocking” effect in the course of the collision of the flow front and accumulations of the previous Genal phase, including their subsequent compression. The detachment structures with flat surface in the rear parts of the ridges attract attention, as well as their curve in the direction of mass displacement and rather distinct thrust shape of the contact with the underlying Genal flow phase.

Within the bounds of the Kani accumulation phase with unified flow morphology, two sub-phases can be marked out: leading, marked as II₁ and posterior II₂ (fig. 8, 9).

Judging by the surface morphology, the leading accumulation sub-phase (II₁) was moving mainly along the left board of the depression towards the Karmadon Gates after the mass thrust onto the Genal accumulation phase. When ice masses were being “pressed in” the considerably narrow space in front of the Karmadon gates between the steep rock board of the depression and Genal accumulation phase, a multitudinous grid of parallel dendritic detachment cracks, appeared, which can be taken kinematically as shear deformations inside the flow.

Fig. 8. Kani phase, leading sub-phase (marked by brown)

The formation of the detachment cracks – left-side displacement was followed by the ice mass pressing in the lower parts of the ravines on the left board of the depression, where the vector of mass displacement was partly directed after the front impact on the Genal phase of the flow. The detachment cracks, which were often situated parallel and had a wing form in horizontal plane, were formed completely by the time when the flow stopped. As a result of the ice mass displacement along the left board of the Karmadon depression and its crowding in the frontal part, a positive longitudinal step was formed in the relief up to the Karmadon gates, where it was the most clear-cut. The longitudinal step between Genal and leading sub-phase of the II₁ Kani phase is well observed in the relief by the presence of bench and parallel system of cracks which separate them in the Karmadon gates.

The subsequent accumulation sub-phase (II₂) was determined by its morphological features in the central part of the Karmadon depression (fig. 9). The front of accumulations, sharply defined in the relief as a bank, bent in horizontal plane, partly moved up to the leading accumulation phase. It was situated between the settlements Kani and Genal.

Fig. 9. Kani phase, subsequent sub-phase (marked by brown)

The contact surface between the sub-phases II₁ and II₂ has a bent shape.

In the basis of the frontal bank, a line of the interface is observed, which represents morphologically a thrust surface. The displacement surface between the sub-phases II₁ and II₂ of the Kani accumulation phase has a ground character due to the slipping on the surface of underlying accumulations. The accumulation sub-phase II₂ is partially stretching in the direction of the settlement Saniba.

Saniba (final) accumulation phase.

Saniba or final, rear accumulation phase (fig. 10) is terminating the formation of the quasi-glacier ice body. In the model of the Suisse Federal Institute is looks in the following way (fig. 11).

It was formed when almost all the Karmadon depression was filled with previous accumulations. The phase originated from the tail part of the ice-rock flow, which was moving in the valley Genaldon with the less speed than its previous stages and which had as a consequence, less carrying force and was water-enriched. It explains the presence of the element of mass flowing which is seen clearly in the relief of its frontal part.

Fig. 10. Saniba or final, rear accumulation phase.

Fig. 11. The view of the Saniba phase on the model of the Swiss Federal Research Institute WSL

The front bank is as sharply-defined morphologically, as in previous cases, with the mass hummocking and presence of border seam with the underlying accumulations of the Kani phase.

The “slipping” of the accumulations of the Saniba phase on the Kani accumulations’ surface has a bent shape in horizontal plane with the turn of masses in the direction of the river Kauridon valley, that is well observed on the picture (fig. 12).

Fig. 12. The contact of Saniba phase accumulations on the surface of the Kani accumulations.

Results

The work resulted in following:

• A decoding scheme of accumulations in the focus of dam formation, in the glacier Kolka bed and the river Genaldon valley, formed after 20.09.2002, was worked out;
• A variant of interpretation of ice-rock and mud-flow formation dynamics, their transit and accumulation;
• Preliminary regularities of the solid component distribution in the quasi-glacier ice body, as well as in the transit and discharge zones were revealed.

A scheme of the event was reconstructed by means of remotely sensed materials, and it agrees with the modeling data.

A description of the ice-rock deposits, conditions of their bedding and positional relationship with underlying bed deposits were made.

A secant and superposed positional relationship of deposits of nonsimultaneous phases inside the general flow, the presence of complex kinematics of longitudinal and cross wave fluctuations were observed.

At least three flow fluctuations were revealed:

• Initial “Genal” phase, with the maximal front impact on the slopes and avalanche-like/air uprush of the overlapped debris material. The phase was initiated by the ice-rock mass collapse from the slope Dzhimarai-Khokh;
• Main “Kani” phase, consisting of two sub-phases which filled up the central part and the left board of the depression to the Karmadon gates;
• Final “Saniba” phase, which has a picture of plastic flow with the traces, observed in the near-bottom part of the bed, which are superposed on the previous phases.

Acknowledgements

The authors express their gratitude to the Suisse Agency for Development and Cooperation of the Suisse Ministry of Foreign Affairs and personally, to Mr. Dieter Dreyer for the possibility of collaboration between Russian and Suisse scientists.