Glacial catastrophe of 20 September 2002 in North Osetia

Discussion of Results

1. The Break Up of the Firn Fields

Figure 27

[70] The photographs of the source area, obtained from the helicopter on 22 September 2002, clearly showed two fumaroles on the northeastern Dzhimarai-Hoh slope (Figure 27). Both of them emitted light-color opaque gas which slided slowly downward as a long cloud. The attempt of landing a group of researchers in the vicinity of the glacier was cancelled because of the strong hydrogen sulfide odor. The landing was cancelled.

[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.

Figure 28

[72] This scenario agrees with the potential slow decay of the firn fields in some local area. The endogenic gas flows at the bottom of the firn field were accompanied by thermocarst development. During the further development of this destructive process, the ice-firn massif lost its integrity and, hence, its strength. The firn field, loosened by the thermocarst, began to crumble and collapse (Figure 28). This photograph was made simultaneously with the photograph A (see Figure 9) by the tourists who visited this area at the end of August 2002. These photographs were included into the field of Figure 13, where the review photograph (13-1) shows all of the sites of this survey. Comparing Figure 28 and Figure 9a, one can see that the degradation of the firn fields proceeded in accordance with the fumarole positions.

[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.

Figure 29

[76] Turning to Figure 29, it should be noted that the Dzhimarai-Hoh firn fields are obviously unrelated to the Kolka Glacier motion in 1969-1970, yet, the latter did occur. The different character of the Kolka movements in the two latter cases can be explained by the difference in the systems and mechanisms of fault formation in the glacier body, as the restrictive forces of a critical level accumulated in it.

Figure 30

[77] It appears that the "pulsation", or to be more exact, the tendency of the Kolka Glacier to lose periodically its rigidity is controlled by its ability to form a zone with a high content of a stone material in the lower level of its body. The high strength of this formation is undoubtful: "Rigel" withstood this catastrophe and survived (Figure 30).