The Devdoraki Glacier in the Georgian Caucasus Keeps Collapsing

On May 17, 2014, a catastrophic rock-ice avalanche and glacial mudflow took place in the Tergi (Dariali) gorge, blocking strategic infrastructure in Georgia. The disaster resulted in the death of nine people. About 200 people were evacuated by helicopter from a border crossing checkpoint and nearby areas. Glacial mudflow destroyed the Trans-Caucasus gas pipeline, Dariali Hydropower Plant, and an international road connecting Georgia and Russia. This event inflicted several tens of millions of Georgian lari in damages to the country’s budget.

Sequences of the collapse

According to archival data, at least six ice and ice-rock avalanches fell from the Devdoraki Glacier onto the Tergi River valley during the period 1776-1876, the two largest occurring on June 18, 1776 and on August 13, 1832. The first blocked the Tergi River for three days and was breached catastrophically; the second was about 100 meters high and about 2 kilometers wide and blocked the Tergi River for 8 hours. After breaking the dam, the glacial muflow caused a great amount of damage to Vladikavkaz in North Ossetia, Russia.

Since 1832, several new blockages were forecasted, but either the ice-debris masses did not reach the Tergi River, or the forecasts failed altogether. For example, the Devdoraki Glacier advanced in 1866 and 1867, raising alarm and forcing researchers to monitor its position. But the ice debris developed slowly and the Tergi River was not blocked. Again, in 1876, there was a danger of a blockage since the glacier greatly increased and advanced by about 150 meters.

Scientists have published other observations of the Devdoraki Glacier, up to the first decade of the 20th century (Tielidze et al., 2019).

Latest investigation

I, along with several colleauges, published in April work that presents the sequence of the Devdoraki Glacier hazards and analyzes the latest collapse, which occurred on May 17, 2014.

An ASTER image from May 16, 2014 shows traces of relatively small rock fall, revealing instability in the glacier. (Figure 1a). The result of the disaster is shown on the Landsat image from July 11, 2014 (Figure 1b) and in the PLEIADES image from May 18, 2014 (Figure 1c).

Figure 1. a – ASTER image 16/05/2014; b – Landsat L8 image 11/07/2014; c – PLEIADES image 18/05/2014

The resulting mudflow into the Tergi (Dariali) Gorge blocked the Tergi River for several hours, creating a 20-30 meter-deep lake (Figure 2) with a volume of at least 150,000 cubic meters. The height the ice and rock debris fell from the glacier face to the gorge was about 3.2 km, while the distance was about 10.2 km.

We estimate that the leading face of the Devdoraki Glacier advanced about 180 m between 2014 and 2015, which was caused mostly by rock-ice avalanche deposits. This part of the glacier should countine to be monitored as it could heighten debris flow activity in the future.  

Figure 2. Tergi (Dariali) gorge, result of Devdoraki glacial-mudflow (17/05/14) (Source: Levan Tielidze).

Possible causes

We considered the main hypotheses behind these events, namely a) tectonic and seismic (Figure 3a), b) permafrost (Figure 3b), c) volcanic, and d) morphological factors; interpreted the data for mechanisms and velocities of the catastrophic movement, and argued that the 2014 event should not be classified as a glacier surge, althoughthe possibility of similar glacial surges can not be excluded.

Figure 3. a – Tectonic map of the study region (compiled by authors). b – Permafrost zonation index map

The Kazbegi-Jimara massif should be considered as a natural laboratory that enables the investigation of rock-ice avalanches and glacial mudflows.

Recommendation

We recommend to construct a road tunnel on the east (right) slope in the Tergi valley (Figure 1c) and to discontinue the Dariali Hydropower Plant construction in order to mitigate risk and avoid incidents including deaths in the future.

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Dispatch from the Cryosphere: Glacier Decrease in the Georgian Caucasus

The Greater Caucasus extend along the northern territory of Georgia for about 750 kilometers. The spatial distribution of modern glaciers in the territory of Georgia is stipulated by the peculiarities of atmospheric processes, morphological-morphometric conditions, and their interaction. The northern slopes and watersheds of the Greater Caucasus contain more glaciers than the southern slopes, which is due to the relatively cold climate, higher relief and extremely partitioned slopes, gorges, and cirque depressions that are associated with the Würm glaciation. Georgian glaciers are concentrated mostly in the southern watersheds, as well as in the sub-ranges of the Greater Caucasus and Kazbegi massif.

The importance of studying Georgia’s glaciers

Regular and detailed observations of alpine glacier behaviour are necessary in regions such as the Georgian Caucasus, where glaciers are an important source of water for agricultural production, and runoff in large glacially fed rivers (Kodori, Enguri, Rioni, Tskhenistskali, Nenskra) supply hydroelectric power stations. In addition, glacier outburst floods and related debris flows are a significant hazard in Georgia and in the Caucasus.

In the last century, some experience was gained in the study of glaciers in Georgia, but after the economic difficulties of the 1990s, glaciological studies stopped. In recent years, though, glaciological research has been restored, and nowadays a glaciological group is studying the glacier variations in the Georgian Caucasus in different river basins.

The latest study

In the scientific work that I have published in The Cryosphere, the changes in the area and number of glaciers in the Georgian Caucasus were examined over the last century by comparing recent Landsat and ASTER images with older topographical maps and images.

Glacier reduction over the last few decades

Chalaati is one of the largest glaciers in Georgia, consisting of two flows and fed by the slopes of the over 4,000-meter-high peaks of Ushba, Chatini, Kavkasi, and Bzhedukhi Mountains. Among the glaciers on the southern slopes of the Greater Caucasus, this glacier has the lowest terminus position for the whole Caucasus region — 1,980 m above sea level and intrudes into the forest zone.

Due to the impact climate change, the area of Chalaati Glacier decreased from about 12.2 square km to 9.2 square km over the last century. It is possible to identify the drastic change of the glacier by comparing of old and modern images.

Chalaati Glacier reduction seen by comparing images from 1890 (left) and 2011 (right) (Source: Levan Tielidze)

Kirtisho is the largest glacier in the Rioni River basin with an area of about 4.4 square km. It is a valley glacier lying in the central section of the Greater Caucasus. This glacier is connected to the firn basin of the Bartui Glacier on the northern slope of the Greater Caucasus. In the years of 1930–1940, its leading edge hung over the ledge in front of it at an elevation of about 2,400 m. Today, the ice tongue terminates at a height of 2,660 m.

Kirtisho Glacier terminus in the 1930s (above) and 2010 (below) (Source: Levan Tielidze)

Gergeti (Ortsveri) is one of the largest glacier in the Tergi (Terek) River basin. It flows down the south-eastern slope of Kazbegi massif (5,047 m). A glacier firn basin is located at about 3,900 m. According to data from the 1960s (Levan Tielidze, 2017), the area of Gergeti Glacier was about 6.8 square km. Its sharply pointed tongue terminated at an elevation of 2,880 m. During the last half century the glacier has diminished by about 0.9 square km.

Using repeat photography, it is possible to depict the dramatic change to the glacier over the last century.

Gergeti Glacier reduction seen in images from the 1890s (above), the 1950s (middle), and 2011 (below) (Source: Levan Tielidze)

Overall, according to my research, the Georgian Caucasus region experienced glacier area loss over the last century at an average annual rate of 0.4 percent with a higher rate in the eastern Caucasus than in the central and western sections. Glacier melt is faster for southern glaciers than northern ones. A combination of topographic factors including glacier geometry and elevation, as well as climatic aspects such as southern aspect and higher radiation input, are related to the observed spatial trends in the glacier change analysis.

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