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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