Devdoraki Glacier, Kazbek: history of studies of natural hazards in XIX and the beginning of XXI centuries

The Devdorak Glacier located on the Eastern slope of Mt. Kazbek is known since the end of the 19th century for its catastrophic ice discharges into the river Terek canyon. The so-called «Kazbek blockages» stopped the river flow, thus leading to formation of a dammed lake. The lake was then broken through by the heavy floods. Evidences of such events are available for 1776, 1785, 1808, 1817, and 1832. Later on, the glacier surges did sometimes occur, but they never reached the river. The blockages interrupted the traffic on the Georgian Military Highway – the basic way across the main ridge of the Caucasus, for long time periods. Investigations of the Devdorak and other Mt. Kazbek glaciers were organized in 1862 and lasted until the end of 19th century. But the scientists could not reach a common consensus in resolving the main issues, i.e. the causes of the «blockages» and possibilities of their soon repetitions. Different hypotheses explaining the ice discharges by either morphology of the glacier and the river valley or by earthquakes were proposed. Some authors insisted on a probability of occurrence of new «blockages». But the mostly widespread opinion was that since all the Kazbek glaciers were in the state of degradation any risk of new «blockages» was absent while this tendency remained. Since the previous disasters, the Devdorak Glacier posed no threat for about two centuries. However in May 2014, a huge downfall of rock and ice suddenly came down on the glacier in its upper zone. As a result a large mass of rock, stones, and mud blocked the Terek river bed again. This event was not related to regime of the glacier itself. Most likely it was a new manifestation of the Mt. Kazbek volcanic activity.