Kolka Glacier

Kolka Glacier Хъолхъа
Kolka Glacier in 2001.
Type	Cirque / Valley / Hanging
Location	North Ossetia–Alania, Russia
Coordinates	42°44′23″N 44°28′24″E / 42.73972°N 44.47333°E / 42.73972; 44.47333
Area	2.47 km2 / 3.74 km2 (including the hanging parts)
Length	3130 m
Terminus	Moraine
Status	Growing

Kolka Glacier (Ossetian: Хъолхъа) is a glacier in North Ossetia, Russia, near Mount Kazbek, known for its surging properties. The most recent and the most powerful surge took place on 20 September 2002, resulting in the death of at least 125 people.

There are only a small number of glaciers in the Genaldon River's basin, the largest being Maili at approximately 6.8 km² (2.6 sq mi) in area. The Kolka Glacier, located next to Maili, is a cirque / valley glacier, with some hanging parts.

Kolka is fed by avalanches and collapses of firn and ice all year round. Its lowest and highest points are located at 3,000 m (9,800 ft) and 3,450 m (11,320 ft) above mean sea level respectively. More than two-thirds of the ablation zone's surface is covered by a morainal layer up to 1 m (3 ft 3 in) thick. This and other features, such as relatively gentle slopes, a deep cirque and the presence of a lateral moraine restricting the ice flow and forcing it to make a sharp turn, makes the glacier very prone to accumulation of subglacial meltwater.

Historically, the local population have been well aware of the dangers associated with the glacier, which is evident in the unusual locations of the auls. Most settlements of the Caucasian Mountain valleys were built on the valley floor, however, all the old auls of the Karmadon Valley were built on the valley slopes or even on the crests of the nearby ridges. More recently however, a number of settlements have been built on the valley floor.

The first well-documented surge occurred on July 3, 1902, in the midst of an unusually hot summer, when the mean temperature was 2.7 °С higher than normal. A series of heavy rains occurred in June and early July, filling the river basins with rain and melt water and by the middle of June, a tongue of the Kolka glacier was on the move. Loud crackling was heard in the nearby settlements and, at times, the Genaldon river was turned into a stream of black mud. By the end of June, the heavily cracked glacier tongue was seen in a narrow gorge next to the Maili glacier. The tongue then partially collapsed, temporarily damming the river. A pulp of ice, water and morainal material then formed a mudflow which streamed down the river's course, stopping near the Tmenikau aul high on the valley slope. The glacier, which was still on the move, then blocked the gorge causing it to fill up with meltwater.