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Merzbacher's disappearing lake

This unique lake 3,500m above sea level was first discovered by the German mountaineer and geographer Gottfried Merzbacher in 1902. Whilst on an expedition for the Russian Geographical Association that was attempting to reach Khan Tengri peak by way of the South Inylchek Glacier, Merzbacher observed the unique phenomenon of a glacial lake that lost all of its water in the space of just three days.
Making another journey to the same region the following year he was able to observe that the lake had fully replenished its waters and that the filling and rapid draining were actually part of an annual cycle. How this process takes place is unclear. The lake first starts to appear when an ice dam blocks the gorge and melt-water starts to accumulate from the glacier. There is a higher basin 400m above the lower one and it is icebergs that have plunged down from this that combine to form the ice dam. The lower lake grows to around 3.5km in length and 1,2km wide until a point is reached, usually in mid-August, when the lake's waters have risen to such a point that the ice dam is lifted and the accumulated water suddenly breaks free underneath the floating ice.

This is one theory; another suggests that the pressure of the water causes the ice wall to deform, opening cracks that allow the water to escape. A third theory links the drainage of the lake with a canyon in the South Inylchek Glacier, which when it fills with water and subsequently drains away, it is suggested, creates a suction effect that draws the water away from the glacial lake. Whatever the true science of the matter, the rapid drainage causes floods in the valleys of the Inylchek and Sary-Jaz rivers for about a week afterwards. The lake is then left completely empty until it starts to fill the next spring, repeating the annual cycle.

Although the emptying of the lake might appear to be a unique occurrence, there are a handful of similar events that take place elsewhere in the world - in Iceland, Greenland and Switzerland - but it is at Kyrgyzstan's Merzbacher Lake that the phenomenon is so regular and reliable. The timing of the August event is not written in stone, however - in 2003, it took place in July.