Lake breakout

Lake breakout is a geological term that refers to the collapse of a (usually high-altitude) lake. High-altitude lakes tend to form in volcanic craters – where they are called crater lakes – or in valleys dammed as the result of earthquakes or glacial or volcanic deposition. Lake breakouts are most common a few weeks or months after a volcanic eruption as a river becomes blocked by volcanic debris.

Process

The walls of such lakes can be unstable and may be breached after fresh earthquakes or because of erosion. As water rushes outwards, the initial channel is cut wider and deeper, further increasing the flow. This may cause the lake's rim to collapse abruptly. The usual result is for huge amounts of water to be displaced, incorporating a great deal of sediment which increases it in volume by as much as two or four times, or even more. This produces violent floods and lahars with devastating effects for any settlements in their path.

Historical events