climateadaptation:

Video of a glacier literally exploding. It’s called a “jökulhlaup,” a type of glacial flood caused by volcanic or geothermal pressure. An extremely rare event, it’s rarely caught on camera. The above catastrophic jökulhlaup occurred in 2010 when the Eyjafjallajökull erupted.

A jökulhlaup (Icelandic pronunciation: [ˈjœːkʏl̥ˌl̥øip]) is a glacial outburst flood. It is an Icelandic term that has been adopted by the English language. It originally referred to the well-known subglacial outburst floods from Vatnajökull, Iceland which are triggered by geothermal heating and occasionally by a volcanic subglacial eruption, but it is now used to describe any large and abrupt release of water from a subglacial or proglacial lake/reservoir. 

Since jökulhlaups emerge from hydrostatically-sealed lakes with floating levels far above the threshold, their peak discharge can be much larger than that of a marginal or extra-marginal lake burst. The hydrograph of a jökulhlaup from Vatnajökull typically either climbs over a period of weeks with the largest flow near the end, or it climbs much faster during the course of some hours. These patterns are suggested to reflect channel melting, and sheet flow under the front, respectively.

Similar processes on a very large scale occurred during the deglaciation of North America after the last ice age (e.g. Lake Agassiz), and presumably at earlier times, although the geological record is not well preserved. Via Wikipedia (great entry!)