What are Jökulhlaup's

What is a jökulhlaup:

Sudden and rapid draining of a glacier dammed lake or of water impounded within a glacier

Effects:

	Flooding, fast and without much warning
	Loss of life
	Destruction of roads, railways etc.

What causes jökulhlaup:

	Glacier blocks a stream in a valley
	Geothermal melt collects beneath the glacier
	Moraine left by retreating glacier

How big are jökulhlaup:

	Grímsvötn, Iceland, 1934: Peak flow 5 *10⁴ m³ s^-1 (about 1000 times the normal Snohomish river discharge)
	Lake Missoula: 10⁷ m³ s^-1 estimated

For more of this short tutorial, with a few examples and a tiny bit of physics visit
http://www.turdus.net/science/jhlaup/