When the levee breaks

A levee to control the glacial river Markarfljót in S-Iceland, seen from the mount Stóra-Dímon, which stands in midst of the sandy riverbed plain. Markarfljót used to meander back and forth across the plain until it was tamed by levees, starting in the 1930s. This has been successful, so that much of the protected land is revegetated and even part of new farms. Geologists have found evidence of vast floods in the past, triggered by sub-glacial volcanoes, mainly Katla in Mýrdals glacier. The last time it erupted, in 1918, it triggered a flood surpassing the Amazon for a brief time. Katla's floods usually fall to the southeast, but now it is known that they can run to the west, into Markarfljót, and authorities are on alert if this happens. So, if these levees break, it will probably be in a spectacular flood. UPDATE: On 14 April 2010, there was a huge volcanic flood in Markarfljót, triggered by an eruption in a 2 km long fissure underneath the glacier Eyjafjallajökull.