Ash cloud root of Dark Ages

December 1, 2000

A pall of ice clouds could have ringed the globe following the colossal eruption of an Indonesian volcano, blamed by some for triggering the Dark Ages.

Computer simulations have added weight to suggestions by historian David Keys that a volcanic catastrophe in AD535 caused prolonged worldwide climate change and agricultural failure that helped destroy old civilisations and raise new ones.

Ken Wohletz, a scientist at Los Alamos National Laboratory, New Mexico, and past collaborator with Keys, has simulated the possible consequences of a caldera eruption of Krakatoa. His results will be presented at the American Geophysical Union meeting in a fortnight.

The simulations suggest a huge eruption could have sent a 25-50km high plume of 100 cubic km of vapourised seawater into the atmosphere. Large amounts of steam would have reached the stratosphere to produce ice clouds with superfine ash.

After discussions with climate modellers at Los Alamos, Wohletz suggested this plume could have formed a cloud layer over much of the northern and southern hemispheres that could have destabilised the climate for decades.

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