I do stand corrected. It was not Katla, but Laki, which is blamed for the famine in Europe. (There are plenty of sources available which make this mistake, and they got me) Having said that, Katla can produce the type of eruption which is a “once in a hundred years” type of event, think Pinatubo. Eruptions of this magnitude have a greater impact on climate than anything civilization can muster, even including Al Gore. Here are some nice lists of Geological Events: http://www.uwgb.edu/dutchs/platetec/topten.htm
Hey, that's catchy.
When the scientists were trying to trace what they eventually figured out was the Toba eruption 75,000 years ago, one of the volcanos they suspected was Laki.
Laki is the big Kahuna. TEOTWAWKI time!
If you use Google maps and look at Iceland, you can see that it looks like the whole island is a caldera!