http://news.bbc.co.uk/1/hi/uk/966968.stm
Geologists have told the UK Government that the country risks being hit by a giant wave of water that could destroy many coastal communities.
Experts at University College London (UCL) have contacted the science minister Lord Sainsbury to warn him that a collapsing volcano in the Canary Islands could send a wall of water, hundreds of metres high, sweeping out over the Atlantic Ocean.
Their research suggests the Caribbean and the east coast of the US would take the brunt of the devastation, but high water could also submerge large parts of the west coast of Britain.
There's also this one, about the Yellowstone "super volcano":
http://www.solcomhouse.com/yellowstone.htm