Well the Siberian traps probably trigered the largest mass extinction in the history of the planet.
Don't give him nightmares.
There is a lake under antartica called lake vostok
http://en.wikipedia.org/wiki/Lake_Vostok
It's water under the ice.
Personally I'd take the theme and go with the discovery of another huge sub glacial lake kept liquid bu a supervolcano beneath antarctica and drill a hole through to it and sink a hydrogen bomb through the water into the neck of the supervolcano to release the rock plug and trigger the volcano.
It doesn't have to be scienticically accurate just credible - as Michael Crighton can testify