Much as we just saw at the summit of Greenland, when it rains higher up on the summit of volcanoes you get water into the inner most layers which are also a cause of larger eruptions. Was also a recent study I think by the European Geological society that said that increasing landslides caused by rain can also 'uncap' volcanoes--releving down pressure--allowing for eruptions to suddenly occure!
We definitely don't need some 'SUPERVOLCANO' to change weather and cause years without summer. To my knowledge, the worst event was in 1815~ and two other large volcanoes in the 1800s also caused the effect. A chilian volcano in the 1600~ cause 1/3rd of russians to die of starvation as well...
These 'COOLING' effects of volcanoes is the exact reason we can't just up and decide to spray SO2 up in the atmosphere in hopes of cooling the earth, as if we did... And there was an eruption, such geoengineering would only compound this global cooling event!
