"A research team led by the Woods Hole Oceanographic Institution (WHOI) has uncovered evidence of explosive volcanic eruptions deep beneath the ice-covered surface of the Arctic Ocean. Such violent eruptions of splintered, fragmented rock—known as pyroclastic deposits—were not thought possible at great ocean depths because of the intense weight and pressure of water and because of the composition of seafloor magma and rock."

Read more (http://www.whoi.edu/page.do?pid=7545&tid=282&cid=44586&ct=162)

Seems like all that water pressure would aid in the corking, enabling high pressure buildup by the same factor that requires it.

I wonder what the volatiles in volcanoes are. Hydrocarbons perhaps?

"Next to nothing is known about the sources of the volatile components of magmas or how they are distributed and transported between the mantle and the shallow levels of the crust." -- Howel Williams, 1979

"Petroleum is the product of a distillation from great depth and issues from the primitive rocks beneath which the forces of all volcanic action lie." -- Alexander Von Humboldt, 1804

"All the petroleum, natural gas, and bituminous fields or deposits cannot be regarded as anything else but the products of solfotaric volcanic emanations condensed and held in their passage upward in the porous tanks of all ages of the crust of the earth from the Archaean rocks to the Quaternary. Nothing is so simple and therefore nothing so natural as this origin, and we will see that it can be abundantly proven." -- Eugene Coste, 1903

Seems like all that water pressure would aid in the corking, enabling high pressure buildup by the same factor that requires it.

Yes, it seems the composition of the seafloor and the pressures still allows the explosive eruptions (at least at that location).