Undersea volcano

The Earth Institute at Columbia University:

"The yet-unnamed volcano is significant in that it exists on a continental shelf (in this case, on the edge of the Antarctic continental mass) and in the vicinity of a deep trough across the seafloor carved out by past glacial expansion."

We have an undersea volcano on the edge of Antarctica. Apparently there are more of them around the world. There's one near Samoa will swarms of eels in it. New Zealand and the USA have jointly been studying South Pacific Volcanos


How can they be volcanos if they are under the ocean? Do they have to match certain criteria? Do they erupt? How can they generate heat with that much ocean water on and around them?