The below videos show eruptions of the West Mata volcano, the deepest erupting volcano discovered by a team of scientists funded by NOAA and the National Science Foundation in May 2009. The eruptions occurred at nearly 4,000 feet below the surface of the Pacific Ocean, in an area bounded by Fiji, Tonga and Samoa.
The video below was taken from the ROV Jason in May.
http://www.youtube.com/watch?v=FCH6dVcxL3c http://www.youtube.com/watch?v=-qR_xMXJoBM
Read more about this discovery at NOAA.org.