Researchers unveiled new pictures from the ocean floor which they described as "a major geological discovery" in San Francisco on Thursday.
They said their video was the first to show the eruption of a deep-sea volcano.
The pictures show the fiery bubbles of molten lava as they exploded 4,000 feet (1,200 metres) deep in the Pacific Ocean.
A submersible robot witnessed the eruption during an underwater expedition in May near Samoa, and the high-definition videos were presented at a geophysics conference in San Francisco.
The mission was funded by the National Science Foundation (NSF) and the National Oceanic and Atmospheric Administration (NOAA), along with Washington University.
Scientists hope that the images, data and samples obtained during the mission will shed new light on how the ocean's crust was formed and how the earth behaves when tectonic plates collide.
The eruption was a spectacular sight. Video showed bright-red magma bubbles releasing a smoke-like cloud of sulphur, then freezing almost instantly in the cold sea water, causing black rock to sink to the to the sea floor.
The submersible hovered near the blasts, its robotic arm reaching into the lava to collect samples.
Eighty percent of the earth's volcanic activity occurs in the sea, making scientific observation difficult. Researchers from NOAA and the National Science Foundation had studied deep-sea volcanoes extensively but never witnessed an eruption.
The mission's chief scientist, Joseph Resing, last year detected volcanic material in the water in the area and realised it was erupting.
In May, the researchers travelled to the area and sunk the submersible robot, called Jason, hoping to make scientific history.
Scientists said the water around the volcano was more acidic than battery acid, but that shrimp and certain microbes seemed able to thrive.
Biologists will study these creatures to see if they are unique to this volcanic environment.
Researchers will also continue to monitor the changing West Mata volcano, about 140 miles (250 kilometres) southwest of Samoa.
Earth and ocean scientists also said the eruption allowed them to see the real-time creation of a rock called boninite, which had previously been found only in samples a million or more years old.