West Mata is an active submarine volcano located in the northeastern Lau Basin, roughly 200 km (124 mi) southwest of the Samoan Islands.

The volcano was first discovered in 2008 by scientists aboard the R/V Thompson research vessel, using sonar mapping and a remotely operated vehicle (ROV) to explore the seafloor.

[4] At the time of exploration, West Mata was the deepest undersea volcano eruption ever recorded, nearly −1,200 m (−3,937 ft) below the surface of the ocean.

Its study has provided important insights into the geology, chemistry, and biology of hydrothermal vents, as well as the dynamics of submarine volcanic systems.

The seaward rollback of the Tonga Trench is thought to be the main reason of the diverging action in this region.

On the northern border of the basin can be found the area where the Kermadec-Tonga subduction zone transitions into a convergent strike-slip boundary.

[11] Most volcanic extrusions in the NE Lau Basin region structures usually erupt dacite lavas, some with unusual morphologies, which are quite rare in submarine volcanoes.

Other than dacitic lavas, rift zones in the region have been also found to erupt basaltic andesite compositions.

[12] The hydrothermal ecology of the Lau Basin is home to many endemic organisms, including the Lamellibrachia columna which shows similarity to Lamellibrachia satsuma that can be found in Japan;[13] Neobrachylepas relica, a close relative to the Brachylepadomorpha which was extinct since the Miocene;[14] and more.

During the eruption of 2008–10 it was observed that there were only large groups of opaepele shrimp on the seamount and the normal hydrothermal vent community was not present.

[16] In November 2008, during a hydrographic survey in the region, an intense hydrothermal plume over the summit of West Mata consisting of high levels of hydrogen and pieces of volcanic glass was detected, which suggested it was likely erupting.

[17] Following this event, 6 months later, the 2009 Northeast Lau Response Cruise was led by the NOAA on board the R/V Thomas G. Thompson and carrying ROV Jason to deploy it in the area.