page_title: West Mata
section_title: Geology
hierarchical_section_title: West Mata / Geology
caption_attribution_description: English: The summit of the West Mata Volcano is nearly a mile below the ocean surface (1165 meters / 3882 feet), and the base descends to nearly two miles (3000 meters / 9842 feet) deep. The eruptive activity occurred at several places along the summit, in an area approximately the length of a football field. The volcano has a six-mile long rift zone running along its spine from SW to NE. Pacific Ocean, Northeast Lau Basin, Fiji area.
context_page_description: West Mata is a submarine volcano at 1,100 meters depth 200 kilometres southwest of the Samoas. Its eruptions are currently the deepest observed.
context_section_description: West Mata is just west of the north in Tonga Ridge where the Tonga Trench makes a sharp turn to the west. It is in the NE Lau Basin about 35 km east of the Lau spreading center and about 70 km northeast of the currently erupting NE Lau spreading center. The Research Vessel Thompson surveyed the area during November 2008 and May 2009. In November 2008, the researchers detected a plume of material over West Mata which indicated likely erupting lava flows and/or pyroclastic materials. The sulfur and iron rich plume contained mineral and/or glass shards. The shard compositions indicated that the erupted material was boninite (an olivine-bronzite andesite with little or no feldspar) which had never been observed from an active volcano.
  On 6–7 May 2009, the Jason 2 ROV (remotely operated vehicle) was used to observe eruptions from two vents of the linear West Mata peak, Prometheus (at or near the summit) and Hades (slightly to the SW). The Hades vent was erupting both effusively and explosively at the same time on both days (6–7 May). Small bursts were occurring at one end of an erupting fissure ~ 5 m long at a depth of 1,208 m, while pillow lavas were being extruded from the other end. By the next night (7 May) the activity had become more vigorous, sometimes blowing glowing bubbles as much as a meter across from the fissure.
caption: Undersea topography of West Mata
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