DEEP SUBMARINE ERUPTION STYLES AT WEST MATA VOLCANO REVEALED BY VIDEO OBSERVATIONS AND DEPOSIT MAPPING

West Mata volcano is an active rear-arc submarine volcano in the NE Lau Basin (Resing et al., Nat. Geosci., 2011). Itt has erupted from its 1200 m deep summit and from deeper flank vents over the past decade (Embley et al., G-cubed, 2014). Direct observations of its eruptions, including the first observations of active deep sea lava flows and the first historical observation of boninite magma being erupted on Earth, were made during a May 2009 multidisciplinary event response expedition to the volcano. In this video-intensive presentation, I will discuss the range of explosive and effusive eruptive conditions that were observed, the deposit types they produce, and their relationships to the multiple volcanic vent structures that were active during our observations. High crystallinity (40-50%) magma was documented erupting effusively and explosively. A significant range of eruptive styles was observed, particularly with respect to conditions, styles, extent, and locus of fragmentation, which varied in space and time during our 4 days of observations in 2009. Our group revisited the volcano with ROV in 2012, finding major changes at the summit (pit crater formation, mass wasting, and cessation or hiatus in active volcanism). Collectively, observations made during the 2009 and 20012 surveys, plus deposit mapping and lava dating, allow one to reconstruct variations in eruption conditions and styles before, during, and after the period of direct observations, revealing apparent waxing and waning of eruption intensity and the distributions of eruption products.