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Monowai volcano: fast outpouring of magma observed over 5 days

Bathymetry of summit of Monowai Cone May/June 2011.How fast can a volcano spew out magma? This is a question that has perplexed volcanologist for a very long time. Recently a team of scientists, led by A.B. Watts of Oxford University, conducting a routine bathymetric survey onboard the research vessel SONNE, were fortunate enough to be in the proximity of Monowai seamount volcano when a dramatic eruption occurred.** Monowai is located along the 2,500 km-long Tonga-Kermadec Arc, where a submarine volcano can be found approximately every 50 km.Eruptive volume versus duration of magmatism for submarine volcanoes. Monowai is not small. It is a 10-12 km-wide strato-volcanoe approximately 1 km high with a 7-10 km wide caldera in its summit, approximately 0.6 km deep. Since it was first discovered in 1944 it has had a history of activity (discoloured water emanations and seismic ity). On May 14, 2011, the scientific team observed gassy discoloured water on the summit of the Monowai Cone. Three days later, a swarm of seismic events began and lasted for 5 days. On June 1, after the seismic activity subsided, the ship returned and carried out a second survey of the cone. They found significant changes in depth at the volcano. The main differences were (1) an increase in depth of up to 18.8 meters attributed to collapse structures on the flanks of the volcano, and (2) a decrease in depth of up to 71.9 m due to growth by eruption of new lava flows. The most striking feature of the surveys was a new cone near the summit. From its dimensions (100 m diameter at its base, at least 40 m high), it appears that about 0.00875 cubic kilometres of magma was erupted, most likely during the 5-day swarm of seismic activity. Extrapolating these rates to annual output, Monowai joins Kilauea, Iceland, Montserrat, the Azores, Hawaii, and the Canary Islands withoutput on the order of 0.1 cubic kilometres per year.

**Reported in A.B. Watts, et al., Rapid rates of growth and collapse of Monowai submarine volcano in the Kermadec Arc, Nature Geoscience, Advance publication, doi: 10.1038/NGE01473, posted May 13, 2012. Featured on Geology.com on May 15, 2012.

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