Lateral Dispersion of Volcanic Ash From the Flanks of an Actively Erupting Submarine Volcano

Details Lateral Dispersion of Volcanic Ash From the Flanks of an Actively Erupting Submarine Volcano Lateral Dispersion of Volcanic Ash From the Flanks of an Actively Erupting Submarine Volcano

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.v23b0610w&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #V23B-0610

Other

3075 Submarine Tectonics And Volcanism, 8424 Hydrothermal Systems (0450, 1034, 3017, 3616, 4832, 8135), 8427 Subaqueous Volcanism, 8450 Planetary Volcanism (5480, 6063, 8148)

Scientific paper

NW Rota-1 is an actively erupting submarine volcano along the Mariana Arc, rising some 2500 m from the local seafloor. Eruptions at Brimstone Pit, located about 30 m below the summit on the south side of the volcano at 550 m water depth, have been directly observed since 2004. Water column surveys (using CTD-O vertical cast and tow methods) in 2003, 2004 and 2006 mapped the distribution of both persistent and variable particle plumes over the summit and down the flanks. In all years, there was a non-buoyant laterally dispersing plume over the summit that was optically intense and very thin (25-30 m plume maximum), measurable up to 2-3 km from the summit. The plume was most intense in 2003 and 2004 with dNTU values reaching 5 (the upper limit of the optical backscatter sensor). High concentrations of particulate sulfur in the plume contribute to these unusually intense optical signals, as sulfur particles are efficient optical backscatters. The plume maxima depth has steadily declined over 3 years: 460 m in 2003, 485 m in 2004, and 505-530 m in 2006. In 2003, both hydrothermal and volcanic components were detected in the plume, so it is not certain that the 2003 data represent pre-eruption conditions. Deeper layers of turbidity were absent in 2003, but were observed in multiple layers surrounding the volcano in 2004 and 2006 from depths of about 700 m extending to >2500 m, and were detectable at distances up to 18 km from the summit. Microscopy and chemical analysis indicates that the particles in these layers are overwhelmingly glass fragments rather than hydrothermal precipitates. Over the scale of 3-6 days, repeat tows showed significant decreases in particle concentrations, implying some of the particles settled rapidly from these plumes. The most likely source of these layers is gravity flow of volcanic ash down the flanks, fed by violent eruptions at the summit. Detachment from the seafloor may be controlled by turbulence from current flow or internal waves, after which layers spread laterally on isopycnals at various depths. Two such layers in 2006 could be traced 8 and 18 km, respectively, from the volcano. Eruptions at Brimstone Pit are explosive and periodic in nature, with several phases of increased activity over the course of a few days. Thus the multiple layers of particles on the flanks of NW Rota-1 during our surveys may represent multiple episodes of flows rather than the separation of flows from a single eruptive event.

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