HR: 0800h
AN: V21C-0728    [Abstracts]
TI: Submarine Strombolian Eruptions Observed at NW Rota-1 Volcano, Mariana Arc
AU: * Chadwick, W W
EM: bill.chadwick@noaa.gov
AF: CIMRS, Oregon State University, 2115 SE OSU Drive, Newport, OR 97365, United States
AU: Cashman, K V
EM: cashman@uoregon.edu
AF: Department of Geological Sciences, University of Oregon, Eugene, OR 97403, United States
AU: Embley, R W
EM: robert.w.embley@noaa.gov
AF: NOAA, Pacific Marine Environmental Laboratory, Newport, OR 97365, United States
AU: Dziak, R P
EM: robert.p.dziak@noaa.gov
AF: CIMRS, Oregon State University, 2115 SE OSU Drive, Newport, OR 97365, United States
AU: de Ronde, C
EM: Cornel.deRonde@gns.cri.nz
AF: GNS Science, 30 Gracefield Road, Lower Hutt, POB 31-312, New Zealand
AU: Matsumoto, H
EM: haru.matsumoto@noaa.gov
AF: CIMRS, Oregon State University, 2115 SE OSU Drive, Newport, OR 97365, United States
AU: Deardorff, N
EM: ndeardor@uoregon.edu
AF: Department of Geological Sciences, University of Oregon, Eugene, OR 97403, United States
AU: Merle, S G
EM: susan.merle@noaa.gov
AF: CIMRS, Oregon State University, 2115 SE OSU Drive, Newport, OR 97365, United States
AB: Extraordinary video and hydrophone observations of a submarine explosive eruption were made with a remotely operated vehicle in April 2006 at a depth of 550-560 m on NW Rota-1, a conical, basaltic-andesite submarine volcano in the Mariana arc. The observed eruption evolved from effusive to explosive, while the eruption rate increased from near zero to 10-100 m³/hr. During the peak in activity, cyclic explosive bursts 2-6 minutes long were separated by shorter non-eruptive pauses lasting 10-100 seconds. The size of the ejecta increased with the vigor of the explosions. A portable hydrophone deployed near the vent recorded sounds correlated with the explosive bursts; the highest amplitudes were at frequencies between 10-50 Hz, but extended up to at least 1500 Hz. The acoustic data allow us to quantify the durations, amplitudes, and evolution of the eruptive events over time. The low eruption rate, high gas/lava ratio, and rhythmic eruptive behavior at NW Rota-1 are most consistent with a Strombolian eruptive style. We interpret that the eruption was primarily driven by the venting of magmatic gases, which was also the primary source of the sound recorded during the explosive bursts. The rhythmic nature of the bursts can be explained by partial gas segregation in the conduit and upward migration in a transitional regime between bubbly flow and fully-developed slug flow. The strongest explosive bursts were accompanied by flashes of red glow and oscillating eruption plumes in the vent, apparently caused by magma- seawater interaction and rapid steam formation and condensation. These data are unique because this is the first time submarine explosive eruptions have been witnessed with simultaneous near-field acoustic recordings.
DE: 8413 Subduction zone processes (1031, 3060, 3613, 8170)
DE: 8427 Subaqueous volcanism
DE: 8428 Explosive volcanism
DE: 8430 Volcanic gases
DE: 8434 Magma migration and fragmentation
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting