HR: 14:10h
AN: V13F-03    [Abstracts]
TI: Collapse and Re-growth of Monowai Submarine Volcano, Kermadec Arc, 1998-2004
AU: * Chadwick, W W
EM: bill.chadwick@noaa.gov
AF: Oregon State University, 2115 SE OSU Drive, Newport, OR 97365 United States
AU: Wright, I C
EM: i.wright@niwa.co.nz
AF: National Institute of Water and Atmospheric Research, 301 Evans Bay Parade, Greta Point, Private Bag 14-901, Kilbirnie, Wellington, 6003 New Zealand
AU: de Ronde, C E
EM: Cornel.deRonde@gns.cri.nz
AF: Institute of Geological and Nuclear Sciences, 30 Gracefield Road, Lower Hutt, POB 31-312 New Zealand
AU: Reymond, D
EM: reymond.d@labogeo.pf
AF: Laboratoire de Geophysique, CEA/DASE/LDG, Tahiti, Papeete, BP 640 French Polynesia
AU: Hyvernaud, O
EM: hyvernaud@labogeo.pf
AF: Laboratoire de Geophysique, CEA/DASE/LDG, Tahiti, Papeete, BP 640 French Polynesia
AU: Bannister, S
EM: s.bannister@gns.cri.nz
AF: Institute of Geological and Nuclear Sciences, 30 Gracefield Road, Lower Hutt, POB 31-312 New Zealand
AU: Stoffers, P
EM: pst@gpi.uni-kiel.de
AF: Institute of Geosciences, University of Kiel, Olshausenstr. 40, Kiel, D-24098 Germany
AB: Monowai submarine volcano is located at 25°53.5'S/177°11.1'W, about 1400 km NNE of New Zealand along the Kermadec arc, and consists of a shallow symmetrical cone with a summit depth of ~100 m. Monowai is one of the most active submarine volcanoes in the Kermadec arc, based on visual reports from overflights, oceanographic surveys of hydrothermal plumes, and seismoacoustic monitoring from French Polynesia and elsewhere. Since the late 1970's, Monowai has been the source of frequent swarms of acoustic T-wave events every few years. On 24 May 2002 there was a particularly large seismoacoustic event with a duration of 6-8 minutes and an exceptional amplitude that was 4-5 times larger than any other T-wave signal recorded from Monowai. Bathymetric surveys of Monowai that bracket this event were collected with multibeam sonars in 1998 and 2004 by R/V Sonne (Hydrosweep) and R/V Tangaroa (EM300), respectively. A new collapse feature is apparent on the SE side of the volcano in the 2004 bathymetry. The two surveys were compared using a quantitative technique that has been used for documenting depth changes due to volcanic eruptions on mid-ocean ridges. The results of this comparison show that the summit depth of Monowai changed from 69 m below sealevel in 1998 to 135 m in 2004, a difference of -66 m, and the location of the shallowest point moved ~200 m to the NNW. However, the maximum depth change between the surveys is -105 m and is located near the 1998-summit, which in 2004 is south of the new headwall scarp on the SE flank of the volcano. The total area of significant depth change is 1.26 x 10⁶ m², and the decrease in volume is 6.12 x 10⁷ m³ (or 0.06 km³). From the distribution of the depth changes it is also clear that two things occurred between the surveys: removal of volume from slope failure and the subsequent addition of volume from an eruptive vent within the new slide scar. Therefore, the volume removed by slope failure was probably closer to 0.1 km³ whereas the volume added back by eruption is approximately 0.03 km³. It is not known whether the slide triggered the eruption or visa versa, but the recent history of frequent volcanic activity at Monowai suggests that an eruption-triggered slide may be more likely.
DE: 3070 Submarine landslides
DE: 7280 Volcano seismology (8419)
DE: 8185 Volcanic arcs
DE: 8427 Subaqueous volcanism
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005