HR: 13:55h
AN: V13F-02 INVITED     [Abstracts]
TI: Submarine Volcano Collapses in the Tonga-Kermadec Arc
AU: * Arculus, R J
EM: Richard.Arculus@anu.edu.au
AF: Richard J. Arculus, Department of Earth and Marine Sciences, Australian National University, Canberra, ACT 0200 Australia
AU: Wright, I C
EM: i.wright@niwa.cri.nz
AF: Ian C. Wright, National Institute of Water and Atmospheric Research, Wellington, 6003 New Zealand
AU: de Ronde, C E
EM: Cornel.deRonde@gns.cri.nz
AF: Cornel E.J. de Ronde, Institute of Geological and Nuclear Sciences, Lower Hutt, 6009 New Zealand
AB: In the last few years, discoveries by multibeam swath and hydrothermal plume mapping plus rock dredging during several research voyages (NZAPLUME I to III, Sonne 135 and 167, TELVE and NoToVE) include about 70 new major volcanic edifices, most with basal diameters >15 km, spaced approximately 30 km apart along the length (2,500 km) of the Tonga-Kermadec arc. About 40 percent of these are hydrothermally active. The edifices comprise stratovolcanoes of variable complexity, and steep-walled calderas with diameters <12 km. Large-scale sector collapses occur on many of these structures, and concentric ridges on the outer flanks of some calderas appear to be mega-bedforms associated with mass flows and edifice failures. Topographic rims of many calderas are capped by numerous conical vents; cones are also present within many calderas. Overall relationships exist along arc between depth of basement, nature of volcanic structures, and magma composition; more felsic (dacite to rhyolite) lavas are associated with higher basement elevation, multi-vent stratovolcanoes, and caldera complexes, but the exact relationship between formerly contiguous arc-remnant arc basement prior to formation of the Havre Trough-Lau Basin and establishment of the current arc edifices is complex. The predominant mode of formation of felsic magma-dominated calderas is interpreted to be mass pyroclastic discharge with syn-eruptive caldera collapse in water depths <1000 m. Other types of edifice failure are: sector collapses extending for full volcano flank heights that feed debris fields, and in some cases expose radial fissure dikes; mega-bedforms comprising a series of ridges striking parallel to adjacent projected caldera margins. Close to the caldera, these ridges have relative relief of about 150m decreasing to <10m at distances >20 km from the caldera. Terrain between many adjacent submarine volcanic edifices is blanketed by degraded and subdued equivalents of these mega-bedforms. Overall, these debris flows constitute a significant mode of arc crustal formation. Sites of hydrothermal venting (and volcanoes?) are commonly located at crustal-scale fault and fracture intersections and more locally, near the base of caldera walls. Localised failure of caldera walls may be related to rock alteration by hydrothermal activity.
DE: 8404 Volcanoclastic deposits
DE: 8413 Subduction zone processes (1031, 3060, 3613, 8170)
DE: 8414 Eruption mechanisms and flow emplacement
DE: 8427 Subaqueous volcanism
DE: 8440 Calderas
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005