Caldera structure of submarine Volcano #1 on the Tonga Arc at 21°09′S, southwestern Pacific: Analysis of multichannel seismic profiling

Abstract

Volcano #1 is a large submarine stratovolcano with a summit caldera in the south central part of the Tonga Arc. We collected and analyzed multichannel seismic profiles in conjunction with magnetic data from Volcano #1 to investigate the structure of the intracaldera fill and processes of caldera formation. The intracaldera fill, exhibiting stratified units with a maximum thickness of 2 km, consists of at least four seismic units and a thick wedge of landslide debris derived from the caldera wall. The structural caldera floor, deepening toward the northwestern rim, suggests asymmetric collapse in the initial stage, which, in turn, appears to have contributed to the creation of a caldera elongated to the northwest by enhancing gravitational instability along the northwestern caldera boundary. Occasional, but repeated, eruptions resulted in a thick accumulation of the intracaldera fill and further subsidence in the mode of piston collapse. Magnetization lows are well-defined along the structural rim of the caldera that is interpreted as the inner principal ring fault. The magnetization lows indicate sites of submarine hydrothermal vents that caused an alteration of magnetic minerals. Faults recognized on the outer slope of the volcano are interpreted to be involved in hydrothermal fluid circulation.

Tectonics of Volcanogenic Massive Sulphide (VMS) Deposits at Flores Back Arc Basin: A Review

“…Many large calderas collapse during an eruption that produces a volcanic ash flow followed by a subsidence process and then caldera wall sliding (Lipman, 1997). This evidence Kim et al, 2013) of caldera collapses happened in the submarine volcano at Tonga, South Pacific (Kim et al, 2013).…”

“…The collapsed caldera was caused by an inner steep reverse fault or triggered by an outer normal fault associated with the extension of the caldera rim (Cole et al, 2005;Acocella, 2007, in Kim, et al, 2013. Intracaldera fill is a caldera formation process.…”

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“…Velocity data from the regional multichannel seismic lines were not obtained due to the streamer length being too short. Thus, velocities of 2.5 km/s-similar to those used by Kim et al (2013) for welded and consolidated volcaniclastics (but greater than the 1.5 km/s used by these authors for relatively homogeneous but unconsolidated volcanic ash and flows near the seafloor) infilling a submarine caldera volcano of the Tonga arc-were used to estimate thicknesses of volcanic units at Brothers.…”

Detailed bathymetry and magnetic anomaly in the Central Ryukyu Arc, Japan: implications for a westward shift of the volcanic front after approximately 2.1 Ma

“…Such geophysical surveys are known to be useful in delineating submarine volcanic features (e.g., Kim et al 2013). This survey was performed in 2012 during the Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), GH12 cruise of R/V Hakurei.…”