InSAR Data Detect Shallow Dyke Intrusion at the Rabaul Volcano, Papua New Guinea – Potential Site for Caldera Geothermal Field
Manoj MUKHOPADHYAY and Suame AMPANA
[University of Technology, Lae, Papua New Guinea, Papua New Guinea]
InSAR data detect shallow dyke intrusion at the Rabaul Volcano, Papua New Guinea – Potential site for caldera geothermal field by:Suame AMPANA* & Manoj MUKHOPADHYAY Dept. Applied Physics, University of Technology, Lae, Morobe Province, Papua New Guinea, *Correspondence: firstname.lastname@example.org Abstract The Rabaul Volcano Complex (RVC) is composed of twin calderas, namely; the Tavurvur and Vulcan, in the New Britain Island, Papua New Guinea. This is developed as an elliptical volcanic complex of 9 x 14 km2 within the Bismarck Volcanic Arc (Fig. 1). Central part of the RVC is breached by sea-water, causing inundation, between the eruptive centers. Consequently it produced a series of caldera collapse structures and a group of basalt–andesite volcanic centers. After a major twin eruption in 1994, Vulcan has ceased activity while Tavurvur has continued intermittent eruptions with last major eruption in 2014. Local seismicity is monitored by the Rabaul Volcanology Observatory (RVO) that is operational since 1937. The Rabaul seismic zone is elliptical ~5 x 9 km2 oriented NNE/SSW, extending from near surface to a depth of 4 km. This corresponds to the walls of eventual caldera collapse, leading to outward-dipping ring-fault structure. Such gross pattern is also corroborated by 3-D seismic tomography which reveal low velocity zone underneath. Two popular models are advocated in literature to explain its current deformation: (i) Point pressure source, called the Mogi model and (ii) Radial dike intrusions along the caldera wall, leading to outward-dipping ring-fault structure. Here we make use of the conventional geodetic data as well as the Interferometric Synthetic Aperture Radar (InSAR) data to detect ground deformation to further constrain the possible pressure sources, Mukhopadhyay et al., (2018). Using ALOS PALSAR and GPS datasets, we model a shallow dike intrusion at 1 km depth to explain the localized deformation observed on the NE-edge of the Tavurvur cone and a 4 km deep Mogi source model at the center of the caldera just south of Matupit. Finally, the shallow dike intrusion is interpreted here to represent the root plumbing system beneath the RVC at this specific locality. Large, young calderas and associated volcanic rocks are indicators of potentially immense geothermal resources. It is envisaged that for every km3 of material erupted, between 3 and 9 km3 of partly molten rock resides below the volcanic field, most likely within the upper 10 km of crust. The geothermal resource beneath a caldera exists as long as eruptive activity continues; what appears to be the most likely case for RVC. Here we infer that the interpreted dike intrusion model bear significant potential for geothermal resource. RVC hydrothermal systems are likely to be confined to caldera ring fractures and caldera-crossing faults, which form zones of fracture permeability. Further studies are however, warranted in this direction to establish its nature.
|        Topic: Geophysics||Paper Number: 13100|