[S-VC42] 火山噴火のダイナミクスと素過程

[SVC42-04] Eruption mechanics of the 2012 eruption of Mount Tongariro, NZ: Revealed by temporal Magnetotellurics

*Graham Hill^1,2、Hugh Bibby³、Jared Peacock⁴、Erin Wallin⁵、Yasuo Ogawa⁶、Luca Caricchi⁷、Harry Keys⁸、Stewart Bennie³、Yann Avram⁹ (1.Institute of Geophysics, Czech Academy of Science, Prague, Czech Republic、2.Gateway Antarctica, University of Canterbury, Christchurch, New Zealand、3.GNS Science, Lower Hutt, New Zealand、4.United States Geological Survey, Menlo Park CA, USA、5.United States Army Corps of Engineers, Huntsville AL, USA、6.Volcanic Fluid Research Centre, Tokyo Institute of Technology, Tokyo, Japan、7.Department of Earth Sciences, University of Geneva, Geneva, Switzerland、8.Department of Conservation, Turangi, New Zealand、9.Phoenix Geophysics, Toronto, Canada)

キーワード：magnetotelluric, eruption dynamics, Taupo Volcanic Zone, Tongariro

Monitoring dynamics of volcanic eruptions with geophysics is challenging. In August and November, 2012, two small eruptions from Mount Tongariro provided a unique opportunity to image subsurface changes caused by the eruptions. A detailed magnetotelluric survey of the Tongariro volcanic complex completed prior to the eruption (2008-2010) provides the pre-eruption structure of the magmatic system. A subset of the initial measurement locations was reoccupied in June 2013. Significant changes were observed in phase tensor response at sites close to the eruptive centre. Although, subsurface electrical resistivity changed, the geometry of the pre-eruptive magmatic system did not. These subsurface resistivity variations are interpreted as being predominantly caused by interaction of partial melt and the overlying brine layer causing volume reduction of the brine layer through phreatic eruption. The ability to detect significant changes within the magma system associated with eruptive activity suggests that magnetotellurics can be a valuable volcano monitoring tool.