Magnetic and electric field monitoring of Taal volcano, Philippines Part I: Magnetic measurements

We have started electromagnetic (EM) monitoring of Taal volcano, Philippines. Taal is a basaltic-andesite volcano which has many eruption histories and is close to Metro Manila. On Taal, various geophysical and geochemical observations have been conducted by the government basis, but not the EM monitoring. A cooperative project for EM studies between PHIVOLCS and EMSEV/IUGG has been started. Measurements of total magnetic field (TMF), self-potential (SP), ground temperature and carbon dioxide degassing were made during the first survey in January 2005. Distinct anomalies in TMF and SP were found in the geothermal areas in Taal. Repeated survey in February detected changes in TMF up to a few tens of nT and enhancement of positive SP anomaly during the one and half-months period, when the surface geothermal activities were high. We believe that the combination of mechanical and electromagnetic measurements is uniquely effective in deciphering the volcanic activity. (Communicated by Seiya UYEDA, M.J.A.)