The 2010 seismovolcanic crisis at Taal Volcano (Philippines)

International audienceTypical eruptions of Taal Volcano in the Philippines are frequent and violently explosive. The last devastating phreatomagmaticeruption from 1965 to 1977 resulted in the death of about 200 persons. For this and other earlier events,no warnings of impending eruptions were issued. Since this time, volcanic crises involving episodes of seismicity,deformation, gas release, temperature change, etc., have occurred frequently.Each of these did not, but possiblycould have, evolved into an explosive eruption. One such event occurred between April 2010 and March 2011. Thispaper reports various types of geophysical data (electric/magnetic field, ground temperature, seismicity and grounddeformation) taken during this period of activity together with the current state of geophysical knowledge about thevolcano in order to throw light on activity evolution. While the 2010 seismovolcanic crisis was preceded by unusualchanges in electric field, ground tilting and uplift, the major signals from all data were concomitant with the evolutionof the crisis. On April 20, 2010, felt earthquakes first started to occur. The numbers increased sharply after April 29with repeated pulses of seismicity that ended finally in March 2011. Overall, we can identify three periods of seismicactivity, from April 20 to August 4–8, from August 4–8 to November 18, and from November 18 to March 28, 2011.Although only a single tiltmeter was in operation, it recorded three phases of deformation that correspond generallywith the pulses in seismic activity. Phase 1 appears to correspond to inflation at a depth of about 5 km just to theNW of Main Crater Lake from April 20 to June 11, 2010. This resulted in an eastward tilting of the northern flank of thevolcano. This apparently triggered rapid but shallower inflation (Phase 2) in the hydrothermal region of the volcanounder the northern edge of Main Crater Lake from June 11 to July 13 just to the SE of the initial deeper source asindicated by northward tilting of the volcano’s northern flank. Progressive deflation began after July 13. By March 28,2011, the deformation state recovered to the pre-crisis level and felt seismic activity ceased. Apparent related changesin seismicity, tilt, magnetic and electric fields occur during smaller NS inflations in the Phase 3 deflation—Phase 3a(July 13 to August 4–8), Phase 3b (August 4–8 to November 18) and Phase 3c (November 18 to March 28, 2011). Theselikely result from interrelated stress change, fluid/gas migration and thermal activity at depth and in the hydrothermalsystem. The rapidity of changes in the state of the volcano over a matter of hours during this entire process indicatesrapid communication occurs between processes at depth and in the hydrothermal system and this could easily resultin the dramatic evolution to violent phreatic explosions with little warning