IUGG2015 poster BATUTARA

Poster no VS14p-472 Dynamics of strombolian eruptions at Batu Tara volcano (Indonesia) P. Scarlato, E. Del Bello, T. Ricci, J. Taddeucci Istituto Nazionale di Geofisica e Vulcanologia, Roma, Italy Straight Distance 450 m The small isolated island of Batu Tara in the Flores Sea (about 50 km N of Lembata) is very similar to the Italian Stromboli Volcano in both eruptive style and edifice morphology. It is characterized by several strong episodic strombolian and vulcanian eruptions with recurrence time of minutes to hours. Crater Height ca. 400 m a.s.l. FLIR Crater Width ca. 40 m OPTRONIS CW SD CH GOPRO In September 2014, highspeed imaging and acoustic data were acquired during 3 days of almost continuous recording (04-06/09/2015). The field experiment aimed at investigating degassing and explosive dynamics using a combination of GPS synchronised devices deployed in direct view of the active vent Some results GO-PRO GO- a highspeed visible camera acquiring images at 500 frames per second (fps), a thermal infrared (FLIR) camera acquiring at 50-200 fps FLIR OPTRONIS a visible timelapse camera (GO-PRO) acquiring at 0.2-0.5 Hz (2 - 5 s interval) OPTRONIS two broadband microphones (Freq. range of kHz to 0.1 Hz) sampled at 10 kHz Explosions can be grouped into three main types (A, B, C) according to their visual and acoustic features. These different time evolutions suggest that there are at least three repitable explosion dynamics occurring in the conduit, with comparable gas overpressure, source depth and amount of gas involved. TYPE A 15:34:04.533 During a selected period of ca. 18 hours information retrieved from the integrated, continuous dataset are: i) the cumulative distribution of events shows that a minimum of 5 to a maximum of 11 events per hour occurred; ii) the observed recurrence time is between 2 and 36 minutes, with the most frequent intervals being ca. 5 and 12 m; iii) there is no obvious correlation between recurrence interval and time during the time span consdered. These explosions are characterised by a first sudden radial ejction of large spatter and bombs (main pulse), evenually followed by other similar events (secondary pulses), with very little amount of ash involved. 15:34:05.733 15:34:05.133 15:34:06.333 15:34:06.933 15:34:07.533 15:34:08.133 15:34:08.733 15:34:09.333 15:34:09.933 15:34:10.533 Infrasonic waveforms are characterised by a first, high amplitude transient, with a first positive peak pressure followed by rapid dampening. This wavefrom is typical of a Strombolian eruption. TYPE B 12:36:43.192 Such explosions are characterised by the sustained ejection of a dense jet of ash, with abundant decimeter to meter sized spatter and hot blocks. 12:36:43.792 12:36:44.392 12:36:44.992 12:36:45.592 12:36:46.192 12:36:46.792 12:36:47.392 12:36:47.992 12:36:48.592 12:36:49.192 12:36:49.792 12:36:50.392 12:36:50.992 12:36:51.592 12:36:52.192 12:36:52.792 These signals do not show maximum peak pressure at the eruption onset. Spectrograms show a high frequency component propagating for the entire duration of the signal. TYPE C Such explosions are characterised by a first bomb-rich ash-poor pulse, followed by the the emission of concentrated ash and pyroclasts. These eruptions can last up to 40 seconds, much longer then the previous (usually lasting than 10 seconds). 00:48:45.394 00:48:45.994 00:48:46.594 00:48:47.194 00:48:47.794 00:48:48.394 00:48:48.994 00:48:49.594 00:48:50.194 A first, high amplitude transient of type A is followed by a type B coda.