Dynamics of strombolian eruptions at Batu Tara volcano (Indonesia)

Abstract:

In September 2014, high-speed imaging and acoustic data were acquired during 3 days of almost continuous recording (04-06/09/2015) at Batu Tara Volcano, in the small isolated island of Pulau Komba, in the Flores Sea (about 50 km N of Lembata). This volcano is very similar to the Italian Stromboli Volcano in both eruptive style and edifice morphology. The field experiment aimed at investigating degassing and explosive dynamics using a combination of GPS synchronized devices deployed in direct view of the active vent: i) a high-speed visible camera acquiring images at 500 frames per second (fps),ii) a thermal infrared (FLIR) camera acquiring at 50-200 fps, iii) a visible time lapse camera (GO-PRO) acquiring at 0.2-0.5 Hz (2 - 5 s interval), iv) two broadband microphones (Freq. range of kHz to 0.1 Hz) sampled at 10 kHz. Explosions can be discriminated in type according to their visual, thermal and acoustic features.Some explosions are characterized by a first sudden radial ejection of large spatter and bombs (main pulse), eventually followed by other similar events (secondary pulses), with very little amount of ash involved. In these eruptions, infrasonic waveforms are characterized by a first, high amplitude transient, with a first positive peak pressure followed by rapid dampening, typical of a Strombolian eruption.Other explosions are characterized by the sustained ejection of a dense jet of ash, with abundant decimeter to meter sized spatter and hot blocks.These eruptions are not accompanied by a maximum peak pressure at the eruption onset. Spectrograms show a high frequency component propagating for the entire duration of the signal.These two distinct types are sometimes overlapping and eruptions show a high amplitude transient followed by a high frequency coda. These different evolutions suggest that there are at least two repeatable explosion dynamics occurring in the conduit, with comparable gas overpressure, source depth and amount of gas involved