Degassing of open-vent low-silica volcanoes

Open-vent activity at volcanoes of low-silica composition, such as Stromboli (Italy), Villarrica (Chile), Mt. Erebus (Antarctica), Masaya (Nicaragua), is characterised by persistent passive gas emission and recurrent mild explosive outgassing. Four styles of bubble bursting activity have been recognised in such volcanoes: seething magma, small short-lived lava fountains, strombolian explosions and gas puffing. Whilst strombolian explosions are perhaps the most common among these volcanoes, seething magma and small lava fountains have been observed only at the surface of active lava lakes. At Villarrica, one of the two case study volcanoes of this thesis, seething magma consists of continual bursts of bubbles up to a few meters in diameter, with varying strength over the entire surface of the lava lake. Small lava fountains, seen as a vigorous extension of seething magma, commonly lasts 20-120 s and reach 10-40 m high above the lava free-surface. Strombolian explosions exhibit a wide range of behaviour. For instance, they can last for less than a second in a single bubble burst that erupts mainly bombs, as seen at the lava lake of Mt. Erebus and Villarrica volcanoes, or for more than 30 seconds accompanied by large amounts of ash, as seen at Stromboli and Mt. Etna volcanoes. At Stromboli, the second case study volcano, gas puffing consists of small but repetitive bubble bursts with a generally table eruption frequency in the range 0.2-1.2 s⁻¹. More vigorous explosive phenomena, such as hundreds-metres high lava fountains or very strong (paroxysmal) explosions, may occur during eruptions or episodes of elevated activity. Multi-parameter monitoring offers a fuller recognition and understanding of the processes governing the volcanic activity at this type of volcano. For instance, correlations between seismicity and visual observations at Villarrica volcano indicate that the seismic tremor is mostly caused by explosive outgassing.EThOS - Electronic Theses Online ServiceGBUnited Kingdo