Vulcanian eruption

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Vulcanian eruption in 1982 at Galunggung on Java.
1998 volcanic eruption at Tavurvur in Papua New Guinea .

A Vulcanian eruption is a type of volcanic eruption , named after an eruption pattern of the Vulcano on the Aeolian island of the same name off Italy. The term was introduced into volcanology in 1907 by Giuseppe Mercalli .

Vulcanian eruptions typically occur on volcanoes with more viscous magma from andesitic to dacitic composition. The pattern consists of short, cannon-like explosions (with corresponding shock waves ) that can occur individually or in series for up to a few hours. In the main, highly fragmented volcanic ash is produced, which can rise up to 20 km in an eruption column . In addition, volcanic bombs are ejected, which can fall within a radius of up to 5 km. The strength of the eruption is between a Strombolian and a Plinian eruption , i.e. about level two to four on the VEI .

Volcanoes that show Vulcanian eruptions are e.g. B. Soufrière Hills on Montserrat, the Ngauruhoe in New Zealand and Galeras in Colombia.

causes

Two causal mechanisms of action could be identified for Vulcanian explosions:

  1. Explosions initiated near the surface result from the rise of gas-rich, highly viscous magma. Due to the pressure relief during the magma ascent (decreasing load pressure), dissolved fluids accumulate in gas bubbles and generate a rising gas pressure in the magma that is significantly higher than the atmospheric pressure on the earth's surface. For example, seismic waves , internal magmatic processes or a reduction in the load pressure due to the collapse of a lava dome can result in a destabilization of the pressure differential (gas pressure in the magma vs. atmospheric pressure). This destabilization initiates the Vulcanian explosion and leads to a fragmentation of fresh magma in the upper volcanic vent and the eruption of pyroclastic material . The downward pressure wave can drain the upper volcanic vent up to a depth of 2 km.
  2. Depth-initiated explosions are initiated by a sudden decompression of the magma chambers (> 5 km depth) lasting a few minutes and a simultaneous pressure build-up in the volcanic vent above. The most likely cause for this is a collapse of already existing fluid pockets in magma chambers and the rise of the released fluids into the conveyor passage. If the pressure built up in the conveyor passage exceeds a critical value, the gases break through to the surface of the earth in an explosion, with the fragmentation of fresh magma and increased ballistic ejection of dome material.

Both types of Vulcanian explosions can occur on the same volcano and the distribution does not follow any pattern. The clear distinction between the trigger mechanisms is only possible syn-eruptive with high-resolution seismic / geodetic measuring instruments. A later analysis of the ejected material can also provide information about the causal trigger mechanism of an explosion. Despite previous pressure changes in the magmatic system in the event of depth-initiated explosions, the lead time (between 1 and 5 min) is too short for an efficient early warning. In addition, a suitable observation network is only installed at a few volcanoes worldwide. Vulcanian explosions therefore remain an unpredictable danger.

literature

  • Meghan M. Morrissey and Larry G. Mastin in Encyclopedia of Volcanoes . Academic Press, 1999, ISBN 978-0-12-643140-7 . Page 463ff.

Web links

Individual evidence

  1. ↑ a b Stefanie Hautmann, Fred Witham, Thomas Christopher, Paul Cole, Alan T. Linde: Strain field analysis on Montserrat (WI) as a tool for assessing permeable flow paths in the magmatic system of Soufrière Hills Volcano . In: Geochemistry, Geophysics, Geosystems . tape 15 , no. 3 , March 2014, p. 676-690 , doi : 10.1002 / 2013GC005087 .
  2. ^ A b J. Gottsmann, S. De Angelis, N. Fournier, M. Van Camp, S. Sacks: On the geophysical fingerprint of Vulcanian explosions . In: Earth and Planetary Science Letters . tape 306 , no. 1-2 , June 2011, pp. 98-104 , doi : 10.1016 / j.epsl.2011.03.035 .
  3. ↑ Mikhail Alidibirov, Donald B. Dingwell: Magma fragmentation by rapid decompression . In: Nature . tape 380 , no. 6570 , March 1996, p. 146-148 , doi : 10.1038 / 380146a0 .
  4. ↑ B. Voight, D. Hidayat, S. Sacks, A. Linde et. al: Unique strainmeter observations of Vulcanian explosions, Soufrière Hills Volcano, Montserrat, July 2003: SHV VULCANIAN EXPLOSIONS-2003 . In: Geophysical Research Letters . tape 37 , no. October 19 , 2010, doi : 10.1029 / 2010GL042551 .