Lava dome
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A lava dome (after English lava dome : lava dome ), also called dome or volcanic dome , is a hill-shaped or columnar ( lava needle ) elevation, which is created by the eruption of very viscous lava with a high silicon dioxide content from a volcano. Rapid cooling and very small flow distances create a plug-shaped lava dome directly above the exit point, which closes the volcanic vent at the top.
hazards
Lava domes hold a high risk potential. Continuous pressing out of the lava makes the dome relatively unstable. It can collapse or large rock regions can break off its steep flanks and generate gravitationally accelerated pyroclastic currents that plunge into the valley at 100–400 km / h and temperatures of 200–700 ° C and wreak havoc on their way. Lava domes can become very explosive when they come into contact with groundwater and due to high gas levels. The pressure inside a volcano can be explosively discharged. The formation of a dome within an explosive crater (such as in Mount St. Helens or numerous volcanoes in Indonesia) increases the risk of a future volcanic catastrophe.
Origin and structure
Typical rocks for volcanic domes are andesite and dacite . Dome-forming volcanoes are usually located in regions in which one continental plate is pushed ( subducted ) under the other . Here z. B. Sedimentary rocks melted and a gas-rich magma rises in the earth's crust. Magma chambers can linger in the upper areas of the earth's crust for a long time without a volcano becoming active. If new, basaltic magma then rises into such a magma chamber, the so-called "magma mixing effect" occurs, which heats the cooler melt and activates this magma together with chemical recrystallization processes. This can create an enormously high pressure that presses a relatively cool magma (approx. 800–980 ° C) onto the surface.
Lava domes arise in periods of a few days to a few decades. Their growth rate also varies within wide limits. Long-lasting domes can reach heights of many hundreds of meters.
Occurrence
Well-known lava domes are z. B. on the Gunung Merapi in Java , on the Soufrière Hills in Montserrat and on Mount St. Helens in the USA . The latter has two domes; the first was created in the years after the eruption in 1980, the new one, whose height has now exceeded that of the old one, has formed anew since October 2004 and grew until the beginning of 2008. In November 2007 a lava dome was formed in the crater of Kelud in Indonesia.
Lava domes can also arise next to existing volcanoes; the best known example of this is the Novaruptadom , which was formed not far from Mount Katmai in Alaska.
Volcanic areas with numerous lava domes in Europe are the Chaîne des Puys with the Puy de Dôme , the Methana peninsula and the islands of Milos , Nisyros and Lipari .
literature
- Schmincke HU (2000) Volcanism. 2nd edition, Scientific Book Society Darmstadt. ISBN 3-534-14102-4
Web links
- Lava domes in the Global Volcanism Program (English)
- V. Camp: Lava Domes. How Volcanoes Work , Dept. of Geological Sciences, San Diego State University (English)
Individual evidence
- ↑ USGS: Mount St. Helens returns to Slumber , July 10, 2008 (accessed January 31, 2010).