A lava dome (after eng lava dome. Lava dome ), also called dome or lava, is a hill-shaped or columnar ( Lavanadel ) survey, which arises from a volcano by the eruption of very viscous lava with a high silica content. By rapid cooling and very low flow ranges arises as directly over the exit of a pfropfenförmiger lava dome, which closes the volcanic vent upwards.
Lava domes carry a high risk potential. By continuously pressing out of the lava dome is relatively unstable. It can collapse or large rock regions can cancel from its steep flanks and generate gravitationally accelerated pyroclastic flows that plunge with 100 to 400 km / h and temperatures of 200 ° C to 700 ° C in the valley and can cause extensive devastation in its path. In ground water contact and high pent-up gas content lava domes can be very explosive. The pressure in the interior of a volcano can discharge explosively. Through the formation of a dome inside the crater of an explosive (such as at Mount St. Helens or numerous volcanoes in Indonesia ) the risk of a future volcanic disaster increases.
Formation and structure
Typical rocks of volcanic domes are andesite and dacite. Most are dombildende volcanoes in regions where among the other pushed a continental plate ( subducted ) is. This sedimentary rocks are melted, for example, and a gas-rich magma rises in the earth's crust. Magma chambers can spend a longer time in the upper areas of the crust without a volcano is active. Then rises new basaltic magma in such a magma chamber, so there is the so-called "Magma - mixing effect," which heats the cooler and melt together with chemical Umkristallisierungsprozessen enabled this magma. This can result in an enormously high pressure (about 800-980 ° C) pressed against the surface a relatively cool magma.
Lava domes occur in time intervals of a few days to a few decades. Their growth rate varied within wide limits. Durable Dome can reach a height of several hundred meters.
Known lava domes are located eg on the Mount Merapi in Java, on the Soufriere Hills in Montserrat and at Mount St. Helens in the United States. The latter has two cathedrals; the first was built in the years after the eruption of 1980, the new, the amount of which now surpasses the old, has re-formed in October 2004 and grew up in early 2008. In November 2007, the lava dome was built in the crater of Kelud in Indonesia.
Lava domes can also occur alongside existing volcanoes; the most famous example of this is the Novaruptadom, which has formed near the Mount Katmai in Alaska.