Rhyolitic Volcanoes
Friday, 9. October 2009, 10:23:55
Even if you don’t know what a rhyolitic volcano is, you will certainly have heard of volcanoes like Vesuvius, Krakatoa, Mount St. Helens, and Chaiten - names that have gone down in history for inflicting loss of life and massive damage. These volcanoes are rhyolitic. Volcanoes in this category provide some of Earth's most explosive events.
During the eruptions of Chaitén in 2008 Ralph Harrington at the Volcanism Blog followed the events with some magnificent posts.
Rhyolite is an extrusive igneous rock that is the volcanic equivalent of (intrusive) granite. Rhyolite has solidified quickly (cooling at the surface) and is fine-grained - granite has solidified slowly underground and is coarse-grained. Rhyolite often erupts explosively because its high silica content results in extremely high viscosity (resistance to flow), which hinders degassing. When bubbles form, they can cause the magma to explode, fragmenting the rock into pumice and tiny particles of volcanic ash.
It now turns out that magma from Chaitén shot through Earth's crust at around a metre per second, a speed highlighting the perils from rhyolitic volcanoes, scientists reported recently in the journal Nature.
The Chaitén volcano in Chile erupted unexpectedly and explosively on 1 May 2008, and it is still erupting. The eruption has displaced over 5,000 people, and resulted in millions of euros of lost revenue in Chile. It has also provided geophysicists the rare opportunity of directly observing a rhyolite magma fuelled eruption. Castro and Dingwell present petrological and experimental evidence to show that the hydrous rhyolite magma at Chaitén ascended very rapidly, with velocities of the order of a metre per second. Such rapid ascent, contrasting markedly with the behaviour of most silicic magmas, implies a transit time from storage depths greater than 5 km to the near surface of only 4 hours, leaving little warning time for such eruptions. This work suggests that rhyolitic volcanoes that have been active during the Holocene — that is since the last Ice Age, around 10,000 years ago — should be closely monitored, especially those near major centres of population.
During the eruptions of Chaitén in 2008 Ralph Harrington at the Volcanism Blog followed the events with some magnificent posts.
Rhyolite is an extrusive igneous rock that is the volcanic equivalent of (intrusive) granite. Rhyolite has solidified quickly (cooling at the surface) and is fine-grained - granite has solidified slowly underground and is coarse-grained. Rhyolite often erupts explosively because its high silica content results in extremely high viscosity (resistance to flow), which hinders degassing. When bubbles form, they can cause the magma to explode, fragmenting the rock into pumice and tiny particles of volcanic ash.
It now turns out that magma from Chaitén shot through Earth's crust at around a metre per second, a speed highlighting the perils from rhyolitic volcanoes, scientists reported recently in the journal Nature. The Chaitén volcano in Chile erupted unexpectedly and explosively on 1 May 2008, and it is still erupting. The eruption has displaced over 5,000 people, and resulted in millions of euros of lost revenue in Chile. It has also provided geophysicists the rare opportunity of directly observing a rhyolite magma fuelled eruption. Castro and Dingwell present petrological and experimental evidence to show that the hydrous rhyolite magma at Chaitén ascended very rapidly, with velocities of the order of a metre per second. Such rapid ascent, contrasting markedly with the behaviour of most silicic magmas, implies a transit time from storage depths greater than 5 km to the near surface of only 4 hours, leaving little warning time for such eruptions. This work suggests that rhyolitic volcanoes that have been active during the Holocene — that is since the last Ice Age, around 10,000 years ago — should be closely monitored, especially those near major centres of population.
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http://www.nature.com/nature/journal/v461/n7265/edsumm/e091008-07.html
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http://www.physorg.com/news174143402.html
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http://www.google.com/hostednews/afp/article/ALeqM5jGdfTQ5L1GLQ47ptv_QApnSlNMyw
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http://scienceblogs.com/eruptions/2009/10/the_speedy_magma_of_chaiten_an.php
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http://volcanism.wordpress.com/2009/10/08/chaiten-magmas-surprising-speed/
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