May 18, 2011
The List: Five Volcanoes to Watch
On the 31st Anniversary of the eruption of Mount St. Helens, we look at other volcanoes to watch. Photo courtesy of the Global Volcanism Program|NMNH|SI
On 8:32 AM, May 18, 1980, Mount St. Helens erupted. The Sunday morning earthquake measured a 5.1 on the Richter scale and in its wake, "nearly 150 square miles of forest was blown over or left dead and standing," according to the USDA Forest Service. "The eruption lasted 9 hours, but Mount St. Helens and the surrounding landscape were dramatically changed within moments." That was 31 years ago. So, what about today? Which volcanoes pose great danger?
On the anniversary of the eruption of Mount St. Helens, the ATM blog team, with the help of curator Elizabeth Cottrell, director of the Global Volcanism Program in the Department of Mineral Sciences at the National Museum of Natural History, has compiled a list of five volcanoes that currently threaten population centers. They are:
1. Ecuador: Tungurahua—This stratovolcano is one of Ecuador's most active, and it has been erupting this year. Tungurahua threatens multiple nearby populations, especially the city of Baños, located at the foot of the volcano. In 1999, Baños was temporarily evacuated due to a long-term eruption.
2. United States: Mt. Rainier—The highest peak of the Cascade Mountain Range, located southeast of Seattle, Washington, Mt. Ranier last erupted in 1894. A new eruption could melt its glacial ice, sending landslides of mud and ash (called lahar) into the Seattle-Tacoma metro area.
3. Indonesia: Merapi—In one of the world's most densely populated areas lies one of Indonesia's most active volcanoes. Merapi has been erupting for the past year, killing hundreds and displacing hundreds of thousands of residents in the Jakarta area.
4. Italy: Vesuvius—Best known for its massively destructive eruption in 79 AD that buried the Roman cities of Pompeii and Herculaneum, Vesuvius last erupted in 1944. It is the only volcano on the European mainland that has erupted within the past hundred years. Vesuvius threatens millions of people living in or near the city of Naples.
5. Mexico: Popocatépetl—From the Aztec word for smoking mountain,Volcán Popocatépetl is the second-highest volcano in North America. Currently erupting, this stratovolcano threatens Mexico City.
To learn more about these and other volcanoes, visit the Plate Tectonics Gallery in the Geology, Gems and Minerals Hall of the National Museum of Natural History and check out the website of the Global Volcanism Program.
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Scientists move closer to predicting volcano hazard
18 May 2011, by Tamera Jones
UK and Russian scientists say they are a step closer to predicting how dangerous a volcano is after developing a method that lets them figure out how individual volcanoes are 'plumbed'.
The crater of Mt St Helens showing the active dome belching steam and volcanic gases.
The new approach means researchers need only analyse a single chunk of rock from a volcano to work out how big and deep its magma chamber is.
The same method also lets them calculate the length and width of the vent that brings the magma from the chamber to the surface.
Having both measurements is vital for predicting how hazardous a volcano will be.
'Generally speaking if a volcano has a big magma chamber and a narrow, short vent, the volcano tends to be more explosive than a volcano with a small chamber and wide vent,' says Professor Jon Blundy from the University of Bristol, a member of the research team.
'So, if we know the details of the plumbing system underneath a volcano, we're in a better position to say how dangerous it is likely to be,' he adds.
Being able to predict how hazardous a volcano is has long been the Holy Grail for volcanologists. But the size and depth of magma chambers underneath volcanoes varies hugely, and finding out the inner dimensions of individual volcanoes' plumbing systems has until now proved time-consuming, challenging and expensive.
'If we know the details of the plumbing system underneath a volcano, we're in a better position to say how dangerous it is likely to be.'
Professor Jon Blundy, University of Bristol
Now researchers at the University of Bristol and Moscow State University have developed a mathematical model that is cheap, safe and easy to apply.
It relies on a fact volcanologists have known about for some time: as magma moves from the magma chamber towards the surface, both crystals and gas bubbles form inside the magma. The rate at which crystals and bubbles grow depends on just how quickly the magma rises to the surface, which in turn depends on the diameter of the vent through which it travels.
'Magma from explosive volcanoes produces rocks with lots of bubbles in it, whereas rocks from volcanoes that ooze magma more slowly contain crystals of different sizes,' explains Blundy.
The researchers have taken this further: using their mathematical model they show that the range of sizes and types of crystal in volcanic rock also tells them about the plumbing for different volcanoes.
'Counting the size of the crystals gives us a window into the subterranean plumbing of a volcano,' says Blundy.
To test their model, the researchers applied it to a rock sample from Mount St Helens volcano in the US, which erupted in the 1980s.
Their model predicted a vent diameter of around 30 metres, connecting the volcanic crater to a magma chamber at a depth of around 14 kilometres. These predictions fit with other estimates using more traditional techniques like satellites or seismometers.
'The idea is to use this surprisingly simple and low cost technique in conjunction with some of the other methods to tell us about individual volcanoes' plumbing systems, that then inform our models of how volcanoes operate during eruptions,' Blundy says.
The study is published in the April 2011 edition of the journal Geology.
Oleg E. Melnik, Jonathan D. Blundy, Alison C. Rust and Duncan D. Muir, Subvolcanic plumbing systems imaged through crystal size distributions, Geology v. 39 no. 4 p. 403-406, First published online March 8, 2011, doi: 10.1130/G31691.1
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