MAGMA, VOLCANOES – ΜΑΓΜΑ, ΗΦΑΙΣΤΕΙΑ

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A very hot mix of articles by Our Amazing Planet

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Tiny Gravity Changes Show Magma’s Underground Movements

Charles Q. Choi, OurAmazingPlanet Contributor – Aug 30, 2012 03:11 PM ET

Kilauea’s current eruption is still going strong after 29 years.
CREDIT: USGS/HVO.

The secret movements of magma deep inside a volcano can be detected by tracking the subtle changes in gravity they cause. Surprising readings from a Hawaiian volcano have researchers hoping to better understand volcanic activity through gravity monitoring.

Continuous gravity measurements of active volcanoes are relatively rare, with most results coming from Mount Etna in Italy.

“One problem is the expense,” researcher Michael Poland, a geophysicist at the U.S. Geological Survey’s Hawaiian Volcano Observatory, explained. “Gravity measurements have always been a really expensive endeavor. The big users are oil and mining companies.”

Now scientists have monitored the gravity at Kīlauea, a popular tourist destination on Hawaii’s Big Island, and discovered a regular cycle of fluctuations that suggest magma is churning a kilometer (0.6 miles) below the surface.

The way magma churns in underground chambers below volcanic vents is key to understanding how persistent volcanoes are, and whether or not they might catastrophically erupt in the future. However, what goes on deep under the Earth’s surface is difficult to monitor.

One way to peer underground is by looking at Earth’s gravity, the researchers said. Anything that has mass has a gravity field that pulls objects toward it. The strength of this field depends on the amount of mass. Since the Earth’s mass is not spread out evenly, this means the strength of the planet’s gravitational pull is stronger in some places and weaker in others. As such, the flow of magma from one place to another can be detected from above.

Most active volcano

“Kīlauea is the world’s most active volcano,” Poland said. “It’s erupted almost continuously since 1983. It’s a natural ‘lab volcano’ ―a great place to try and study something like gravity measurements.”

The researchers installed two continuous gravity meters at the summit of the volcano in 2010. One was about 1.2 miles (2 kilometers) northwest of the eruptive vent at the summit and recorded measurements every10 seconds, while the other was placed about 500 feet (150 meters) east and recorded data every second.

They detected gravity fluctuations that came in a cycle about 150 seconds long.

“There was no expectation for that kind of result,” Poland told OurAmazingPlanet. “That gravity oscillation came out of nowhere. It points to the idea that there’s probably a lot of things going on in volcanoes, glaciers, wherever you look, but we haven’t developed the tools to detect these sorts of things.”

Magma movements

Magma feeding the eruption at the volcano climbs from the Earth’s mantle layer and passes through a complex system of reservoirs, where it may be stored before it flows to the eruption site.

The researchers’ computer models suggest the fluctuations they saw were caused by magma churning in a reservoir about 0.6 miles (1 km) below the surface.

“Ultimately we want to predict eruptions better — predict the time, place and magnitude,” Poland said. “Gravity measurements are one of many techniques that will help move us toward real predictions of eruptions, which comes from a better understanding of what’s happening beneath our feet.”

Poland and his colleague, Daniele Carbone, detailed their findings in the September issue of the journal Geology.

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Hawaii’s Magma Chamber May Be World’s Shallowest

Andrea Mustain, OurAmazingPlanet Staff Writer – Dec 14, 2010 09:52 AM ET

Hawaii Volcanoes National Park. 1972-1974 eruption of Kilauea Volcano. Fountain along the base of the west wall of Pauahi Crater.
CREDIT: D.W. Peterson, May 5, 1973.

The huge, underground pocket of molten rock  that feeds Hawaii’s volcanoes may be a lot closer to the Earth’s surface than previously thought; it could be the shallowest in the world, new chemical analysis suggests.

The new findings may help researchers better predict when the islands’ volcanoes are going to erupt.

“Hawaii was already unique among volcanic systems, because it has such an extensive plumbing system, and the magma that erupts has a unique and variable chemical composition,” said Julie Ditkof, an honors undergraduate student in earth sciences at Ohio State University.

Using a technique developed by Michael Barton, a professor of earth sciences at Ohio State, Ditkof studied nearly 1,000 magma samples from Hawaii. She presented her findings on Tuesday, Dec. 14 at the American Geophysical Union Meeting in San Francisco.

For his own research on Iceland’s volcanoes , Barton determined that the chemical composition of once-liquid magma can indicate the pressure at which it crystallized. That information can then be used to determine how far under the Earth’s surface the magma originated.

When Ditkof applied the technique to Hawaii’s volcanoes, she found the islands’ fiery mountains share a single so-called magma chamber, which lies a mere 1.9 to 2.5 miles (3 to 4 kilometers) below Hawaii.

“Now we know the chamber is at a shallow depth not seen anywhere else in the world,” Ditkof said.

In comparison, the magma chambers beneath Iceland lie at an average depth of 12.4 miles (20 km).

Researchers could use Barton’s chemical analysis technique to regularly monitor pressures inside Hawaii’s magma chamber and make more precise estimates of when eruptions are going to occur.

Barton said that, ultimately, the finding might be more important in terms of energy.

“Hawaii has huge geothermal resources that haven’t been tapped fully,” he said, adding that scientists would have to determine whether tapping that energy was practical — or safe.

“You’d have to drill some test bore holes . That’s dangerous on an active volcano, because then the lava could flow down and wipe out your drilling rig,” Barton said.

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Massive Japan Earthquake Altered Earth’s Gravity

Charles Q. Choi, OurAmazingPlanet Contributor – Oct 05, 2011 11:25 AM ET

ESA’s GOCE mission has delivered the most accurate model of the ‘geoid’ ever produced. Red corresponds to points with higher gravity, and blue to points with lower gravity. CREDIT: ESA/HPF/DLR

The devastating earthquake that struck Japan earlier this year was powerful enough to slightly alter the pull of gravity under the affected area, scientists now find.

Anything that has mass has a gravity field that attracts objects toward it. The strength of this field depends on a body’s mass. Since the Earth’s mass is not spread out evenly, this means its gravity field is stronger in some places and weaker in others .

The magnitude 9.0 Tohoku-Oki temblor in March was the most powerful earthquake to hit Japan and the fifth-most powerful quake ever recorded . To see how the temblor might have deformed the Earth there, scientists used the Gravity Recovery and Climate Experiment (GRACE) satellites to analyze the area’s gravity field before and after the quake.

The researchers found the Tohoku-Oki quake reduced the gravity field there by an average of two- millionths of a gal by slightly thinning the Earth’s crust. In comparison, the strength of the gravitational pull at the Earth’s surface is, on average, 980 gals. (The gal, short for Galileo, is a unit of acceleration; one gal is defined as one centimeter per second squared.)

“The most important implication of our findings is that the massive Tohoku-Oki earthquake brings significant changes to not only the ground but also the underground structure of Japan,” researcher Koji Matsuo, a geophysicist at Hokkaido University in Japan, told OurAmazingPlanet.

The GRACE satellites had previously detected gravity changes caused by the magnitude 9.1 to 9.3 2004 Sumatra-Andaman quake, the third-most powerful earthquake ever recorded, and the magnitude 8.8 earthquake that hit Chile in 2010, the eighth-most powerful on record. These reduced the gravity fields in the areas struck in much the same way as the Tohoku-Oki quake, since they were all similar types of earthquakes.

The researchers are now interested in seeing if they can detect post-quake gravity field changes as the crust settles back into place.

Matsuo and his colleague Kosuke Heki detailed their findings online Sept. 22 in the journal Geophysical Research Letters.

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Best Gravity Map Yet Shows a Lumpy, Bumpy Earth

Nola Taylor Redd, SPACE.com Contributor – Jun 02, 2011 05:19 PM ET

ESA’s GOCE mission has delivered the most accurate model of the ‘geoid’ ever produced. Red corresponds to points with higher gravity, and blue to points with lower gravity. CREDIT: ESA/HPF/DLR

Take a clay model of Earth and squish it with your fingers, and the result may look similar to the geoid — the latest and best-ever map of our planet’s gravitational field.

The latest Earth gravity map is the most accurate model of gravity fluctuations around the world. It was recorded by the European Space Agency’s GOCE satellite, whose instruments show Earth as a lumpy, multi-colored mesh of high and low points.

That’s because gravity is not the same at all points on Earth; more massive features have a stronger pull. [6 Weird Facts About Gravity]

“If Earth were a sphere and its density constant, then gravity would be the same everywhere,” Reiner Rummel, Chairman of the GOCE Mission Advisory Group, told SPACE.com in an email interview when the geoid was unveiled earlier this year.

But that’s not the case.

The solid, rocky crust under the continents is almost 20 miles (32 kilometers) thick, while the crust beneath the ocean spans just 6 miles (10 km). Some regions contain lighter materials, some heavier. Actions within the mantle cause variations in density.

All of these factors result in Earth’s gravity being stronger at some points than others, researchers said.

Measuring Earth’s gravity

Circling Earth lower than any other observational satellite, the ESA’s Gravity field and steady-state Ocean Circulation Explorer (GOCE) mapped the geoid by using its own orbit as a tool.

“When the satellite approaches, for example, the Alps, the mountains pull the satellite slightly towards them,” explained mission scientist Roger Haagmans via email. “So by very precisely analyzing the orbit of the satellite, we learn about the scale effects of our gravity field irregularities.”

GOCE also carries a gradiometer, which measures the numerical change of the magnetic field. The two together present a full picture of Earth’s gravity.

Mapping the geoid helps scientists learn more about the Earth’s oceans and climate. Combining the geoid with information on seismology and magnetism reveals more about the internal structure of the planet, including earthquake-related processes.

“In principle, the situation before the earthquake at a location where continental and oceanic plates meet and subduction [where one tectonic plate moves beneath another] takes place has a specific fingerprint in terms of gravity,” Haagmans said. “After the earthquake, the plates have moved significantly and cause a different fingerprint.”

Still gathering data

Comparing such before-and-after measurements helps scientists to refine their models and gain a greater understanding of earthquakes, researchers said.

While the geoid remains relatively constant overall, earthquakes, melting polar ice, and changes in sea level can all cause subtle changes. “The temporal variations are very small — millimeters in the geoid — but measureable,” Rummel said.

Launched in March 2009, GOCE finished its main gravity-mapping mission six weeks ahead of schedule. But it will continue to study the planet’s gravity through 2012, allowing for even more precise measurements.

This article was provided by SPACE.com, a sister site to OurAmazingPlanet.

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Magma in Ethiopia Could Predict Future Eruptions

Andrea Leontiou, OurAmazingPlanet Staff – Oct 19, 2010 09:04 AM ET

Steaming volcanic cones along the line of lava that erupted in the Afar Desert in June 2009.
CREDIT: David Ferguson, University of Oxford

Columns of magma that shove their way into rocks on the surface could help scientists predict where volcanic eruptions may occur, new research suggests.

When magma – molten rock that will be known as lava after it reaches the surface – travels through underground chambers, the ground changes, with some surface areas deflating as the magma moves away and other areas inflating as the magma moves upward, creating intrusions of magma called dykes . This deflation and inflation creates stress on the ground surface.

Scientists have long wondered whether this stress was linked to later volcanic events and whether they could be used to predict those eruptions. To test that out, a study team investigated the rifting of Earth’s surface that is occurring in Ethiopia.

“The idea that the stress change, caused by a magmatic intrusion, may affect the location of future events is not new. However, it has never been systematically demonstrated,” said study team member Ian Hamling of the University of the International Center for Theoretical Physics, in Italy. “The ongoing rifting episode in Ethiopia provided a unique opportunity to test whether a link exists.”

The episode drawing the team’s attention began in September 2005, when a volcanic event in Ethiopia’s Afar Desert forced magma up through rocks in a crack, resulting in a tear in Earth’s crust 37 miles long (60 km). Over the next four years, 12 more dykes were created in the same region near the Red Sea.

An interferogram showing the deformation associated with a dyke intrusion emplaced in October 2008. The black line shows the location of the rift axis.
CREDIT: Ian Hamling, International Centre for Theoretical Physics/University of Leeds, using Generic Mapping Tools

The researchers found that the sequential positioning of dykes was not random. Instead, the stress events created by a new dyke’s intrusion were a factor in the location of the next magma intrusions. In the cases of nine of the 12 dykes created after the initial intrusion, at least half the opening was in a region that had been jacked apart by the preceding dyke.

To monitor the surface changes around each dyke throughout the event, the scientists used Synthetic Aperture Radar Interferometry (InSAR) on satellite data taken from the initial dyke between 2005 and 2009, and they produced interferogram images.

InSAR involves combining two or more radar images of the same ground location in such a way that very precise measurements (within a few millimeters) can be made of any ground movements between images.

Combining them with GPS data, scientists discovered that the later eruptions were connected.

While this discovery will enable researchers to get a better idea of where the next event will happen, it doesn’t answer every question.

“These findings are unique and will help us better predict the location of future eruptions and help authorities issue timely evacuation warnings,” said co-author Tim Wright of the University of Leeds.

The researchers plan to continue tracking stress events.

“A team of international scientists are continuing to monitor the rifting episode using a variety of geophysical methods. As new intrusions occur we will track the evolving stress field to allow us to predict the location of further magmatism,” Hamling said.

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''Gravity, Magma,Volcanoes'' as an unmodified copy of Our Amazing Planet's articles by Tracing Knowledge is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.
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