The role of gravitational instabilities in deposition of volcanic ash: The example of Eyjafjallajökull

Figure 1 from Manzella et al.: Original and processed snapshot of the video of the Eyjafjallajökull (Iceland) plume as observed on 4 May 2010. White arrows indicate finger positions. This article is Open Access.

Boulder, Colo., USA – Volcanic ash poses a significant hazard for areas close to volcanoes and for aviation. For example, the 2010 eruption of Eyjafjallajökull, Iceland, clearly demonstrated that even small-to-moderate explosive eruptions, in particular if long-lasting, can paralyze entire sectors of societies, with significant, global-level, economic impacts. In this open-access Geology article, Irene Manzella and colleagues present the first quantitative description of the dynamics of gravitational instabilities and particle aggregation based on the 4 May 2010 eruption.

Their analysis also reveals some important shortcomings in the Volcanic Ash Transport and Dispersal Models (VATDMs) typically used to forecast the dispersal of volcanic ash. In particular, specific processes exist that challenge the view of sedimentation of fine particles from volcanic plumes and that are currently poorly understood: particle aggregation and gravitational instabilities. These appear as particle-rich "fingers" descending from the base of volcanic clouds and have commonly been observed during volcanic explosive eruptions.

Based on direct observations of the 2010 Eyjafjallajökull plume, on the correlation with the associated fallout deposit, and on dedicated laboratory analogue experiments, Irene Manzella and colleagues show how fine ash in these particle-rich fingers settles faster than individual particles and that aggregation and gravitational instabilities are closely related. Both phenomena can significantly contribute to reducing fine-ash lifetime in the atmosphere and, therefore, it is crucial to include them in VATDMs in order to provide accurate forecasting of ash dispersal and sedimentation.

Source: Gsa

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The Textbook theory behind volcanoes may be wrong

Tungurahua volcano eruption. Credit: © Sunshine Pics / Fotolia

In the typical textbook picture, volcanoes, such as those that are forming the Hawaiian islands, erupt when magma gushes out as narrow jets from deep inside Earth. But that picture is wrong, according to a new study from researchers at Caltech and the University of Miami in Florida.

New seismology data are now confirming that such narrow jets don't actually exist, says Don Anderson, the Eleanor and John R. McMillian Professor of Geophysics, Emeritus, at Caltech. In fact, he adds, basic physics doesn't support the presence of these jets, called mantle plumes, and the new results corroborate those fundamental ideas.

"Mantle plumes have never had a sound physical or logical basis," Anderson says. "They are akin to Rudyard Kipling's 'Just So Stories' about how giraffes got their long necks."

Anderson and James Natland, a professor emeritus of marine geology and geophysics at the University of Miami, describe their analysis online in the September 8 issue of the Proceedings of the National Academy of Sciences.

According to current mantle-plume theory, Anderson explains, heat from Earth's core somehow generates narrow jets of hot magma that gush through the mantle and to the surface. The jets act as pipes that transfer heat from the core, and how exactly they're created isn't clear, he says. But they have been assumed to exist, originating near where Earth's core meets the mantle, almost 3,000 kilometers underground -- nearly halfway to the planet's center. The jets are theorized to be no more than about 300 kilometers wide, and when they reach the surface, they produce hot spots.

While the top of the mantle is a sort of fluid sludge, the uppermost layer is rigid rock, broken up into plates that float on the magma-bearing layers. Magma from the mantle beneath the plates bursts through the plate to create volcanoes. As the plates drift across the hot spots, a chain of volcanoes forms -- such as the island chains of Hawaii and Samoa.

"Much of solid-Earth science for the past 20 years -- and large amounts of money -- have been spent looking for elusive narrow mantle plumes that wind their way upward through the mantle," Anderson says.

To look for the hypothetical plumes, researchers analyze global seismic activity. Everything from big quakes to tiny tremors sends seismic waves echoing through Earth's interior. The type of material that the waves pass through influences the properties of those waves, such as their speeds. By measuring those waves using hundreds of seismic stations installed on the surface, near places such as Hawaii, Iceland, and Yellowstone National Park, researchers can deduce whether there are narrow mantle plumes or whether volcanoes are simply created from magma that's absorbed in the sponge-like shallower mantle.

No one has been able to detect the predicted narrow plumes, although the evidence has not been conclusive. The jets could have simply been too thin to be seen, Anderson says. Very broad features beneath the surface have been interpreted as plumes or super-plumes, but, still, they're far too wide to be considered narrow jets.

But now, thanks in part to more seismic stations spaced closer together and improved theory, analysis of the planet's seismology is good enough to confirm that there are no narrow mantle plumes, Anderson and Natland say. Instead, data reveal that there are large, slow, upward-moving chunks of mantle a thousand kilometers wide.

In the mantle-plume theory, Anderson explains, the heat that is transferred upward via jets is balanced by the slower downward motion of cooled, broad, uniform chunks of mantle. The behavior is similar to that of a lava lamp, in which blobs of wax are heated from below and then rise before cooling and falling. But a fundamental problem with this picture is that lava lamps require electricity, he says, and that is an outside energy source that an isolated planet like Earth does not have.

The new measurements suggest that what is really happening is just the opposite: Instead of narrow jets, there are broad upwellings, which are balanced by narrow channels of sinking material called slabs. What is driving this motion is not heat from the core, but cooling at Earth's surface. In fact, Anderson says, the behavior is the regular mantle convection first proposed more than a century ago by Lord Kelvin. When material in the planet's crust cools, it sinks, displacing material deeper in the mantle and forcing it upward.

"What's new is incredibly simple: upwellings in the mantle are thousands of kilometers across," Anderson says. The formation of volcanoes then follows from plate tectonics -- the theory of how Earth's plates move and behave. Magma, which is less dense than the surrounding mantle, rises until it reaches the bottom of the plates or fissures that run through them. Stresses in the plates, cracks, and other tectonic forces can squeeze the magma out, like how water is squeezed out of a sponge. That magma then erupts out of the surface as volcanoes. The magma comes from within the upper 200 kilometers of the mantle and not thousands of kilometers deep, as the mantle-plume theory suggests.

"This is a simple demonstration that volcanoes are the result of normal broad-scale convection and plate tectonics," Anderson says. He calls this theory "top-down tectonics," based on Kelvin's initial principles of mantle convection. In this picture, the engine behind Earth's interior processes is not heat from the core but cooling at the planet's surface. This cooling and plate tectonics drives mantle convection, the cooling of the core, and Earth's magnetic field. Volcanoes and cracks in the plate are simply side effects.

The results also have an important consequence for rock compositions -- notably the ratios of certain isotopes, Natland says. According to the mantle-plume idea, the measured compositions derive from the mixing of material from reservoirs separated by thousands of kilometers in the upper and lower mantle. But if there are no mantle plumes, then all of that mixing must have happened within the upwellings and nearby mantle in Earth's top 1,000 kilometers.

The paper is titled "Mantle updrafts and mechanisms of oceanic volcanism."

Source: California Institute of Technology

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New view of Mount Rainier's volcanic plumbing: Electrical images show upward flow of fluids to magma chamber

This image was made by measuring how the ground conducts or resists electricity in a study co-authored by geophysicist Phil Wannamaker of the University of Utah Energy & Geoscience Institute. It shows the underground plumbing system that provides molten and partly molten rock to the magma chamber beneath the Mount Rainier volcano in Washington state. The scale at left is miles depth. The scale at bottom is miles from the Pacific Coast. The Juan de Fuca plate of Earth's Pacific seafloor crust and upper mantle is shown in blue on the left half of the image as it dives or 'subducts' eastward beneath Washington state. The reddish orange and yellow colors represent molten and partly molten rock forming atop the Juan de Fuca plate or 'slab.' The image shows the rock begins to melt about 50 miles beneath Mount Rainier (the red triangle at top). Some is pulled downward and eastward as the slab keeps diving, but other melts move upward to the orange magma chamber shown under but west of Mount Rainier. The line of sensors used to make this image were placed north of the 14,410-foot peak, so the image may be showing a lobe of the magma chamber that extends northwest of the mountain. Red ovals on the left half of the page are the hypocenters of earthquakes. [show less] Credit: R Shane McGary, Woods Hole Oceanographic Institution.

By measuring how fast Earth conducts electricity and seismic waves, a University of Utah researcher and colleagues made a detailed picture of Mount Rainier's deep volcanic plumbing and partly molten rock that will erupt again someday.

"This is the most direct image yet capturing the melting process that feeds magma into a crustal reservoir that eventually is tapped for eruptions," says geophysicist Phil Wannamaker, of the university's Energy & Geoscience Institute and Department of Civil and Environmental Engineering. "But it does not provide any information on the timing of future eruptions from Mount Rainier or other Cascade Range volcanoes."

The study was published today in the journal Nature by Wannamaker and geophysicists from the Woods Hole Oceanographic Institution in Massachusetts, the College of New Jersey and the University of Bergen, Norway.

In an odd twist, the image appears to show that at least part of Mount Rainier's partly molten magma reservoir is located about 6 to 10 miles northwest of the 14,410-foot volcano, which is 30 to 45 miles southeast of the Seattle-Tacoma area.

But that could be because the 80 electrical sensors used for the experiment were placed in a 190-mile-long, west-to-east line about 12 miles north of Rainier. So the main part of the magma chamber could be directly under the peak, but with a lobe extending northwest under the line of detectors, Wannamaker says.

The top of the magma reservoir in the image is 5 miles underground and "appears to be 5 to 10 miles thick, and 5 to 10 miles wide in east-west extent," he says. "We can't really describe the north-south extent because it's a slice view."

Wannamaker estimates the reservoir is roughly 30 percent molten. Magma chambers are like a sponge of hot, soft rock containing pockets of molten rock.

The new image doesn't reveal the plumbing tying Mount Rainier to the magma chamber 5 miles below it. Instead, it shows water and partly molten and molten rock are generated 50 miles underground where one of Earth's seafloor crustal plates or slabs is "subducting" or diving eastward and downward beneath the North America plate, and how and where those melts rise to Rainier's magma chamber.
The study was funded largely by the National Science Foundation's Earthscope program, which also has made underground images of the United States using seismic or sound-wave tomography, much like CT scans show the body's interior using X-rays.

The new study used both seismic imaging and magnetotelluric measurements, which make images by showing how electrical and magnetic fields in the ground vary due to differences in how much underground rock and fluids conduct or resist electricity.

Wannamaker says it is the most detailed cross-section view yet under a Cascades volcanic system using electrical and seismic imaging. Earlier seismic images indicated water and partly molten rock atop the diving slab. The new image shows melting "from the surface of the slab to the upper crust, where partly molten magma accumulates before erupting," he adds.

Wannamaker and Rob L. Evans, of the Woods Hole Oceanographic Institution, conceived the study. First author R Shane McGary -- then at Woods Hole and now at the College of New Jersey -- did the data analysis. Other co-authors were Jimmy Elsenbeck of Woods Hole and Stéphane Rondenay of the University of Bergen.

Mount Rainier: Hazardous Backdrop to Metropolitan Seattle-Tacoma
Mount Rainier, the tallest peak in the Cascades, "is an active volcano that will erupt again," says the U.S. Geological Survey. Rainier sits atop volcanic flows up to 36 million years old. An ancestral Rainier existed 2 million to 1 million years ago. Frequent eruptions built the mountain's modern edifice during the past 500,000 years. During the past 11,000 years, Rainier erupted explosively dozens of times, spewing ash and pumice.

Rainier once was taller until it collapsed during an eruption 5,600 years ago to form a large crater open to the northeast, much like the crater formed by Mount St. Helens' 1980 eruption. The 5,600-year-old eruption sent a huge mudflow west to Puget Sound, covering parts or all of the present sites of the Port of Tacoma, Seattle suburbs Kent and Auburn, and the towns Puyallup, Orting, Buckley, Sumner and Enumclaw.

Rainier's last lava flows were 2,200 years ago, the last flows of hot rock and ash were 1,100 years ago and the last big mudflow 500 years ago. There are disputed reports of steam eruptions in the 1800s.

Subduction Made Simple -- and a Peek beneath a Peak
The "ring of fire" is a zone of active volcanoes and frequent earthquake activity surrounding the Pacific Ocean. It exists where Earth's tectonic plates collide -- specifically, plates that make up the seafloor converge with plates that carry continents.

From Cape Mendocino in northern California and north past Oregon, Washington state and into British Columbia, an oceanic plate is being pushed eastward and downward -- a process called subduction -- beneath the North American plate. This relatively small Juan de Fuca plate is located between the huge Pacific plate and the Pacific Northwest.

New seafloor rock -- rich with water in cracks and minerals -- emerges from an undersea volcanic ridge some 250 miles off the coast, from northern California into British Columbia. That seafloor adds to the western edge of the Juan de Fuca plate and pushes it east-northeast under the Pacific Northwest, as far as Idaho.

The part of the plate diving eastward and downward is called the slab, which ranges from 30 to 60 miles thick as it is jammed under the North American plate. The part of the North American plate above the diving slab is shaped like a wedge.

When the leading, eastern edge of the diving slab descends deep enough, where pressures and temperatures are high, water-bearing minerals such as chlorite and amphibole release water from the slab, and the slab and surrounding mantle rock begin to melt. That is why the Cascade Range of active volcanoes extends north-to-south -- above the slab and parallel but about 120 miles inland from the coast -- from British Columbia south to Mount Shasta and Lassen Peak in northern California.
In the new image, yellow-orange-red areas correspond to higher electrical conductivity (or lower resistivity) in places where fluids and melts are located.

The underground image produced by the new study shows where water and molten rock accumulate atop the descending slab, and the route they take to the magma chamber that feeds eruptions of Mount Rainier:

-- The rock begins to melt atop the slab about 50 miles beneath Mount Rainier. Wannamaker says it is best described as partly molten rock that contains about 2 percent water and "is a mush of crystals within an interlacing a network of molten rock."
-- Some water and partly molten rock actually gets dragged downward atop the descending slab, to depths of 70 miles or more.

-- Other partly molten rock rises up through the upper mantle wedge, crosses into the crust at a depth of about 25 miles, and then rises into Rainier's magma chamber -- or at least the lobe of the chamber that crosses under the line of sensors used in the study. Evidence suggests the magma moves upward at least 0.4 inches per year.

-- The new magnetotelluric image also shows a shallower zone of fluid perhaps 60 miles west of Rainier and 25 miles deep at the crust-mantle boundary. Wannamaker says it is largely water released from minerals as the slab is squeezed and heated as it dives.

The seismic data were collected during 2008-2009 for other studies. The magnetotelluric data were gathered during 2009-2010 by authors of the new study.

Wannamaker and colleagues placed an east-west line of magnetotelluric sensors: 60 that made one-day measurements and looked as deep as 30 miles into the Earth, and 20 that made measurements for a month and looked at even greater depths.

Source: University of Utah

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The Giant earthquakes help predict volcanic eruptions

Imaging seismic susceptibility makes it possible to detect regions affected by high-pressure volcanic fluids. The image in the background is catalogued as 'Red Fuji' (Katsushika Hokusai, 1830). Credit: Copyright Florent Brenguier

Researchers at the Institut des Sciences de la Terre (CNRS/Université Joseph Fourier/Université de Savoie/IRD/IFSTTAR) and the Institut de Physique du Globe de Paris (CNRS/Université Paris Diderot/IPGP), working in collaboration with Japanese researchers, have for the first time observed the response of Japanese volcanoes to seismic waves produced by the giant Tohoku-oki earthquake of 2011. Their conclusions, published in Science on July 4, 2014, reveal how earthquakes can impact volcanoes and should help to assess the risk of massive volcanic eruptions worldwide.

Until the early 2000s, seismic noise* was systematically removed from seismological analyses. This background noise is in fact associated with seismic waves caused by ocean swell. These waves, which can be compared to permanent, continuous microseisms, can be used by seismologists instead of earthquakes (which are highly localized over a limited time period) to image Earth's interior and its evolution over time, rather like an ultrasound scan on a global scale.

Now, seismic noise has been used for the continuous measurement of perturbations of the mechanical properties of Earth's crust. Researchers at the Institut des Sciences de la Terre (CNRS/Université Joseph Fourier/Université de Savoie/IRD/IFSTTAR) and the Institut de Physique du Globe de Paris (CNRS/Université Paris Diderot/IPGP) have applied this novel method while working in collaboration with Japanese colleagues using the Hi-net network, which is the world's densest seismic network (comprising more than 800 seismic detectors throughout Japan).

After the giant Tohoku-oki earthquake of 2011, the researchers analyzed over 70 terabytes of seismic data from the network. For the first time, they showed that the regions where the perturbations of Earth's crust were the greatest were not those where the shocks were the strongest. They were in fact localized under volcanic regions, especially under Mount Fuji. The new method thus enabled the scientists to observe the anomalies caused by the perturbations from the earthquake in volcanic regions under pressure. Mount Fuji, which exhibits the greatest anomaly, is probably under great pressure, although no eruption has yet followed the Tohoku-oki earthquake. The 6.4-magnitude seism that occurred four days after the 2011 quake confirms the critical state of the volcano in terms of pressure.

These findings lend support to theories that the last eruption of Mount Fuji in 1707 was probably triggered by the giant 8.7-magnitude Hoei earthquake, which took place 49 days before the eruption.
More generally, the results show how regions affected by high-pressure volcanic fluids can be characterized using seismic data from dense seismic detector networks. This should help to anticipate the risk of major volcanic eruptions worldwide.

*Seismic noise includes all the unwanted components affecting an analysis, such as the noise produced by the measuring device itself or external perturbations inadvertently picked up by the measuring devices.

Source: CNRS

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The Yellowstone geyser eruptions influenced more by internal processes

The intervals between geyser eruptions depend on a delicate balance of underground factors, such as heat and water supply, and interactions with surrounding geysers. Some geysers are highly predictable, with intervals between eruptions (IBEs) varying only slightly.

The predictability of these geysers offer earth scientists a unique opportunity to investigate what may influence their eruptive activity, and to apply that information to rare and unpredictable types of eruptions, such as those from volcanoes.

Dr. Shaul Hurwitz took advantage of a decade of eruption -- spanning from 2001 to 2011 -- for two of Yellowstone's most predictable geysers, the cone geyser Old Faithful and the pool geyser, Daisy.

Dr. Hurwitz's team focused their statistical analysis on possible correlations between the geysers' IBEs and external forces such as weather, earth tides and earthquakes. The authors found no link between weather and Old Faithful's IBEs, but they did find that Daisy's IBEs correlated with cold temperatures and high winds. In addition, Daisy's IBEs were significantly shortened following the 7.9 magnitude earthquake that hit Alaska in 2002.

The authors note that atmospheric processes exert a relatively small but statistically significant influence on pool geysers; IBEs by modulating heat transfer rates from the pool to the atmosphere. Overall, internal processes and interactions with surrounding geysers dominate IBEs; variability, especially in cone geysers.

Source: Wiley

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The New insight may help predict volcanic eruption behavior

Using friction experiments University of Liverpool scientists have shown that frictional melting plays a role in determining how a volcano will erupt. Credit: Dr. Jackie Kendrick

A new discovery in the study of how lava dome volcanoes erupt may help in the development of methods to predict how a volcanic eruption will behave, say scientists at the University of Liverpool.

Volcanologists at the University have discovered that a process called frictional melting plays a role in determining how a volcano will erupt, by dictating how fast magma can ascend to the surface, and how much resistance it faces en-route.

The process occurs in lava dome volcanoes when magma and rocks melt as they rub against each other due to intense heat. This creates a stop start movement in the magma as it makes its way towards Earth's surface. The magma sticks to the rock and stops moving until enough pressure builds up, prompting it to shift forward again (a process called stick-slip).

Volcanologist, Dr Jackie Kendrick, who lead the research said: "Seismologists have long known that frictional melting takes place when large tectonic earthquakes occur. It is also thought that the stick-slip process that frictional melting generates is concurrent to 'seismic drumbeats' which are the regular, rhythmic small earthquakes which have been recently found to accompany large volcanic eruptions.
"Using friction experiments we have shown that the extent of frictional melting depends on the composition of the rock and magma, which determines how fast or slow the magma travels to the surface during the eruption."

Analysis of lava collected from Mount St. Helens, USA and the Soufrière Hills volcano in Montserrat by volcanology researchers from the University's School of Environmental Sciences revealed remnants of pseudotachylyte, a cooled frictional melt. Evidence showed that the process took place in the conduit, the channel which lava passes through on its way to erupt.

Dr Kendrick, from the University's School of Environmental Sciences, added: "The closer we get to understanding the way magma behaves, the closer we will get to the ultimate goal: predicting volcanic activity when unrest begins. Whilst we can reasonably predict when a volcanic eruption is about to happen, this new knowledge will help us to predict how the eruption will behave.

"With a rapidly growing population inhabiting the flanks of active volcanoes, understanding the behaviour of lava domes becomes an increasing challenge for volcanologists."

Source: University of Liverpool

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The Hot mantle drives elevation, volcanism along mid-ocean ridges

Temperature, not chemistry. What appears on the surface correlates with temperature deep in the Earth. Higher ridge elevation indicates a hotter mantle -- as in Iceland, above, which also appears to sit atop a mantle plume, a vertical jet of hot rock originating from deep in the Earth. Credit: Allison Gale/University of Wisconsin

Scientists have shown that temperature differences deep within Earth's mantle control the elevation and volcanic activity along mid-ocean ridges, the colossal mountain ranges that line the ocean floor. The findings, published April 4 in the journal Science, shed new light on how temperature in the depths of the mantle influences the contours of Earth's crust.

Mid-ocean ridges form at the boundaries between tectonic plates, circling the globe like seams on a baseball. As the plates move apart, magma from deep within Earth rises up to fill the void, creating fresh crust as it cools. The crust formed at these seams is thicker in some places than others, resulting in ridges with widely varying elevations. In some places, the peaks are submerged miles below the ocean surface. In other places -- Iceland, for example -- the ridge tops are exposed above the water's surface.
"These variations in ridge depth require an explanation," said Colleen Dalton, assistant professor of geological sciences at Brown and lead author of the new research. "Something is keeping them either sitting high or sitting low."

That something, the study found, is the temperature of rocks deep below Earth's surface.
By analyzing the speeds of seismic waves generated by earthquakes, the researchers show that mantle temperature along the ridges at depths extending below 400 kilometers varies by as much as 250 degrees Celsius. High points on the ridges tend to be associated with higher mantle temperatures, while low points are associated with a cooler mantle. The study also showed that volcanic hot spots along the ridge -- volcanoes near Iceland as well as the islands of Ascension, Tristan da Cunha, and elsewhere -- all sit above warm spots in Earth's mantle.

"It is clear from our results that what's being erupted at the ridges is controlled by temperature deep in the mantle," Dalton said. "It resolves a long-standing controversy and has not been shown definitively before."

A CAT scan of Earth
The mid-ocean ridges provide geologists with a window to the interior of Earth. The ridges form when mantle material melts, rises into the cracks between tectonic plates, and solidifies again. The characteristics of the ridges provide clues about the properties of the mantle below.

For example, a higher ridge elevation suggests a thicker crust, which in turn suggests that a larger volume of magma was erupted at the surface. This excess molten rock can be caused by very hot temperatures in the mantle. The problem is that hot mantle is not the only way to produce excess magma. The chemical composition of the rocks in Earth's mantle also controls how much melt is produced. For certain rock compositions, it is possible to generate large volumes of molten rock under cooler conditions. For many decades it has not been clear whether mid-ocean ridge elevations are caused by variations in the temperature of the mantle or variations in the rock composition of the mantle.

To distinguish between these two possibilities, Dalton and her colleagues introduced two additional data sets. One was the chemistry of basalts, the rock that forms from solidification of magma at the mid-ocean ridge. The chemical composition of basalts differs depending upon the temperature and composition of the mantle material from which they're derived. The authors analyzed the chemistry of nearly 17,000 basalts formed along mid-ocean ridges around the globe.

The other data set was seismic wave tomography. During earthquakes, seismic waves are sent pulsing through the rocks in the crust and mantle. By measuring the velocity of those waves, scientists can gather data about the characteristics of the rocks through which they traveled. "It's like performing a CAT scan of the inside of the Earth," Dalton said.

Seismic wave speeds are especially sensitive to the temperature of rocks. In general, waves propagate more quickly in cooler rocks and more slowly in hotter rocks.

Dalton and her colleagues combined the seismic data from hundreds of earthquakes with data on elevation and rock chemistry from the ridges. Correlations among the three data sets revealed that temperature deep in the mantle varied between around 1,300 and 1,550 degrees Celsius underneath about 61,000 kilometers of ridge terrain. "It turned out," said Dalton, "that seismic tomography was the smoking gun. The only plausible explanation for the seismic wave speeds is a very large temperature range."

The study showed that as ridge elevation falls, so does mantle temperature. The coolest point beneath the ridges was found near the lowest point, an area of very deep and rugged seafloor known as the Australian-Antarctic discordance in the Indian Ocean. The hottest spot was near Iceland, which is also the ridges' highest elevation point.

Iceland is also where scientists have long debated whether a mantle plume -- a vertical jet of hot rock originating from deep inside Earth -- intersects the mid-ocean ridge. This study provides strong support for a mantle plume located beneath Iceland. In fact, this study showed that all regions with above-average temperature are located near volcanic hot spots, which points to mantle plumes as the culprit for the excess volume of magma in these areas.

Understanding a churning planet
Despite being made of solid rock, Earth's mantle doesn't sit still. It undergoes convection, a slow churning of material from the depths of the Earth toward the surface and back again.
"Convection is why we have plate tectonics and earthquakes," Dalton said. "It's also responsible for almost all volcanism at the surface. So understanding mantle convection is crucial to understanding many fundamental questions about the Earth."

Two factors influence how that convection works: variations in the composition of the mantle and variations in its temperature. This work, says Dalton, points to temperature as a primary factor in how convection is expressed on the surface.

"We get consistent and coherent temperature measurements from the mantle from three independent datasets," Dalton said. "All of them suggest that what we see at the surface is due to temperature, and that composition is only a secondary factor. What is surprising is that the data require the temperature variations to exist not only near the surface but also many hundreds of kilometers deep inside the Earth."

The findings from this study will also be useful in future research using seismic waves, Dalton says. Because the temperature readings as indicated by seismology were backed up by the other datasets, they can be used to calibrate seismic readings for places where geochemical samples aren't available. This makes it possible to estimate temperature deep in Earth's mantle all over the globe.

That will help geologists gain a new insights into how processes deep within Earth mold the ground beneath our feet.

Source: Brown University

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The Earthquakes caused by clogged magma a warning sign of volcanic eruption

Researchers studied Augustine Volcano in Alaska which erupted in 2006 and found that precursory earthquakes were caused by a block in the lava flow. Credit: Alaska Volcano Observatory and photographer Cyrus Read.

New research in Geophysical Research Letters examines earthquake swarms caused by mounting volcanic pressure which may signal an imminent eruption. The research team studied Augustine Volcano in Alaska which erupted in 2006 and found that precursory earthquakes were caused by a block in the lava flow.

36 hours before the first magmatic explosions, a swarm of 54 earthquakes was detected across the 13-station seismic network on Augustine Island. By analyzing the resulting seismic waves, the authors found that the earthquakes were being triggered from sources within the volcano's magma conduit.
"Our article talks about a special type of volcanic earthquake that we think is caused by lava breaking, something that usually can't happen because lava is supposed to flow more like a liquid, rather than crack like a piece of rock," said Dr. Helena Buurman from the University of Alaska Fairbanks. "Much like breaking a piece of chewing gum by stretching it really fast, lab tests show that hot lava can break when stretched quickly enough under certain pressures like those that you might find in the conduit of a volcano. "

The authors found that over the course of the two hour swarm, the earthquakes' focus moved 35 meters deeper down into the magma conduit, an indication that the conduit was becoming clogged. The resulting buildup of pressure may have contributed to the explosive eruption the next day.

"We think that these earthquakes happened within the lava that was just beginning to erupt at the top of Augustine. The earthquakes show that the lava flow was grinding to a halt and plugging up the system. This caused pressure to build up from below, and resulted in a series of large explosions 36 hours later," concluded Dr. Buurman. "We believe that these types of earthquakes can be used to signal that a volcano is becoming pressurized and getting ready to explode, giving scientists time to alert the public of an imminent eruption. "

Summary:
New research examined earthquake swarms caused by mounting volcanic pressure which may signal an imminent eruption. The research team studied Augustine Volcano in Alaska which erupted in 2006 and found that precursory earthquakes were caused by a block in the lava flow. 36 hours before the first magmatic explosions, a swarm of 54 earthquakes was detected across the 13-station seismic network on Augustine Island. By analyzing the resulting seismic waves, the authors found that the earthquakes were being triggered from sources within the volcano’s magma conduit.

Source: Wiley

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The Large, deep magma chamber discovered below Kilauea volcano: Largely unknown internal plumbing of volcanoes

A new study led by scientists at the University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science uncovered a previously unknown magma chamber deep below the most active volcano in the world – Kilauea. Credit: Image courtesy of University of Miami Rosenstiel School of Marine & Atmospheric Science

A new study led by scientists at the University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science uncovered a previously unknown magma chamber deep below the most active volcano in the world -- Kilauea. This is the first geophysical observation that large magma chambers exist in the deeper parts of the volcano system.

Scientists analyzed the seismic waves that travel through the volcano to understand the internal structure of the volcanic system. Using the seismic data, the researchers developed a three-dimensional velocity model of a magma anomaly to determine the size, depth and composition of the lava chamber, which is several kilometers in diameter and located at a depth of 8-11 km (5 -- 6.8 miles).

"It was known before that Kilauea had small, shallow magma chambers," said Guoqing Lin, UM Rosenstiel School assistant professor of geology and geophysics and lead author of the study. "This study is the first geophysical observation that large magma chambers exist in the deep oceanic crust below."

The study also showed that the deep chamber is composed of "magma mush," a mixture of 10-percent magma and 90-percent rock. The crustal magma reservoir below Kilauea is similar to those widely observed beneath volcanoes located at mid-ocean ridges.

"Understanding these magma bodies are a high priority because of the hazard posed by the volcano," said Falk Amelung, co-author and professor of geology and geophysics at the UM Rosenstiel School. "Kilauea volcano produces many small earthquakes and paying particular attention to new seismic activity near this body will help us to better understand where future lava eruptions will come from."
Scientists are still unraveling the mysteries of the deep internal network of magma chambers and lava tubes of Kilauea, which has been in continuous eruption for more than 30 years and is currently the most active volcano in the world.

Source: University of Miami Rosenstiel School of Marine & Atmospheric Science

Summary: A new study has uncovered a previously unknown magma chamber deep below the most active volcano in the world -- Kilauea. This is the first geophysical observation that large magma chambers exist in the deeper parts of the volcano system.

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