Tag Archives: magma

A new study provides our best-yet prediction of what a metallic volcano might look like

If you like volcanoes, Earth isn’t a bad place to live on. After all, our planet is quite geologically active, and that also translates into a respectable level of volcanism. But when it comes to having a variety of flavors, the Earth can be a bit lacking.

 a) Metallic flow (yellow) emerging from underneath the silicate flow (orange-black) before cooling and b) metallic flow appears gray/silver, with the silicate flow black, after cooling. Image credits A. Soldati et al., (2021), Nature.

A new paper, however, comes to estimate what one type of not-yet-seen volcanic activity might look like. Called ‘ferrovolcanism’, it is likely a hallmark of geologically active worlds whose composition is mainly metallic. The study, although still purely theoretical, could help us better understand some of the more peculiar alien landscapes out there. And even though ‘metal volcanoes’ sounds like something pretty jagged and oppressive-looking, the team’s findings suggest that they’re actually quite mellow.

Metal volcanoes

“Cryovolcanism is volcanic activity on icy worlds, and we’ve seen it happen on Saturn’s moon Enceladus,” says Arianna Soldati, assistant professor of marine, earth and atmospheric sciences at NC State and lead author of a paper describing the work. “But ferrovolcanism, volcanic activity on metallic worlds, hasn’t been observed yet.”

The study, published by researchers at the North Carolina State University, aimed to give us an idea of how volcanic activity would look on a planet made predominantly of metal.

Volcanoes are born when magma, the partially-molten material found beneath a planet’s surface, erupts. The exact nature and behavior of this magma is closely related to the chemical composition of the planet. On Earth, therefore, magmas tend to be mostly molten rock (i.e. silica molecules). On icy worlds, however, magma is in fact a mixture of fluids such as water, ammonia, or methane, all super-chilled.

What the team wanted to find out, however, is how volcanism would look on 16 Psyche, a 140-mile diameter asteroid floating merrily in the asteroid belt between Mars and Jupiter. Infrared and radar analysis of its surface suggests that 16 Psyche is formed mainly of iron and nickel. Even better, though, it’s also the target for an upcoming NASA mission. This inspired Soldati to try and determine what volcanism would look like on the asteroid.

“When we look at images of worlds unlike ours, we still use what happens on Earth—like evidence of volcanic eruptions—to interpret them,” Soldati says. “However, we don’t have widespread metallic volcanism on Earth, so we must imagine what those volcanic processes might look like on other worlds so that we can interpret images correctly.”

The team defined two types of ferrovolcanism that they believe are possible. Type 1, or ‘pure’ ferrovolcanism, occurs on bodies made entirely of metal. Type 2, or ‘spurious’ ferrovolcanism, is what we’re likely to see on bodies that have both rocky and metal elements in their chemical mix.

Together with members of the Syracuse Lava Project, the researchers then simulated the second type, in which metal separates from rock as the magma melts down, in the lab.

“The Lava Project’s furnace is configured for melting rock, so we were working with the metals (mainly iron) that naturally occur within them,” Soldati says. “When you melt rock under the extreme conditions of the furnace, some of the iron will separate out and sink to the bottom since it’s heavier.”

“By completely emptying the furnace, we were able to see how that metal magma behaved compared to the rock one.”

Metallic lava (magma becomes lava once it reaches the surface) can flow up to 10 times faster, and spreads more thinly, than rock lava, the team found. As it flows, this material also separates into an abundance of braided channels, they add. Furthermore, metal lava tended to flow largely beneath the rock one, and emerged at the leading edge of the lava body.

Another important finding of the study is that the thin, braided layers of metallic lava, once cooled, give a distinctive appearance to a planet’s surface. This is very different in nature from those produced by rocky lava flows, Soldati explains, meaning that the two types of volcanism should be easy to spot from afar.

“Although this is a pilot project, there are still some things we can say,” Soldati says. “If there were volcanoes on 16 Psyche—or on another metallic body—they definitely wouldn’t look like the steep-sided Mt. Fuji, an iconic terrestrial volcano. Instead, they would probably have gentle slopes and broad cones. That’s how an iron volcano would be built—thin flows that expand over longer distances.”

The paper “Imagining and constraining ferrovolcanic eruptions and landscapes through large-scale experiments” has been published in the journal Nature Communications.

Hawaii volcano.

Volcanoes are fed by ‘mush reservoirs’ instead of magma chambers, study suggests

Eruptions are more of a ‘squeeze’ than a ‘bang’, a new study suggests.

Hawaii volcano.

Image credits Adrian Malec.

New research shows that volcanoes aren’t fed by large reservoirs of magma as previously believed. Instead, all that molten rock builds up into ‘mush reservoirs’ from which it later pops. These reservoirs consist of mostly solid crystals (i.e. rocks), with magma filling the pores and cracks in between them.

Mushcanoes

Our understanding of volcanic processes is currently built upon the magma chamber model. Boiled down, the model posits that each volcano lies atop a large chamber or cave filled with liquid magma. If you’ve seen Lord of the Rings, imagine that scene (spoiler alert) on Mount Doom when the ring gets destroyed in a river of magma; the chambers we’re talking about are pretty much the same, only deeper underground (and usually capped with cold, hard rock).

Students in Geology 101 are taught this model, and, for the most part, it works quite elegantly. It helps us make heads and tails of why certain volcanoes erupt while others lie dormant, fits with indirect evidence (such as pre-eruption events observed on the surface and geophysical readings), and is easy to wrap your head around.

The concept of magma chambers gained so much appeal in geology for a simple reason: volcanoes need a source of magma to erupt, and they need a lot of it. Furthermore, that magma needs to contain relatively few solid crystals, so that it’s flowy enough. A magma chamber would be able to store enough material and allow any cooler crystals to precipitate, satisfying both of a volcano’s requirements.

However, nobody has actually seen one of these chambers directly. Recent magma chemistry analyses have challenged the model. Instead of a huge chamber, such studies point to smaller pools of magma formed in the gaps between solid crystals — all of which points to the ‘mush reservoir’ model. The catch was that such a structure couldn’t explain how magmas with relatively few crystals form and reach volcanoes in order to fuel surface eruptions.

The new study, published by researchers at Imperial College London and the University of Bristol, suggests the assumption of a magma chamber needs a re-think.

“We now need to look again at how and why eruptions occur from mush reservoirs,” says lead author Matthew Jackson, a Professor at the Department of Earth Sciences and Engineering at Imperial.

“We can apply our findings to understanding volcanic eruptions with implications for public safety and also to understand the formation of metal ore deposits associated with volcanic systems.”

The team digitally modeled a mush reservoir to see exactly how it would function — and function they do, indeed! Within a mush reservoir scenario, the team reports, magma rises through the nooks and crannies since it’s less dense than the surrounding crystals. It chemically interacts with the crystals on its way up, partially melting them — this is more pronounced in areas of magma build-up, creating areas with relatively few crystals.

It’s these pockets — although short-lived — that can lead to eruptions, they explain:

“A major mystery about volcanoes is that they were thought to be underlain by large chambers of molten rock. Such magma chambers, however, were very difficult to find,” says co-author Stephen Sparks, a Professor at the University of Bristol’s School of Earth Sciences.

“The new idea developed by geologists at Imperial and Bristol is that molten rock forms within largely crystalline hot rocks, spending most of its time in little pores within the rock rather than in large magma chambers. However, the rock melt is slowly squeezed out to form pools of melt, which can then erupt or form ephemeral magma chambers.”

Even better, the mush reservoir model also fits with other phenomena observed in volcanic systems: how the chemical composition of magma changes over time, for example, or the occasional inclusion of very old crystals in ‘young’ magmas. All in all, things seem to be going in its favor, and the days of the magma chamber model may be numbered.

The paper “Chemical differentiation, cold storage and remobilization of magma in the Earth’s crust” has been published in the journal Nature.

What Can Quartz Crystals Really Do?

Image in public domain.

Crystals and quartz

Crystals have caught the eye of humans since the dawn of time. Some scientists have even speculated that the origins of life on Earth may trace its origins to crystals. It shouldn’t come as a surprise that these gleaming mineral formations appear frequently in pop culture often as having supernatural powers (even though they don’t). A few examples of this reoccurring theme are the Silmarils in the Lord of the Rings universe and the sunstones in James Gurney’s Dinotopia.

The atoms which make up a crystal lie in a lattice which repeats itself over and over. There are several methods for generating crystals artificially in a lab, with superheating being the most common process. Likewise, in nature, a hot liquid (eg: magma) cools down, and as this happens, the molecules are attracted to each other, bunching up and forming that repeating pattern which leads to crystal formation.

Quartz is one of the most abundant minerals found on the planet. This mineral is known to be transparent or have the hues of white, yellow, pink, green, blue, or even black. It is also the most common form of crystalline silica which has a rather high melting point and can be extremely dangerous if inhaled in its powdered form. This mineral compound is present in the majority of igneous rocks. Some quartzes are considered semiprecious stones. Aside from mere bedazzlement, they have been used in countless industries.

Industrial, not magical uses

If a pressure is applied to the surface of a quartz crystal, it can give off a small electrical charge. This effect is the result of the electrically charged atoms (the ions) dispersing and spreading away from the area to which the pressure is being applied. This can be done in a number of ways, including simply squeezing the crystal. It also dispenses an electric current if a precise cut is made at an angle to the axis.

Since it possesses this property, quartz has been a component of devices such as radios, TV’s, and radar systems. Some quartz crystals are capable of transmitting ultraviolet light better than glass (by the way, quartz sand is used in making glass). Because of this, low-quality quartz is often used for making specific lenses; optical quartz is made exclusively from quartz crystals. Quartz which is somewhat clouded or which is not as transparent as the stuff used for optics is frequently incorporated into lab instrumentation.

Scientists have employed quartz for many things, and they have considered its role in the Earth sciences a crucial one. Some have stated it directly brings about the reaction which forms mountains and causes earthquakes! It continues to be used in association with modern technology, and it likely will lead us to more discoveries in the future.

Warm rock beneath New England hints of upcoming volcanic eruption millions of years from now

This magma eruption could happen in some parts of New England, but not in the next couple million years. Credit: Pixabay.

This lava eruption could happen in some parts of New England, but not in the next couple million years. Credit: Pixabay.

Geologists have identified a “mass of warm rock” that is rising beneath northern New England. The formation could be an ominous sign of a possible volcanic eruption millions of years from now.

“The upwelling we detected is like a hot air balloon, and we infer that something is rising up through the deeper part of our planet under New England,” said lead author Vadim Levin, a geophysicist at Rutgers University. “It is not Yellowstone (National Park)-like, but it’s a distant relative in the sense that something relatively small – no more than a couple hundred miles across – is happening.”

“Our study challenges the established notion of how the continents on which we live behave,” Levin said. “It challenges the textbook concepts taught in introductory geology classes.”

Levin and colleagues tapped into the EarthScope program which employs thousands of seismometers, each spaced 46.6 miles apart, covering the continental United States. The scale of the program, whose mission is to reveal the structure and evolution of the North American continent, is unprecedented.

Credit: A colored map of mantle flow under the North American tectonic plate. The warm colors indicate lower speed, implying that rock in those regions is less dense, likely warmer and rising toward the surface. Credit: Vadim Levin/Rutgers University-New Brunswick.

By studying seismic waves recorded over the last two years, the Rutgers researchers could peer inside Earth’s interior, where they could see the shapes and texture of structures but also changes in the state of materials. Levin’s team focused their study on the New England area because that’s where an anomalous area of great warmth in the upper mantle was previously reported.

Following a careful assessment of this area of interest, the researchers detected an upwelling pattern beneath central Vermont and western New Hampshire but also parts of western Massachusetts. In this region, mantle flow indicators are the smallest, likely because warmer rock flows upward and disrupts the horizontal flow. Given enough time, the magma could erupt to the surface.

New England residents shouldn’t be too worried that a volcano will suddenly pop up in their backyards. Such an event looks to be millions of years away.

“The Atlantic margin of North America did not experience intense geologic activity for nearly 200 million years,” Levin said. “It is now a so-called ‘passive margin’ – a region where slow loss of heat within the Earth and erosion by wind and water on the surface are the primary change agents. So we did not expect to find abrupt changes in physical properties beneath this region, and the likely explanation points to a much more dynamic regime underneath this old, geologically quiet area.”

“It will likely take millions of years for the upwelling to get where it’s going,” he added. “The next step is to try to understand how exactly it’s happening.”

Findings were reported in the journal Geology

 

Magma is building up beneath a town in New Zealand

Known for its magnificent landscapes and spectacular volcanoes, New Zealand never disappoints. Unfortunately, this time, the volcanism seems to be expanding under inhabited areas, a new study found.

The nearby Mount Tarawera. Image: Carl Lindberg

The good news is that there’s no need to panic – an eruption is not imminent and likely won’t be for a few centuries, but when it pops, it’s gonna be pretty big. Estimates show that there’s enough magma to fill 80,000 Olympic-size swimming pools, lifting the ground beneath the coastal town of Matata by 40 centimeters.

Matata is home to only a few hundred people, and hasn’t had a history of volcanism for over 400,000 years, so geologists weren’t expecting to discover something beneath it. But a series of surprising earthquakes caught their attention.

“It was quite a big surprise,” lead researcher Ian Hamling told Nick Perry for the Associated Press (AP).

A graphic representation of what’s happening with the magma pool. Image via Ian Hamling.

The magma pool is calculated to be some 9.5 km beneath the surface, which means it may never even turn into a volcano. Instead, it may simply accumulate and subsequently cool off and harden. But monitoring this process and understanding the magmatic evolution will help us in other places on Earth, where the threat is imminent.

“Although the ultimate fate of the magma remains unclear, its presence may represent the birth of a new magma chamber on the margins of arguably the world’s most active region of silicic volcanism, which has witnessed 25 caldera-forming eruptions over the last 1.6 million years,” the researchers write in Science Advances.

Tremors around St. Helens may hint at a new eruption

On May 18, 1980 Mount St. Helens erupted with terrifying force, the violence of the explosion destroying the upper part of the mountain. The event claimed the lives of 57 people and severely damaged the homes and infrastructure in the area. Since then, a $3 million study has been commissioned on the volcano to study its internal workings in the hope that a future eruption can be detected in time to prevent such a tragic event from happening again.

Mt. St. Helens
Image via wikipedia

The findings reveal that there’s a real danger that the volcano possibly erupting again — geologists identified an enormous second chamber, buried between 7 to 23 miles (11-37 km) deep under the surface. The reservoir is connected to a smaller chamber that rests directly beneath the volcano.

This connection, correlated with seismic data from the site, is helping them piece together what happened prior to the 1980 eruption, the deadliest in recorded U.S. history.

In the months leading to the explosion, geologists recorded a series of tremors. They were puzzled at the time, but with the benefit of new data they concluded that magma pumping between the two chambers caused pressure to increase in the upper reservoir. As the structures around it adjusted to the increased pressure, the tremors were a way for the rocks to release lithological stresses. They couldn’t adjust fast enough and compress enough however, so the pressure built up gradually and resulted in the deadly explosion.

“We can only now understand that those earthquakes are connecting those magma reservoirs,” said Eric Kiser, seismologist at Rice University. “They could be an indication that you have migration of fluid between the two bodies.”

And now, more tremors have been registered in the area, the team reported at the annual meeting of the Geological Society of America in Baltimore, Maryland on Nov. 3rd. This suggests that fresh magma is being injected upwards into the volcanic structure, hinting at a new eruption.

“A cluster of low frequency events, typically associated with injection of magma, occurs at the northwestern boundary of this low Vp column,” the researchers reported. “Much of the recorded seismicity between the shallow high Vp/Vs body and deep low Vp column took place in the months preceding and hours following the May 18, 1980 eruption. This may indicate a transient migration of magma between these two reservoirs associated with this eruption.”

The Vp/Vs is the ratio of compressional and shear wave velocity, i.e. how fast the two main types of seismic waves travel through a structure. This can be processed and reveals information about rock composition, underground structures, shapes and many other geological characteristics.

After the 1980 eruption, Mount St. Helens started to erupt again in 2004 and released magma through gradual extrusion [i.e. non-explosive release of magma] up to 2008. Despite this, the Mount is considered to be a high risk volcano, under close observation by the U.S. Geological Survey.

The researchers said that their findings could offer a crucial early warning system of a potential eruption.

Evidence of granite found on Mars – Red Planet geology more complex than previously thought

Geologists have now found the most compelling evidence of granites on Mars – something which prompts more complex theories about the geology and tectonic activity on the Red Planet.

Granites and basalts

Basalt and Granite. Credits: Rice University.

Granites are igneous rocks, pretty common on the surface of Earth. It is often called a ‘felsic’ (white rock) – because it is very rich in so-called white minerals, such as quartz or feldspar. It is contrasted with mafic rocks (for example basalt), which are relatively richer in magnesium and iron. Now, large amounts of feldspar have been found in a Martian volcano. Interestingly enough, minerals commonly found in basalts are completely absent from that area; considering how basalts are almost ubiquitous on Mars, this initially came as a shock, but now, geologists have come up with a theory to explain this.

Granite, or its eruptive equivalent, rhyolite, is often found on Earth in tectonically active regions such as subduction zones. However, since Mars isn’t tectonically active, there are no subduction zones there, so there has to be a different cause. The team studying the case concluded that prolonged magmatic activity on Mars can also produce these granitic compositions on very large scales.

“We’re providing the most compelling evidence to date that Mars has granitic rocks,” said James Wray, an assistant professor in the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology and the study’s lead author.

Red Planet geology

A 'spectral window' into the Martian geology - bright magenta outcrops have a distinctive feldspar-rich composition. (Credit: NASA/JPL/JHUAPL/MSSS)

A ‘spectral window’ into the Martian geology – bright magenta outcrops have a distinctive feldspar-rich composition. (Credit: NASA/JPL/JHUAPL/MSSS)

For many years, the geology of Mars has been considered to be very simplistic, consisting of mostly one single type of rock: basalt – a common extrusive igneous (volcanic) rock formed from the rapid cooling of basaltic lava exposed at or very near the surface. The dark rock can also be found on Earth in many volcanically active areas, such as Hawaii or Iceland for example.

But earlier this year, the Mars Curiosity started to cast some doubt on those beliefs, when it reported finding soils with a composition similar to granite. No one really knew what to make of this discovery, but since it appeared to be very localized, it was just considered a local anomaly. However, this new research analyzed things at a much larger scale, using remote sensing techniques with infrared spectroscopy to survey a large volcano on Mars that was active for billions of years. The volcano is perfect for this type of study, because it is dust free (a true rarity on Mars) – some of the fastest-moving sand dunes on Mars sweep away any would-be dust particles on this volcano.

Much to the delight of researchers, the limitations of the remote sensing technology were an advantage in this case:

“Using the kind of infrared spectroscopic technique we were using, you shouldn’t really be able to detect feldspar minerals, unless there’s really, really a lot of feldspar and very little of the dark minerals that you get in basalt,” Wray said.

Separating the white and the black

So we have an island of white feldspar amidst an ocean of black basalt – how did it form?

When you have magma in the subsurface, it cools off very, very slowly. In a tectonically inactive planet like Mars, this process can be very stable. While the magma slowly cools off, low density melt separates from high density crystals, and if the conditions are just right, this process can take place for billions of years, leading to the creation of granitic rocks, as computer simulations showed.

“We think some of the volcanoes on Mars were sporadically active for billions of years,” Wray said. “It seems plausible that in a volcano you could get enough iterations of that reprocessing that you could form something like granite.”

While we are trying to figure out the existence (or lack of it) of life on Mars, this is another wake-up call, showing just how little we understand about the geologic processes on the Red Planet – which ultimately govern the appearance of life. Anyway, the geology of Mars just got a lot more interesting.

Journal Reference:

  1. James J. Wray, Sarah T. Hansen, Josef Dufek, Gregg A. Swayze, Scott L. Murchie, Frank P. Seelos, John R. Skok, Rossman P. Irwin, Mark S. Ghiorso. Prolonged magmatic activity on Mars inferred from the detection of felsic rocksNature Geoscience, 2013; DOI: 10.1038/NGEO1994

Another Source of Potentially Disruptive Icelandic Volcanoes Found

New research by The Open University and Lancaster University showed that another type of volcanic eruption in Iceland could cause significant disruption throughout the Old Continent. Published in Geology, the study found magma that is twice as ‘fizzy’ as previously believed, which increases the likelihood of disruptive ash clouds from future eruptions.

 

Volcanoes in Iceland.

Volcanoes in Iceland.

Magma can be mo re liquid (like in the Hawaii lava flows, for example), or more viscuous – the viscosity being mainly a function of silica content. The more silica, the more viscuous. Typically, Icelandinc eruptions are very rich in silica, which makes their eruptions explosive or at least… fizzy. It is the gases dissolved in the magma that create this explosive character; at high temperatures and pressures, inside the magmatic chamber, the gases are steadily dissolved, but as they rise at the surface, they expand dramatically, causing the magma to froth and accelerate upwards as a foam.

Now, Drs Jacqui Owen and Hugh Tuffen (Lancaster University) and Dave McGarvie (The Open University) have analysed pumice and lava from an eruption at Iceland’s Torfajökull volcano some seventy thousand years ago. In these samples, they found tiny pockets of magma, called melt inclusions, which trapped the original gas; they measured how much gas was dissolved within the melt inclusions, in order to calculate the fizziness.

iceland 2

PhD student Jacqui Owen said:

“I was amazed by what I found. I measured up to five per cent of water in the inclusions, more than double what was expected for Iceland, and similar in fact to the values for explosive eruptions in the Pacific ‘Ring of Fire’. We knew the Torfajökull volcanic eruption was huge — almost 100 times bigger than recent eruptions in Iceland — but now we also know it was surprisingly gas-rich.”

By accurately measuring the original gas content of Icelandic explosive eruptions for the first time, the research concluded that Iceland volcanoes have the potential to generate the fine ash that can be then transported to the continent.

“We know that large explosive eruptions have occurred at infamous volcanoes such as Hekla and Katla, but it is important also to appreciate that large explosive eruptions are also produced by less well-known Icelandic volcanoes such as Torfajökull and Öraefajökull.”

Dr Hugh Tuffen, Royal Society University Research Fellow at Lancaster University, concluded:

“The discovery is rather worrying, as it shows that Icelandic volcanoes have the potential to be even more explosive than anticipated. Added to this is the view of several eminent scientists that Iceland is entering a period of increased volcanic activity. Iceland’s position close to mainland Europe and the north Atlantic flight corridors means air travel could be affected again.”

Geophysicists find a layer of liquefied rock in the Earth’s mantle that acts as a lubricant for tectonic plates

Scientists at Scripps Institution of Oceanography at UC San Diego have found a layer of liquefied molten rock in Earth’s mantle that may be acting as a lubricant for the sliding motions of the planet’s tectonic plates. This discovery has very far reaching implications, which can solve some of the long standing geological puzzles, as well as lead to a better understanding of earthquakes and volcanism.

Electromagnetic measurements

plate tectonics1

They used a relatively common, but uniquely improved geophysical technique (magnetotellurics), which involved advanced seafloor electromagnetic imaging technology. They imaged a 25-kilometer- (15.5-mile-) thick layer of partially melted mantle rock below the edge of the Cocos plate where it moves underneath Central America. They basically deployed a vast array of seafloor sensors that monitor the natural electromagnetic signals to map features of the crust and mantle. Back in 2010, they started noticing something was weird – they were finding magma in unexpected places.

cocos plate 2

“This was completely unexpected,” said Key, an associate research geophysicist in the Cecil H. and Ida M. Green Institute of Geophysics and Planetary Physics at Scripps. “We went out looking to get an idea of how fluids are interacting with plate subduction, but we discovered a melt layer we weren’t expecting to find at all-it was pretty surprising.”

cocos plate

The marine electromagnetic technology employed in the study was originated by Charles “Chip” Cox, an emeritus professor of oceanography at Scripps, and further improved by Constable and Key. The method has been so successful, that since 2000, they have been working with big oil companies to map out offshore oil and gas reservoirs.

The planetary engine

Plate tectonics is, if you will, the backbone of modern geology and geophysics. It is not perfect, by any standards, but it is a good theory that describes the large-scale motions of Earth’s lithosphere; one thing that’s been puzzling is the exact forces and mechanisms that allow the planet’s tectonic plates to slide across the earth’s mantle; one theory was that as minerals go deeper in the mantle, the water they contain is ejected, and this results in a more ductile mantle that would facilitate tectonic plate motions. However, no clear data has been provided to confirm or infirm this theory.

“Our data tell us that water can’t accommodate the features we are seeing,” said Naif, a Scripps graduate student and lead author of the paper. “The information from the new images confirms the idea that there needs to be some amount of melt in the upper mantle and that’s really what’s creating this ductile behavior for plates to slide.”

Indeed, if there isn’t some major flaw with this study, then it could pretty much change the way we view this sliding mechanism.

tectonics lubricant

The orange area inside the dashed lines is the lubricant layer which facilitates the plate motion. The blue areas represents the Cocos plate subducting beneath the central American continent, and the black points are the earthquakes.

“This new image greatly enhances our understanding of the role that fluids, both seawater and deep subsurface melts, play in controlling tectonic and volcanic processes,” said Bil Haq, program director in the National Science Foundation’s Division of Ocean Sciences.

To get to the conclusion that there is a layer which acts as a lubricant, they studied the fluid content of the subducting plate offshore Nicaragua and Costa Rica. Magnetotellurics and controlled source electromagnetics imaged the porosity variations associated with lithospheric bending and cracking near the trench, as was suggested by a previous reflection seismic imaging. Analyzing the obtained parameters, they modeled this lubricant layer.

Their results, if valid, could help geologists better understand the genesis of some earthquakes, as well as some questions unanswered for decades.

“One of the longer-term implications of our results is that we are going to understand more about the plate boundary, which could lead to a better understanding of earthquakes,” said Key.

Now, the next step is to figure out how exactly is this layer formed and the source that supplies this magma.

Via Scripps Research Institute

New type of volcanic eruption described

The general classification splits volcanic eruptions in two: explosive or effusive. An explosive eruption is, well, explosive and violent (think Mount Helens), while an effusive eruption is associated with lava flows (think Hawaii). However, in a new study conducted by New Zealand and UK researchers described another, new type of eruption.

Eruption

Inside volcanoes, magma often has dissolved gases as a function of the very high pressures and chemistry of the magma. Much in the same way you open a carbonated drink – when you take the lid off, the bubbles burst out – when magma erupts as lava, the pressure is relieved and the gases exsolve (the opposite of dissolve). In explosive eruptions, this phenomena is so strong that it fragments the lava, violently ejecting it, along with anything caught along. When this happens, the ejected lava expands so quickly the resulting rock cools and degasses to form solidified pumice that can be sufficiently light to float on water.

After studying the Macauley volcano in the Pacific Ocean however, volcanologists found an entirely different story.

“By documenting the shape and density of bubbles in pumices generated by an underwater caldera volcano in the southwest Pacific Ocean – the Macauley volcano – we found large differences in the number and shape of “bubbles” in the same pebble-sized samples, different to anything previously documented,” said co-author Ian Wright, from U.K.’s National Oceanography Centre. “This range of bubble densities distinct in these pumice samples indicates that the lava erupting from the caldera was neither vigorous enough for an explosive eruption, nor gentle enough for an effusive flow,” Wright said in a statement.

 

Pumice floating

Pumice floating

In oceans, when pumice is located, it generally represents the spot of a volcanic eruption – an explosive eruption. The mechanism proposed for this special type of pumice though is more complicated; it suggests that rather exploding in the neck of the volcano, the formation and expansion of bubbles in the magma created a buoyant foam, rising to the seafloor and then buoyantly detaching itself from the volcano as molten pumice, but with cooler margins. The vesicles within the molten interior would have continued to expand as the pressure – this time from the weight of the seawater – reduced.

“These processes explain the unique bubble structure seen in the samples analysed, which could have only occurred with an intermediate eruption style and in an underwater setting,” said Professor Wright. “We conclude that the presence of widespread deposits of pumice on underwater volcanoes does not necessarily indicate large-scale explosive volcanism.”

The authors proposed that this type of eruption be named Tangaroan, the Maori god of the sea, and name of the research vessel used to collect the samples.

Source

Asteroid Vesta is a lot like Earth, study shows

The cold, lifeless Vesta asteroid might be a lot more like our planet than astronomers believed – having a very active life in the early stages of the solar system evolution, a study of a Saharan meteorite shows.

The planet that wasn’t

asteorid

Vesta might host a magmatic layer under its rocky exterior, allowing minerals to travel between softer and harder layers of material, according to a study published online Sunday by the journal Nature Geoscience. If this were true, then Vesta is a lot more Earth like than previously believed.

“People think asteroids are big, gray, cold, almost potato-shaped lumps of rock that sometimes crash into the Earth and threaten us,” said study leader Beverley Tkalcec, a planetary geologist at Goethe University in Frankfurt, Germany. Instead, she said, “it has a dynamic interior similar to what might have been at the beginning of the Earth.”

Hot or not, Vesta is just big enough to have experienced melting inside. When this happens, the thicker, heavier material sinks towards the center and the lighter stuff gets pushed towards the crust. In this way, Vesta (much like its “cousin” Ceres) are planetary embryos that never really came to life, and since there are no tectonics to recirculate the rocks, the rocks are probably as old as the solar system.

The crystal and the electron

The study was conducted on a meteorite which is believed to have carved out Vesta’s mantle by impact; they made the connection between the meteorite by analysing its chemical and isotopical composition. However, unlike other studies which focus on the composition, this one focused on how the matter is distributed; if Vesta were indeed active beneath the surface and have a magmatic layer, then some clues should pop out.

The researchers used a technique called electron backscatter diffraction, in which basically electrons are bounced off crystals to determine their structure. They focused their research on a mineral called olivine (we’ve occasionally written about this mineral, see here) and found that instead of a regular pile of crystals with one sitting on top of each other, the crystal lattice was severely deformed.

olivine

Olivine crystals

They then tried to find something equivalent to this, and they found that the only rocks which resemble this type of structure is with igneous rocks formed by forces in Earth’s mantle – something which led to the natural conclusion that the meteorite is probably a result of the same process on Vesta, with the heavier elements sinking in.

They then plugged this data into a computer model of Vesta and found that, given specific conditions, the asteroid could host a magma ocean.

“When you have dense solid material over partially molten material, then it’s unstable,” said Harry McSween, a planetary geoscientist at the University of Tennessee in Knoxville and co-investigator for the Dawn mission. “The top’s trying to become the bottom and the bottom’s trying to become the top.”

Among other things, Vesta is believer to host water and have a mountain 3 times bigger than the Everest.

Understanding magma in the mantle: rocks melt at greater depth than previously thought

Magma forms much deeper than geologists previously believed, according to a new study conducted by Rice University.

Magma and Crust

 

mantle

The group led by geologist Rajdeep Dasgupta put very small samples of peridotite under very large pressures, to find out if the rock can liquify, at least in small amounts, as deep as 250 km beneath the ocean floor. Peridotite is the dominant rock of the Earth’s mantle above a depth of about 400 km, and it was previously believed that the mineral doesn’t liquify above that depth.

mantle structure

The Rice team focused on mantle beneath oceans because that is where the crust is typically formed; in a much-simplified version, the silicate melts (magma) rise with the convective currents, cool as they reach the crust and then solidify to create new crust. The starting point for melting has long been thought to be at 70 kilometres beneath the seafloor.

 

Geophysics

 

In order to determine the mantle’s density and properties, geophysicists used seismic information; seismic waves from earthquakes travel the globe much like sound waves, and by measuring their speed, we can estimate some the medium’s properties. These waves travel faster in solids (especially in denser solids), and slower in liquids; the first questions arose here.

Seismologists have observed anomalies in their velocity data as deep as 200 kilometers beneath the ocean floor,” Dasgupta said. “Based on our work, we show that trace amounts of magma are generated at this depth, which would potentially explain that.”

seismic wave

So it didn’t really add up – and this wasn’t the only clue. Geophysicists have also struggled to explain the bulk electrical conductivity of the oceanic mantle – something which was observed but couldn’t really be figured out.

“The magma at such depths has a high enough amount of dissolved carbon dioxide that its conductivity is very high,” Dasgupta said. “As a consequence, we can explain the conductivity of the mantle, which we knew was very high but always struggled to explain.”

The thing is, we cannot really dig down to the mantle – this is miles away from happening, both figuratively and literally, so we have to rely on indirect measurements (seismology, electric measurements, etc), lab experiments and surface extrapolations. Another interesting they found in this experiment was that carbonated rocks melt at significantly lower temperatures than non-carbonated.

“This deep melting makes the silicate differentiation of the planet much more efficient than previously thought,” Dasgupta said. “Not only that, this deep magma is the main agent to bring all the key ingredients for life — water and carbon — to the surface of the Earth.”

Volcanic windows

However, Dasgupta believes that volcanic rocks are the key to understanding our planet’s mantle.

“Our field of research is called experimental petrology,” he said. “We have all the necessary tools to simulate very high pressures (up to nearly 750,000 pounds per square inch for these experiments) and temperatures. We can subject small amounts of rock samples to these conditions and see what happens.”

A surfaced volcanic rock - peridotite

A surfaced volcanic rock – peridotite

To subject the rocks to these hellish conditions, they use massive hydraulic presses.

“When rocks come from deep in the mantle to shallower depths, they cross a certain boundary called the solidus, where rocks begin to undergo partial melting and produce magmas,” Dasgupta said. “Scientists knew the effect of a trace amount of carbon dioxide or water would be to lower this boundary, but our new estimation made it 150-180 kilometers deeper from the known depth of 70 kilometers,” he said.

These findings have major implications for all planetary sciences:

“What we are now saying is that with just a trace of carbon dioxide in the mantle, melting can begin as deep as around 200 kilometers. And when we incorporate the effect of trace water, the magma generation depth becomes at least 250 kilometers. This does not generate a large amount, but we show the extent of magma generation is larger than previously thought and, as a consequence, it has the capacity to affect geophysical and geochemical properties of the planet as a whole.”

The paper will be published this week in Nature

Melt rises up 25 times faster than previously believed

lava_lake_night

Scientists have for the first time determined the actual permeability of the asthenosphere in Earth’s upper mantle, which is basically responsible for how fast the melt rises towards the surface of the earth, and the results were surprising to say the least. Researchers found that it actually moves 25 times faster than previously assumed, which forces us to reconsider every volcanic model that includes melt.

A huge centrifuge measuring 2 meters in diameter was embedded in the cellar’s floor. It spins at 2800 rotations per minute and creates an acceleration about 3000 times bigger than Earth’s gravity; when at full capacity, it creates 120 decibels, which is about as loud as an airplane, according to Max Schmidt, a professor from the Institute for Mineralogy and Petrology at ETH Zurich. It can reach 850 km/h, and after it reaches this speed, if you would turn it off, it takes about an hour to stop.

This globally unique centrifuge cast a whole new light on how we perceive magmatism. The researchers used it to simulate the transport of molten lava made of basaltic glass from the mid-ocean ridge. The matrix through which the melt passed through consisted of olivine, which makes about 2/3 of the upper mantle. They applied a temperature of 1300 degrees and a pressure of 1 giga pascal. After the basaltic mass melted, they accelerated to about 700 g’s and were then able to calculate the permeability directly by microscopic analysis and were then able to correlate porosity to permeability, which is a main part for thermo-mecanical models.

In the light of these new discoveries, these models have to be revised; if the magma ascends much faster that means it interacts a lot less with the rock it penetrates. It also explains a few things, such as why volcanoes are active for only a few thousand years.