̽��ֱ�� of Cambridge - lava

‘Crystal clocks’ used to time magma storage before volcanic eruptions

sc604 — Thu, 18 Jul 2019 18:00:00 +0000

Researchers from the ̽��ֱ�� of Cambridge used volcanic minerals known as ‘crystal clocks’ to calculate how long magma can be stored in the deepest parts of volcanic systems. This is the first estimate of magma storage times near the boundary of the Earth’s crust and the mantle, called the Moho. ̽��ֱ��results are reported in the journal Science.

“This is like geological detective work,” said Dr Euan Mutch from Cambridge’s Department of Earth Sciences, and the paper’s first author. “By studying what we see in the rocks to reconstruct what the eruption was like, we can also know what kind of conditions the magma is stored in, but it’s difficult to understand what’s happening in the deeper parts of volcanic systems.”

“Determining how long magma can be stored in the Earth’s crust can help improve models of the processes that trigger volcanic eruptions,” said co-author Dr John Maclennan, also from the Department of Earth Sciences. “ ̽��ֱ��speed of magma rise and storage is tightly linked to the transfer of heat and chemicals in the crust of volcanic regions, which is important for geothermal power and the release of volcanic gases to the atmosphere.”

̽��ֱ��researchers studied the Borgarhraun eruption of the Theistareykir volcano in northern Iceland, which occurred roughly 10,000 years ago, and was fed directly from the Moho. This boundary area plays an important role in the processing of melts as they travel from their source regions in the mantle towards the Earth’s surface. To calculate how long the magma was stored at this boundary area, the researchers used a volcanic mineral known as spinel like a tiny stopwatch or crystal clock.

Using the crystal clock method, the researchers were able to model how the composition of the spinel crystals changed over time while the magma was being stored. Specifically, they looked at the rates of diffusion of aluminium and chromium within the crystals and how these elements are ‘zoned’.

“Diffusion of elements works to get the crystal into chemical equilibrium with its surroundings,” said Maclennan. “If we know how fast they diffuse we can figure out how long the minerals were stored in the magma.”

̽��ֱ��researchers looked at how aluminium and chromium were zoned in the crystals and realised that this pattern was telling them something exciting and new about magma storage time. ̽��ֱ��diffusion rates were estimated using the results of previous lab experiments. ̽��ֱ��researchers then used a new method, combining finite element modelling and Bayesian nested sampling to estimate the storage timescales.

“We now have really good estimates in terms of where the magma comes from in terms of depth,” said Mutch. “No one’s ever gotten this kind of timescale information from the deeper crust.”

Calculating the magma storage time also helped the researchers determine how magma can be transferred to the surface. Instead of the classical model of a volcano with a large magma chamber beneath, the researchers say that instead, it’s more like a volcanic ‘plumbing system’ extending through the crust with lots of small ‘spouts’ where magma can be quickly transferred to the surface.

A second paper by the same team, recently published in Nature Geoscience, found that that there is a link between the rate of ascent of the magma and the release of CO2, which has implications for volcano monitoring.

̽��ֱ��researchers observed that enough CO2 was transferred from the magma into gas over the days before eruption to indicate that CO2 monitoring could be a useful way of spotting the precursors to eruptions in Iceland. Based on the same set of crystals from Borgarhraun, the researchers found that magma can rise from a chamber 20 kilometres deep to the surface in as little as four days.

̽��ֱ��research was supported by the Natural Environment Research Council (NERC).

References:
Euan J.F. Mutch et al. ‘Millennial storage of near-Moho magma.’ Science (2019). DOI: 10.1126/science.aax4092

Euan J.F. Mutch et al. ‘Rapid transcrustal magma movement under Iceland.’ Nature Geoscience (2019). DOI: 10.1038/s41561-019-0376-9

̽��ֱ��molten rock that feeds volcanoes can be stored in the Earth’s crust for as long as a thousand years, a result which may help with volcanic hazard management and better forecasting of when eruptions might occur.

This is like geological detective work

Euan Mutch

Bob White

Magma erupting at the Holuhraun lava field in August 2014

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‘Bulges’ in volcanoes could be used to predict eruptions

sc604 — Wed, 28 Jun 2017 18:00:12 +0000

Using a technique called ‘seismic noise interferometry’ combined with geophysical measurements, the researchers measured the energy moving through a volcano. They found that there is a good correlation between the speed at which the energy travelled and the amount of bulging and shrinking observed in the rock. ̽��ֱ��technique could be used to predict more accurately when a volcano will erupt. Their results are reported in the journal Science Advances.

Data was collected by the US Geological Survey across Kīlauea in Hawaii, a very active volcano with a lake of bubbling lava just beneath its summit. During a four-year period, the researchers used sensors to measure relative changes in the velocity of seismic waves moving through the volcano over time. They then compared their results with a second set of data which measured tiny changes in the angle of the volcano over the same time period.

As Kīlauea is such an active volcano, it is constantly bulging and shrinking as pressure in the magma chamber beneath the summit increases and decreases. Kīlauea’s current eruption started in 1983, and it spews and sputters lava almost constantly. Earlier this year, a large part of the volcano fell away and it opened up a huge ‘waterfall’ of lava into the ocean below. Due to this high volume of activity, Kīlauea is also one of the most-studied volcanoes on Earth.

̽��ֱ��Cambridge researchers used seismic noise to detect what was controlling Kīlauea’s movement. Seismic noise is a persistent low-level vibration in the Earth, caused by everything from earthquakes to waves in the ocean, and can often be read on a single sensor as random noise. But by pairing sensors together, the researchers were able to observe energy passing between the two, therefore allowing them to isolate the seismic noise that was coming from the volcano.

“We were interested in how the energy travelling between the sensors changes, whether it’s getting faster or slower,” said Clare Donaldson, a PhD student in Cambridge’s Department of Earth Sciences, and the paper’s first author. “We want to know whether the seismic velocity changes reflect increasing pressure in the volcano, as volcanoes bulge out before an eruption. This is crucial for eruption forecasting.”

One to two kilometres below Kīlauea’s lava lake, there is a reservoir of magma. As the amount of magma changes in this underground reservoir, the whole summit of the volcano bulges and shrinks. At the same time, the seismic velocity changes. As the magma chamber fills up, it causes an increase in pressure, which leads to cracks closing in the surrounding rock and producing faster seismic waves – and vice versa.

“This is the first time that we’ve been able to compare seismic noise with deformation over such a long period, and the strong correlation between the two shows that this could be a new way of predicting volcanic eruptions,” said Donaldson.

Volcano seismology has traditionally measured small earthquakes at volcanoes. When magma moves underground, it often sets off tiny earthquakes, as it cracks its way through solid rock. Detecting these earthquakes is therefore very useful for eruption prediction. But sometimes magma can flow silently, through pre-existing pathways, and no earthquakes may occur. This new technique will still detect the changes caused by the magma flow.

Seismic noise occurs continuously, and is sensitive to changes that would otherwise have been missed. ̽��ֱ��researchers anticipate that this new research will allow the method to be used at the hundreds of active volcanoes around the world.

Reference
C. Donaldson et al. ‘Relative seismic velocity variations correlate with deformation at Kīlauea volcano’. Science Advances (2017) DOI: 10.1126/sciadv.1700219

Inset image: Lava Waterfall, Kilauea Volcano, Hawaii. Credit: Dhilung Kirat

A team of researchers from the ̽��ֱ�� of Cambridge have developed a new way of measuring the pressure inside volcanoes, and found that it can be a reliable indicator of future eruptions.

This could be a new way of predicting volcanic eruptions.

Clare Donaldson

Kiauea

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Chasing the volcano

tdk25 — Fri, 01 Jul 2016 06:00:00 +0000

Faced with the prospect of an imminent volcanic eruption, most people would head for safety, but for one group of Cambridge research students, the aim is to get as close as they realistically can.

That opportunity suddenly presented itself when, on the night of August 28, 2014, members of the ̽��ֱ��’s Volcano Seismology group were shaken awake by a series of low-magnitude earthquakes. ̽��ֱ��tremors were being caused by the movement of an underground channel of molten rock which they had been tracking for 10 days as it forced its way north-east from the Barðarbunga volcano in central Iceland.

̽��ֱ��group’s work involves measuring and studying such seismic events, which warn that a volcanic eruption may be about to take place. As it became clear that this was now imminent, the team hastily finished deploying field instruments around the tip of the area where they knew the channel was flowing. Just hours later, it ruptured the Earth’s surface, disgorging huge fountains of magma that reached up to 150 metres high, announcing the start of Iceland’s biggest volcanic event for 200 years.

Click image to enlarge

̽��ֱ��story of the group’s dramatic fieldwork – and why it matters – is now the subject of a display at this year’s Royal Society Summer Science Exhibition, which will be taking place in London from 4-10 July 2016.

During the build-up to the eruption, a total of 30,000 mini earthquakes occurred as the molten rock forged a crack through the earth, several kilometres beneath the surface. By analysing these earthquakes, the team were able to understand more about the physical process that was happening under their feet. This knowledge helps to inform both early warning tools that can be used to anticipate a volcanic eruption, and scenario-planning around its potential consequences.

Robert Green, a Seismology PhD student from St John’s College, ̽��ֱ�� of Cambridge, was one of the Cambridge researchers responsible for assessing the tremors around Barðarbunga. “Most people think of a volcano as being a large mountain where molten rock comes straight up from under the ground and erupts directly from the summit, either explosively creating a huge ash cloud, or producing lava which flows down the sides,” he said.

“Those are certainly options, but this one was different. Instead the molten rock moved 46 kilometres underground away from the volcano before it emerged in a completely different place. When it did, the eruption formed a curtain of fire the height of Big Ben.”

Earthquakes such as those measured by Green and his colleagues are caused by the molten flow cracking through rock in the Earth’s crust. As the rocks slide past one another, they cause the ground to shake. In August 2014, it was this seismic activity that indicated that one of these so-called “dyke intrusions” had developed from the Barðarbunga volcano.

̽��ֱ��scientific community was quick to respond, deploying researchers from 26 different institutions, including the Cambridge team. This group effectively chased the volcano, travelling in helicopters, snow scooters and offroad vehicles to install seismometers and track its subterranean progress.

They also worked closely with civil and aviation authorities to keep them up to date about potential impact. Airlines feared a repeat of the 2010 Eyjafjallajökull eruption, when a plume of volcanic ash infamously led to the cancellation of 100,000 flights during the Easter holidays.

When the fissure eruption finally happened, it was at the Holuhraun lava field, the site of a 19^th Century volcanic event north of Barðarbunga itself. Some of the Cambridge group’s seismometers had been positioned so close that they had to be hastily retrieved in the face of the advancing lava flow.

̽��ֱ��eruption was on a huge scale, lasting from August 2014 until February 2015. During its early stages, about 500 tonnes of rock were flung out of the Earth every second at temperatures of about 1,300 degrees C. ̽��ֱ��thermal energy was calculated to be equivalent to one Hiroshima atomic bomb being detonated every two minutes for almost six months.

For the researchers, it was an unprecedented opportunity to gather data about the effects of the movement of magma under the ground during such events. “Earthquakes accompanying the movement of magma underground are the best volcano monitoring tool we have, but we don't yet understand the mechanics of it - precisely why, when and where the earthquakes occur, and why, when and where they don't,” said Jenny Woods, another member of the team, based at Cambridge’s Department of Earth Sciences. “These are important things to learn if we want to understand the behaviour of volcanoes and improve eruption prediction.”

In the case of the 2014 eruption, scientists and government teams had to consider the possibility that lava might erupt beneath a local ice cap, causing an ash cloud which could disrupt flights, and a major flood. Even more frightening was the possibility was that it might continue moving until it met another reservoir of molten rock beneath the Askja volcano, triggering a major eruption that would have had devastating consequences for much of northern Iceland.

“There is no certainty during these events that it will even erupt at all,” Green added. “ ̽��ֱ��whole time we were looking at several possible scenarios, one of which was that the lava would just stay in the ground.”

“Tracking the Bárdarbunga intrusion and witnessing the eruption was an utterly surreal experience: arriving in Iceland, deploying instruments in an evacuation zone, being shaken awake by an earthquake, and then being the first group on the scene at the eruption in the middle of the night under the northern lights,” said Woods. “It was a real reminder of the raw power trapped in the earth beneath our feet!”

̽��ֱ��study also involved an assessment of the stress changes that occurred within the Earth’s crust as a result of the tremors. These findings could, among other things, help with the assessment of human activities that have a similar effect, not least the highly sensitive question of where and when it is safe to undertake “fracking” for shale gas.

̽��ֱ��group’s display at the Royal Society Summer Exhibition, which is aptly entitled “Explosive Earth”, will feature several hands-on activities enabling visitors to discover how researchers monitor the movement of molten rock under the ground, how they triangulate the point of origin from tremors to track the magma’s course, and how an earthquake itself is measured.

In 2014, Cambridge researchers monitored a series of seismic shocks which preceded Iceland’s biggest volcanic eruption in 200 years. ̽��ֱ��dramatic story of their work, and its scientific value, is now part of this year’s Royal Society Summer Science Exhibition.

̽��ֱ��eruption formed a curtain of fire the height of Big Ben.

Robert Green

EXPLOSIVE EARTH - Royal Society Summer Science Exhibition 4-10 July 2016

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Did dinosaur-killing asteroid trigger largest lava flows on Earth?

jeh98 — Tue, 12 May 2015 10:15:26 +0000

̽��ֱ��team of researchers, which included Dr Sally Gibson from Cambridge ̽��ֱ��’s Department of Earth Sciences, argue that the impact may have triggered most of the immense eruptions of lava in India known as the Deccan Traps. In a paper published in ̽��ֱ��Geological Society of America Bulletin they claim this would explain the “uncomfortably close” coincidence between the Deccan Traps eruptions and the impact, which has always cast doubt on the theory that the asteroid was the sole cause of the end-Cretaceous mass extinction.

̽��ֱ��Deccan Traps are a vast accumulation of igneous rock, and one of the largest volcanic features on Earth, located on the Deccan Plateau in India. Formed by huge lava flows, they cover an area of approximately 500,000km² and stretch across the Indian subcontinent from Mumbai to Kolkata.

“If you try to explain why the largest impact we know of in the last billion years happened within 100,000 years of these massive lava flows at Deccan … the chances of that occurring at random are minuscule,” said team leader Mark Richards, Professor of Earth and Planetary Science at the ̽��ֱ�� of California, Berkeley. “It’s not a very credible coincidence.”

While the Deccan lava flows, which started before the impact but erupted for several hundred thousand years after, probably spewed immense amounts of carbon dioxide and other noxious, climate-modifying gases into the atmosphere, it’s still unclear if this contributed to the demise of most of life on Earth at the end of the Age of Dinosaurs. “This connection between the impact and the Deccan lava flows is a great story and might even be true, but it doesn’t yet take us closer to understanding what actually killed the dinosaurs,” Richards added.

̽��ֱ��disappearance of the landscape-dominating dinosaurs is widely credited with ushering in the age of mammals, eventually including humans.

“Paul Renne’s group at Berkeley showed years ago that the Central Atlantic Magmatic Province is associated with the mass extinction at the Triassic/Jurassic boundary 200 million years ago, and the Siberian Traps are associated with the end-Permian extinction 250 million years ago, and now we also know that a big volcanic eruption in China called the Emeishan Traps is associated with the end-Guadalupian extinction 260 million years ago,” Richards said.

“Then you have the Deccan eruptions – including the largest mapped lava flows on Earth – occurring 66 million years ago coincident with the mass extinction of the dinosaurs. So what really happened?”

Richards teamed up with a multi-disciplinary group of experts to try to discover faults with his idea that the impact off the coast of Mexico triggered the Deccan eruptions, but instead came up with supporting evidence. Paul Renne, a Professor in Residence in the ̽��ֱ�� of California, Berkeley’s Department of Earth and Planetary Science and Director of the Berkeley Geochronology Center, re-dated the asteroid impact and mass extinction two years ago and found them essentially simultaneous. He also found they were within approximately 100,000 years of the largest Deccan eruptions, referred to as the Wai subgroup flows, which produced about 70 percent of the lavas that now stretch across the Indian subcontinent.

Richards and his team found pronounced weathering surfaces marking the onset of the huge Wai subgroup flows, which may indicate a period of inactivity in Deccan volcanism prior to the asteroid impact. Since the team’s manuscript was accepted for publication, new radioisotopic ages published by scientists at Princeton ̽��ֱ�� and preliminary ages from the Berkeley group have confirmed that the Wai lava flows closely postdate the asteroid impact.

“This was an existing massive volcanic system that had been there probably several million years, and the impact gave this thing a shake and it mobilised a huge amount of magma over a short amount of time,” Richards said.

“Based on the distances between erupting volcanoes and the epicentres of earthquakes, a large asteroid impact in Mexico could generate a huge earthquake (equivalent to magnitude 9 or greater) that would have enough seismic energy to shake magma chambers deep in the Earth below the Deccan and cause a sudden massive outpouring of lava, 100,000 years or so after the impact event itself,” explains Gibson.

“Our findings have broad implications for studies of past climate change, evolutionary biology, and how earthquakes might trigger volcanic eruptions.”

Inset image: Cross-sectional diagram to schematically illustrate the Deccan plume melting in the mantle beneath the Indian subcontinent 60 million years ago (from Richards et al., 2015)

Article originally published by the ̽��ֱ�� of California, Berkeley

̽��ֱ��asteroid that slammed into the ocean off Mexico 66 million years ago and killed off the dinosaurs probably rang the Earth like a bell, triggering volcanic eruptions around the globe, according to a multi-disciplinary team of scientists.

If you try to explain why the largest impact we know of in the last billion years happened within 100,000 years of these massive lava flows at Deccan … the chances of that occurring at random are minuscule

Mark Richards, ̽��ֱ�� of California Berkeley

SA Gibson

̽��ֱ��Deccan Traps in western India

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Luck and lava

sc604 — Mon, 06 Oct 2014 09:34:16 +0000

̽��ֱ��team, led by Professor Bob White, has been monitoring activity near the Bárðarbunga and Holuhraun volcanoes since 2006, using up to 70 broadband seismometers.

Luckily, the seismometers and field researchers were still in Iceland at the time that this most recent volcanic activity began, as the team had recently finished recovering 25 seismometers from the Vatnajökull ice cap where they had been used for a study of small quakes caused by ice cracking.

Here, White and PhD student Tim Greenfield discuss their work, and what it’s like to be up close to such a spectacular eruption.

A team of researchers from Cambridge’s Department of Earth Sciences have recently returned from Iceland where, thanks to a bit of luck, they have gathered the most extensive dataset ever from a volcanic eruption, which will likely yield considerable new insights into how molten rock moves underground, and whether or not it erupts.

Luck and lava

Simon Redfern

Aerial view of Bárðarbunga

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