̽��ֱ�� of Cambridge - magma

Lava from 2021 Icelandic eruption gives rare view of deep churnings beneath volcano

cmm201 — Fri, 16 Sep 2022 14:30:00 +0000

̽��ֱ��study, published in the journal Nature and led by the ̽��ֱ�� of Iceland, reports that the eruption was unusual because it was supplied by a particularly deep reservoir of magma originating around 15 kilometres beneath the surface, at the base of Earth’s crust.

Their results also show that volcanoes like this can be fed by complex plumbing systems, where different batches of magma can mix and travel to the surface in just a matter of days or weeks.

̽��ֱ��researchers took measurements of lava and volcanic gases during the first 50 days of the eruption — giving them a near-real time report on the changing magma supply.

“I never expected to see the chemical composition of erupting lava change this quickly, showing us just how fast things can change in the depths beneath volcanoes,” said Simon Matthews from the ̽��ֱ�� of Iceland.

̽��ֱ��chemical fingerprint of lavas and the crystals inside them — together with the volcanic gases erupted — helped the researchers decode where the magma originated from and its journey to the surface. Until now, there has been a lack of information about the deepest parts of magmatic systems.

̽��ֱ��results showed that, during the initial phases of the eruption, the lava was predominately coming from around the boundary between the crust and underlying mantle – the thick, rocky layer that makes up most of Earth’s interior. But over the following weeks, the composition of the lava changed, indicating the eruption was directly tapping magma from greater depths.

“Ever since Enlightenment thinkers started writing about volcanoes, scientists have drawn cross-sections to visualise how they might work below ground,” said co-author Professor Clive Oppenheimer from Cambridge’s Department of Geography. “This study draws together different strands of information from monitoring the chemistry of lava and gas emissions to describe what is happening up to 20 kilometres down.”

They used indicators including the magnesium contents of the lava and carbon dioxide levels in the volcanic gases as barometers to gauge how hot and deep the magma feeding the eruption was. They suggest that, for the magma to come from 15 kilometres below the surface, the eruption was fed by something like a high-speed train direct to the mantle.

“We’ve known for a while that magma coming from the mantle is variable,” said co-author Professor John Maclennan from Cambridge’s Department of Earth Sciences, “But we’ve had to work hard to find clues as to how this complex mixing happens.”

̽��ֱ��authors point out that it has long been argued that different kinds of magma can mix deep in magmatic systems before an eruption. ̽��ֱ��new research shows that new magma can flow into a deep reservoir and mix with existing magma rapidly, in as little as 20 days.

Normally scientists use lavas erupted from old or extinct volcanoes to get a below ground view of volcanoes. But these samples are often too old to unravel processes happening over the course of a few days, “I’ve looked at hundreds of samples from dead volcanoes, but never had the chance to observe such a spectacular example of magma mixing in real-time,” said Maclennan.

Magma mixing has been shown to be an important process in triggering volcanic eruptions, so the study findings could have implications for understanding what drove the eruption and for future monitoring of volcanic activity in Iceland and at similar volcanoes.

Reference:
Sæmundur A. Halldórsson et al. ‘Rapid shifting of a deep magmatic source at Fagradalsfjall volcano, Iceland.’ Nature (2022). DOI: 10.1038/s41586-022-04981-x.

After centuries without volcanic activity, Iceland’s Reykjanes peninsula sprang to life in 2021 when lava erupted from the Fagradalsfjall volcano. New research involving the ̽��ֱ�� of Cambridge helps us see what is going on deep beneath the volcano by reading the chemistry of lavas and volcanic gases almost as they were erupted.

I’ve looked at hundreds of samples from dead volcanoes, but never had the chance to observe such a spectacular example of magma mixing in real-time

John Maclennan

Fagradalsfjall volcano

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‘Slushy’ magma ocean led to formation of the Moon’s crust

sc604 — Thu, 13 Jan 2022 14:00:00 +0000

̽��ֱ��scientists, from the ̽��ֱ�� of Cambridge and the Ecole normale supérieure de Lyon, have proposed a new model of crystallisation, where crystals remained suspended in liquid magma over hundreds of millions of years as the lunar ‘slush’ froze and solidified. ̽��ֱ��results are reported in the journal Geophysical Research Letters.

Over fifty years ago, Apollo 11 astronauts collected samples from the lunar Highlands. These large, pale regions of the Moon – visible to the naked eye – are made up of relatively light rocks called anorthosites. Anorthosites formed early in the history of the Moon, between 4.3 and 4.5 billion years ago.

Similar anorthosites, formed through the crystallisation of magma, can be found in fossilised magma chambers on Earth. Producing the large volumes of anorthosite found on the Moon, however, would have required a huge global magma ocean.

Scientists believe that the Moon formed when two protoplanets, or embryonic worlds, collided. ̽��ֱ��larger of these two protoplanets became the Earth, and the smaller became the Moon. One of the outcomes of this collision was that the Moon was very hot – so hot that its entire mantle was molten magma, or a magma ocean.

“Since the Apollo era, it has been thought that the lunar crust was formed by light anorthite crystals floating at the surface of the liquid magma ocean, with heavier crystals solidifying at the ocean floor,” said co-author Chloé Michaut from Ecole normale supérieure de Lyon. “This ‘flotation’ model explains how the lunar Highlands may have formed.”

However, since the Apollo missions, many lunar meteorites have been analysed and the surface of the Moon has been extensively studied. Lunar anorthosites appear more heterogeneous in their composition than the original Apollo samples, which contradicts a flotation scenario where the liquid ocean is the common source of all anorthosites.

̽��ֱ��range of anorthosite ages – over 200 million years – is difficult to reconcile with an ocean of essentially liquid magma whose characteristic solidification time is close to 100 million years.

“Given the range of ages and compositions of the anorthosites on the Moon, and what we know about how crystals settle in solidifying magma, the lunar crust must have formed through some other mechanism,” said co-author Professor Jerome Neufeld from Cambridge’s Department of Applied Mathematics and Theoretical Physics.

Michaut and Neufeld developed a mathematical model to identify this mechanism.

In the low lunar gravity, the settling of crystal is difficult, particularly when strongly stirred by the convecting magma ocean. If the crystals remain suspended as a crystal slurry, then when the crystal content of the slurry exceeds a critical threshold, the slurry becomes thick and sticky, and the deformation slow.

This increase of crystal content occurs most dramatically near the surface, where the slushy magma ocean is cooled, resulting in a hot, well-mixed slushy interior and a slow-moving, crystal-rich lunar ‘lid’.

“We believe it’s in this stagnant ‘lid’ that the lunar crust formed, as lightweight, anorthite-enriched melt percolated up from the convecting crystalline slurry below,” said Neufeld. “We suggest that cooling of the early magma ocean drove such vigorous convection that crystals remained suspended as a slurry, much like the crystals in a slushy machine.”

Enriched lunar surface rocks likely formed in magma chambers within the lid, which explains their diversity. ̽��ֱ��results suggest that the timescale of lunar crust formation is several hundreds of million years, which corresponds to the observed ages of the lunar anorthosites.

Serial magmatism was initially proposed as a possible mechanism for the formation of lunar anorthosites, but the slushy model ultimately reconciles this idea with that of a global lunar magma ocean.

̽��ֱ��research was supported by the European Research Council.

Jerome Neufeld is also affiliated with the Department of Earth Sciences. He is a Fellow of Trinity College.

Reference:
Chloé Michaut and Jerome A Neufeld. ‘Formation of the lunar primary crust from a long-lived slushy magma ocean.’ Geophysical Research Letters (2022). DOI: 10.1029/2021GL095408

Adapted from an ENS-Lyon press release.

Scientists have shown how the freezing of a ‘slushy’ ocean of magma may be responsible for the composition of the Moon’s crust.

Cooling of the early magma ocean drove such vigorous convection that crystals remained suspended as a slurry, like the crystals in a slushy machine.

Jerome Neufeld

NASA/Goddard Space Flight Center

Magma ocean and first rocky crust on the Moon

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Size matters: if you are a bubble of volcanic gas

sc604 — Mon, 06 Aug 2018 11:13:18 +0000

A team of scientists, including a volcanologist and mathematician from the ̽��ֱ�� of Cambridge, discovered the phenomenon through detailed observations of gas emissions from Kīlauea volcano in Hawaii.

At many volcanoes around the world, gas emissions are monitored routinely to help with forecasting eruptions. Changes in the output or proportions of different gases - such as carbon dioxide and sulphur dioxide – can herald shifts in the activity of a volcano. Volcanologists have considered that these chemical changes reflect the rise and fall of magma in the Earth’s crust but the new research reveals that the composition of volcanic gases depends also on the size of the gas bubbles rising up to the surface.

Until the latest spectacular eruption opened up fissures on the flank of the volcano, Kīlauea held a vast lava lake in its summit crater. ̽��ֱ��behaviour of this lava lake alternated between phases of fiery ‘spattering’ powered by large gas bubbles bursting through the magma, and more gentle gas release, accompanied by slow and steady motion of the lava.

In the past, volcanic gases have been sampled directly from steaming vents and openings called fumaroles. But this is not possible for the emissions from a lava lake, 200 metres across, and at the bottom of a steep-sided crater. Instead, the team used an infrared spectrometer, which is employed for routine volcano monitoring by co-authors of the study, Jeff Sutton and Tamar Elias from the Hawaiian Volcano Observatory (US Geological Survey).

̽��ֱ��device was located on the edge of the crater, pointed at the lava lake, and recorded gas compositions in the atmosphere every few seconds. ̽��ֱ��emissions of carbon- and sulphur-bearing gases were measured during both the vigorous and mild phases of activity.

Each individual measurement was used to compute the temperature of the volcanic gas. What immediately struck the scientists was that the gas temperatures ranged from 1150 degrees Celsius – the temperature of the lava – down to around 900 degrees Celsius. “At this temperature, the lava would freeze,” said lead author Dr Clive Oppenheimer, from Cambridge’s Department of Geography. “At first, we couldn’t understand how the gases could emerge much colder than the molten lava sloshing in the lake.”

̽��ֱ��clue to this puzzle came from the variation in calculated gas temperatures – they were high when the lava lake was placid, and low when it was bubbling furiously. “We realised it could be because of the size of the gas bubbles,” said co-author Professor Andy Woods, Director of Cambridge’s BP Institute. “Larger bubbles rise faster through the magma and expand rapidly as the pressure reduces, just like bubbles rising in a glass of fizzy drink; the gas cools down because of the expansion.” Larger bubbles form when smaller bubbles bump into each other and merge.

Woods and Oppenheimer developed a mathematical model to account for the process, which showed a very good fit with the observations.

But there was yet another surprising finding from the gas observations from Hawaii. As well as being cooler, the emissions from the large gas bubbles were more oxidised than expected – they had higher proportions of carbon dioxide to carbon monoxide.

̽��ֱ��chemical balance of volcanic gases such as carbon dioxide and carbon monoxide (or sulphur dioxide and hydrogen sulphide) is generally thought to be controlled by the chemistry of the surrounding liquid magma but what the new findings showed is that when bubbles get large enough, most of the gas inside follows its own chemical pathway as the gas cools.

̽��ֱ��ratio of carbon dioxide to carbon monoxide when the lava lake was in its most energetic state was six times higher than during the most stable phase. ̽��ֱ��scientists suggest this effect should be taken into account when gas measurements are being used to forecast major changes in volcanic activity.

“Gas measurements are critical to our monitoring and hazard assessment; refining our understanding of how magma behaves beneath the volcano allows us to better interpret our observations,” said co-author Tamar Elias from the Hawaiian Volcano Observatory.

And there is another implication of this discovery – not for eruptions today but for the evolution of the Earth’s atmosphere billions of years ago. “Volcanic emissions in Earth’s deep past may have made the atmosphere more oxidising than we thought,” said co-author Bruno Scaillet. “A more oxygen-rich atmosphere would have facilitated the emergence and viability of life on land, by generating an ozone layer, which shields against harmful ultraviolet rays from the sun.”

Reference:
Clive Oppenheimer et al “Influence of eruptive style on volcanic gas emission chemistry and temperature” Nature Geoscience (2018). DOI: 10.1038/s41561-018-0194-5

Inset image: Clive Oppenheimer in Hawaii. Credit: Clive Oppenheimer

̽��ֱ��chemical composition of gases emitted from volcanoes – which are used to monitor changes in volcanic activity – can change depending on the size of gas bubbles rising to the surface, and relate to the way in which they erupt. ̽��ֱ��results, published in the journal Nature Geoscience, could be used to improve the forecasting of threats posed by certain volcanoes.

At first, we couldn’t understand how the gases could emerge much colder than the molten lava sloshing in the lake.

Clive Oppenheimer

Kīlauea eruption, 2018

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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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