̽��ֱ�� of Cambridge - volcano

Into the underworld: the mountains beneath our feet

lkm37 — Tue, 14 Jan 2025 10:41:16 +0000

Sanne Cottaar is Professor of Global Seismology in Earth Sciences. She wants to understand Earth’s inner structure: how it shaped the surface and allowed life to form.

2023 was the hottest summer in two thousand years

sc604 — Tue, 14 May 2024 15:00:00 +0000

Although 2023 has been reported as the hottest year on record, the instrumental evidence only reaches back as far as 1850 at best, and most records are limited to certain regions.

Now, by using past climate information from annually resolved tree rings over two millennia, scientists from the ̽��ֱ�� of Cambridge and the Johannes Gutenberg ̽��ֱ�� Mainz have shown how exceptional the summer of 2023 was.

Even allowing for natural climate variations over hundreds of years, 2023 was still the hottest summer since the height of the Roman Empire, exceeding the extremes of natural climate variability by half a degree Celsius.

“When you look at the long sweep of history, you can see just how dramatic recent global warming is,” said co-author Professor Ulf Büntgen, from Cambridge’s Department of Geography. “2023 was an exceptionally hot year, and this trend will continue unless we reduce greenhouse gas emissions dramatically.”

̽��ֱ��results, reported in the journal Nature, also demonstrate that in the Northern Hemisphere, the 2015 Paris Agreement to limit warming to 1.5C above pre-industrial levels has already been breached.

Early instrumental temperature records, from 1850-1900, are sparse and inconsistent. ̽��ֱ��researchers compared early instrumental data with a large-scale tree ring dataset and found the 19th century temperature baseline used to contextualise global warming is several tenths of a degree Celsius colder than previously thought. By re-calibrating this baseline, the researchers calculated that summer 2023 conditions in the Northern Hemisphere were 2.07C warmer than mean summer temperatures between 1850 and 1900.

“Many of the conversations we have around global warming are tied to a baseline temperature from the mid-19th century, but why is this the baseline? What is normal, in the context of a constantly-changing climate, when we’ve only got 150 years of meteorological measurements?” said Büntgen. “Only when we look at climate reconstructions can we better account for natural variability and put recent anthropogenic climate change into context.”

Tree rings can provide that context, since they contain annually-resolved and absolutely-dated information about past summer temperatures. Using tree-ring chronologies allows researchers to look much further back in time without the uncertainty associated with some early instrumental measurements.

̽��ֱ��available tree-ring data reveals that most of the cooler periods over the past 2000 years, such as the Little Antique Ice Age in the 6th century and the Little Ice Age in the early 19th century, followed large-sulphur-rich volcanic eruptions. These eruptions spew huge amounts of aerosols into the stratosphere, triggering rapid surface cooling. ̽��ֱ��coldest summer of the past two thousand years, in 536 CE, followed one such eruption, and was 3.93C colder than the summer of 2023.

Most of the warmer periods covered by the tree ring data can be attributed to the El Niño climate pattern, or El Niño-Southern Oscillation (ENSO). El Niño affects weather worldwide due to weakened trade winds in the Pacific Ocean and often results in warmer summers in the Northern Hemisphere. While El Niño events were first noted by fisherman in the 17th century, they can be observed in the tree ring data much further back in time.

However, over the past 60 years, global warming caused by greenhouse gas emissions are causing El Niño events to become stronger, resulting in hotter summers. ̽��ֱ��current El Niño event is expected to continue into early summer 2024, making it likely that this summer will break temperature records once again.

“It’s true that the climate is always changing, but the warming in 2023, caused by greenhouse gases, is additionally amplified by El Niño conditions, so we end up with longer and more severe heat waves and extended periods of drought,” said Professor Jan Esper, the lead author of the study from the Johannes Gutenberg ̽��ֱ�� Mainz in Germany. “When you look at the big picture, it shows just how urgent it is that we reduce greenhouse gas emissions immediately.”

̽��ֱ��researchers note that while their results are robust for the Northern Hemisphere, it is difficult to obtain global averages for the same period since data is sparse for the Southern Hemisphere. ̽��ֱ��Southern Hemisphere also responds differently to climate change, since it is far more ocean-covered than the Northern Hemisphere.

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

Reference:
Jan Esper, Max Torbenson, Ulf Büntgen. ‘2023 summer warmth unparalleled over the past 2,000 years.’ Nature (2024). DOI: 10.1038/s41586-024-07512-y

Researchers have found that 2023 was the hottest summer in the Northern Hemisphere in the past two thousand years, almost four degrees warmer than the coldest summer during the same period.

When you look at the long sweep of history, you can see just how dramatic recent global warming is

Ulf Büntgen

trekandshoot via Getty Images

Morning sun over Los Angeles, USA.

̽��ֱ��text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

Yes

Effect of volcanic eruptions significantly underestimated in climate projections

sc604 — Fri, 23 Jun 2023 10:49:47 +0000

While this effect is far from enough to offset the effects of global temperature rise caused by human activity, the researchers, led by the ̽��ֱ�� of Cambridge, say that small-magnitude eruptions are responsible for as much as half of all the sulphur gases emitted into the upper atmosphere by volcanoes.

̽��ֱ��results, reported in the journal Geophysical Research Letters, suggest that improving the representation of volcanic eruptions of all magnitudes will in turn make climate projections more robust.

Where and when a volcano erupts is not something that humans can control, but volcanoes do play an important role in the global climate system. When volcanoes erupt, they can spew sulphur gases into the upper atmosphere, which forms tiny particles called aerosols that reflect sunlight back into space. For very large eruptions, such as Mount Pinatubo in 1991, the volume of volcanic aerosols is so large that it single-handedly causes global temperatures to drop.

However, these large eruptions only happen a handful of times per century – most small-magnitude eruptions happen every year or two.

“Compared with the greenhouse gases emitted by human activity, the effect that volcanoes have on the global climate is relatively minor, but it’s important that we include them in climate models, in order to accurately assess temperature changes in future,” said first author May Chim, a PhD candidate in the Yusuf Hamied Department of Chemistry.

Standard climate projections, such as the Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report, assume that explosive volcanic activity over 2015–2100 will be at the same level as the 1850–2014 period, and overlook the effects of small-magnitude eruptions.

“These projections mostly rely on ice cores to estimate how volcanoes might affect the climate, but smaller eruptions are too small to be detected in ice-core records,” said Chim. “We wanted to make a better use of satellite data to fill the gap and account for eruptions of all magnitudes.”

Using the latest ice-core and satellite records, Chim and her colleagues from the ̽��ֱ�� of Exeter, the German Aerospace Center (DLR), the Ludwig-Maximilians ̽��ֱ�� of Munich, Durham ̽��ֱ��, and the UK Met Office, generated 1000 different scenarios of future volcanic activity. They selected scenarios representing lower, median and high levels of volcanic activity, and then performed climate simulations using the UK Earth System Model.

Their simulations show that the impacts of volcanic eruptions on climate, including global surface temperature, sea level and sea ice extent, are underestimated because current climate projections largely underestimate the plausible future level of volcanic activity.

For the median future scenario, they found that the effect of volcanoes on the atmosphere, known as volcanic forcing, is being underestimated in climate projections by as much as 50%, due in large part to the effect of small-magnitude eruptions.

“We found that not only is volcanic forcing being underestimated, but small-magnitude eruptions are actually responsible for as much as half of all volcanic forcing,” said Chim. “These small-magnitude eruptions may not have a measurable effect individually, but collectively, their effect is significant.

“I was surprised to see just how important these small-magnitude eruptions are – we knew they had an effect, but we didn’t know it was so large.”

Although the cooling effect of volcanoes is being underestimated in climate projections, the researchers stress that it does not compare with human-generated carbon emissions.

“Volcanic aerosols in the upper atmosphere typically stay in the atmosphere for a year or two, whereas carbon dioxide stays in the atmosphere for much, much longer,” said Chim. “Even if we had a period of extraordinarily high volcanic activity, our simulations show that it wouldn’t be enough to stop global warming. It’s like a passing cloud on a hot, sunny day: the cooling effect is only temporary.”

̽��ֱ��researchers say that fully accounting for the effect of volcanoes can help make climate projections more robust. They are now using their simulations to investigate whether future volcanic activity could threaten the recovery of the Antarctic ozone hole, and in turn, maintain relatively high levels of harmful ultraviolet radiation at the Earth’s surface.

̽��ֱ��research was supported in part by the Croucher Foundation and ̽��ֱ��Cambridge Commonwealth, European & International Trust, the European Union, and the Natural Environment Research Council (NERC), part of UK Research and Innovation (UKRI).

Reference:
Man Mei Chim et al. ‘Climate Projections Very Likely Underestimate Future Volcanic Forcing and Its Climatic Effects.’ Geophysical Research Letters (2023). DOI: 10.1029/2023GL103743

Researchers have found that the cooling effect that volcanic eruptions have on Earth's surface temperature is likely underestimated by a factor of two, and potentially as much as a factor of four, in standard climate projections.

These small-magnitude eruptions may not have a measurable effect individually, but collectively, their effect is significant.

May Chim

Andreas Weibel via Getty Images

Volcano erupting near El Paso, La Palma, Spain

̽��ֱ��text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

Yes

Medieval monks accidentally recorded some of history’s biggest volcanic eruptions

sc604 — Wed, 05 Apr 2023 14:58:42 +0000

An international team, including researchers from the ̽��ֱ�� of Cambridge, drew on readings of medieval texts, along with ice core and tree ring data, to accurately date some of the biggest volcanic eruptions the world has ever seen. Their results, reported in the journal Nature, uncover new information about one of the most volcanically active periods in Earth’s history, which some think helped to trigger the Little Ice Age, a long interval of cooling that saw the advance of European glaciers.

It took the researchers, led by the ̽��ֱ�� of Geneva (UNIGE), almost five years to examine hundreds of annals and chronicles from across Europe and the Middle East, in search of references to total lunar eclipses and their colouration.

Total lunar eclipses occur when the moon passes into the Earth’s shadow. Typically, the moon remains visible as a reddish orb because it is still bathed in sunlight bent round the Earth by its atmosphere. But after a very large volcanic eruption, there can be so much dust in the stratosphere – the middle part of the atmosphere starting roughly where commercial aircraft fly – that the eclipsed moon almost disappears.

Medieval chroniclers recorded and described all kinds of historical events, including the deeds of kings and popes, important battles, and natural disasters and famines. Just as noteworthy were the celestial phenomena that, to the chroniclers, might foretell such calamities. Mindful of the Book of Revelation, a vision of the end times that speaks of a blood-red moon, the monks were especially careful to take note of the moon’s colouration.

Of the 64 total lunar eclipses that occurred in Europe between 1100 and 1300, the chroniclers had faithfully documented 51. In five of these cases, they also reported that the moon was exceptionally dark.

Asked what made him connect the monks’ records of the brightness and colour of the eclipsed moon with volcanic gloom, the lead author of the work, UNIGE’s Sébastien Guillet said: “I was listening to Pink Floyd's Dark Side of the Moon album when I realised that the darkest lunar eclipses all occurred within a year or so of major volcanic eruptions. Since we know the exact days of the eclipses, it opened the possibility of using the sightings to narrow down when the eruptions must have happened.”

̽��ֱ��researchers found that scribes in Japan took equal note of lunar eclipses. One of the best known, Fujiwara no Teika, wrote of an unprecedented dark eclipse observed on 2 December 1229: ‘the old folk had never seen it like this time, with the location of the disk of the Moon not visible, just as if it had disappeared during the eclipse... It was truly something to fear.’

̽��ֱ��stratospheric dust from large volcanic eruptions was not only responsible for the vanishing moon. It also cooled summer temperatures by limiting the sunlight reaching the Earth’s surface. This in turn could bring ruin to agricultural crops.

“We know from previous work that strong tropical eruptions can induce global cooling on the order of roughly 1°C over a few years,” said Markus Stoffel from the ̽��ֱ�� of Geneva, a specialist in converting measurements of tree rings into climate data, who co-designed the study. “They can also lead to rainfall anomalies with droughts in one place and floods in another.”

Despite these effects, people at the time could not have imagined that the poor harvests or the unusual lunar eclipses had anything to do with volcanoes – the eruptions themselves were all but one undocumented.

“We only knew about these eruptions because they left traces in the ice of Antarctica and Greenland,” said co-author Professor Clive Oppenheimer from Cambridge’s Department of Geography. “By putting together the information from ice cores and the descriptions from medieval texts we can now make better estimates of when and where some of the biggest eruptions of this period occurred.”

To make the most of this integration, Guillet worked with climate modellers to compute the most likely timing of the eruptions. “Knowing the season when the volcanoes erupted is essential, as it influences the spread of the volcanic dust and the cooling and other climate anomalies associated with these eruptions,” he said.

As well as helping to narrow down the timing and intensity of these events, what makes the findings significant is that the interval from 1100 to 1300 is known from ice core evidence to be one of the most volcanically active periods in history. Of the 15 eruptions considered in the new study, one in the mid-13th century rivals the famous 1815 eruption of Tambora that brought on ‘the year without a summer’ of 1816. ̽��ֱ��collective effect of the medieval eruptions on Earth’s climate may have led to the Little Ice Age, when winter ice fairs were held on the frozen rivers of Europe.

“Improving our knowledge of these otherwise mysterious eruptions, is crucial to understanding whether and how past volcanism affected not only climate but also society during the Middle Ages,” said Guillet.

̽��ֱ��research was supported in part by the Swiss National Science Foundation.

Reference:
Sébastien Guillet et al. ‘Lunar eclipses illuminate timing and climate impact of medieval volcanism.’ Nature (2023). DOI: 10.1038/s41586-023-05751-z

By observing the night sky, medieval monks unwittingly recorded some of history’s largest volcanic eruptions, according to a new analysis of 12th and 13th century European and Middle Eastern chronicles.

Recueil de poésies françaises. Consolation de Boèce, Ms. 822, fol. 61v, Bibliothèque Municipale de Toulouse /Gallica, BnF

An illuminated manuscript from the late 14th to the early 15th century, depicting two individuals observing a lunar eclipse

̽��ֱ��text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

Yes

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

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

Yes

Risk of volcano catastrophe ‘a roll of the dice’, say experts

fpjl2 — Wed, 17 Aug 2022 15:05:49 +0000

̽��ֱ��world is “woefully underprepared” for a massive volcanic eruption and the likely repercussions on global supply chains, climate and food, according to experts from the ̽��ֱ�� of Cambridge’s Centre for the Study of Existential Risk (CSER).

In an article published in the journal Nature, they say there is a “broad misconception” that risks of major eruptions are low, and describe current lack of governmental investment in monitoring and responding to potential volcano disasters as “reckless”.

However, the researchers argue that steps can be taken to protect against volcanic devastation – from improved surveillance to increased public education and magma manipulation – and the resources needed to do so are long overdue.

“Data gathered from ice cores on the frequency of eruptions over deep time suggests there is a one-in-six chance of a magnitude seven explosion in the next one hundred years. That’s a roll of the dice,” said article co-author and CSER researcher Dr Lara Mani, an expert in global risk.

“Such gigantic eruptions have caused abrupt climate change and collapse of civilisations in the distant past.”

Mani compares the risk of a giant eruption to that of a 1km-wide asteroid crashing into Earth. Such events would have similar climatic consequences, but the likelihood of a volcanic catastrophe is hundreds of times higher than the combined chances of an asteroid or comet collision.

“Hundreds of millions of dollars are pumped into asteroid threats every year, yet there is a severe lack of global financing and coordination for volcano preparedness,” Mani said. “This urgently needs to change. We are completely underestimating the risk to our societies that volcanoes pose.”

An eruption in Tonga in January was the largest ever instrumentally recorded. ̽��ֱ��researchers argue that if it had gone on longer, released more ash and gas, or occurred in an area full of critical infrastructure – such as the Mediterranean – then global shock waves could have been devastating.

“ ̽��ֱ��Tonga eruption was the volcanic equivalent of an asteroid just missing the Earth, and needs to be treated as a wake-up call,” said Mani.

̽��ֱ��CSER experts cite recent research detecting the regularity of major eruptions by analysing traces of sulphur spikes in ancient ice samples. An eruption ten to a hundred times larger than the Tonga blast occurs once every 625 years – twice as often as had been previously thought.

“ ̽��ֱ��last magnitude seven eruption was in 1815 in Indonesia,” said co-author Dr Mike Cassidy, a volcano expert and visiting CSER researcher, now based at the ̽��ֱ�� of Birmingham.

“An estimated 100,000 people died locally, and global temperatures dropped by a degree on average, causing mass crop failures that led to famine, violent uprisings and epidemics in what was known as the year without summer,” he said.

“We now live in a world with eight times the population and over forty times the level of trade. Our complex global networks could make us even more vulnerable to the shocks of a major eruption.”

Financial losses from a large magnitude eruption would be in the multi-trillions, and on a comparable scale to the pandemic, say the experts.

Mani and Cassidy outline steps they say need to be taken to help forecast and manage the possibility of a planet-altering eruption, and help mitigate damage from smaller, more frequent eruptions.

These include a more accurate pinpointing of risks. We only know locations of a handful of the 97 eruptions classed as large magnitude on the “Volcano Explosivity Index” over the last 60,000 years. This means there could be dozens of dangerous volcanoes dotted the world over with the potential for extreme destruction, about which humanity has no clue.

“We may not know about even relatively recent eruptions due to a lack of research into marine and lake cores, particularly in neglected regions such as Southeast Asia,” said Cassidy. “Volcanoes can lie dormant for a long time, but still be capable of sudden and extraordinary destruction.”

Monitoring must be improved, say the CSER experts. Only 27% of eruptions since 1950 have had a seismometer anywhere near them, and only a third of that data again has been fed into the global database for “volcanic unrest”.

“Volcanologists have been calling for a dedicated volcano-monitoring satellite for over twenty years,” said Mani. “Sometimes we have to rely on the generosity of private satellite companies for rapid imagery.”

̽��ֱ��experts also call for increased research into volcano “geoengineering”. This includes the need to study means of countering aerosols released by a massive eruption, which could lead to a “volcanic winter”. They also say that work to investigate manipulating pockets of magma beneath active volcanoes should be undertaken.

Added Mani: “Directly affecting volcanic behaviour may seem inconceivable, but so did the deflection of asteroids until the formation of the NASA Planetary Defense Coordination Office in 2016. ̽��ֱ��risks of a massive eruption that devastates global society is significant. ̽��ֱ��current underinvestment in responding to this risk is simply reckless.”

While funding is pumped into preventing low-probability scenarios such as asteroid collision, the far more likely threat of a large volcanic eruption is close to ignored – despite much that could be done to reduce the risks, say researchers.

̽��ֱ��risks of a massive eruption that devastates global society is significant

Lara Mani

Dr Mike Cassidy

Mount Rinjani in Indonesia, which had one of the largest eruptions in the last millennium in 1257 (magnitude 7).

Yes

Scientists 'see' puzzling features deep in Earth’s interior

cmm201 — Thu, 19 May 2022 09:00:00 +0000

̽��ֱ��enigmatic area of rock, which is located almost directly beneath the Hawaiian Islands, is one of several ultra-low velocity zones – so-called because earthquake waves slow to a crawl as they pass through them.

̽��ֱ��research, published in Nature Communications, is the first to reveal the complex internal variability of one of these pockets in detail, shedding light on the landscape of Earth’s deep interior and the processes operating within it.

“Of all Earth’s deep interior features, these are the most fascinating and complex. We’ve now got the first solid evidence to show their internal structure - it’s a real milestone in deep earth seismology,” said lead author Zhi Li, PhD student at Cambridge’s Department of Earth Sciences.

Earth’s interior is layered like an onion: at the centre sits the iron-nickel core, surrounded by a thick layer known as the mantle, and on top of that a thin outer shell — the crust we live on. Although the mantle is solid rock, it is hot enough to flow extremely slowly. These internal convection currents feed heat to the surface, driving the movement of tectonic plates and fuelling volcanic eruptions.

Scientists use seismic waves from earthquakes to 'see' beneath Earth’s surface — the echoes and shadows of these waves reveal radar-like images of deep interior topography. But, until recently, 'images' of the structures at the core-mantle boundary, an area of key interest for studying our planet’s internal heat flow, have been grainy and difficult to interpret.

̽��ֱ��researchers used the latest numerical modelling methods to reveal kilometre-scale structures at the core-mantle boundary. According to co-author Dr Kuangdai Leng, who developed the methods while at the ̽��ֱ�� of Oxford, “We are really pushing the limits of modern high-performance computing for elastodynamic simulations, taking advantage of wave symmetries unnoticed or unused before.” Leng, who is currently based at the Science and Technology Facilities Council, says that this means they can improve the resolution of the images by an order of magnitude compared to previous work.

̽��ֱ��researchers observed a 40% reduction in the speed of seismic waves travelling at the base of the ultra-low velocity zone beneath Hawaii. This supports existing proposals that the zone contains much more iron than the surrounding rocks – meaning it is denser and more sluggish. “It’s possible that this iron-rich material is a remnant of ancient rocks from Earth’s early history or even that iron might be leaking from the core by an unknown means,” said project lead Dr Sanne Cottaar from Cambridge Earth Sciences.

̽��ֱ��research could also help scientists understand what sits beneath and gives rise to volcanic chains like the Hawaiian Islands. Scientists have started to notice a correlation between the location of the descriptively-named hotspot volcanoes, which include Hawaii and Iceland, and the ultra-low velocity zones at the base of the mantle. ̽��ֱ��origin of hotspot volcanoes has been debated, but the most popular theory suggests that plume-like structures bring hot mantle material all the way from the core-mantle boundary to the surface.

With images of the ultra-low velocity zone beneath Hawaii now in hand, the team can also gather rare physical evidence from what is likely the root of the plume feeding Hawaii. Their observation of dense, iron-rich rock beneath Hawaii would support surface observations. “Basalts erupting from Hawaii have anomalous isotope signatures which could either point to either an early-Earth origin or core leaking, it means some of this dense material piled up at the base must be dragged to the surface,” said Cottaar.

More of the core-mantle boundary now needs to be imaged to understand if all surface hotspots have a pocket of dense material at the base. Where and how the core-mantle boundary can be targeted does depend on where earthquakes occur, and where seismometers are installed to record the waves.

̽��ֱ��team’s observations add to a growing body of evidence that Earth’s deep interior is just as variable as its surface. “These low-velocity zones are one of the most intricate features we see at extreme depths – if we expand our search, we are likely to see ever-increasing levels of complexity, both structural and chemical, at the core-mantle boundary,” said Li.

They now plan to apply their techniques to enhance the resolution of imaging of other pockets at the core-mantle boundary, as well as mapping new zones. Eventually they hope to map the geological landscape across the core-mantle boundary and understand its relationship with the dynamics and evolutionary history of our planet.

Reference:
Zhi Li, Kuangdai Leng, Jennifer Jenkins, Sanne Cottaar. 'Kilometer-scale structure on the core–mantle boundary near Hawaii.' Nature Communications (2022), DOI: 10.1038/s41467-022-30502-5

New research led by the ̽��ֱ�� of Cambridge is the first to obtain a detailed 'image' of an unusual pocket of rock at the boundary layer with Earth’s core, some three thousand kilometres beneath the surface.

Of all Earth’s deep interior features, these are the most fascinating and complex

Zhi Li

gnuckx

Etna volcano eruption, 12 January 2011

Yes

Licence type:

Public Domain

Earliest human remains in eastern Africa dated to more than 230,000 years ago

sc604 — Wed, 12 Jan 2022 15:28:02 +0000

̽��ֱ��age of the oldest fossils in eastern Africa widely recognised as representing our species, Homo sapiens, has long been uncertain. Now, dating of a massive volcanic eruption in Ethiopia reveals they are much older than previously thought.