̽��ֱ�� of Cambridge - ̽��ֱ�� of Geneva

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

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Volcanic eruption influenced Iceland’s conversion to Christianity

sc604 — Mon, 19 Mar 2018 00:48:16 +0000

A team of scientists and medieval historians, led by the ̽��ֱ�� of Cambridge, has used information contained within ice cores and tree rings to accurately date a massive volcanic eruption, which took place soon after the island was first settled.

Having dated the eruption, the researchers found that Iceland’s most celebrated medieval poem, which describes the end of the pagan gods and the coming of a new, singular god, describes the eruption and uses memories of it to stimulate the Christianisation of Iceland. ̽��ֱ��results are reported in the journal Climatic Change.

̽��ֱ��eruption of the Eldgjá in the tenth century is known as a lava flood: a rare type of prolonged volcanic eruption in which huge flows of lava engulf the landscape, accompanied by a haze of sulphurous gases. Iceland specialises in this type of eruption – the last example occurred in 2015, and it affected air quality 1400 kilometres away in Ireland.

̽��ֱ��Eldgjá lava flood affected southern Iceland within a century of the island’s settlement by Vikings and Celts around 874, but until now the date of the eruption has been uncertain, hindering investigation of its likely impacts. It was a colossal event with around 20 cubic kilometres of lava erupted – enough to cover all of England up to the ankles.

̽��ֱ��Cambridge-led team pinpointed the date of the eruption using ice core records from Greenland that preserve the volcanic fallout from Eldgjá. Using the clues contained within the ice cores, the researchers found that the eruption began around the spring of 939 and continued at least through the autumn of 940.

“This places the eruption squarely within the experience of the first two or three generations of Iceland’s settlers,” said first author Dr Clive Oppenheimer of Cambridge’s Department of Geography. “Some of the first wave of migrants to Iceland, brought over as children, may well have witnessed the eruption.”

Once they had a date for the Eldgjá eruption, the team then investigated its consequences. First, a haze of sulphurous dust spread across Europe, recorded as sightings of an exceptionally blood-red and weakened Sun in Irish, German and Italian chronicles from the same period.

Then the climate cooled as the dust layer reduced the amount of sunlight reaching the surface, which is evident from tree rings from across the Northern Hemisphere. ̽��ֱ��evidence contained in the tree rings suggests the eruption triggered one of the coolest summers of the last 1500 years. “In 940, summer cooling was most pronounced in Central Europe, Scandinavia, the Canadian Rockies, Alaska and Central Asia, with summer average temperatures 2°C lower,” said co-author Professor Markus Stoffel from the ̽��ֱ�� of Geneva’s Department of Earth Sciences.

̽��ֱ��team then looked at medieval chronicles to see how the cooling climate impacted society. “It was a massive eruption, but we were still amazed just how abundant the historical evidence is for the eruption’s consequences,” said co-author Dr Tim Newfield, from Georgetown ̽��ֱ��’s Departments of History and Biology. “Human suffering in the wake of Eldgjá was widespread. From northern Europe to northern China, people experienced long, hard winters and severe spring-summer drought. Locust infestations and livestock mortalities occurred. Famine did not set in everywhere, but in the early 940s we read of starvation and vast mortality in parts of Germany, Iraq and China.”

“ ̽��ֱ��effects of the Eldgjá eruption must have been devastating for the young colony on Iceland – very likely, land was abandoned and famine severe,” said co-author Professor Andy Orchard from the ̽��ֱ�� of Oxford’s Faculty of English. “However, there are no surviving texts from Iceland itself during this time that provide us with direct accounts of the eruption.”

But Iceland’s most celebrated medieval poem, Vǫluspá (‘ ̽��ֱ��prophecy of the seeress’) does appear to give an impression of what the eruption was like. ̽��ֱ��poem, which can be dated as far back as 961, foretells the end of Iceland’s pagan gods and the coming of a new, singular god: in other words, the conversion of Iceland to Christianity, which was formalised around the turn of the eleventh century.

Part of the poem describes a terrible eruption with fiery explosions lighting up the sky, and the Sun obscured by thick clouds of ash and steam:

“ ̽��ֱ��sun starts to turn black, land sinks into sea; the bright stars scatter from the sky.
Steam spurts up with what nourishes life, flame flies high against heaven itself.”

̽��ֱ��poem also depicts cold summers that would be expected after a massive eruption, and the researchers link these descriptions to the spectacle and impacts of the Eldgjá eruption, the largest in Iceland since its settlement.

̽��ֱ��poem’s apocalyptic imagery marks the fiery end to the world of the old gods. ̽��ֱ��researchers suggest that these lines in the poem may have been intended to rekindle harrowing memories of the eruption to stimulate the massive religious and cultural shift taking place in Iceland in the last decades of the tenth century.

“With a firm date for the eruption, many entries in medieval chronicles snap into place as likely consequences – sightings in Europe of an extraordinary atmospheric haze; severe winters; and cold summers, poor harvests; and food shortages,” said Oppenheimer. “But most striking is the almost eyewitness style in which the eruption is depicted in Vǫluspá. ̽��ֱ��poem’s interpretation as a prophecy of the end of the pagan gods and their replacement by the one, singular god, suggests that memories of this terrible volcanic eruption were purposefully provoked to stimulate the Christianisation of Iceland.”

Reference:
Clive Oppenheimer et al “ ̽��ֱ��Eldgjá eruption: timing, long-range impacts and influence on the Christianisation of Iceland.” Climatic Change (2018). DOI: 10.1007/s10584-018-2171-9

Inset image: Codex Regius, which contains a version of the Vǫluspá.

Memories of the largest lava flood in the history of Iceland, recorded in an apocalyptic medieval poem, were used to drive the island’s conversion to Christianity, new research suggests.

With a firm date for the eruption, many entries in medieval chronicles snap into place as likely consequences.

Clive Oppenheimer

Eldgjá fissure in southern Iceland

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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Exoplanet hunter: in search of new Earths and life in the Universe

lw355 — Mon, 15 Feb 2016 09:59:48 +0000

When the numbers began to filter through from the spectrograph that was measuring small shifts in light from distant stars, Didier Queloz at first thought they were wrong. He certainly didn’t think he’d discovered an exoplanet. He checked and re-checked.

“At some point I realised the only explanation could be that the numbers were right.”

Today, many regard the discovery of 51 Pegasi b by Queloz and Professor Michel Mayor at the ̽��ֱ�� of Geneva in 1995 as a moment in astronomy that forever changed the way we understand the universe and our place within it. It was the first confirmation of an exoplanet – a planet that orbits a star other than our Sun. Until then, although astronomers had speculated as to the existence of these distant worlds, no planet other than those in our own solar system had ever been found.

“For centuries, we only had the one single example of our own solar system on which to base our knowledge of planets,” says Queloz, who moved to Cambridge’s Department of Physics two years ago. “If you wanted to understand botany, you wouldn’t build the botanic picture from one single flower – you need all the others.”

Of the 1,900 or so confirmed exoplanets that have now been found – a tenth of these by Queloz himself – many are different to anything we ever imagined, challenging existing theories of planet formation.

Fifty light years from Earth, the exoplanet 51 Peg resembles the gas giant Jupiter. But unlike our distant cousin, which is located in the further reaches of our solar system and takes 10 years to orbit the Sun, 51 Peg ‘hugs’ its sun, orbiting every four days. It’s been hailed as an example of a whole new class of ‘roaster planets’ or ‘Hot Jupiters’ and has prompted scientists to wonder if large planets are able to migrate closer to their suns over millions of years.

“We are constantly surprised by the diversity of the other worlds,” says Queloz. Super-Earths like the volcanic planet 55 Cancri e with a temperature gradient across it of a thousand degrees; rogue planets like PSO J318.5-22, which roam freely between stars; Kepler-186f, which is lit by the light of a red star; and icy Kepler-16b with its double sunset. “For some, we don’t even have names to describe what they are.”

But, as yet, no planet has been discovered that could be considered a twin of our own. “We are finding planets of a similar size and mass to Earth but nothing at the right temperature – so-called Goldilocks planetary systems in the habitable zone close enough to the sun to be warmed by it but not so close that the presence of water and life is a sheer impossibility,” explains Queloz.

“Of course the question everyone would like to answer is whether there is life out there, because we are curious and we can’t resist – it’s how we are,” says Queloz.

Queloz believes that a new era of terra hunting is fast approaching. “ ̽��ֱ��past 20 years has seen a ‘brute force’ hunt for exoplanets. We are now confident that they are practically everywhere you look for them. To find an Earth twin, however, we need to look at specific planets for longer.”

It’s not possible to see an exoplanet directly – it’s far too close to a blinding source of light, its star – so astronomers use two techniques to look indirectly. Focusing on a star, they use NASA’s Kepler telescope to look for the dimming of starlight as the planet transits in front of it. From this, they calculate the planet’s size and temperature.

̽��ֱ��breakthrough that Queloz and Mayor pioneered was a technique to look for signs of ‘wobble’ caused by the gravitational pull exerted by the planet on the star as it orbits. ̽��ֱ��technique needed to be accurate enough to detect a wobble of only 10 m/s – the speed of a running man. To put this in context, the Earth moves at the speed of 30,000 m/s.”

Current technology works well for finding large exoplanets but to find planets the size of the Earth in the habitable zone astronomers need to look at smaller stars, and they need to overcome ‘stellar noise’, or natural variability in the data caused by physical motions of gas at the surface of the star.

“This noise is slowing further progress but we believe that it can be overcome by careful analysis and by extending the length of time we are able to observe a planet for,” adds Queloz. “Intensive runs on a small number of stars where an observation is carried out every night for years is far more valuable than unevenly spaced data taken over years.”

As techniques improve and with the launch of NASA's James Webb Space Telescope, astronomers will be able to ask whether what we understand as the basic molecules of life – carbon, oxygen and hydrogen – are present in the atmosphere of exoplanets, opening up the possibility of understanding their astrobiology and geophysics.

“My feeling is that life will be found, although life like us may be extremely rare because otherwise we probably would have seen it by now,” he adds. “It may take a long time, and many scientists, to find life, but maybe that’s part of the fun – it would be too easy otherwise!”

On the door of Queloz’s office is a spoof poster published by NASA in celebration of 20 years of exoplanet discoveries. Offering greetings from the Exoplanet Travel Bureau, it suggests 51 Pegasi b as a dream destination, or indeed “any planet you wish – as long as it’s far beyond our solar system.” Could this be reality one day? “It’s far too hard to say,” says Queloz. “But I would hope that sending a tiny probe of perhaps a few grams in weight might be possible in the next century.”

At one stage in recent years, Queloz was almost finding an exoplanet a week. His terra hunting has slowed while he focuses on improving the equipment and techniques that he believes will help find an Earth twin. But the excitement never goes away, he says. “I must admit that every time I find a planet I feel like a child – it’s a surprise because it’s a new system. I used to joke with people asking me about sci-fi – the reality is far more exciting and diverse than any sci-fi movie you can imagine!”

Inset images: top: Didier Queloz; bottom: 'travel' poster by NASA /JPL-Caltech

Other worlds: Professor Didier Queloz and Dr William Bains consider what life might be like under the light of other suns at the Cambridge Science Festival on 17 March 2016

In 1995, in Geneva, PhD student Didier Queloz discovered a planet orbiting another sun – something that astronomers had predicted, but never found. Today he continues his terra hunting for extreme worlds and Earth twins in Cambridge.

We are constantly surprised by the diversity of the other worlds.

Didier Queloz

Exoplanet Hunter: In search of new Earths and life in the Universe

ESO/L. Calçada

Artist’s impression of a super-Earth exoplanet orbiting its nearby star

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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Increase in volcanic eruptions at the end of the ice age caused by melting ice caps and glacial erosion

sc604 — Tue, 02 Feb 2016 06:00:00 +0000

̽��ֱ��combination of erosion and melting ice caps led to a massive increase in volcanic activity at the end of the last ice age, according to new research. As the climate warmed, the ice caps melted, decreasing the pressure on the Earth’s mantle, leading to an increase in both magma production and volcanic eruptions. ̽��ֱ��researchers, led by the ̽��ֱ�� of Cambridge, have found that erosion also played a major role in the process, and may have contributed to an increase in atmospheric carbon dioxide levels.

“It’s been established that melting ice caps and volcanic activity are linked – but what we’ve found is that erosion also plays a key role in the cycle,” said Dr Pietro Sternai of Cambridge’s Department of Earth Sciences, the paper’s lead author, who is also a member of Caltech’s Division of Geological and Planetary Science. “Previous attempts to model the huge increase in atmospheric CO₂ at the end of the last ice age failed to account for the role of erosion, meaning that CO₂ levels may have been seriously underestimated.”

Using numerical simulations, which modelled various different features such as ice caps and glacial erosion rates, Sternai and his colleagues from the ̽��ֱ�� of Geneva and ETH Zurich found that erosion is just as important as melting ice in driving the increase in magma production and subsequent volcanic activity. ̽��ֱ��results are published in the journal Geophysical Research Letters.

Although the researchers caution not to draw too strong a link between anthropogenic (human-caused) climate change and increased volcanic activity as the timescales are very different, since we now live in a period where the ice caps are being melted by climate change, they say that the same mechanism will likely work at shorter timescales as well.

Over the past million years, the Earth has gone back and forth between ice ages, or glacial periods, and interglacial periods, with each period lasting for roughly 100,000 years. During the interglacial periods, such as the one we live in today, volcanic activity is much higher, as the lack of pressure provided by the ice caps means that volcanoes are freer to erupt. But in the transition from an ice age to an interglacial period, the rates of erosion also increase, especially in mountain ranges where volcanoes tend to cluster.

Glaciers are considered to be the most erosive force on Earth, and as they melt, the ground beneath is eroded by as much as ten centimetres per year, further decreasing the pressure on the volcano and increasing the likelihood of an eruption. A decrease in pressure enhances the production of magma at depth, since rocks held at lower pressure tend to melt at lower temperatures.

When volcanoes erupt, they release more carbon dioxide into the atmosphere, creating a cycle that speeds up the warming process. Previous models that attempted to explain the increase in atmospheric CO₂ during the end of the last ice age accounted for the role of deglaciation in increasing volcanic activity, but did not account for erosion, meaning that CO₂ levels may have been significantly underestimated.

A typical ice age lasting 100,000 years can be characterised into periods of advancing and retreating ice – the ice grows for 80,000 years, but it only takes 20,000 years for that ice to melt.

“There are several factors that contribute to climate warming and cooling trends, and many of them are related to the Earth’s orbital parameters,” said Sternai. “But we know that much faster warming that cooling can’t be caused solely by changes in the Earth’s orbit – it must be, at least to some extent, related to something within the Earth system itself. Erosion, by contributing to unload the Earth’s surface and enhance volcanic CO₂ emissions, may be the missing factor required to explain such persistent climate asymmetry.”

Reference:
Pietro Sternai et al. ‘Deglaciation and glacial erosion: a joint control on magma productivity by continental unloading.’ Geophysical Research Letters (2016). DOI: 10.1002/2015GL067285

Inset image: 3D model simulation of a glaciation on the Villarrica Volcano (Chile). Credit: Pietro Sternai

Researchers have found that glacial erosion and melting ice caps both played a key role in driving the observed global increase in volcanic activity at the end of the last ice age.

It’s been established that melting ice caps and volcanic activity are linked – but what we’ve found is that erosion also plays a key role in the cycle.

Pietro Sternai

Matthew.landry at English Wikipedia

Arenal Volcano in November 2006

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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