GeoLog

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This guest post was contributed by a scientist, student or a professional in the Earth, planetary or space sciences. The EGU blogs welcome guest contributions, so if you've got a great idea for a post or fancy trying your hand at science communication, please contact the blog editor or the EGU Communications Officer Laura Roberts Artal to pitch your idea.

Extraordinary iridescent clouds inspire Munch’s ‘The Scream’

Screaming clouds

Edvard Munch’s series of paintings and sketches ‘The Scream’ are some of the most famous works by a Norwegian artist, instantly recognisable and reproduced the world over. But what was the inspiration behind this striking piece of art?

The lurid colours and tremulous lines have long been thought to represent Munch’s unstable state of mind; a moment of terror caught in shocking technicolour. At the same time, scientists have recently identified the connection between the great works of artists such as William Turner and the red and orange sunsets which can be a result of the global impact of volcanic aerosols. However, research presented this week at the European Geosciences Union General Assembly in Vienna by atmospheric scientists in Oslo Norway, suggests that the painting might show us evidence of something much stranger, and rarer – nacreous clouds.

Nacreous or mother-of-pearl clouds, are an extremely rare form of cloud created 20-30km above sea level – in the polar stratosphere when the air is extremely cold (between -80 and -85 degrees centigrade) and exceptionally humid,. So far observed mostly in the Scandinavian countries, these clouds are formed of microscopic and uniform particles of ice, orientated into thin clouds. When the sun is below the horizon (before sunrise or after sunset), these clouds are illuminated in a surprisingly vibrant way blazing across the sky in swathes of red, green, blue and silver. They have a distinctive wavy structure as the clouds are formed in the lee-waves behind mountains.

In 2014, these clouds were seen again over the skies of Oslo and given their extreme colouration and unexpected appearance, a photographer, Svein Fikke, immediately thought of Munch’s work. This perceived similarity between the mother of pearl clouds and the striking clouds and sense of tension in the painting is only reinforced when reading Munch’s writings about his experiences on the day that inspired the painting.

“I went along the road with two friends – the sun set

I felt like a breath of sadness –

– The sky suddenly became bloodish red

I stopped, leant against the fence, tired to death – watched over the

Flaming clouds as blood and sword

The city – the blue-black fjord and the city

– My friends went away – I stood there shivering from dread – and

I felt this big, infinite scream through nature”

                            Edvard Munch’s Diary Notes 1890-1892 (Tøjner and Gundersen, 2013)

Scientists have, in the past, used artworks to infer environmental conditions; from paintings of the ‘frost fairs’ held on the River Thames that show the gradual environmental change in Europe, to the discovery that several artists depict the influence of volcanic aerosols on global atmosphere in their paintings.

In a study conducted in 2007 (and 2014), scientists found that the visible impact that volcanic aerosols have on the atmosphere has in fact been recorded in the works of many of the great masters – particularly William Turner (Zerefos et al, 2007)). Several of Turner’s paintings depict sunsets with a distinct red/orange hue, distinct from his usual work of other years. This was correlated with significant volcanic eruptions in the same time period and the researchers found that these reddish paintings were all created in the years of, or immediately following, a major eruption (shown in the graph below).

Graph to show the relationship between colour and volcanic aerosols (a)The mean annual value of R/G measured on 327 paintings. (b)The percentage increase from minimum R/G value shown in (a). (c)The corresponding Dust Veil Index (DVI). The numbered picks correspond to different eruptions as follows: 1. 1642 (Awu, Indonesia-1641), 2. 1661 (Katla, Iceland-1660), 3. 1680 (Tongkoko and Krakatau, Indonesia-1680), 4. 1784 (Laki, Iceland-1783), 5. 1816 (Tambora, Indonesia-1815), 6. 1831 (Babuyan, Philippines-1831), 7. 1835 (Coseguina, Nicaragua-1835). 8. 1883 (Krakatau, Indonesia-1883). From Zerefos et al (2007).

For many years ‘The Scream’ was thought to also show the influence of a volcanic eruption, most likely the catastrophic eruption of Krakatoa in 1883 (described here by Volcanologist David Pyle), but whereas volcanic skies tend to tint the whole sky a red/orange, the skies in the scream have a distinct pattern, only seen in these extremely rare nacreous clouds.

How rare are they? Well, researcher Dr Helene Muri, a researcher based at the University of Oslo, who presented the research at the press conference, said that in her lifetime living mostly in Norway as an atmospheric researcher she has only seen them once. And what about Munch’s feeling of dread and ‘breath of sadness’?

Well, having a glowing swathe of iridescent petrol coloured clouds flare into bright relief after sunset, only for them to disappear 30 minutes later would be pretty shocking for any of us, even in our modern days of fluorescent streetlamps and light polluted skies.

By Hazel Gibson, EGU Press Assistant at the EGU 2017 General Assembly

Imaggeo on Mondays: In the belly of the beast

In the belly of the beast . Credit: Alexandra Kushnir (distributed via imaggeo.egu.eu)

Conducting research inside a volcanic crater is a pretty amazing scientific opportunity, but calling that crater home for a week might just be a volcanologist’s dream come true, as Alexandra postdoctoral researcher at the Institut de Physique du Globe de Strasbourg, describes in this week’s Imaggeo on Mondays.

This picture was taken from inside the crater of Mount St Helens, a stratovolcano in Washington State (USA). This particular volcano was made famous by its devastating explosive eruption in 1980, which was triggered by a landslide that removed most of the volcano’s northern flank.

Between 2004 and 2008 Mount St Helens experienced another type of eruption – this time effusive (where lava flowed out of the volcano without any accompanying explosions). Effusive eruptions produce lava flows that can be runny (low-viscosity) like the flows at Kilauea (Hawaii) or much thicker (high viscosity) like at Mount St Helens. Typically, high viscosity lavas can’t travel very far, so they begin to clump up in and around the volcano’s crater forming dome-like structures.  Sometimes, however, the erupting lava can be so rigid that it juts out of the volcano as a column of rock, known as a spine.

The 2004 to 2008 eruption at Mount St Helens saw the extrusion of a series of seven of these spines. At the peak of the eruption, up to 11 meters of rock were extruded per day. As these columns were pushed up and out of the volcanic conduit – the vertical pipe up which magma moves from depth to the surface – they began to roll over, evoking images of whales surfacing for air.

‘Whaleback’ spines are striking examples of exhumed fault surfaces – as these cylinders of rock are pushed out of the volcano their sides grind against the inside of the volcanic conduit in much the same way two sides of a fault zone move and grind past each other. These ground surfaces can provide scientists with a wealth of information about how lava is extruded during eruption. However, spines are generally unstable and tend to collapse after eruption making it difficult to characterize their outer surfaces in detail and, most importantly, safely.

Luckily, Mount St Helens provided an opportunity for a group of researchers to go into a volcanic crater and characterise these fault surfaces. While not all of the spines survived, portions of at least three spines were left intact and could be safely accessed for detailed structural analysis. These spines were encased in fault gouge – an unconsolidated layer of rock that forms when two sides of a fault zone move against one another – that was imprinted with striations running parallel to the direction of extrusion, known as slickensides. These features can give researchers information about how strain is accommodated in the volcanic conduit. The geologist in the photo (Betsy Friedlander, MSc) is measuring the dimensions and orientations of slickensides on the outer carapace of one of the spines; the southern portion of the crater wall can be seen in the background.

Volcanic craters are inherently changeable places and conducting a multi-day field campaign inside one requires a significant amount of planning and the implementation of rigorous safety protocols. But above all else, this type of research campaign requires an acquiescent mountain.

Because a large part of Mount St Helens had been excavated during the 1980 eruption, finding a safe field base inside the crater was possible. Since the 2004-2008 deposits were relatively unstable, the science team set up camp on the more stable 1980-1986 dome away from areas susceptible to rock falls and made the daily trek up the eastern lobe of the Crater Glacier to the 2004-2008 deposits.

Besides being convenient, this route also provides a spectacular tableau of the volcano’s inner structure with its oxidized reds and sulfurous yellows. The punctual peal of rock fall is a reminder of the inherent instability of a volcanic edifice, and the peculiar mix of cold glacier, razor sharp volcanic rock, and hot magmatic steam is otherworldly. That is, until an errant bee shows up to check out your dinner.

By Alexandra Kushnir, postdoctoral researcher at the Institut de Physique du Globe de Strasbourg, France.

This photo was taken in 2010 while A. Kushnir was a Masters student at the University of British Columbia and acting as a field assistant on the Mount St Helens project.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

 

Knowing the ocean’s twists and turns

Knowing the ocean’s twists and turns

Navigating the ocean demands a knowledge of its movements. In the past, sailors have used this knowledge to their advantage, following the winds and the ocean currents to bring them on their way.

Prior to mutiny in 1789, Captain Bligh – on the HMS Bounty – famously spent a month attempting to pass westward through the Drake Passage, around Patagonia’s Cape Horn. Here the westerly winds were strong (as they are today) and drove the waters hard against the ship as it persisted against the flow. But they could not pass, and were forced to reach the Pacific by crossing back south of Africa, through the Indian Ocean, costing the mission many months.

It is the winds which predominantly drive the currents at the ocean’s surface. Depending on where you are on the planet, the winds blow in a variety of prevailing directions, exerting control over the surface of the oceans, over which they roll. Where the Earth’s westerlies prevail (moving eastwards, between the 30 to 60 degree latitude belt, in both hemispheres) we encounter some of the world’s fastest currents, including the Atlantic’s Gulf Stream, and the Kuroshio Current off Japan. These currents bring with them huge amounts of heat from tropical and subtropical areas; which is why Western Europe experiences much milder winters than other regions at similar latitudes (think Newfoundland, for example).

Also under the influence of the westerly winds is the world’s largest ocean current, the Antarctic Circumpolar Current, which circles Antarctica in the southern hemisphere. The Antarctic Circumpolar Current lies under the influence of the infamous Roaring Forties, Furious Fifties, and Screaming Sixties westerly wind bands, and acted as a major stretch along the historical clipper route between Europe, Australia, and New Zealand in the 19th century.

The trade winds (also known as the easterlies, circling the Earth between 0 and 30 degrees latitude, in both hemispheres) are typically weaker than the westerlies, but sufficiently strong to have enabled European expansion into the Americas over the centuries. The trades drive ocean currents such as the Canary Current and North Equatorial Current in the Atlantic Ocean, and the California Current and North Equatorial Current in the Pacific.

Also within these latitudes – particularly near the equator – are the doldrums, which are areas characterised by weak or non-existent winds. These regions became well known in the past as sailors were regularly stranded whilst crossing equatorial regions – immobile for days or weeks, resting in seas of calm – awaiting the winds to pick up and move them onwards.

As well as at the surface, the ocean is moving in its interior, with large scale sinking to depths of over 4000 meters in cold polar regions, and upwelling in the warmer tropics and subtropics. The ocean turns over on itself like a bathtub of water heated unevenly from above. Below the surface the deep waters move slowly (centimeters per second, rather than meters per second at the surface), mostly unaffected by wind. Here huge ocean scale water masses move (largely) because of density differences between regions, determined by variations in heat and salinity (salt content). Cold, salty water is dense, and sinks, while warmer water rises.

This large-scale overturning, which characterizes the movement of the world’s ocean as a whole, is known as the global conveyor belt, or the thermohaline circulation (thermo for heat, and haline for salt). Along the conveyor it takes thousands of years for water masses to complete a cycle around the planet.

But like many other features of our Earth system, it is now thought that the behaviour of the ocean’s circulation is beginning to change. Back at the surface oceanographers now expect that ocean currents will undergo substantial change in response to anthropogenic global warming. Computer simulations of the ocean and atmosphere are used to predict whether certain wind systems will strengthen or weaken in the future, and to look at the effect this might have on the underlying ocean currents.

We know from historical evidence that the strength of the ocean’s currents has varied in the past, so this coming century we can expect some changes along our ocean routes; an obvious and well highlighted example being the opening of commercial routes in the new ice-free Arctic.

Whatever the nature of the future ocean, modern technology including real-time satellite-sourced ocean data, and advanced ocean weather and wave forecasts, will allow us to constantly track changes, so that no matter the winds or current speeds, we should always be able to get where we’re going.

By Conor Purcell is a Science and Nature Writer with a PhD in oceanography.

Conor is based in Dublin, Ireland, and can be found on twitter @ConorPPurcell, with some of his other articles at cppurcell.tumblr.com. He is also the founder-editor at www.wideorbits.com.

Imaggeo On Mondays: Halo

Imaggeo On Mondays: Halo

One of the main perks of being a geoscientist is that, often, research takes scientists all around the globe to conduct their work. While fieldwork can be hard and challenging it also offers the opportunity to see stunning landscapes and experiencing unusual phenomenon. Aboard the Akademik Tryoshnikov research vessel, while cruising the Kara Sea (part of the Arctic Ocean north of Siberia) Tatiana Matveeva was witness to an interesting optical phenomenon, a halo. In today’s post she tells us more about how the elusive halos form and how best to spot them.

It was one of many mornings on the Kara Sea, but the sunrise was very unusual – we saw halo. Because more often than not, the skies over the Arctic seas are covered in cloud, we were very lucky to see a halo!

Halos are produced by ice crystals trapped in thin and wispy cirrus or cirrostratus clouds, which form high (5–10 km) in the upper troposphere. The hexagon ice crystals behave like prisms and mirrors, refracting and reflecting sunlight between their faces, sending shafts of light in different directions.

Halos can have many forms, ranging from colored or white rings to arcs in the sky. The particular shape and orientation of the ice crystals is responsible for the type of halo observed. For example, halos may be due to the refraction of light that passes through the crystals or the reflection of light from crystal faces or a combination of both effects. Refraction effects give rise to colour separation because of the slightly different bending of the different colours composing the incident light as it passes through the crystals. On the other hand, reflection phenomena are whiteish in colour, because the incident light is not broken up into its component colours, each wavelength being reflected at the same angle. The most common halo is circular halo (sometimes called 22° halo) with the Sun or Moon at its centre. The order of coloration is red on the inside and blue on the outside, you can see it in this picture.

Historically, halos were used as an empirical means of weather forecasting before meteorology was developed.

Anecdotally, in the Anglo-Cornish dialect of English, a halo around the Sun or the Moon is called a ‘cock’s eye’ and is a token of bad weather. The term is related to the Breton word kog-heol (sun cock) which has the same meaning. In Nepal, a halo around the sun is called Indrasabha – the Hindu god of lightning, thunder and rain.

To see a halo, don’t look directly into the sun. Block the sun from your view with your hand, so you can just see the clouds around it. And enjoy beautiful optical phenomenon!

By Tatiana Matveeva, researcher at the Moscow State University

 

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

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