GeoLog

Imaggeo on Mondays

Photo Contest finalists 2017 – who will you vote for?

The selection committee received over 300 photos for this year’s EGU Photo Contest, covering fields across the geosciences. The fantastic finalist photos are below and they are being exhibited in Hall X2 (basement, Brown Level) of the Austria Center Vienna – see for yourself!

Do you have a favourite? Vote for it! There is a voting terminal (also in Hall X2), just next to the exhibit. The results will be announced on Friday 28 April during the lunch break (at 12:15).

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/.

 

Imaggeo on Mondays: Atmospheric gravity waves

Imaggeo on Mondays: Atmospheric gravity waves

From the tiny vibrations which travel through air, allowing us to hear music, to the mighty waves which traverse oceans and the powerful oscillations which shake the ground back and forth during an earthquake, waves are an intrinsic part of the world around us.

As particles vibrate repeatedly, they create an oscillation, which when accompanied by the transfer of energy, creates a wave.  The way in which waves travel varies hugely. Take for instance a ripple in a pond: vibrations there are perpendicular to the direction in which the wave is travelling – transverse waves. When a slinky moves (or sound waves), on the other hand, vibrations happen in the same direction in which the wave travels – longitudinal waves. Ocean waves are more complex. The motion there combines surface waves, created by the friction between wind and surface water, and the energy passing through the water causes it to move in a circular motion. With a little imagination, it’s not so difficult to visualise these different phenomena.

But not all waves on Earth are so intuitive.

Unlike the waves we’ve discussed up until now, internal gravity waves oscillate within a fluid medium, rather than on its surface. In the Earth’s atmosphere, internal gravity waves transfer energy from the troposphere (the layer closest to the Earth’s surface) to the stratosphere (where the ozone layer is found) to the very cold mesosphere, which starts some 50 km away from the planet’s surface. They are usually created at weather fronts: the boundary where two pockets of air at different temperatures and humidity meet. Air flowing over mountains can also generate them.

Because they propagate across layered fluids (the different layers of the atmosphere, for example), internal gravity waves can be responsible for transferring considerable amounts of energy over large distances, which is one of the main reasons why they are important in atmospheric and ocean dynamics.

But only with improved satellite and remote sensing technologies have scientists been able to observe them clearly. Today’s featured image is a great example of one such wave.  It was acquired by the European Space Agency’s Envisat satellite (which aimed to carry out the largest civilian Earth observation mission to date – launched in 2002), on September 16th 2004.

A short animation showing just how impressive these waves are when travelling across the Mozambique Channel – using data from the Meteosat 5 satellite. (Credit: Jorge Magalhaes and Jose da Silva)

The image covers an area of about 580 by 660 km and was acquired as the satellite flew over the Mozambique Channel. The two-dimensional horizontal structure of a very large-scale atmospheric internal wave can be seen in the center of the image travelling southwest. The crest length of the leading wave, in this case, extends for more than 500 km and its crest-to-crest spatial scale is approximately 10 km on average.

It is interesting to note that several (but not all) of these individual waves are made visible by characteristic cloud bands, which form as the vertical oscillations find the necessary conditions (high moisture in the atmosphere) for condensation to occur.

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/.

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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