GeoLog

Geochemistry, Mineralogy, Petrology & Volcanology

Studying an active volcano – in pictures

Studying an active volcano – in pictures

Santiaguito volcano in Guatemala is one of the most active volcanoes in Central America: currently erupting every 45-90 mintues, from its active lava dome Caliente, while at the same time sending a lava flow down its flanks. This makes it an ideal study object for volcanology. A group of volcanologists from the University of Liverpool, in the UK, installed a network of geophysical stations around the volcano in November 2014, (you can find out more about that trip here). They’ve since been back to Guatemala to download the data recorded by the stations and carry out some maintenance. This photo diary blog post, by Felix Von-Aulock, a postdoctoral researcher at the University of Liverpool, gives a snap shot of what it is like to carry out research on an active volcano: it’s challenging, packed full of adventure and rewarding in equal mesure!

Image credit: Felix Von-Aulock

Image credit: Felix Von Aulock

The Institute for Seismology, Volcanology, Meteorology and Hydrology (INSIVUMEH) are working hard to deliver updates on the activity of at least 3 erupting volcanoes to public, governmental bodies, and scientists. They do a really good job, despite the constant lack of funding, personel and equipment. This is our first stop on our way to Santiaguito, picking up equipment we left here last time, and catching up with Gustavo Chigna, a volcanolgist at INSIVUMEH.

Image credit: Felix Von-Aulock

Image credit: Felix Von Aulock

A few hours drive from Guatemala City, we finally see our destination, the Cerro Quemado/ Almolonga complex, with Santa Maria volcano (the tallest peak) in the background.

Image credit: Felix Von-Aulock

Image credit: Felix Von Aulock

It’s not all about the science! Guatemala is one of the biggest producers of coffee in the world and a lot of the volcanoes are surrounded by coffee plantations.

Image credit: Felix Von-Aulock

Image credit: Felix Von Aulock

While the volcanoes produce very fertile soils for the coffee to grow on, they can be very destructive. This farm at the base of Santiaguito has faced major hazards from lahars – torrents of hot or cold water, laden with rock fragments, ash and other volcaninc debris which hurtle down the flank of a volcano or valley following an eruption.

Image credit: Felix Von-Aulock

Image credit: Felix Von Aulock

The canyons fromed by the lahars cut right through the farm and the workers’ homes.

Image credit: Felix Von-Aulock

Image credit: Felix Von Aulock

Another hazard faced by the local communities is that posed by pyroclastic flows: high-density mixtures of hot, dry rock fragments and hot gases that move away from an eruptive volcaninc vent (as defined by the USGS).
Pictured above is the flow path of the pyroclastic flow of May 2014. The  flow paved the way for many Lahars which formed this canyon. The pyroclastic flow also nearly wiped out the volcano observatory and missed it only by 20m.

Image credit: Felix Von-Aulock

Image credit: Felix Von Aulock

In total we deployed 11 stations around the volcano. This trip’s main purpose was to maintain them and download the data aquired since they were installed in November 2014. We were excited to find that the first station we visited had actually been recording data until the week before we arrived. We were less excited to discover that bean plants were being planted right next to it, possibly leading to some ploughing noise in our data.

Image credit: Felix Von-Aulock

Image credit: Felix Von Aulock

Our room, three hours after our arrival. The chaos didn’t vanish, however, the smell got increasingly bad after 2 weeks of three guys sharing this room. Amongst the chaos, lots of expensive equipment and a kitten!

Image credit: Felix Von-Aulock

Image credit: Felix Von Aulock

After sorting out supplies and taking care of the stations at the base of the volcano in Quetzeltenango, we finally started our hike towards the active dome. While we (Felix Von-Aulock, pictured in the far right and Adrian Hornby, a volcanology PhD student, picture in the centre) went down towards Santiaguito Dome, Oliver, also volcanology PhD student, (pictured second from the right),  went to the top of Santa Maria to film with a thermal camera. Don Geronimo, on the far left, is a local who helped Oliver carry equipment and water to the 3700m high peak. Armando Pineda (second f. l) was our guide down the tricky path to the dome.

Image credit: Felix Von-Aulock

Image credit: Felix Von Aulock

It feels good to be finally walking after weeks of preparation and travelling, despite the packs being pretty heavy and the long day ahead of us.

Image credit: Felix Von-Aulock

Image credit: Felix Von Aulock

The first two days were hard work: a constant mix of rain and sun, heavy packs we were not quite used to yet and some extra walks made us feel sore pretty quickly.

Image credit: Felix Von-Aulock

Image credit: Felix Von Aulock

When there was rain, the sun would come out quickly thereafter and the beautiful surrounding made up for the hard work.

Image credit: Felix Von-Aulock

Image credit: Felix Von Aulock

A morning view from our campsite below the chain of domes that was formed during the last century. The riverbed below had a pretty decent river in it just the night before during a thunderstorm. We got caught by that thunderstorm, trying to move car batteries uphill, but luckily decided to turn around to the tent before the river and potential lahars would cross our route.

Image credit: Felix Von-Aulock

Image credit: Felix Von-Aulock

The valley that leads to the active dome (Agua de Caliente) is an always changing channel, washed out by the frequent lahars. Good to have an experienced guide like Armando with us.

Image credit: Felix Von-Aulock

Image credit: Felix Von Aulock

The combination of a thin layer of ash and the frequent rain made some sections a bit tricky with the heavy packs.

Image credit: Felix Von-Aulock

Image credit: Felix Von Aulock

Here we’re digging out the first station, from here on we need to wear helmets as we’re about 300m from the active dome.

Image credit: Felix Von-Aulock

Image credit: Felix Von Aulock

The stations combine measurements of the sound (infrasound), the volcano’s seismicity and the tilt of the flanks of the volcano.

Image credit: Felix Von-Aulock

Image credit: Felix Von Aulock

The volcano is erupting frequently and every hour or so, we can see an ash plume rising into the sky above our heads.

Image credit: Felix Von-Aulock

Image credit: Felix Von Aulock

An eruption of the lava dome of Santiaguito observed from our tent around 300m from the crater.

Image credit: Felix Von-Aulock

Image credit: Felix Von Aulock

We also brought along a little quadcopter to take pictures of the dome. And although it was not the main subject of our mission it proved quite successful (we didn’t crash it!) Trying to follow a tiny spot in the sky is not easy though. And I just kept thinking:

“This must be one of the best jobs in the world, flying a little helicopter over an active volcano!”

By Felix Von Aulock , Postdoctoral researcher at the University of Liverpool

We are grateful to Rüdiger Escobar-Wolf for helping us improve an earlier version of this blog post.

Do you have some stunning field work photographs that you’d like to share with the wider community? Why not upload them to the EGU’s online open access geosciences image repository, Imaggeo? 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/

Field work is an intrinsic part of the geosciences and yet the stories behind data aquisition are often left untold in scientific publlications. If you’d like to share your field work and/or lab tales, we’d love to hear from you! Part of what makes GeoLog a great read is the variety that guest posts add to our regular features, and we welcome contributions from scientists, students and professionals in the Earth, planetary and space sciences. Got an idea? If you would like to contribute to GeoLog, please send a short paragraph detailing your idea to the EGU Communications Officer, Laura Roberts  at roberts@egu.eu.

 

Imaggeo on Mondays: A fold belt within a grain

Imaggeo on Mondays: A fold belt within a grain

Tiny crinkly folds form the main basis of today’s Imaggeo on Mondays. Folding can occur on a number of scales; studying folds at all scales can reveal critical information about how rocks behave when they are squeeze and pinched, as described by Sina Marti, from the University of Basel.

Although many geoscientists have seen such fold structures many times before, if you noticed the scale bar in the lower left of the image, you might be surprised of the small scale of these folds!

The presented image is a high-magnification image taken on an electron microscope, showing sub-micrometer scale folds developed within a deformed pyroxene grain – a chain silicate mineral, for example common in the oceanic crust of the earth. The folded layers are primary exsolution lamellae of more calcium rich and calcium poor chemical composition. These lamellae formed during the early, magmatic history of the pyroxene grain, where it crystallized and cooled down in a shallow intrusion. The folding subsequently took place during deformation and the following text will try to give a short overview on why and how these folds have formed.

The presented image was made using a back-scattered electron (BSE) detector, where different grey values indicate different chemical compositions. This effect originates from the fact, that some of the electrons, which “bombard” the sample in the electron microscope, are back scattered by the atoms near the sample surface and then detected by the BSE. Heavier atoms (with a greater atomic number, Z) have a higher probability to generate a backscattered electron. Consequently, where heavy atoms occur, more backscattered electrons reach the detector and the area appears bright, compared to dark- appearing areas, where light atoms prevail. Because of this sensitivity of the BSE image on chemical composition, we can see the exsolution lamellae in the pyroxene with different grey values.

Although the folds in this image occur on the nanometer- to micrometer scale, their geometry and mode of formation is the same as is observed in large-scale fold belts (e.g. the Helvetic nappes in the Swiss Alps). There, this fold type develops mainly in layered sediments, which have contrasting properties: alternating series of competent and incompetent layers leads to boundary instabilities and thus to folding. In the present case, the contrasting properties of the layers – also known as anisotropy – is a result of the formation of the exsolution lamellae and enables folding even at the very small scales seen within this single grain. One can even see the difference between the layers in the image: The darker lamellae change their layer thickness more readily (best seen in fold hinges – the place of strongest bend in the fold) than the brighter layers, indicating that the darker layers deform more easily..

This folded pyroxene is an astonishing example that certain processes, which generate geological structures, operate over multiple orders of magnitude in scale. Without a scale bar provided, it would not be possible to determine the scale of these structures and tell them apart from folds formed in outcrop or even on larger scales. Now, it should not be confused: such a pyroxene grain will not be encountered in the same tectonic regime as large-scale fold belts. But exactly for this reason, it is a beautiful example displaying the overall controlling importance of anisotropy over most other material properties, independent of scale. For the deformation of rocks, anisotropy almost always plays a key role in the deformability, and in general controls the development of structures such as folds like in the present case.

By Sina Marti, Department of Environmental Science, Geological Institute, Basel

Sina would like to thank  the Center of Microscopy (ZMB) at the University of Basel, where the image was taken and also thank the ZMB for providing the infrastructure.

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/.

GeoTalk: How hydrothermal gases change soil biology

The biosphere is an incredible thing – whether you’re looking at it through the eye of a satellite and admiring the Amazon’s vast green landscape, or looking at Earth’s surface much more closely and watching the life that blossoms on scales the naked eye might never see, you are sure to be inspired. Geochemist, Antonina Lisa Gagliano has been working on the slopes of Pantelleria Island in an effort to find out what can make soil and its biota change enormously over just a few metres. Following her presentation at the EGU General Assembly, she spoke to Sara Mynott, shedding light on what makes volcanic soils so special…

Antonina Lisa Gagliano out in the field. Credit: Antonina Lisa Gagliano

Antonina Lisa Gagliano out in the field. Credit: Antonina Lisa Gagliano

What’s your scientific background, and what drew you to soil biota?

I am a geologist with a background in Natural Sciences and, in 2011, I started my research in biogeochemistry during my PhD in Geochemistry and Volcanology at the University of Palermo. I’ve always tried to look at the interactions between different factors in all sorts of subjects, but if you apply this concept to biotic and abiotic factors, it is particularly interesting and fascinating. I started the study on soil biota when my supervisors introduced me to the biogeochemistry of a geothermal area, thinking that I could have enough scientific background and enthusiasm to start studying something new in our team.

Tell me about your field site – what makes it a great place to study?

Pantelleria Island, a volcano located in the Sicily channel, is a really interesting place. It is an active volcanic system – at present quiescent – that hosts a high-energy geothermal system, with a high temperature gradient and gaseous manifestations all over the island. We studied the most active area, Favara Grande, sampling soils and soil gases from its geothermal field. A first look at the island’s geochemistry suggested high methane fluxes from the soil and high surface temperatures – reaching up 62 °C at only 2 cm below the surface. Indirect evidence of methanotrophic activity led us to better investigate soil biota and how it interacts with methane emissions. It is a great place to study because the peculiar composition of the geofluids is extraordinarily rich in methane and hydrogen, and because the geothermal system is stable both in space and time.

Geothermal area at Favara Grande, Pantelleria Island, Italy. Credit: Walter D’Alessandro.

Geothermal area at Favara Grande, Pantelleria Island, Italy. Credit: Walter D’Alessandro.

During the General Assembly, you highlighted key differences in soil sites that were only 10 metres apart – what did you find and why are they different?

We investigated two really close sites in the Favara Grande geothermal field. They released similar gases (CH4, H2, CO2) and had similar surface temperatures, but at the same time they showed differences in soil chemistry (in particular, pH, NH4+, H2O, sulphur, salinity, and oxides). Amazingly, one site showed high methane consumption and the other was totally inactive, despite both sites being characterised by high methane emissions.

These differences were due to the hydrothermal flux from the ground. As the gasses rise, the gas mixture is influenced by several factors including changes in soil and subsoil properties, such as fracturing, level of alteration, permeability and many others. Variations in even only one of these factors can change the flux velocity, which directly regulates soil temperature. When the temperature goes below 100 ⁰C the most soluble species (H2S and NH3), start to dissolve, releasing hydrogen ions and changing the soil’s characteristics.

The condition of one site was much more mild than the other (higher pH, lower amounts of NH4+, sulphur, soil water content and salinity). These differences were due to a lowering of the hydrothermal flux velocity in deeper layers at the milder site, leading to the depletion of soluble species in the surface soil layers. These conditions created two totally different environments for bacterial populations thriving in the two sites.

How did you identify the different species? How many did you find?

Nowadays, Next-Generation-Sequencing techniques (NGS) are available to screen the microbiota in different substrates. We extracted total bacterial and archeal DNA from soil samples and from the geothermal field at Favara Grande. We found an extraordinary diversity of methanotrophs, that use methane as sole source of carbon and energy in the milder site. In the harsher site, we found a high diversity of chemolithotrophs, that use inorganic reduced substrates to produce energy. Here, there was no methanotrophic activity, nor any evidence of the presence of methanotrophs.

On the left, the harsher site – the stains on the surface are signs of the soil alteration. To the right, the milder site – here, soil alteration is much harder to see without a microscope. Credit: Walter D’Alessandro.

On the left, the harsher site – the stains on the surface are signs of the soil alteration. To the right, the milder site – here, soil alteration is much harder to see without a microscope. Credit: Walter D’Alessandro.

Has anything like this been found before, perhaps at another volcanic site, hot spring or hydrothermal vent?

Currently, integrated studies of bacteria thriving in geothermal soils are still at the pioneer stage and few studies on similar work are available; What we found in terms of chemolithotrophic species is similar to other volcanic sites, but the diversity of methanotrophs detected in our soil samples seem to be unique, probably because the geothermal soils are still under-investigated in this regard.

What do you hope to work on next?

Several questions regarding the relationship between biotic and abiotic factors at our sampling sites are open, so our next challenge is to better investigate the dynamics in this geothermal field. We would also like to extend this research to other sites and establish new collaborations to study different areas and discover new things.

What are your biggest challenges in the field and how do you overcome them?

The first challenge is to find a good sampling site; sampling is like a closed box, particularly when you don’t have anything for comparison terms or any state of art equipment at your disposal. But we overcome these challenges with good planning ahead of the field campaign.

If you could give an aspiring biogeochemist one piece of advice, what would it be?

Biogeochemistry puts together several spheres of knowledge (geochemistry and biology, above all), so my first advice is never stop studying, because when you think to know a lot about something, it’s likely that you may completely overlook the other aspects of the argument. Secondly, go outside the scheme of classical and sectorial research and collaborate with scientists of different sectors to increase your expertise and look at problems from other points of view.

Interview by Sara Mynott, PhD student at the University of Exeter.

Iceland’s Bárðarbunga-Holuhraun: a remarkable volcanic eruption

Iceland’s Bárðarbunga-Holuhraun: a remarkable volcanic eruption

A six month long eruption accompanied by caldera subsidence and huge amounts of emitted gasses and extruded lavas; there is no doubt that the eruption of the Icelandic volcano in late 2014 and early 2015 was truly remarkable. In a press conference, (you can live stream it here), which took place during the recent EGU General Assembly, scientists reported on the latest from the volcano.

Seismic activity in this region of Iceland had been ongoing since 2007, but in late August 2014 a swarm of earthquakes indicated that the activity at Bárðarbunga-Holuhraun was ramping up a notch. By August 18th, over 2600 earthquakes had been registered by the seismometer network, ranging in magnitude between M1.5 and M4.5. Scientist now know that one of the main drivers of the activity was the collapse of the ice-filled Bárðarbunga caldera.

Caldera collapses -where the roof of a magma chamber collapses as a result of the chamber emptying during a volcanic eruption – are rare; there have only been seven recorded events this century. The Bárðarbunga eruption is the first caldera collapse to have occurred in Iceland since 1875. They can be very serious events which result in catastrophic eruptions (e.g. the Toba eruption of 74,000 BP). In other cases the formation of the large cauldron happens over time, with the surface of the volcano slowly subsiding as vast amounts of magma are drained away via surface lava flows and the formation of dykes. Bárðarbunga caldera subsided slowly and progressively, much more so than is common for this type of eruption, to form a depression approximately 8km wide and 60m deep.

“The associated volcanic eruption, which took place 40km away from the caldera, was the largest, by volume and mass of erupted materials, recorded in Iceland in the past 230 years”, described Magnus T. Gudmundsson, Professor at the Institute of Earth Sciences at the University of Iceland, during the press conference.

If the facts and figures above aren’t sufficiently impressive, the eruption at Holuhraun also produced the largest amount of lava on the island since 1783, with a total volume of over 1.6 km3 and stretching over more than 85 km4. In places, the lava flows where 30 m thick!

The impressive figures shouldn’t detract from the significance of the events that took place during those six months: scientists were able to observe the processes by which new land is made on Earth! Major rifting episodes like this “only happen once every 50 years or so”, explained Gudmundsson.

So what exactly have scientists learnt? Most divergent boundaries – where two plates pull apart from one another – are found at Mid-Ocean Ridges, meaning there is little opportunity to study rifting episodes at the Earth’s surface. The eruption at Bárðarbunga-Holuhraun offered researchers the unique opportunity to take a closer look at how rifting takes place; something which so far has only been possible at the Afar rift in Ethiopia.

New crust is generated at divergent plate margins, commonly fed by vertical sheet dykes – narrow, uniformly thick sheets of igneous material originating from underlying magma chambers. Dykes at divergent plate boundaries are common because the crust is being stretched and weakened. One of the clusters of seismic activity at Bárðarbunga-Holuhraun was consistent with the formation of a dyke. The seismic signal showed that the magma from the Bárðarbunga caldera, rather than being transported vertically upwards to the surface, was in fact being transported laterally, forming a magma filled fissure which stretched 45 km away from Bárðarbunga. This video, from the Icelandic Met Office, helps to visualise the growth of the dyke over time.

The figure shows all the earthquakes which took place in the region in and around Bárðarbunga, from 16 August 2016 until 3 May 2015. The bar on the right counts days since the onset of events, and it gives a colour code indicative of the time passed. The dark blue colour implies the oldest earthquakes whereas the red colour implies the youngest earthquakes. The earthquakes clearly show the growth of a lateral dyke, headed northeast, away from the Bárðarbunga caldera. Click here to enlarge the map. (Credit: Icelandic Meteorological Office)

The figure shows all the earthquakes which took place in the region in and around Bárðarbunga, from 16 August 2016 until 3 May 2015. The bar on the right counts days since the onset of events, and it gives a colour code indicative of the time passed. The dark blue colour implies the oldest earthquakes whereas the red colour implies the youngest earthquakes. The earthquakes clearly show the growth of a lateral dyke, headed northeast, away from the Bárðarbunga caldera. Click here to enlarge the map. (Credit: Icelandic Meteorological Office)

Further study of the dyke using understanding gained the from propagating seismicity, ground deformation mapped by Global Positioning System (GPS), and interferometric analysis of satellite radar images (InSAR), allowed scientists to observe how the ground around the dyke changed in height and shape. The measurements showed the dyke was not a continuous feature, but rather it appeared broken into segments which had variable orientations. Modelling of the dyke revealed that it was the interaction of the laterally moving magma with the local topography, as well as stresses in the ground cause by the divergent plates, that lead to the unusual shape of the dyke.

On average, magma flowed in the dyke at a rate of 260 m3/s, but the speed of its propagation was extremely variable. When the magma reached natural barriers, it would slow down, only picking up momentum again once pressure built up sufficiently to overcome the barriers. Shallow depressions observed in the ice of Vatnajokull glacier (the white area in the map above) – known as Ice cauldrons – were caused by minor eruptions underneath the ice at the tips of some of the dyke segments. The dyke propagation slowed down once the fissure eruption at Holuhraun started in September 2014.

What has the Bárðarbunga-Holuhraun taught scientists about rifting processes? It seems that at divergent plate boundaries, in order to create new crust over long distances, magma generated at central volcanoes (in this case Bárðarbunga), is distributed via segmented lateral dykes, as opposed to being erupted directly above the magma chamber.

 

By Laura Roberts Artal, EGU Communications Officer

 

Further reading and references

You can stream the full press conference here: http://client.cntv.at/egu2015/PC7

Details of the speakers at the press conference are available at: http://media.egu.eu/press-conferences-2015/#volcano

The speakers at the press conference also reported on the gas emissions as a result of the Holuhraun fissure eruption and the implications for human health. You can read more on this here: Bardarbunga eruption gases estimated.

Sigmundsson, F., A. Hooper, Hreinsdóttir, et al.: Segmented lateral dyke growth in a rifting event at Bárðarbunga volcanic system, Iceland, Nature, 517, 191-195, doi:10.1038/nature1411, 2015.

Sigmundsson, F., A. Hooper, Hreinsdóttir, et al.: Segmented lateral dyke growth in a rifting event at Bárðarbunga volcanic system, Iceland, Geophys. Res. Abstr.,17, EGU2015-10322-1, 2015 (conference abstract).

Hannah I. Reynolds, H. T., M. T. Gudmundsson, and T. Högnadóttir: Subglacial melting associated with activity at Bárdarbunga volcano, Iceland, explored using numerical reservoir simulation, Geophys. Res. Abstr.,17, EGU2015-10753-2, 2015 (conference abstract).

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