GeoLog

Tectonics and Structural Geology

Imaggeo on Mondays: The road to nowhere – natural hazards in the Peloponnese

Imaggeo on Mondays: The road to nowhere – natural hazards in the Peloponnese

The Gulf of Corinth, in southern Greece, separates the Peloponnese peninsula from the continental mainland. The structural geology of the region is complex, largely defined by the subduction of the African Plate below the Eurasian Plate (a little to the south).

The Gulf itself is an active extensional marine basin, i.e., one that is pulling open and where sediments accumulate. Sedimentary basins result from the thinning, and therefore sinking, of the underlying crust (though other factors can also come into play). The rifting in the region is relatively new, dating back some five million years, and results in rare but dangerous earthquakes.

The active tectonics result in a plethora of other natural hazards, not only earthquakes.  Minor and major faults crisscross the area and have the potential to trigger landslides, posing a threat to lives and infrastructure. A road, swept away in a landslide, in the northern Peloponnese (along the southern margin of the Corinth rift) is a clear example of the hazard.

“This photo was taken in the Valimi fault block [editor’s note: a section of bedrock bound on either side by faults], east of the Krathis valley. West of this valley, the landscape is characterised by  narrow and deep gorges as the present day rivers cut into the well-consolidated conglomerates deposited during the active extension of the basin,” explains Romain Hemelsdaël, author of this week’s imaggeo on Mondays photograph.

Characteristically, sediments deposited in actively extensional rifts where the Earth’s crust and lithosphere are being pulled apart, as at the Gulf of Corinth, change in size (both horizontally and vertically) and composition. To the east of the Krathis valley, the sediments are being uplifted and are dominated by less competent sandstones and siltstones, as opposed to the conglomerates found in the Valimi fault block.

“The present landscape along this part of the rift margin forms large valleys covered by active landslides,” clarifies Romain. “In this photograph, the road was initially constructed directly on silts which were deposited by lakes and rivers. Up the hill, a temporary track currently replaces the road but this track still remains within an active landslide.”

 

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/

What is in your field rucksack? Camping in Iceland

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When you head out into the field, which is the one item you can’t do without? For Rebecca Williams, a volcanologist at the University of Hull, good footwear is essential!

Inspired by a post on Lifehacker on what your average geologist carries in their rucksack/backpack, we’ve put together a few blog posts showcasing what a range of our EGU members carry in their bags whilst in the field!

Beautiful, eyrie, the land where fire meets ice: Iceland. An Earth scientist’ dream, complete with lava, volcanoes, earthquakes, impossible landscapes, ice, snow, the ocean…Iceland, is a top destination for many scientist who want to better understand the processes which shape our planet. Among them, Rebecca Williams, a volcanologist at the University of Hull, who spent a few days camping on the volcanic island this summer.

This bag belongs to: Rebecca Williams, University of Hull.

Field Work location: Þórsmörk, Iceland

Duration of field work: 10 days

What was the aim of the research?: I was working with Dave McGarvie and Jonathan Moles, from the Open University. They are working on a volcano in the area and had come across the Þórsmörk Ignimbrite. Ignimbrites are the deposits from pyroclastic density currents. This unit is quite complicated and not well understood. It is best exposed in Þórsmörk, so we spent 4 days here doing a recce of the exposure in the Þórsmörk area, trying to understand its many facies and their relationship to each other. I then spent the remainder of the time with a field assistant (Steph Walker from Royal Holloway) doing some detailed work on the best exposures, collecting some samples and recording the details of the deposit. We also recce’d some new areas to try to determine the extent of the deposit and finding new localities for future work.

The one item I couldn’t live without:

Footwear! We covered over 10 miles of rough ground and varied terrain each day, so good footwear is essential. I was very thankful for the trekking sandals when fording the rivers. One fording point is on the famous Laugavegur trekking from the hot springs area of Landmannalaugar to the glacial valley of Þórsmörk. We would often see people trying to ford the river in trainers, crocs and even bare feet! It was clear that this wasn’t ideal, and from some of the screeches, very difficult! But in these trekking sandals, I was able to wade over in relative ease and comfort.

Rebecca in the field. Credit: Rebecca Williams

Rebecca in the field. Credit: Rebecca Williams

In the picture of me in the field, you can see what I actually carry when I’m out and about. The zip off trousers were great for fording rivers – I wasn’t expecting it to be hot enough in Iceland to wear them to work! Strapped to my bag are my sandals for fording rivers, and my hammer. The poles were great for getting around on slopes like the one in the background, and for helping out when fording rivers. Here I’m also carrying a spade – acquired once in Iceland. This is unusual for me, I’m used to working with much harder rocks like the welded ignimbrites in Pantelleria. The spade was very useful for digging through scree slopes and material broken up and crushed by glaciers.

 

If you’ve been on field work recently, or work in an industry that requires you to carry equipment, and would like the contents of your bag to feature on the blog, we’d love to hear from you. Please contact the EGU’s Communication Officer, Laura Roberts (networking@egu.eu)

Imaggeo on Mondays: A Bubbling Cauldron

Imaggeo on Mondays: A Bubbling Cauldron

Despite being a natural hazard which requires careful management, there is no doubt that there is something awe inspiring about volcanic eruptions. To see an erupting volcano up close, even fly through the plume, is the thing of dreams. That’s exactly what Jamie  Farquharson, a researcher at Université de Strasbourg (France) managed to do during the eruption of the Icelandic volcano Bárðarbunga. Read about his incredible experience in today’s Imaggeo on Monday’s post.

The picture shows the Holuhraun eruption and was taken by my wife, Hannah Derbyshire. It was taken from a light aircraft on the 11th of November of 2014, when the eruption was still in full swing, looking down into the roiling fissure. Lava was occasionally hurled tens of metres into the air in spectacular curtains of molten rock, with more exiting the fissure in steady rivers to cover the surrounding landscape.

Iceland is part of the mid-Atlantic ridge: the convergent boundary of the Eurasian and North American continental plates and one of the only places where a mid-ocean ridge rears above the surface of the sea. It’s situation means that it is geologically dynamic, boasting hundreds of volcanoes of which around thirty volcanic systems are currently active. Holuhraun is located in east-central Iceland to the north of the Vatnajökull ice cap, sitting in the saddle between the Bárðarbunga and Askja fissure systems which run NE-SW across the Icelandic highlands.

Monitored seismic activity in the vicinity of Bárðarbunga volcano had been increasing more-or-less steadily between 2007 and 2014. In mid-August 2014, swarms of earthquakes were detected migrating northwards from Bárðarbunga, interpreted as a dyke intruding to the east and north of the source. Under the ice, eruptions were detected from the 23rd of August, finally culminating in a sustained fissure eruption which continued from late-August 2014 to late-February of the next year.

My wife and I were lucky enough to have booked a trip to Iceland a month or so before the eruption commenced and, unlike its (in)famous Icelandic compatriot Eyjafjallajökull, prevailing wind conditions and the surprising lack of significant amounts of ash from Holuhraun meant that air traffic was largely unaffected.

At the time the photo was taken, the flowfield consisted of around 1000 million cubic metres of lava, covering over 75 square kilometres. After the eruption died down in February 2015, the flowfield was estimated to cover an expanse of 85 square kilometres, with the overall volume of lava exceeding 1400 million cubic metres, making it the largest effusive eruption in Iceland for over two hundred years (the 1783 eruption of Laki spewed out an estimated 14 thousand million cubic metres of lava).

Numerous “breakouts” could be observed on the margins of the flowfield as the emplacing lava flowfield increased in both size and complexity. Breakouts form when relatively hot lava, insulated by the cooled outer carapace of the flow, inflates this chilled carapace until it fractures and allows the relatively less-viscous (runnier) interior lava to spill through and form a lava delta. Gas-rich, low-viscosity magma often results in the emission of high-porosity (bubbly) lava. My current area of research examines how gases and liquids can travel through volcanic rock, a factor that is greatly influenced by the evolution of porosity during and after lava emplacement.

Flying through the turbulent plume one is aware of a strong smell of fireworks or a just-struck match: a testament to the emission of huge volumes of sulphur dioxide from the fissure. Indeed, the Icelandic Met Office have since estimated that 11 million tons of SO2 were emitted over the course of the six-month eruption, along with almost 7 million tons of CO2 and vast quantities of other gases such as HCl. These gases hydrate and oxidise in the atmosphere to form acids, in turn leading to acid rain. The environmental impact of Holuhraun as a gas-rich point source is an area of active research.

By Jamie Farquharson, PhD researcher at Université de Strasbourg (France)

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: an impressive testimony to the collision between Africa and Europe

Imaggeo on Mondays: an impressive testimony to the collision between Africa and Europe

The huge fold in the flank of the 2969 m high Dent de Morcles (in Waadtland Alps, Switzerland) is an impressive testimony to the collision between Africa and Europe (which began some 65 million years ago). The layers, originally deposited on the sea floor in a horizontal position, were compressed and shifted. The darker parts developed during the Tertiary period (66 million years ago). They are younger than the greyish and yellowish limestone of the Cretaceous period (which began 145.5 million years ago and ended 79 million years later).

With the aim to capture the Dent de Morcles, this spectacular geological feature, I took a photo flight in the Waadtland Alps in Switzerland. We started with a helicopter from a little airport around 20 kilometres away from this location. The weather was mixed – sunny with a few clouds around. But when we reached Dent de Morcles the sun was hidden by a cloud which didn’t move away. We circled and circled around waiting for sun rays to light up the fold structure. I got quite nervous because every minute up there costs a lot of money. Suddenly a little whole opened in this huge cloud and Dent de Morcles was illuminated,  exactly as I’d hoped for. Only for some seconds. But enough time to take this aerial shot.

By Angelika Jung-Hüttl (Freelance science author) and Bernhard Edmaier (geologist and photographer)

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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