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Geodynamics

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/

Imaggeo on Mondays: Living flows

Imaggeo on Mondays: Living flows

There are handful true wildernesses left on the planet. Only a few, far flung corners, of the globe remain truly remote and unspoilt. To explore and experience untouched landscapes you might find yourself making the journey to the dunes in Sossuvlei in Namibia, or to the salty plain of the Salar Uyuni in Bolivia. But it’s not necessary to travel so far to discover an area where humans have, so far, left little mark. One of the last wilds is right here in Europe, in the northern territories of Sweden. Today’s spectacular photograph of the Laitaure delta is brought to you by Marc Girons Lopez, one of the winners of the 2016 edition of the EGU’s Photo Contest!

The photograph shows a part of the Laitaure delta, at the entrance of Sarek National Park (Northern Sweden). Sarek is one of the oldest national parks in Europe and it is often considered to be one of the last wild areas in Europe. The Sami people, however, have traditionally used these lands.

This delta is formed by the Rapa River when it flows into Lake Laitaure. The Rapa River springs from the Sarektjåkkå glacier and is fed by over thirty glaciers. The specific flow of the Rapa River — the ratio between its flow and the area of its catchment — is the highest in Sweden. The magnitude of the flow has strong seasonal fluctuations which are reflected in the sediment transport, which can be as high as 10,000 tons per day during the summer. This heavy sediment load gives the river its characteristics greyish colour. The different colours in the backwater zones may be produced by dissolved organic matter from decomposing vegetation.

The delta in this area is flanked by  patches of montane forests along the river banks in an area otherwise covered by marshes. Regarding the fauna, according to Wikipedia the Eurasian teal, the Eurasian wigeon, the greater scaup, the red-breasted merganser, the sedge warbler and the common reed bunting are common in the Laitaure delta.

By Marc Girons Lopez, researcher at the Centre for Natural Disaster Science, Uppsala 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/.

 

Going deeper underground – why do we want to know how rocks behave?

Going deeper underground – why do we want to know how rocks behave?

Imagine you find yourself standing atop a wooden box in the middle of your home town, on a rainy weekend day, with the sole aim of talking to passersby about your research work. It can be a rather daunting prospect! How do you decide what the take-home message of your work is: which single nugget of information do you want members of the public to take away after having spoken to you? Even more important still, how are you going to grab their attention in the first place? After all, they’ll be going about their business and not expecting to see you there, on top of your box, least of all talk to you about your work! But if you fancy the challenge, then read on, as Stephanie Zihms, the ECS Representative of the Earth Magnetism and Rock Physics Division, describes her experience doing just that!

Now in its 6th year Soapbox Science is spreading and I was selected to take part in the 1st Edinburgh event on July 24th on The Mound. The weather was typically Scottish but it didn’t seem to bother the crowds and it definitely did not dampen the enthusiasm of the 12 speakers.

I have done a range of different outreach events but I was particularly drawn to Soapbox Science because it specifically promotes female scientists and their work. It was great to meet the other scientists and to see the range of soapbox “performances” as well as the variety of props utilised to showcase each research topic.

Photo taken at the Soapbox Science event courtesy of Sarah Caldwell (smcneem)

Photo taken at the Soapbox Science event courtesy of Sarah Caldwell (smcneem)

The scary thing for this type of event is that you don’t know who might stop, listen & ask questions since we were standing on The Mound in Edinburgh – this also means that your  material has to be accessible and engaging to a wide audience.

Here is what I did to explain my research in geomechanics: Going deeper underground – why do we want to know how rocks behave?

I opted for a big PVC banner showing different heights & depths. With help from the audience I added a picture to each line to show what it represented. I used this banner to set the scene for the type of work I do. I’m a researcher in geomechanics – I want to understand why rocks deform the way they do and what part or component of the rock controls the deformation. The rocks I work with are related to a very deep oil field that lies under 2km of ocean and 5km of rocks. It would take me ~1 hour to run this. At this depth the pressure squeezing the rocks is very high – each square meter of rock experiences the pressure of 16 African elephants per km of depth. So at 5km depths that is 80 African Elephants per square meter.

Under these high pressures the slightest change in conditions e.g. through oil production affects the rocks and changes the distribution of this pressure onto the rocks. I want to understand how different rocks respond to these changes. I do this by collecting rock samples that are easy to get to e.g. from quarries. But they have to be similar to the ones found in the oil field of interest – we call this an analogue (or think of it as a sibling).

Rock sample before it is placed into the Hoek Cell. Image Credit: Stephanie Zihms

Rock sample before it is placed into the Hoek Cell. Image Credit: Stephanie Zihms

In the lab at Heriot-Watt University I have an apparatus that lets me deform rocks under different conditions. The sample, usually a core sample (seeimage above) gets placed into a rubber sleeve before being placed into a stainless steel cell called a Hoek Cell. The space between the rubber sleeve and stainless stell cell is filled with oil that can be pressurised. That way the rock samples can be placed under different pressures that mimic the conditions at different depths. After this initial pressurisation the rock is squeezed in a press until it deforms. When the readings pass a peak value it indicates that the rock sample can’t withstand the squeeze pressure any longer and the test is stopped.

Unfortunatley we can’t see what happens to the rock during the squeezing process but we measure the sample before and after testing – we can also take a x-ray images of the entire sample. We do this with the sample before it is deformed and then again afterwards. This technique lets us see inside the rock – similar to having a x-ray in hospital to see if a bone is broken or not.

Using special computer software we can then look at different parts of the rock’s inside – I am particularly interested in the fractures that formed during the deformation and I’m working on ways to relate these observed features to the rock type, grain size and pore shape.

Why is this important? As I mentioned above I look at rocks related to an oil field – and the response of the rocks to oil production could hinder or help extraction. Oil companies are very interested in predicting the rock response to ensure it does not have a negative impact on oil production.

3D reconstruction of the rock sample using the x-ray images. Image Credit: Stephanie Zihms

3D reconstruction of the rock sample using the x-ray images. Image Credit: Stephanie Zihms

Additionally this research is also relevant to other areas: for example geothermal energy. One method of generating geothermal energy is by pumping water into a rock that is hotter than the surface to increase the water temperature. When this water then reaches the surface it can be used to generate electricity. Adding water into the rock also changes the pressure conditions. Another field is Carbon Capture & Storage – If we want to store CO2 securely and long-term into the subsurface e.g. in a disused gas field – understanding how rocks respond to changes in conditions firstly by removal of gas & secondly by filling the rocks with CO2 is important.

By Stephanie Zihms, Postdoctoral researcher and ECS Representative of the Earth Magnetism and Rock Physics Division.

This post was published under the original title:Going deeper underground – My Soapbox Science Edinburgh contribution, on Stephanie Zihms’ personal blog.

Imaggeo on Mondays: Glacier de la Pilatte

Imaggeo on Mondays: Glacier de la Pilatte

The relentless retreat of glaciers, globally, is widely studied and reported. The causes for the loss of these precious landforms are complex and the dynamics which govern them difficult to unravel. So are the consequences and impacts of reduced glacial extent atop the world’s high peaks, as Alexis Merlaud, explains in this week’s edition of Imaggeo on Mondays.

This picture was taken on 20 August 2009 at the Pilatte Hutt (44.87° N, 6.33° E,  2572 m.a.s.l.), located in the massif des Ecrins in the French Alps. It shows the Pilatte Glacier, which  was recently described as being 2.64km2 wide and 2.6 km long.

As most of the glaciers in the world, the Pilatte Glacier has been retreating over the last decades as can be seen from the two pictures in figure 1, taken respectively in 1921 and 2003, and from quantitative measurements since the 19th century. The glacier has lost 1.8 km since the end of the Little Ice Age (1850).

Figure 1: Retreat of the Pilatte Glacier over the last decades (pictures adapted from Bonet et al, 2005, time series from Reynaud and Vincent, 2000).

Figure 1: Retreat of the Pilatte Glacier over the last decades (pictures adapted from Bonet et al, 2005, time series from Reynaud and Vincent, 2000).

Two climatic variables affect glacier extents in opposite directions: the amount of winter precipitations (which accumulates snow converting to ice on the glacier) and the summer temperatures (which determines the melting altitude and thus the glacier ablation area – the zone where ice is lost from the glacier, commonly via melting).

The initial retreat of the Alpine glaciers in the 19th century can’t be explained by summer temperatures which remained stable until the 20th century. It has thus been explained by a reduction in snowfall . On the other hand, a recent study suggests that industrial black carbon could have triggered the end of the little ice age in Europe, by reducing the glaciers’albedo. But the globally observed glacier retreat from the 20th century is attributed to the increasing summer temperatures.

Figure 2: Global mean temperature series (Oerlemans, 2005, supporting online material)

Figure 2: Global mean temperature series (Oerlemans, 2005, supporting online material)

Understanding the relationship between glacier dynamics and climate enables to use glacier extents  as proxies to reconstruct global temperature time series, as was done by Oerlemans (2005). Using 169 glacier across the globe, this study provided independent evidences on the timing and magnitude of the warming, that are useful to corroborate other time series obtained through other proxies (such as tree rings) or by direct temperature measurements (see Figure. 2), all showing a temperature increase by around 0.5K across the 20th century.

Glaciers continued to retreat in the 20th century, at an accelerating rate. In the 2015 foreword of the Bulletin of the World Glacier Monitoring Service, its director Michael Zemp writes: “The record ice loss of  the 20thcentury, observed in 1998, was exceeded in 2003, 2006, 2011, 2013, and probably again in 2014 (based on the ‘reference’ glacier sample)”. Using climate models, it appears now possible to distinguish an increasing anthropogenic signature in this phenomenon.

Figure 3: Average glacier retreat worldwide from 1980 in mm of water equivalent (mm.w.e), a unit representing the average thickness of a glacier (WGMS website)

Figure 3: Average glacier retreat worldwide from 1980 in mm of water equivalent (mm.w.e), a unit representing the average thickness of a glacier (WGMS website)

One of the many problems caused by glaciers depletion is the impact on water supplies: glaciers are huge reservoirs of fresh water and their vanishings affect drinking water stock and irrigation for the neighboring population. In the Alps, the idea of replacing the glaciers by dams is already studied. This solution would probably be more difficult to implement in other parts of the world, such as in nothern Pakistan, an area covered with over 5000 glaciers, whose melting is already problematic, causing in particular severe floods.

 

By Alexis Merlaud, Belgian Institute for Space Aeronomy, Brussels, Belgium

References

Bonet, R., Arnaud, F., Bodin, X., Bouche, M., Boulangeat, I., Bourdeau, P., … Thuiller, W. (2015). Indicators of climate: Ecrins National Park participates in long-term monitoring to help determine the effects of climate change. Eco.mont (Journal on Protected Mountain Areas Research), 8(1), 44–52. http://doi.org/10.1553/eco.mont-8-1s44

Ravanel, L., Dubois, L., Fabre, S., Duvillard, P.-A., & Deline, P. (2015). The destabilization of the Pilatte hut (2577 m a.s.l. – Ecrins massif, France), a paraglacial process? EGU General Assembly 2015, Held 12-17 April, 2015 in Vienna, Austria.  id.8720, 17.

Reynaud, L., Vincent, C., & Vincent, C. (2000). Relevés de fluctuations sur quelques glaciers des Alpes Françaises. La Houille Blanche, (5), 79–86. http://doi.org/10.1051/lhb/2000052

Pointer, T. H., Flanner, M. G., Kaser, G., Marzeion, B., VanCuren, R. A., & Abdalati, W. (2013). End of the Little Ice Age in the Alps forced by industrial black carbon. Proceedings of the National Academy of Sciences of the United States of America, 110(38), 15216–21. http://doi.org/10.1073/pnas.1302570110

Vincent, C., Le Meur, E., Six, D., & Funk, M. (2005). Solving the paradox of the end of the Little Ice Age in the Alps. Geophysical Research Letters, 32(9), L09706. http://doi.org/10.1029/2005GL022552

Oerlemans, J. (2005). Extracting a climate signal from 169 glacier records. Science (New York, N.Y.), 308(5722), 675–7. http://doi.org/10.1126/science.1107046

Farinotti, D., Pistocchi, A., Huss, M., al, A. A. et, Barnett T P, A. J. C. and L. D. P., Bavay M, L. M. J. T. and L. H., … Zemp M, H. W. H. M. and P. F. (2016). From dwindling ice to headwater lakes: could dams replace glaciers in the European Alps? Environmental Research Letters, 11(5), 054022. http://doi.org/10.1088/1748-9326/11/5/054022

Marzeion, B., Cogley, J. G., Richter, K., Parkes, D., Gregory, J. M., White, N. J., … Adams, W. (2014). Glaciers. Attribution of global glacier mass loss to anthropogenic and natural causes. Science (New York, N.Y.), 345(6199), 919–21. http://doi.org/10.1126/science.1254702

WGMS (2008): Global Glacier Changes: facts and figures. Zemp, M., Roer, I., Kääb, A., Hoelzle, M., Paul, F. and Haeberli, W. (eds.), UNEP, World Glacier Monitoring Service, Zurich, Switzerland: 88 pp

 

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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