GeoLog

“Endless fold”, by Jens Rößiger, was taken in the Pyrenees – its location is approximately 42°19’17.29″N, 3°18’49.02″E. This image is distributed by the European Geosciences Union under a Creative Commons licence.

This fold is part of the metamorphic core of the Pyrenees. The shear zone is almost vertical, producing a small parasitic fold (a smaller fold within a larger one), which looks almost as if it continues into the sky. The metamorphic sediments are about 500 million years old and have been deformed several times, most recently during the alpine orogeny. The alpine orogeny was period of extensive mountain building that occurred towards the end of the Mesozoic as the African and Arabian plates collided with the Eurasian, resulting in the formation of the Alpide belt. While the map below only shows the Mediterranean portion of the Alpide belt, this stretch of mountains extends much further East and includes the Himalayas.

The plate tectonics of the Mediterranean, responsible for the alpine orogeny that spans the region (orange) [Source: Wikimedia Commons].

The fold above lies within the Seira Negra (Black Series) at Cap de Creus, Spain. Much of this region is composed of mylonites (fine-grained rocks that have been through ductile deformation), pegmatites (highly crystalline igneous rocks with crystals >2.5 cm wide) and schists (medium-grade metamorphic rocks, with a large proportion of platy minerals – these are responsible for their sheen). The metamorphic grade of rocks in Cap de Creus decreases from north to south. An overview of the region’s metamorphic geology is given in the map below:

Geology of the Cap de Creus area – Jens’ photo was taken just north of the lighthouse (click to enlarge) [source: Carreras, 2001].

Rocks in Cap de Creus have been subject to a lot of shear stress through faulting and other orogenic processes. These processes have caused high strain in the rocks and extensive deformation. The “endless fold” above is composed of quartzite, with numerous quartz veins running throughout it. The fold is caught up in one of the many classical Variscan shear zones found in the area. Variscan shear zones are so named because they formed during the Variscan orogeny, a mountain building event in the late Palaeozoic, when Eurasia and Gondwana collided to form the supercontinent, Pangea. Relatively young volcanic intrusions (pegmatites) exist within the fold, and some of these have been deformed since, as the mountain range continues to build.

References:

Bons, P.D., Druguetb, E., Hamann I., Carreras, J. and Passchier, C.W. (2004). Apparent boudinage in dykes. Journal of Structural Geology. Vol. 26, pp. 625–636.

Carreras, J. (2001). Zooming on Northern Cap de Creus shear zones. Journal of Structural Geology. Vol 23, pp 1457-1486.

Imaggeo is the online open access geosciences image repository of the European Geosciences Union. Every geoscientist who is an amateur photographer (but also other people) can submit their images to this repository. Being open access, it can be used by scientists for their presentations or publications as well as by the press. If you submit your images to imaggeo, you retain full rights of use, since they are licenced and distributed by EGU under a Creative Commons licence.

“Kalalau Valley” by Martin Mergili, taken from Kalalau Lookout on the island of Kauai, distributed by the European Geosciences Union under a Creative Commons License.

At over 5 million years old, the island of Kauai is the oldest island in the Hawaiian Achipelago. Hawaii, Maui and Oahu are all younger and lie further to the southeast. This island chronology is no coincidence – the Archipelago formed as a result of intra-plate volcanic activity.

Intra-plate volcanism occurs where an upwelling magma plume or ‘hot spot’ lies beneath a continental plate. In this case, the Pacific Plate has moved over a hot spot in the northwestern direction, so that the younger and more active islands are located in the southeast, and the older islands are further north. As the plate passes further from the hotspot, the crust cools, becoming less buoyant and causing the oldest islands in the chain to sink and form atolls when fully submerged.

Volcanic has ceased on Kauai and now erosive forces are those that shape the island, resulting in deep gullies and canyons cut into the highlands. In the north and northwest of Kauai the roaring waves of the Pacific Ocean hit the island after travelling for thousands of kilometres undisturbed. These waves meet a steep and rugged coastline with swells that can reach 10 m high on the Na Pali Coast. Running water has cut spectacular valleys into these cliffs, forming the Nualolo and Awaawapuhi, and Kalalau (above) Valleys. During the summer, carbonate sands fringe the island – you can just about see them here, but they are washed away by heavy wave action in the winter months.

This view of the Kalalau Valley was captured by Martin Mergili (Geologist from BOKU, University of Natural Resources and Life Sciences, and keen photographer), who explains that he took “this photo on a holiday trip to Hawaii in August 2010 (as far as a geoscientist can spend a “real” holiday in Hawaii). The viewpoint is called Kalalau Lookout, located in the humid highlands of Kauai, close to the misty Alakai Swamps and Mount Waialeale, one of the wettest places on Earth”.

Imaggeo is the online open access geosciences image repository of the European Geosciences Union. Every geoscientist who is an amateur photographer (but also other people) can submit their images to this repository. Being open access, it can be used by scientists for their presentations or publications as well as by the press. If you submit your images to imaggeo, you retain full rights of use, since they are licenced and distributed by EGU under a Creative Commons licence.

In this month’s Geoscience’s column, Sara Mynott discusses the geological hazards associated with climate warming and how recent research sheds new light on our understanding of rockfall frequency.

Rockfalls are the free-falling movement of bedrock material from a rock face, a phenomenon also encompassed by the terms ‘landslide’, ‘rockslide’ and ‘rock avalanche’. They range from small debris falls of only a few cubic-metres to large ‘bergsturz’ events of over 1 million metres-cubed. The number of rockfalls reported has increased in recent years and is often attributed to global warming, despite the lack of research in this area. The debate among scientists regarding the effect of climate change on geomorphic hazards has led to a lot of confusion among the media and hence, the public.

Climate change is expected to have numerous consequences for natural hazards and the IPCC has predicted that geomorphic hazards will increase in alpine regions as a result. However, recent research published in Natural Hazards and Earth Systems Science suggests that this may not be the case. In a recent assessment of Austrian rockfalls over the period 1990-2010, Oliver Sass and Manfred Oberlechner investigated how temperature influences their frequency. Their dataset was compiled from events that were large enough to be recorded in the media, restricting it to events that have the capacity to affect people and/or infrastructure. The Huben rockslide that occurred in 1999, which resulted in both the loss of alpine road access and the destruction of a local sawmill, presents one such example.

Rockfall in Huben, Austria, that occurred on 11 March 1999, far below the permafrost limit. This rockfall resulted in both the destruction of a sawmill and loss of road access (Source: Sass and Oberlechner, 2012).

Historical records of rockfalls are scarce, making predictions for the future a challenge and, until recently, little research on the temporal frequency of rockfall events had been carried out. This is partly due to the research focus on areas of permafrost, which cover less than 4 % of the Austrian Alps. Consequently, the relationship between surface temperature and rockslide frequency in permafrost regions is well-known. Permafrost, which exists at sub-zero temperatures, cements sediment together and gives it stability. Unsurprisingly, warming causes permafrost to degrade, leading to a loss of sediment stability and an increased risk of geomorphic hazards. The likelihood of these hazards occurring is a function of substrate type. However, areas of public interest (those with infrastructure) tend to be permafrost-free. In fact, 91% of the events studied were below the permafrost limit (less than 2100 m elevation).

Contrary to the IPCC’s predictions, the study found that there was no relationship between temperature and the number of rockfall events below the permafrost limit, nor was there any correlation between precipitation and rockfall frequency. The increasing settlements and infrastructure within the Alps means there is a greater risk of a geomorphic hazard occurring and the increase in availability of information means there appears to be more events than 20 years ago. Thus, the apparent increase in rockfall occurrence in recent years is likely to be due to a reporting bias.

Whilst there is no evidence for warming increasing the annual number of rockfalls, changes in seasonal weather patterns have resulted in a shift in their occurrence throughout the year. Rockfalls are generally more common in spring than at any other time of year as both the increase in water supply (through snowmelt and high precipitation rates) and high degree of freeze-thaw activity (also known as cryoturbation) destabilises the sediment. However, in recent decades, a greater proportion of rockfalls have occurred during the summer months, leading to a more even distribution of these hazards throughout the year.

Below the permafrost limit there is insufficient evidence to support the notion that increasing rockfall events are associated with climate warming. In fact, the study reveals that milder winters may even reduce the number of rockfalls outside areas of permafrost. Whilst Sass emphasises that these results are preliminary, they highlight the complexity of predicting the impacts of climate change and expose an alternative way in which it can affect hazardous earth processes.

By Sara Mynott, EGU Communications Officer

“Rainbow in stone” by Marina Manea, distributed by the European Geosciences Union under a Creative Commons licence.

Nothing better characterises the wild US West than endless landscapes of red hoodoos, spires of rock protruding from the bottom of an arid drainage basin or badland. Found mainly in desert and dry, hot areas, hoodoos are distinctive from similarly-shaped formations, such as spires or pinnacles, because their profiles vary in thickness throughout their length. Their distinctive colour bands are the product of erosional patterns differentially affecting layers of harder and softer minerals.

Nowhere in the world are hoodoos as abundant as in the northern section of Bryce Canyon National Park in Utah, USA. There, these formations, also known as goblins or in French as demoiselles coiffées (“ladies with hairdos”), dominate the landscape.

At Bryce Canyon, hoodoos are formed by two continuously operating weathering processes. The first, frost wedging, occurs as a result of Bryce’s over 200 annual freeze/thaw cycles. In the same way potholes are formed on a paved road, water breaks open the rock when it seeps into cracks, freezes, and expands. Secondly, the hoodoos are also sculpted by rainfall, both physically, because it removes debris, and chemically, because its slightly acidic pH dissolves the limestone.

Marina Manea, who works in the Computational Geodynamics department of the Universidad Nacional Autonoma de Mexico, took this early-morning picture from a helicopter whilst on holiday in Utah in August 2010. She explains, “Bryce Canyon has a unique geology, with deposits from the late Cretaceous and early Cenozoic eras. It is not a classical canyon but, rather, a collection of amphitheaters modelled by the erosional force of frost-wedging and the dissolving power of rainwater acting on the colorful limestone rock of the Claron Formation. In this way, the spires, or ‘hoodoos,’ are formed. The rocks forming the hoodoos are limestone (sedimentary rocks) exhibiting beautiful colours (red, orange, or white). The entire geology of the Bryce Canyon is related to the geology of the Grand Staircase region and Black Mountains volcanic complex. It rained just before this picture was taken, which explains the exceptionally vivid colours on display here.”

The area around Bryce Canyon was originally settled by Native Americans and later by Mormon pioneers. The national park was established in 1928 and today around 1.3 million (2011) people annually travel to witness its wild terrain and spectacular sunset colours.

Imaggeo is the online open access geosciences image repository of the European Geosciences Union. Every geoscientist who is an amateur photographer (but also other people) can submit their images to this repository. Being open access, it can be used by scientists for their presentations or publications as well as by the press. If you submit your images to imaggeo, you retain full rights of use, since they are licenced and distributed by EGU under a Creative Commons licence.

A French and Algerian study team seeks markers of underwater earthquakes off the Algerian coast. The team also matched the site’s paleoseismic history to land-based historical reports. Wayne Deeker reports.

The Mediterranean Sea represents the boundary between the African and Eurasian plates. Yet the fault segment off the Algerian coast is one of the most active in the western Mediterranean. It is associated with a series of moderate to large earthquakes: about 22 magnitude 6+ events since 856 CE. According to historical records, very large events in Algeria have been rare, though approximately one third of documented earthquakes would have been Mw 7+.

One of the most destructive was also the most recent. In May 2003, the Algerian coast experienced a Mw 6.8 earthquake, centred on the town of Boumerdès. It killed more than 2,300 people, injured some 10,000, and did all the usual structural damage earthquakes do in such countries. It also caused a tsunami which affected the western Mediterranean.

Building damage in the city of Boumerdes, Algeria (Credit: Ali Nour CGS; National Center of Applied Research in Earthquake Engineering)

The authors of a 2012 study published in EGU’s Open Access journal Natural Hazards and Earth System Sciences wanted to understand more about this event and earthquake recurrence intervals in the area. They found interesting clues deep underwater, where the quake likely caused landslides that resulted in almost 30 breaks of submarine telecommunications cables.

The researchers say it is especially worthwhile to investigate earthquake threats in areas that, like those surrounding the Algerian fault, have irregular, long-recurrence patterns because people there will be less prepared than where earthquakes are frequent. Another good reason motivates this research. While 2003 was a very well documented earthquake, most studies of its impact were conducted on land, with little attention paid to the effects and signatures offshore. This is unsurprising, as submarine earthquakes are difficult to monitor in real time, especially during catastrophic events. Therefore, the seafloor signatures of such events have remained elusive because they are occasional, erosive, and are a complex combination of many processes.

The damage to Algerian submarine telecommunications cables provides a clue to what happened underwater in 2003. While cable breaks often denote a definite time and place, pinpointing an event which can be interpreted in context with the landscape, the 2003 breaks were vague in all but one case. The location of the recovered cables also did not correspond to the point of damage, which suggests erosive action of turbidity currents (streams of rapidly moving sediment-rich water that deposit to form so-called turdibite sedimentary beds). Satellite images confirmed this, yet the flow pattern must have been quite complex, apparently following different paths along the underwater scarp system.

Resolving this complexity is challenging and, to do it, the researchers focused partly on seafloor morphology, in particular on the signs of seafloor rupture and instability, such as submarine landslides. Once the researchers started looking, they found the scarps had been affected by numerous landslides. The research team also found evidence of significant sediment transport, confined between salt domes and scarp walls. Sonar images showed signatures of high-energy events: ditches formed by erosion, indicating flow direction, plus perpendicular structures interpreted as pebble or gravel waves. These features probably constitute the sought-after signs of undersea earthquake activity, which can now be matched to other sites.

Direct sediment sampling compliments the scans. At the foot of the scarp slopes, the sediments are too mixed up to reveal any bedding that might be dated. Further out, this is not the case, and the presence of  turbidite beds alternating with another type of sedimentary deposit allows for some cautious dating of those layers. Preliminary results, from layers within the upper 1.5m of the core, show at least eleven turbidites accumulated during the Holocene, giving an average recurrence interval of about 800 years in this area. This matches the main seismic cycle on land, supporting the view that large earthquakes in Algeria are the main responsible for the large turbidity flows.

The authors concluded that the 2003 cable breaks were, for the most part, caused by the passage of a turbidity current triggered by the earthquake. The likely path of currents depends on the roughness and the irregularities of the sea floor: seafloor scarps in some cases deflect turbidity flow paths, while perched basins may trap them. The scarps seem prone to sediment failure, and are potential additional sources of cable breaks.

By Wayne Deeker, freelance science writer

Today’s guest post comes from Daniel Minisini, a geologist with a passion for filming and philosophy who created a resource for the geosciences community called minigeology.com. In this post, he tells us a bit more about the website, and the inspiration behind the interviews he conducts and posts online.

Hi! I am Daniel, a sedimentologist and stratigrapher trained as a marine geologist by my maestro Fabio Trincardi in Bologna (Italy). I have studied and worked on modern submarine sediments, ancient turbidites, and black shales, by means of outcrops, cores, seismic data and well logs, around the Mediterranean and North America. Now I work at the Shell Research Laboratories and I live in Houston, capital of geologists. My free time is dedicated to a personal project called minigeology.com, a website where I video-interview protagonists and other characters within the Earth sciences.

It came naturally to me to start video recording the several smart geoscientific minds surrounding me and sharing their thoughts with all of you. Therefore, a couple of years ago, I decided to create a platform to do precisely that. The interviews spark from a variety of thoughts and questions I ask myself, about geology, its origins, its progress, and its relationship with other disciplines.

I still have much to understand about my own research. There are many topics in my research area that I take for granted because I read about them in books and scientific articles, but how did they originate and develop? How does my specific research topic fit in the wider context? And what should I answer when asked: “What is that useful for?”

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Please click here if the video doesn’t play.

Through minigeology.com, I try to find answers to these and other questions by indirectly investigating how geoscientists approach a problem, their work, and their life. The interviews are informal and the format yields a short spontaneous discussion. By asking the ‘right’ questions, the interviews aim to stimulate the viewer to ask his or her own questions in their own research.

All geoscientists are part of minigeology.com, which works as a square to meet personalities in the Earth sciences on one hand, and as a round table for everyone to take part in the discussion on the other. Have an idea for an interview? Then email me by clicking the name below or upload your own video to the website.

By Daniel Minisini

Make sure to check a recent interview Daniel conducted with the 2012 Jean Baptiste Lamarck EGU medalist, Emiliano Mutti!

'My way' by Amirhossein Mojtahedzadeh, distributed by EGU under a Creative Commons license

Rocks within the Earth are constantly being subjected to forces that bend, twist, and fracture them, causing them to change shape and size. This process is known as deformation. Polyphase deformation occurs over time when rocks are affected, or stressed, by more than one phase of deformation.

Geomorphologist Amirhossein Mojtahedzadeh captured this stunning scene whilst on field work. “This photo was taken near Qom in central Iran. These formations are contained by sedimentary rocks, which underwent polyphase deformation and metamorphism – clearly visible in areas at this location,” he says.

Iran covers an area of 1 648 000 square kilometres. The central plateau, located between the bounding mountain ranges, is a major feature of the country’s diverse morphology.

Imaggeo is the online open access geosciences image repository of the European Geosciences Union. Every geoscientist who is an amateur photographer (but also other people) can submit their images to this repository. Being open access, it can be used by scientists for their presentations or publications as well as by the press. If you submit your images to imaggeo, you retain full rights of use, since they are licenced and distributed by EGU under a Creative Commons licence.

Praia das Rodas by Jorge Mataix-Solera, distributed by EGU under a Creative Commons licence.

Often listed as one of the most beautiful beaches in the world, Praia das Rodas is located on the Isla do Faro, part of the three-island Cíes archipelago within the Atlantic Islands of Galicia National Park. The beach faces eastwards, towards Vigo and the Galician coast of northwestern Spain, its accumulation of sand forming a land-bridge between two islands during low tide. All three islands are the visible peaks of submerged granitic mountains.

Soil scientist Jorge Mataix-Solera visited Praia das Rodas in 2007. “The picture was taken when I arrived by boat to the island in the early morning, the day after I was on a PhD thesis evaluation committee at the University of Vigo. This beach is one of the most beautiful beaches in the world, composed of quartz sand from granitic material,” he explains.

Beaches form over thousands of years from the deposit of sediment and other materials that moves from land into the ocean and back again.

To view more from Jorge Mataix-Solera’s astounding collection of photos, please visit: http://www.jorgemataix.com.

Imaggeo is the online open access geosciences image repository of the European Geosciences Union. Every geoscientist who is an amateur photographer (but also other people) can submit their images to this repository. Being open access, it can be used by scientists for their presentations or publications as well as by the press. If you submit your images to imaggeo, you retain full rights of use, since they are licenced and distributed by EGU under a Creative Commons licence.

A sunny morning in Sørfjorden by Martin Mergili, distributed by EGU under a Creative Commons licence.

Located just southeast of Bergen on the Norwegian Atlantic coast, Hardangerfjorden is the third longest fjord in the world, measuring more than 170 km from the Atlantic Ocean to the Hardangervidda mountain plateau. Its longest branch, Sørfjorden, cuts 50 km from the main fjord and ends at Odda.

Geormorphologist Martin Mergili visited the area in 2008, following the 33rd International Geological Congress in Oslo. “The photo was taken from the small town of Odda at the southernmost tip of the Sørfjord, a southern branch of the Hardangerfjord. The western slopes of the deeply incised fjord, which are shown on the photograph, lead up to the Folgefonna, one of the major ice fields of Norway. Partly glacierised highlands and deeply incised fjords are characteristic landforms of western Norway, formed during the Pleistocene. The picture was shot on a sunny and calm morning,” he recollects.

Fjords are formed by abrasion, when a retreating glacier cuts a U-shaped valley into the surrounding bedrock. They are primarily located in mountainous regions, against prevailing westerly marine winds that are orthogonally lifted over the mountains resulting in abundant snowfall to feed the glaciers. Coasts featuring the most pronounced fjords can be found in western Norway, northwestern North America, and southwestern New Zealand.

To view more from Martin Mergili’s collection of photos, many of which have geoscientific relevance, please visit: www.mergili.at/worldimages.

Imaggeo is the online open access geosciences image repository of the European Geosciences Union. Every geoscientist who is an amateur photographer (but also other people) can submit their images to this repository. Being open access, it can be used by scientists for their presentations or publications as well as by the press. If you submit your images to imaggeo, you retain full rights of use, since they are licenced and distributed by EGU under a Creative Commons licence.

Abstract submission for the EGU General Assembly 2012 (EGU2012) is now open. The General Assembly is being held from Sunday 22 Apr 2012 to Friday 27 Apr 2012 at the Austria Center Vienna, Austria.

You can browse through the Sessions online.

Each Session shows the link Abstract Submission. Using this link you are asked to log in to the Copernicus Office Meeting Organizer. You may submit the text of your contribution as plain text, LaTeX, or MS Word content. Please pay attention to the First Author Rule.

The deadline for the receipt of Abstracts is 17 January 2012. In case you would like to apply for support, please submit no later than 15 December 2011. Information about the financial support available can be found on the Support and Distinction part of the EGU GA 2012 website.

Further information about the EGU General Assembly 2012 on it’s webpages. If you have any questions email the meeting organisers Copernicus.