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GeoEd: Why fieldwork is essential to training the next generation of Geoscientists

3 Apr

Our latest GeoEd article is brought to you by Simon Jung, a lecturer and palaeoceanographer from the University of Edinburgh, who highlights what makes fieldwork a brilliant way to understand Earth processes…

Studying geosciences involves training across a broad range of natural sciences. Only equipped with such background knowledge will students be able to grasp key concepts in the various sub-disciplines that geosciences has to offer. So what’s the best way to get ahold of such knowledge?

A substantial part of the theoretical background in geosciences can be delivered via lectures and/or practicals. Using this standard teaching approach, for example, knowledge of the various rock types and the minerals they contain can be conveyed clearly and effectively. Background information on different soil types, or shapes of rivers, can also be passed on in this fashion.

For something more visual, geological or geomorphological maps can create a great 2D representation of a 3D structure, giving basic insights into the relationship between larger sets of strata or geomorphological features in a given region.

There are, however, important limitations as to the level of understanding students can possibly reach through a classroom-only approach. And these can only be overcome through field training.

Viewing a landscape from an elevated spot – or otherwise suitable location – in the field allows much better comprehension of the processes that have shaped a region. For the first time, truly understanding the nature of the succession of different rock types is an eye-opening and life changing event. Similarly, grasping the role of time in allowing long-term erosion to shape a region can only be attained in the field. A visit to the northwest of Scotland is one way to achieve these goals.

Studying an outcrop in northwest of Scotland. (Credit: Simon Jung)

Studying an outcrop in northwest of Scotland. (Credit: Simon Jung)

Geological and geomorphological research in northwest Scotland has been instrumental in laying the foundations of many crucial concepts in geosciences. The area offers easy access to a unique set of rock sequences documenting Scotland’s early geological history, the explosion of life on Earth, as well as how rivers and ice have shaped the modern landscape. Students from the University of Edinburgh are frequently taken out here, where they are exposed to a huge variety of geological and geomorphological phenomena.

The more specific learning outcomes center around three main areas:

  1. Hands on training in the field helps refining all aspects related to fieldwork (e.g. observational skills, mapping)
  2. Using self-generated field data regarding rock sequences and their 3D orientation allows students to comprehend the long-term geological history
  3. Students also obtain a greater understanding of the role of erosion in shaping the landscape in a region. How? By determining river runoff at a number of locations and making measurements of the sediments being transported

Such excursions allow students to develop an improved understanding of the local geological and geomorphological history of a region.  At a larger scale, they will also develop a more comprehensive view of the processes having shaped the Earth. As the video below documents, this journey is not only educating, but fun too!

By Simon Jung, Lecturer in Palaeoceanography, University of Edinburgh

 

Imaggeo on Mondays: A rolling stone gathers no moss

31 Mar

Philippe Leloup brings us this week’s Imaggeo on Mondays, with tales from a mountain trail that show a geologist can never resist a good rock!

In reality, this shiny slab of rock is about 20 centimetres across. Polished to perfection, the layers of marble and amphibole are beautiful to behold. (Credit: Philippe Leloup via imaggeo.egu.eu)

In reality, this shiny slab of rock is about 20 centimetres across. Polished to perfection, the layers of marble and amphibole are beautiful to behold. (Credit: Philippe Leloup via imaggeo.egu.eu)

This image is that of a polished slab of a rock composed of interlayered marbles and amphibolites. The sample was once part of a small dry-stone wall bordering an outdoor kitchen along a trail along the Ailao Mountain Range in China (or Ailao Shan in Chinese).

As I passed by, a small black eye looked at me, and I couldn’t resist asking the owner to give me that stone – one that could easily be replaced by any other rock nearby, and he kindly agreed. The rock was special for me because I felt that its structure would be spectacular.

The Ailao Range is part of the Ailao Shan – Red River shear zone, a region that stretches for more than 1000 kilometres – from southeast Tibet to the Tonkin Gulf. During the Oligo-Miocene, the Indochina bock (encompassing Vietnam, Cambodia, Laos and Thailand) was pushed away from the collision between the Indian and Asian continents and moved several hundreds of kilometres towards the southeast along that ~10 kilometre-wide shear zone. Today, evidence that intense ductile deformation occurred are found in gneiss and marbles showing steep foliation, horizontal lineation, and numerous left-lateral shear features – a type of deformation that leaves rocks looking like this:

 A thin section microphotograph (total width ~0.5 mm) showing several feldspar crystals with bended tails. These tails show that they have slowly rotated counter-clockwise. These rolling structures are characteristic of left-lateral ductile deformation. (Credit: Philippe Leloup via imaggeo.egu.eu).

A thin section microphotograph (the total width is about 0.5 mm) showing several feldspar crystals with bended tails. These tails show that they have slowly rotated counter-clockwise. These rolling structures are characteristic of left-lateral ductile deformation. (Credit: Philippe Leloup via imaggeo.egu.eu).

When I cut the rock it turned out that the amphibole layer had a very special shape, like a Swiss roll, resulting from simple shear – something that revealed spectacular colours and a stunning shape when seen in section.

By Philippe Leloup, University of Lyon

Imaggeo is the EGU’s open access geosciences image repository. Photos uploaded to Imaggeo can be used by scientists, the press and the public provided the original author is credited. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. You can submit your photos here.

Imaggeo on Mondays: Pitter-patter of little paws in Patomsky crater

10 Feb

This week’s Imaggeo on Mondays is brought to you by Dmitry Demezhko, who describes how Patomsky crater may have formed and why it keeps scientists puzzling…

Patomsky crater, also known as Patomskiy crater or the Patom cone, sits in the Irkutsk Region of Eastern Siberia. The site is a curious cone with a crater at the top and a small mound in the center. The cone totals some 39 metres in height and stretches more than 100 metres in diameter (at the base of the cone).

Patomsky crater – view from a helicopter. (Credit: Dmitry Semenov)

Patomsky crater – view from a helicopter. (Credit: Dmitry Semenov)

The crater was discovered in 1949 by Russian geologist Vadim Kolpakov and for a long time it was considered to be an impact structure with a meteoric origin. Later, Viktor Antipin suggested it could be a nascent volcano. But neither meteoritic nor volcanic matter was found there. The crater consists of proterozoic limestone and sandstone debris and, to date, there is no consensus among scientists regarding the crater’s origin.

View from the crater. (Credit: Dmitry Demezhko, distributed via imaggeo.egu.eu)

View from the crater. (Credit: Dmitry Demezhko, distributed via imaggeo.egu.eu)

During a short expedition in August 2010 we conducted a gravimetric survey at the crater and surrounding area, aiming to evaluate its internal structure. The gravity field shows that surface negative anomalies, where the gravity is unusually low, have deep “roots” and a joint source at depth. But the crater’s gravity field differs greatly from the fields of other well-known impact structures, suggesting that it may not have formed during a meteoric impact.

Downward continuation of the Patomsky crater (left) and Popigay impact structure gravity fields (right). (Credit: Demezhko et al., 2011)

Downward continuation of the Patomsky crater (left) and Popigay impact structure gravity fields (right), (click for larger). (Credit: Demezhko et al., 2011)

We suggest this structure formed in two stages. During the first stage tectonic processes similar to mud volcanism created a porous vertical channel. In the second stage, cryogenic processes would have played an important role in breaking apart the rocks to form the cone and crater.

There is a lot of mysticism and superstition surrounding Patomsky. Local residents call the crater “a fabulous Eagle’s Nest” and say that both people and animals bypass it. We didn’t sense anything mystical while working in the crater though – and this cute little animal lives quite comfortably there.

Downward continuation of the Patomsky crater (left) and Popigay impact structure gravity fields (right). (Credit: Demezhko et al., 2011)

“Inside Patomsky crater: a chipmunk” by Dmitry Demezhko. This image is distributed via imaggeo.egu.eu.

By Dmitry Demezhko, Institute of Geophysics UB RAS, Yekaterinburg

References:

Alekseyev, V. R.  Cryovolcanism and the mystery of the Patom Cone, Geodynamics and Tectonophysics, 3, 289-307, 2012 (in Russian)

Demezhko D.Y., Ugryumov I.A., Bychkov S.G.: Gravimetric studies of Patom Crater. In: Patom Crater. Research in the 21st Century. Publishing House of the Irkutsk State University, Irkutsk, p. 42–50, 2011 (in Russian)

If you are pre-registered for the 2014 General Assembly (Vienna, 27 April – 2 May), you can take part in our annual photo competition! Up until 1 March, every participant pre-registered for the General Assembly can submit up three original photos and one moving image on any broad theme related to the Earth, planetary, and space sciences in competition for free registration to next year’s General Assembly!  These can include fantastic field photos, a stunning shot of your favourite thin section, what you’ve captured out on holiday or under the electron microscope – if it’s geoscientific, it fits the bill. Find out more about how to take part at http://imaggeo.egu.eu/photo-contest/information/.

Dense rocks rise higher because isostasy says so

24 Dec

From space, the Brandberg Igneous Complex looks like a coffee-coloured birthmark set upon the bony complexion of the Namibian desert. Perfectly circular, its peaks soar in a ring of mighty topography, its massive granite cliffs etched with the muscular definition of spheroidal weathering. Its bulk seems to rise out of the barren landscape, driven upward by some unseen force.

In fact, granite intrusions like the Brandberg may actually be uplifted by powerful forces, unseen but not unfamiliar. New research, presented at the American Geophysical Union Fall Meeting last week in San Francisco, suggests that granite features like the Brandberg may owe their towering height to the elementary principle of isostasy.

Since Grove Gilbert first measured the formidable hardness and high density of granite in the 19th century, most geologists have attributed the striking topographic relief of many granite peaks to the former; they argued that granite was simply more resistant to erosion. But Jean Braun, of the Institute of Earth Sciences (ISTerre) at University Joseph Fourier in Grenoble, thinks the high density of granite paradoxically deserves the credit.

A Landsat 7 image of the Brandberg Igneous Complex in Namibia (Credit: NASA).

A Landsat 7 image of the Brandberg Igneous Complex in Namibia (Credit: NASA).

As most students learn in Geology 101, crustal rocks float on the asthenosphere like icebergs in the sea. The density contrast between the ice and the water dictates how much of the iceberg rises above the sea surface, and the same is true of rocks. Furthermore, when you melt an iceberg or passively erode a piece of crust, it will rebound to compensate. On average, the crust rebounds by about 700 metres for every kilometre of erosion. “That’s a well-accepted consequence of local isostasy,” Braun says. “The key is that this ratio can easily vary when you change the density of the surface rocks.”

For granite, whose density can exceed that of the rocks it intrudes by hundreds of kilograms per cubic metre, the rate of isostatic rebound can more than double. “There is nothing new about some granites being denser than the rocks they intrude and there is nothing new about the principle of isostasy,” Braun says. What is new is the realisation – albeit a counterintuitive one – that denser rocks will rebound faster than lighter rocks.

Inside the Brandberg Complex, whose peaks rise 2600 meters above sea level. (Credit: Julia Rosen)

Inside the Brandberg Complex, whose peaks rise 2600 meters above sea level. (Credit: Julia Rosen)

Braun and his colleagues demonstrated this by modelling the evolution of a hypothetical landscape using a surface process model that included isostatic effects. They varied the hardness and density of the surface rocks in the model and found that while resistance to erosion played a small role in preserving topographic high points, the enhanced isostatic rebound associated with density changes was the primary factor behind the high elevation of granite features.

However, there is some limit to the amount of isostatic rebound that can occur by this mechanism. “The principle of localised isostasy assumes that the Earth is made of vertical columns of lithosphere that can slide with respect to each other in any way,” Braun says. “However, we know this is not the case.” Instead, the intrusion must be of the same scale as the elastic thickness of the crust – a measure of its lateral strength. For example, in the thick, strong interior of continents, dense features must be about 100 kilometres long to rebound faster than the rocks around them while in weaker crustal regions, even small granite features can experience enhanced uplift.

After presenting these results at conferences like the AGU Fall Meeting, Braun’s idea has been met with nearly universal enthusiasm and support. “It’s too basic to not be true,” jokes Braun. Mostly, he and others just wonder, “how come we didn’t think of this before?”

The preliminary results of Braun’s modeling show that denser features form higher elevations (shown in red). (Courtesy of Jean Braun)

The preliminary results of Braun’s modeling show that denser features form higher elevations (shown in red). (Courtesy of Jean Braun)

On top of explaining the high elevation of granites, Braun’s theory may have broader applications for other places on Earth where surface rocks vary substantially in density. For instance, Braun cites rapidly uplifting mafic domes in a tectonically quiescent corner of the Tibetan Plateau. “These examples show that there is a simple isostatic component that has not been considered many places where you have large variations in rock density,” Braun says.

The next step is to test these theories against low-temperature thermochronology datasets, including apatite fission track and helium dates. These measures provide an estimate of the rate of cooling and uplift for large intrusions, and can be used to validate Braun’s hypothesis. Although the existing data support the idea that dense bodies experience enhanced isostatic rebound, none were collected with this purpose in mind. So next year, Braun and his colleagues will head to the Brandberg, where the granite bulges out of the Namibian desert, to see whether denser rocks really do rise higher.

 By Julia Rosen, freelance writer and PhD student at Oregon State University

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