GeoLog

This week’s Imaggeo on Mondays is brought to you by the photographer herself, Jana Eichel, who tells us about her expedition to the Mingsha Mountains and the stunning aeolian landforms that characterise the landscape.

“Star dune in the Gobi desert, Dunhuang, China” by Jana Eichel, distributed by the the EGU under a Creative Commons licence.

This photo was taken during a journey through Asia in spring 2012, which took me across Bangladesh, India and Nepal through to Western China and into the Gobi Desert. This journey allowed me to appreciate the enormous variety of landscapes in Asia as well as  the different cultures. To experience ‘the desert’, which has fascinated me for quite a while, I joined  four others on an (ever so slightly touristy) overnight camel trek to the borders of the Mingsha Mountains, where this photo was taken. This megadune field is located south of Dunhuang (Gansu province, China) in the Gobi Desert. The dunes, which are aeolian depositional landforms, are between 60 and 170 m heigh and are formed mostly by westerly and southerly winds. In the neighborhood of this dunefield, the World Cultural Heritage of the Mogao Caves is located, which house a large collection of Buddhist art. There is a fear that they will be overrun by the Mingsha Mountains (megadunes) in the future, which are slowly advancing in this direction.

The Gobi Desert (source).

The image was taken from near the top of one of the large pyramid dunes at the northeastern border of the dunefield. From here you can see the foothills of the Mingsha Mountains with various dune types, which are determined by a multitude of influencing factors, including wind direction variability and sand supply. Our camp in the lower left of the picture puts these huge landforms into perspective.

Most prominently in the foreground next to the camp is a star-shaped dune. These dunes are generally formed by multidirectional winds when there is a large sand supply. These conditionscreate a set of slip faces that project out in  multiple directions, such that the dune represents a star – hence the name! Transverse dunes and barchanoid ridges can be seen in the background, where they phase out towards the plains, likely dues to a decreasing sand supply. Dunefields such as this, with a variety of dune types highlight the complexity of geomorphic systems, Aeolian systems, such as the one here are thought to be strongly driven by self-organisation. This means the complex non-linear dynamics of the system do not result in chaos but instead in order: the smallest elements in the system, such as the sand grains, assemble into larger scale objects, such as the dune patterns shown (Dikau, 2006). This emergent behaviour cannot be predicted even if all processes fundamental for the evolution of these dunes are known.

To account for the impressive landscape with its large-scale geomorphic forms, I used a high aperture to give the picture a greater depth. This was amplified by the sunset light, which  created long shadows behind the dunes and gave a better impression of the contours of the dunes, which are partly obscured during the day.

By Jana Eichel, University of Bonn  

References:

Dikau, R. (2006): Complex systems in geomorphology. Mitteilungen der Österreichischen Geographischen Gesellschaft 148, 125-150.

Jianjun, Q., Ning, H., Guangrong, D. and Weimin, Z. (2001): The role and significance of the Gobi Desert pavement in controlling sand movement on the cliff top near the Dunhuang Magao Grottoes. Journal of Arid Environments 48, 3, 357-371.

Kocurek, G. and R.C. Ewing (2005): Aeolian dune field self-organization – implications for the formation of simple versus complex dune-field patterns. Geomorphology 72, 94-105.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their images to this repository and since it is open access, these photos can be used by scientists for their presentations or publications as well as by the press and public for educational purposes and otherwise. If you submit your images to Imaggeo, you retain full rights of use, since they are licensed and distributed by EGU under a Creative Commons licence.

This week’s Imaggeo on Mondays is brought to you by the photographer himself, Fabien Darrouzet who captured the beautiful glacial landscape during a summer expedition to the Arctic. 

“Arctic through a porthole” by Fabien Darrouzet, distributed by the EGU under a Creative Commons Licence.

This picture was taken in Svalbard (78° lat.) in June 2012. I was there for one week in order to observe the transit of the planet Venus in front of the Sun. I came here because at this time of the year, the Sun is shining all day (midnight Sun), so it was possible to see Venus during most of the transit (for over six and a half hours!), and not only during its last minutes, as was the case for most parts of Europe.

During the days before the transit, I made a boat trip inside the fjords around Longyearbyen, and in particular in the Isfjorden, where I took this picture through the porthole of the boat. This is the southern border of a territory of Svalbard named Oscar II Land. This area, and indeed all of Svalbard, is covered by snow most of the time, and just a few plants can germinate during July-August, when the average temperature is 5°C.

Svalbard is a very important island and region because it is dominated  by glaciers (60% of all the surface), which are important indicators of global warming and can reveal possible answers as to what the climate was like up to several hundred thousand years ago. Those glaciers are studied and analysed by scientists in order to better observe and understand the consequences of the global warming on our Earth.

By Fabien Darrouzet, Belgian Institute for Space Aeronomy

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their images to this repository and since it is open access, these photos can be used by scientists for their presentations or publications as well as by the press and public for educational purposes and otherwise. If you submit your images to Imaggeo, you retain full rights of use, since they are licensed and distributed by EGU under a Creative Commons licence.

Étretat is a coastal region in northern France, well known for its stunning geological landscape. Particularly the headland you see here.

“The chalk cliffs of Étretat” by Chiara Arrighi, distributed by the EGU under a Creative Commons licence.

Headland erosion is perhaps one of the best known processes in coastal erosion, where a crack in the headland is opened and enlarged by hydraulic abrasion. Continued wave action causes the widened crack or cave to break through the headland and form an arch. As erosion continues, the arch collapses, leaving behind a stack (or needle) that erodes down to its base to form a much smaller stump. There are some great examples of other coastal processes describes in The British Geographer.

How headlands form and coastal arches erode. Source: Sbsgeog’s Weblog.

But that’s not all there is to Étretat, the chalky cliffs are composed of several layers, clearly distinguishable in Arrighi’s photo. These chalk layers are of varying hardness and can be clustered into three main strata: the lowest is a light, fine, stratified chalk aggregate, rich in foraminifera; the middle stratum is a compact chalk layer with beds that are tens of metres thick, and the uppermost stratum is composed of chalk nodules that, like the lowest stratum, is rich in foraminifera.

These strata provide insight into how the chalk of the region was laid down: the fine strata would have been a calcareous ooze, deposited by gentle currents and the nodular material would have formed as small “bullets”, before accumulating more calcareous material as they are transported and redeposited elsewhere. The sediments that now make up the Étretat chalk sequences were subject to several episodes of deformation and slumping before cementing to form the layered cliffs you see above.

References:

Dercourt, J. and Paquet J. (1985). Sedimentary Facies. Geology Principles and Methods, pp. 195-206.

Bromley, R.G. and Ekdale A.A. (2006) Mass transport in European Cretaceous chalk; fabric criteria for its recognition. Vol. 34, pp.1079-1092.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their images to this repository and since it is open access, these photos can be used by scientists for their presentations or publications as well as by the press and public for educational purposes and otherwise. If you submit your images to Imaggeo, you retain full rights of use, since they are licensed and distributed by EGU under a Creative Commons licence.

Suwanosejima, which lies within the Ryukyu Islands, is one of Japan’s most active volcanoes, erupting almost continuously between the 1950s and mid 1990s. It has two active craters, the central Otake crater and the Bunka crater, to the southwest. While the frequency of these eruptions has declined, the volcano remains active, with strombolian and vulcanian type eruptions occurring every 2 to 4 weeks.

The geology of Suwanosejima, an 8 km long volcanic island. Source: Taketo Shimano/The Smithsonian National Museum of Natural History.

Strombolian eruptions, typified by the activity of the Italian volcano Stromboli, consist of distinct bursts of lava from a magma-filled conduit. The explosions are caused by the bursting of large bubbles of gas that are released from a basaltic to basaltic andesite lava. Vulcanian eruptions, on the other hand, occur when the magma is more viscous (andesitic, dacitic, or rhyolitic). Vulcanian eruptions (characteristic of those from the volcanic island of Vulcano) produce large ash clouds and pyroclastic flows (dense currents of hot ash, gas and rock that flow down the flanks of a volcano). The andesitic composition of Suwanosejima’s magma places its activity between the two, with frequent explosions of lava and ash.

The largest historical eruption at Suwanosejima took place over 1813 to 1814, when lava flows from the southwest crater reached the western coast of the island. This eruption culminated in the collapse of the Otake crater, generating a large debris avalanche and a horseshoe-shaped caldera (the Sakuchi caldera) at the volcano’s summit. The photo below, though, shows a more recent eruption that occurred in the Otake crater during November 2010. Explosive eruptions were followed by continuous lava effusion and degassing and large earthquakes associated with the eruption were followed by harmonic tremor lasting minutes to hours.

“Eruption of Suwanosejima volcano, Japan” by Haruhisa Nakamichi, distributed by the EGU under a Creative Commons licence.

Reference:

Iguchi M, Yakiwara H, Tameguri T, Hirabayashi J (2008). Mechanism of explosive eruption revealed by geophysical observations at the Sakurajima, Suwanosejima and Semeru volcanoes. Journal of Volcanology and Geothermal Research. Vol. 178, pp. 1-9.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their images to this repository and since it is open access, these photos can be used by scientists for their presentations or publications as well as by the press and public for educational purposes and otherwise. If you submit your images to Imaggeo, you retain full rights of use, since they are licensed and distributed by EGU under a Creative Commons licence.

Nothing captures beauty of Arizona’s landscape better than the Grand Canyon and its steeply-sided cliffs that have been carved by the Colorado River. This photo by Lukas Hoertnagl shows this stunning landscape as seen from Lipan Point in the Grand Canyon National Park.

“The Grand Canyon Symphony” by Lukas Hoertnagl. Distributed by the EGU under a Creative Commons licence.

The early geological history of America is preserved in the strata that make up the Grand Canyon’s famed banded landscape, which is composed of nearly 40 clear strata and over 100 rock units – from a 2 billion year-old metamorphic/igneous basement to the park’s dusty surface. Much of the canyon’s strata weren’t exposed until the Colorado River began to snake its way across the landscape.

Lipan Point (A) in the Grand Canyon National Park. Source: Google Maps.

After more than 150 years of study, though, Geologists are still working to understand the processes leading to the canyon’s formation. The biggest question? How the Colorado River came to take this course and start slicing the canyon cake.

The Colorado River as we know it, formed approximately 6 million years ago, following a change in the direction of many streams, which directed water towards a lower region of the Colorado Plateau. The confluence of these streams led to the formation of a large, down cutting river, which since then has sliced through over 1,800 metres of rock. The Colorado River did not have significant erosive power until it was integrated over the Great Welsh Cliffs and it while it flows from the Rockies in the East out West towards the Gulf of California today, this was not always the case.

This is where it starts to get hazy: what caused the course of the river to change? Was it rifting? Sinking of the Colorado Plateaux? A drastic change in the drainage patterns of the Colorado basin? Or was there something else contributing to the change in river flow? For now at least, the jury is out.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their images to this repository and since it is open access, these photos can be used by scientists for their presentations or publications as well as by the press and public for educational purposes and otherwise. If you submit your images to Imaggeo, you retain full rights of use, since they are licensed and distributed by EGU under a Creative Commons licence.

Congratulations to Philipp Stadler, Yiming Wang and Eva van Gorsel, winners of this year’s Imaggeo photo competition!

Winning image: Frost by Philipp Stadler

Second place: Icebear Rising by Yiming Wang

Third place: Regrowth after fires by Eva van Gorsel.

Imageo photos are distributed by EGU under a Creative Commons licence and are available in Imaggeo, the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their images to this repository and since it is open access, these photos can be used by scientists for their presentations or publications as well as by the press. 

The selection committee received close to 200 photos for this year’s EGU Photo Competition, covering fields across the geosciences. The stunning finalist photos are below and they are being exhibited in Hall X (basement, Blue Level) of the Austria Center Vienna, where you will also find voting terminals.

Do you have a favourite? Vote for it! The results will be announced on Friday 12 April during the lunch break.

Gypsum Dunes by Robert Wills

Mendenhall Glacier by Daniele Penna

Mirror, mirror by Anna Nadolna

Greenland Ice Sheet by Andrew Sole

Smooth Ice by Kay Helfricht

Colourful hydrovolcanism by Stephanie Flude

Regrowth after fires by Eva van Gorsel

Icebear Rising by Yiming Wang

Frost by Philipp Stadler

Climate change is in our hands by Stephanie Flude

Black Sand Vortex by Yiming Wang

 These images are distributed by EGU under a Creative Commons licence and are available in Imaggeo, the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their images to this repository and since it is open access, these photos can be used by scientists for their presentations or publications as well as by the press. 

Yellowstone National Park, USA, is well known for its outstanding natural beauty.

“Grand Prismatic Spring” by David Mencin, distributed by the EGU under a Creative Commons licence.

This is the Grand Prismatic Spring in the Midway Geyser Basin, Yellowstone National Park. It is the third largest hotspring in the world and the largest found in the United States, with a maximum diameter of about 90 m. It discharges roughly 2.5 cubic metres of mineral-rich water per minute, which flows down the rocky terraces evenly on all sides. Hotsprings are rich in minerals because warmer water is capable of holding more dissolved solids than colder water – and the water here can reach 87 °C in the centre of the spring!

Little can survive these high temperatures, though there are strains of thermophyllic (heat loving) bacteria and algae (chemoautotrophs and heteroautotrophs) that thrive in these conditions! There is more life found at the edges of the spring where waters are cooler. Rather than producing energy from the sun, as is the case for photosynthetic bacteria, chemoautotrophic bacteria oxidise minerals in the spring-water to produce energy. Heteroautotrpohs, on the other hand, use both photosynthesis and chemoautotrophy to obtain their energy.

These bacteria are also responsible for the bright rings of colour that surround the spring. Coating the rock in large bacterial mats; their energy-harnessing pigments dictate the colours that surround the water. If the bacteria contain more chlorophyll, the mats will be more green in colour and if they contain more carotenoids, the bacterial carpet will be more of an orangey brown.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their images to this repository and since it is open access, these photos can be used by scientists for their presentations or publications as well as by the press and public for educational purposes and otherwise. 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.

The Lena River flows throughout Russia from its source in the Baikal Mountains out into the Arctic Ocean, where the delta’s landscape is dominated by ice-rich Yedoma and thermokarst lakes. Thermokarst lakes have been identified as a source of carbon release to the atmosphere and Yedoma-like lake sediments are known to release more methane than any other sediment due to their incredibly high carbon content. So what is a thermokarst lake?

The Lena River Delta, dominated by Yedoma uplands and thermokarst lakes. Image taken by LANDSAT (source: NASA).

Thermokarst is a landscape that results from the thawing of both icy permafrost and larger ice masses. In northern Siberia, thermokarst starts to develop at the surface: once the ground subsidises, water accumulates in a series of small basins known as alasses. They continue to grow in size to form thermokarst lakes, which can either drain or coalesce with neighbouring lakes to form even larger ones that can reach several kilometres in diameter. When thermokarst lakes drain, they leave behind much smaller lake remnants that lie with a flat basin with steeply sloping sides. Multiple cycles of thermokarst development can occur within a single thermokarst basin to create a complex thermokarst landscape peppered with lakes and islands.

Kurungnakh Island, which lies within the Lena River Delta, formed during the Pleistocene and is part of the region’s thermokarst landscape. The cliff below exposes the Yedoma, a series of silty permafrost deposits with high ice and carbon contents. Permafrost is soil that is either at or below the freezing point of water and forms in regions where the mean annual temperature is below this. Permafrost soils are very rich in carbon, which is stored as peat and methane. The release of this carbon into the atmosphere has the potential to accelerate climate warming through a positive feedback system. That is, where a small change (the release of methane due to permafrost melt) has the capacity to cause a change of even greater magnitude (the presence of more methane in the atmosphere increases the temperature and accelerates the rate of permafrost degradation, releasing even more methane…).

The most immediately recognisable form of permafrost degradation is the presence of thermokarst – you can get a feel for this in the photo below:

“Kurungnakh Island” by Sebastian Zubrzycki. Distributed by the EGU under a Creative Commons licence.

The pale lower unit is comprised of fluvial sand, overlain by ice-rich permafrost (light grey) and capped with a thin covering of Holocene peat. Fluvial sands in this region are relatively ice-poor, which limits the capacity for further thermokarst development. While there is relatively little capacity for further thermokarst development, it is important to consider other processes associated with permafrost degradation and the rates at which they occur. In doing so, we can better quantify future carbon fluxes from permafrost soils in as the climate warms.

Reference:

Morgenstern, A., Grosse, G., Günther, F., Fedorova, I., and Schirrmeister, L.: Spatial analyses of thermokarst lakes and basins in Yedoma landscapes of the Lena Delta, The Cryosphere, 5, 849-867, doi:10.5194/tc-5-849-2011

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their images to this repository and since it is open access, these photos can be used by scientists for their presentations or publications as well as by the press and public for educational purposes and otherwise. 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.

These are the outwash plains for the Icelandic volcano, Katla:

“Sandstorm, Myrdalssandur outwash plain, Iceland” by Ragnar Th Sigurdsson. This image is distributed by the European Geosciences Union under a Creative Commons licence.

An outwash plain (or sandur) is a broad, shallowly sloping region ahead of a glacial front. They are made up of material that has been deposited by glacial meltwater, released either by geothermal heating or a subglacial eruption. The extensive volcanism and abundance of ice-capped volcanoes in southern Iceland means that the outwash plains are particularly well developed here.

The Mýrdalssandur outwash plain in relation to the volcano Katla (Mýrdasljökull) [source: Jóhannesdóttir and Gísladóttir, 2010].

Between flooding events, some vegetation takes hold, but much of the soil is loose and easily transported by wind. Indeed, the soil islands you see in the photo are formed by wind-blown soil and if they were to erode, the area would be a desert consisting of glacial alluvial sediments alone. Sandstorms, such as the one above, carry fine particulate matter (clays and glacial till) from the outwash plains to other areas and even contribute to the particulate pollution in Reykjavík, some 110 km away!

References:

Jóhannesdóttir, G. and Gísladóttir, G.: People living under threat of volcanic hazard in southern Iceland: vulnerability and risk perception, Natural Hazards Earth System Science, 10, 407-420, doi:10.5194/nhess-10-407-2010, 2010.

Thorsteinsson, T., Gísladóttir, G., Bullard, J. and McTainsh, G.: Dust storm contributions to airbourne particulate matter in Reykjavík, Iceland, Atmospheric Environment, 45, 5924-5933.

Warner, N.H.: Catastrophic outwash plains on Earth and Mars: comparisons from Iceland and Chasma Boreale, Mars. PhD thesis, Arisona State University, December, 2008.

You can find more Arctic images from Ragnar Th Sigurdsson here, and more from the Imaggeo open access database here.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their images to this repository and since it is open access, these photos can be used by scientists for their presentations or publications as well as by the press and public for educational purposes and otherwise. 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.