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Imaggeo

Imaggeo on Mondays: Just Passing

Imaggeo on Mondays: Just Passing

If lucky enough to visit Ilulissat Icefjord, you’d find yourself in a truly ancient landscape. From the up to 3.9 billion year old Precambrian rocks, to ice dating back to the Quaternary Ice Age (2.6 thousand years old) and archaeological remains which evidence the past settlement of this remote Greenlandic outpost, it’s no surprise this stunning location has been declared a UNESCO world heritage site.

Today’s Imaggeo on Mondays photograph was taken by Camille Clerc, at Sermermiut, an old inuit settlement at the mouth of the Ilulissat Icefjord. Located 1,000 km up the west coast of Greenland, in the Bay of Disko Bugt, 250 km inside the Arctic Circle, the icefjord is the sea mouth of Jakobshavn Glacier – one of the few glaciers on Greenland which reaches the sea. Confined either side by ancient Precambrian rocks, the icefjord forms a narrow, 3-6 km wide tidewater ice-stream, where vast amounts of meltwater and ice from the Greenland ice-sheet reach the sea.

Jakobshavn (also known as Sermeq Kujalleq) is Greenland’s fastest moving glacier. Huge chunks of ice break off the glacier front via Ilulissat Icefjord in a process known as glacier calving. Annually, over 35 km3 of ice is calved into the sea; equivalent to 10% of the production of all Greenland calf ice and more than any other glacier outside Antarctica! As a result, there is an almost constant production of icebergs, which vary in size from small lumps to bergs which can exceed 100m height. As they make their way towards the sea, the icebergs actively erode the fjord bed, slowly changing its morphology over time.

The tragic sinking of the Titanic on its maiden voyage, as a result of a collision with an iceberg on the night of the 15th April 1912, is part of modern history and was even portrayed in a Hollywood blockbuster. Could one of the mighty icebergs calved from Jakobshavn via Ilulissat Icefjord, be the culprit of the sinking of the White Star Line vessel? Pinpointing the exact location from which the glacier was calved is tricky. Most icebergs found in North Atlantic waters originate from the western coast of Greenland. They are pushed slowly towards more northerly latitudes by the West Greenland Current and then forced towards the Atlantic, hugging the coast of Canada, by the Labrador Current, eventually making their way to the Gulf Stream, along one of the world’s busiest shipping routes. The journey there is long and more often than not, the icebergs take such battering during the voyage that their original size is much diminished.

 

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: Seeing the world through a pothole

Imaggeo on Mondays: Seeing the world through a pothole

A beautiful image of a forest reflected in a pool of water within a pothole in southern Finland is this Monday’s Imaggeo image and it brought to you by Mira Tammelin, a Finish researcher.

The photo illustrates a pothole in the Askola pothole area in southern Finland. The pothole area is situated on the steep slopes next to river Porvoonjoki, approximately 70 kilometers to the northeast from the capital city Helsinki and 30 kilometers to the north from the Gulf of Finland. The potholes are carved into an outcrop of Proterozoic rocks that is surrounded by boreal taiga forest, which consists of mainly of coniferous tress such as pine, spruce and larch.

Potholes are cylinder-shaped cavities that form when stones carried by water start to circle in an eddy and churn the surrounding rock for an extended period of time. The majority of Finnish potholes, including those in Askola, were formed under a melting continental ice sheet during the late stages of the last glaciation 13 000 – 10 000 years ago. The area is also archaeologically important as it is one of the first places in Finland where humans settled after the deglaciation.

The more or less 20 potholes in Askola vary in shapes and sizes and some of them belong to the largest in the world. The largest pothole in Askola, called The Giant’s Tub, is 4.2 meters wide and 10.3 meters deep. The pothole in the picture is one of the smaller potholes in the area with a diameter less than a meter. It has filled with rainwater thus reflecting a beautiful, sunny midsummer day.

By Mira Tammelin, Research Fellow at the University of Turku, Finland.

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: Scales of fluvial dissection

Imaggeo on Mondays: Scales of fluvial dissection

High peaks, winding river channels and a barren landscape all feature in today’s Imaggeo on Mondays image, brought to you by Katja Laute, a geomorphologist from Norway. 

This photo was taken from an airplane flying over the Zagros Mountains in Iran. The Zagros Mountain range stretches south and west from the borders of Turkey and Russia to the Persian Gulf, and is Iran’s largest mountain range. The mountain range has a total length of 1500 km and stretches from north eastern Iraq, to the Strait of Hormuz. Many peaks are higher than 2900 m. The tallest mountain is Zard-Kuh at an elevation of 4548 m.

The Zagros fold and thrust belt was formed by the collision of the two tectonic plates- the Iranian Plate and the Arabian Plate. The collision resulted in parallel folds, which are seen as broad anticlines forming the high mountain peaks, , and orogenically are the same age as the Alps. The Zagros Mountains are made up primarily of limestone and dolomite – a sedimentary carbonate rock primarily composed of the anhydrous carbonate mineral of the same name.

The region exemplifies the continental variation of the Mediterranean climate pattern, with a snowy, cold winter and mild rainy spring followed by a dry summer and autumn. In winter, low temperatures can often drop below – 25 °C and many mountain peaks exhibit snow even in summer. The most common ecosystems in the Zagros Mountains are the forest and steppe areas which have a semi-arid temperate climate.

The photo gives an amazing impression of different scales of fluvial dissection. The landscape consists of valleys and their included channels organized into a connecting system known as a drainage network. The powder snow enhances nicely the dendritic drainage pattern.

 

By Katja Laute, Geomorphologist, Trondheim, Norway

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: A fold belt within a grain

Imaggeo on Mondays: A fold belt within a grain

Tiny crinkly folds form the main basis of today’s Imaggeo on Mondays. Folding can occur on a number of scales; studying folds at all scales can reveal critical information about how rocks behave when they are squeeze and pinched, as described by Sina Marti, from the University of Basel.

Although many geoscientists have seen such fold structures many times before, if you noticed the scale bar in the lower left of the image, you might be surprised of the small scale of these folds!

The presented image is a high-magnification image taken on an electron microscope, showing sub-micrometer scale folds developed within a deformed pyroxene grain – a chain silicate mineral, for example common in the oceanic crust of the earth. The folded layers are primary exsolution lamellae of more calcium rich and calcium poor chemical composition. These lamellae formed during the early, magmatic history of the pyroxene grain, where it crystallized and cooled down in a shallow intrusion. The folding subsequently took place during deformation and the following text will try to give a short overview on why and how these folds have formed.

The presented image was made using a back-scattered electron (BSE) detector, where different grey values indicate different chemical compositions. This effect originates from the fact, that some of the electrons, which “bombard” the sample in the electron microscope, are back scattered by the atoms near the sample surface and then detected by the BSE. Heavier atoms (with a greater atomic number, Z) have a higher probability to generate a backscattered electron. Consequently, where heavy atoms occur, more backscattered electrons reach the detector and the area appears bright, compared to dark- appearing areas, where light atoms prevail. Because of this sensitivity of the BSE image on chemical composition, we can see the exsolution lamellae in the pyroxene with different grey values.

Although the folds in this image occur on the nanometer- to micrometer scale, their geometry and mode of formation is the same as is observed in large-scale fold belts (e.g. the Helvetic nappes in the Swiss Alps). There, this fold type develops mainly in layered sediments, which have contrasting properties: alternating series of competent and incompetent layers leads to boundary instabilities and thus to folding. In the present case, the contrasting properties of the layers – also known as anisotropy – is a result of the formation of the exsolution lamellae and enables folding even at the very small scales seen within this single grain. One can even see the difference between the layers in the image: The darker lamellae change their layer thickness more readily (best seen in fold hinges – the place of strongest bend in the fold) than the brighter layers, indicating that the darker layers deform more easily..

This folded pyroxene is an astonishing example that certain processes, which generate geological structures, operate over multiple orders of magnitude in scale. Without a scale bar provided, it would not be possible to determine the scale of these structures and tell them apart from folds formed in outcrop or even on larger scales. Now, it should not be confused: such a pyroxene grain will not be encountered in the same tectonic regime as large-scale fold belts. But exactly for this reason, it is a beautiful example displaying the overall controlling importance of anisotropy over most other material properties, independent of scale. For the deformation of rocks, anisotropy almost always plays a key role in the deformability, and in general controls the development of structures such as folds like in the present case.

By Sina Marti, Department of Environmental Science, Geological Institute, Basel

Sina would like to thank  the Center of Microscopy (ZMB) at the University of Basel, where the image was taken and also thank the ZMB for providing the infrastructure.

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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