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dunes

Imaggeo on Mondays: Of ancient winds and sands

Imaggeo on Mondays: Of ancient winds and sands

Snippets of our planet’s ancient past are frozen in rocks around the world. By studying the information locked in formations across the globe, geoscientist unpick the history of Earth. Though the layers in today’s featured image may seem abstract to the untrained eye, Elizaveta Kovaleva (a researcher at the University of the Free State in South Africa) describes how they reveal the secrets of ancient winds and past deserts.

In summer 2016 we toured the Western US in a minivan. We visited many of the gems of Utah, Arizona, and New Mexico, such as Monument Valley, Antelope Canyon, Grand Canyon, The Arches, Bryce Canyon, White Sands Monument… But the most precious and memorable for me was Zion National Park in Utah. This canyon is a unique and special place. First, because you access it from the bottom, unlike most of the other canyons, which you observe from cliff tops, such as the Grand Canyon. Thus, as you drive along the road, leading into Zion National Park, you look upward into the magnificent cliffs and rock temples. Small hiking trails lead up to waterfalls, arches and breathtaking views.

The cliffs of Zion National Park are built of Navajo Sandstone and display aeolian deposits, which have been shaped by winds, on a massive scale. They are the remnants of an ancient fossil-bearing sand desert, one of the greatest and largest wind-shaped environments that has ever existed on Earth.

In the Early Jurassic, up to 200 million years ago, the Navajo desert covered most of the Colorado Plateau (which today includes the states of Utah, Colorado, New Mexico and Arizona). Fossils, found in these sand deposits, include ancient trees, dinosaur footprints and rare dinosaur bones.

In Zion National Park, the thickness of sand deposits reaches 762 m. Beautiful cross-beds are cross-sections through fossilized towering sand dunes. They indicate the direction of the ancient winds, which were mainly responsible for moving and accumulating the sand in the Navajo desert. On the top, the Navajo sandstone is abruptly truncated by a regional unconformity, which indicates the erosion of the overlying sediments, and is covered by Middle Jurassic sediments. In remains unknown how much of the Navajo sandstone was eroded from the top of the formation during this weathering episode. It might be that the thickness and height of the Navajo sand dunes used to be even more impressive than it is now.

The cliffs of Zion National Park. Pictured is Checkerboard Mesa (South-Eastern entrance to the Zion National Park. Credit: Credit: Elizaveta Kovaleva.

By Elizaveta Kovaleva, post-doctoral researcher at University of the Free State, in South Africa

Movement of ancient sand is one of the winners of the 2017 Imaggeo Photo Contest.

References

Ron Blakey and Wayne Ranney, Ancient Landscapes of the Colorado Plateau, Grand Canyon Association, 2008, p.156.

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: Coastal erosion

Imaggeo on Mondays: Coastal erosion

Coastlines take a battering from stormy seas, gales, windy conditions and every-day wave action. The combined effect of these processes shapes coastal landscapes across the globe.

In calm weather, constructive waves deposit materials eroded elsewhere and transported along the coast line via longshore-drift, onto beaches, thus building them up. Terrestrial material, brought to beaches by rivers and the wind, also contribute.  In stormy weather, waves become destructive, eroding material away from beaches and sea cliffs.

In some areas, the removal of material far exceeds the quantity of sediments being supplied to sandy stretches, leading to coastal erosion. It is a dynamic process, with the consequences depending largely on the geomorphology of the coast.

Striking images of receding coastlines, where households once far away from a cliff edge, tumble into the sea after a storm surge, are an all too familiar consequence of the power of coastal erosion.

In sandy beaches where dunes are common, coastal erosion can be managed by the addition of vegetation. In these settings, it is not only the force of the sea which drives erosion, but also wind, as the fine, loose sand grains are easily picked-up by the breeze, especially in blustery weather.

Grasses, such as the ones pictured in this week’s featured imaggeo image, work by slowing down wind speeds across the face of the dunes and trapping and stabilising wind-blown sands. The grasses don’t directly prevent erosion, but they do allow greater accumulation of sands over short periods of time, when compared to vegetation-free dunes.

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: Dune ridge perspective

Imaggeo on Mondays: Dune ridge perspective

Imagine taking a hike over soft, ever shifting sands. This is exactly what Martina Klose, a researcher at USDA, did when she captured this beautiful photograph. While most of us will likely think of deserts as inhospitable and static landscapes, they can tell us much about dune forming processes, as Martina explains in today’s blog post.

The photograph shows the view down from the crest of a megadune in the Badain Jaran Desert in China. It was taken during a two-day field trip in the course of the International Conference on Aeolian Research (ICAR) VIII, which took place in Lanzhou, China, in 2014.

Aeolian processes are wind-generated processes, such as the emission, transport, and deposition of sediment

The Badain Jaran desert is located north of the Hexi Corridor in western Inner Mongolia and is one of the largest areas of shifting sands in China. With maximum dune heights of a few hundred meters, the Badain Jaran Sand Sea hosts some of the largest megadunes in the world. The sand sea is not only dry, however – amongst the dunes are a number of lakes of various sizes, creating a picturesque environment. You can see what it looks like from space by following the link to this NASA satellite image!

In general, wind is the driving force for dune formation. In the case of the Badain Jaran Sand Sea, the local topography and the subsurface water source are likely additional factors contributing to the development and evolution of the dune fields.

After a long bus drive on the way to the sand sea, climbing one of the giant dunes was a welcoming exercise for most of the conference participants – rewarded with a stunning view from the dune crest and optionally a fun slide down the dune slope.

 By Martina Klose, USDA-ARS Jornada Experimental Range

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: Escullos

Imaggeo on Mondays: Escullos

This picture shows a Quaternary aeolianite fossil dune at the Escullos beach, in the Nature Reserve of Cabo de Gata (Almeria, Spain). Originally a soft accumulation of sand grains, shaped by the wind into large mounds and ridges, the dunes eventually turn into rock. As the sediments compact under their own pressure and expel any moisture and fluids retained within them, they become lithified and become the structure seen in this week’s Imaggeo image. This particular example is a richly fossilifeorous and contains abundant cidaroid spines. Cidaroids are primitive forms of sea urchins, but unlike the more familiar, well rounded spike covered sea hedgehogs, their spikes are much more separated and sparse.

A present day cidaroid. Note the sparse and relatively flat spines. Credit, Alicia Morugán.

A present day cidaroid. Note the sparse and relatively flat spines. Credit, Alicia Morugán.

Almeria is the eastern most province of Andalucia, located in South East Spain. Almeria province is geologically very interesting as the relationships between tectonics, sedimentary geology and geomorphology are evident throughout the landscape. The province lies within the Baetic Cordillera, an Alpine mountain chain resulting from the collision of the micro-Iberian and African plate from Late Mesozoic to Middle Cenozoic times. This characteristic makes it very tectonically active. Furthermore, Almeria province has the driest climate in Europe, resulting in mean annual precipitation of less than 300 mm. In terms of geomorphology, quaternary alluvial fans are the most common structure in the region. Geologically speaking, aeolianite rocks are the most common rock in the region. A final thanks: thanks Maria Burguet for support editing the picture.

By Alicia Morugán, Universitat de València, València, Spain

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/.