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erosion

Imaggeo on Mondays: The Groapa Ruginoasa

Imaggeo on Mondays: The Groapa Ruginoasa

The Apuseni National Park, in Romania, is a geoscientists paradise. This 187,000 acre Park in the Western Carpathians boasts caves, deep valleys and gorges, karst landscapes, rocky steep walls and underground watercourses. The sheer beauty of the landscape is captured in today’s Imaggeo on Mondays image featuring the Groapa Ruginoasa, a deep sandstone ravine.

“Locality names of morphological features often allow for drawing conclusions on the geological processes that shaped them,” says Martin Reiser, who took the photograph.

The steep, barren slopes of the so called “Groapa Ruginosa” (Romanian for rusty pit) nature monument show a stark contrast to the gentle morphology and green woods of the Apuseni National Park. This spectacular ravine was shaped by headward erosion of an intermittent stream in the Valea Seacă (“Dry Valley”). Headward erosion occurs at the start of channels and streams, causing the origin to move backward and thus elongating the water course. The steepness of the slope on which the channel forms contributes to the speeding up of the erosive processes.

The “rusty pit”  is about 100 m deep and measures ca. 600 m across. Although there are no studies on the rate of erosion at this locality, geological maps from the late 19th century show a fairly small extent of this morphological feature.

“The yellowish to reddish colour of the eroded Permian to Lower Triassic sediments (sandstones, conglomerates and phyllites) gave the ravine its name,” explains Martin. Further downstream, the name of the Valea Galbena (“Yellow Valley”) also relates to the colour of the stream that carries the eroded sediments.

 

By Martin Reiser, University of Innsbruck and Laura Roberts Artal, EGU Communication Officer.

Imaggeo on Mondays: The place where water runs through rocks

Imaggeo on Mondays: The place where water runs through rocks

Antelope Canyon, located in Arizona, USA, was formed by erosion of the Navajo Sandstone, primarily due to flash flooding and secondarily due to other sub-aerial processes (think of physical weathering processes such as freeze-thaw weathering exfoliation and salt crystallisation). Rainwater runs into the extensive basin above the slot canyon sections, picking up speed and sand as it rushes into the narrow passageways. Over time the passageways are eroded away, making the corridors deeper and smoothing hard edges in such a way as to form characteristic ‘flowing’ shapes in the rock.

The Navajo Sandstone was deposited in an aeolian (wind-blown) environment composed of large sand dunes: imagine a sea of sand, or an erg, as it is known scientifically, not dissimilar to the present Sarah desert landscape. The exact age of the Navajo Sandstone is controversial, with dated ages ranging from Triassic to early Jurassic, spanning a time period between 250 million years ago to approximately 175 million years ago. The difficulty in determining the exact age of the unit lies in its lack of age diagnostic fossils. The Navajo Sandstone is not alone in this quandary, dating is a common problem in aeolian sediments.

“The picture was taken during a three week Southwest USA road trip in summer 2012. One of the highlights was the visit to Antelope slot canyon, which is located on Navajo land east of Page, Arizona. The Navajo name for Upper Antelope Canyon is Tsé bighánílíní, which means the place where water runs through rocks,” explains Frederik Tack, an atmospheric scientist from the Belgian Institute for Space Aeronomy and author of today’s Imaggeo on Monday’s photograph.

The erosive processes which form the canyon are still ongoing. There is an elevated risk of flash floods, meaning the canyon can only be visited as part of guide tours.

“The canyon was actually quite crowded which made taking this picture challenging, especially as I wanted to capture the peace and solitude of the landscape,” describes Tack.

The effort was worth it: Waved rocks of Antelope slot canyon was one of the EGU’s 2015 Photo Contest finalists!

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/.

The known unknowns – the outstanding 49 questions in Earth Sciences (Part IV)

We are coming to the end of the known unknowns series and so far we have explored issues which mainly affect the inner workings of our planet. Today we’ll take a look at the surface expression of the geological processes which shape the Earth. Topography significantly affects our daily life and is formed via an interplay between primarily tectonics and climate, but it also affected by biological, mechanical and chemical processes at the Earth’s surface. We’ve  highlighted how advances in technology mean detailed study of previously inaccessible areas has now become possible, but that doesn’t mean there aren’t still plenty of questions left unanswered!

Earth’s landscape history and present environment

Drainage patterns in Yarlung Tsangpo River, China (Credit: NASA/GSFC/LaRC/JPL, MISR Team)

Drainage patterns in Yarlung Tsangpo River, China (Credit: NASA/GSFC/LaRC/JPL, MISR Team)

  • Can we use the increasing resolution of topographic and sedimentary data to derive past tectonic and climatic conditions? Will we ever know enough about the erosion and transport processes? Was also the stocasticity of meteorological and tectonic events relevant in the resulting landscape? And how much has life contributed to shape the Earth’s surface?
  • Can classical geomorphological concepts such as ‘peneplanation’ or ‘retrogressive erosion’ be understood quantitatively? Old mountain ranges such as the Appalachian or the Urals seem to retain relief for > 10^8 years, while fluvial valleys under the Antarctica are preserved under moving ice of kilometric thickness since the Neogene. What controls the time-scale of topographic decay? (Egholm, Nature, 2013)
  • What are the erosion and transport laws governing the evolution of the Earth’s Surface? (Willenbring et al., Geology, 2013) Rivers transport sediment particles that are at the same time the tools for erosion but also the shield protecting the bedrock. How important is this double role of sediment for the evolution of landscapes? (Sklar & Dietrich, Geology, 2011, tools and cover effect); (Cowie et al., Geology, 2008, a field example).
  • Can we predict sediment production and transport for hazard assessment and scientific purposes? (NAS SP report, 2010)
  • What do preserved 4D patterns of sediment flow tell us from the past of the Earth? Is it possible to quantitatively link past climatic and tectonic records to the present landforms? Is it possible to separate the signals of both processes? (e.g. Armitage et al., Nature Geosc, 2011).

    Smaller-scale patterns at the limit between river channels and hillslopes (Credit: Perron Group, MIT)

    Smaller-scale patterns at the limit
    between river channels and hillslopes (Credit: Perron Group, MIT)

  • Can we differentiate changes in the tectonic and climate regimes as recorded in sediment stratigraphy? Some think both signals are indeed distinguishable(Armitage et al., Nature Geosc, 2011). Others, (Jerolmack &Paola, GRL, 2010), argue that the dynamics intrinsic to the sediment transport system can be ‘noisy’ enough to drown out any signal of an external forcing.
  • Does surface erosion draw hot rock towards the Earth’s surface? Do tectonic folds grow preferentially where rivers cut down through them, causing them to look like up-turned boats with a deep transverse incision? (Simpson, Geology, 2004).
  • How resilient is the ocean to chemical perturbations? What caused the huge salt deposition in the Mediterranean known as the Messinian Salinity Crisis? Was the Mediterranean truly desiccated? What were the effects on climate and biology, and what can we learn from extreme salt giants like this? (e.g. Hsu, 1983; Clauzon et al., Geology, 1996; Krijgsman et al., Nature, 1999; Garcia-Castellanos & Villaseñor, Nature, 2011). Were the normal marine conditions truly reestablished by the largest flood documented on Earth, 5.3 million years ago? (Garcia-Castellanos et al., Nature, 2009).

The next post will be our final post in the series and we will list open questions on how climate has contributed to shape the surface of planet Earth, from its surface to the emergence of life and beyond.

Have you been enjoying the series so far? Let us know what you think in the comments section below, particularly if you think we’ve missed any fundamental questions.

By Laura Roberts Artal, EGU Communications Officer, based on the article previously posted on RetosTerricolas by Daniel Garcia-Castellanos, researcher at ICTJACSIC, Barcelona

Imaggeo on Mondays: Soil and water conservation in the Dogon Plateau, Mali

Velio Coviello, a scientist from the Research Institute for Hydrogeological Protection, Italy, and one of the winners of the EGU 2014 Photo Contest, brings us this week’s Imaggeo on Mondays. He sheds light on his winning image and the problems associated with conserving soils and water in Western Africa… 

This picture was taken on Mali’s Dogon plateau during the dry season, in the course of a late sandstorm day. Between November and March, a hot, dust-laden Harmattan haze frequently persists over the whole of  Western Africa. The Harmattan is a hot, dry wind blowing from the Sahara, carrying large amounts of dust and transporting it for hundreds of kilometers. Here, we see two men drawing water from a deep and narrow well excavated by hand. This latter is a task commonly carried out by children, who climb down to dig the well bottom.

Men and children drawing water for irrigation in the Dogon plateau during a sandstorm. (Credit: Velio Coviello via imaggeo.egu.eu)

Men and children drawing water for irrigation during a sandstorm. (Credit: Velio Coviello via imaggeo.egu.eu)

Mali has a low population density, most settlements are concentrated in the southern part of the country and along the Niger River, where the climate is less harsh and water availability is higher. In the north, Mali is arid and only those who raise livestock can make a living.

One of the most important tourist attractions in Mali is the Dogon Plateau, which sits in the central part of the country, east of the Niger River. The plateau gently descends westward to the river valley and ends in abrupt cliffs on the southeast. These cliffs reach an elevation approaching 1,000 meters at Bandiagara, the main village of the Pays Dogon (Land of the Dogon). These geological, archaeological and ethnological interests, together with the striking landscape, make the Dogon Plateau one of West Africa’s most impressive sites.

Ensuring the population has safe and sustainable access to water is one of the major challenges in the Sahelian region. Facing recurring drought events and encroaching desertification, Sahelian countries are currently heavily affected by climate change. Extreme rainfall events and high rainfall intensity are the main cause of soil erosion and land degradation. Consequently, high rates of soil transport can lead to reservoir siltation and the reduction of water availability for agriculture. To cope with these issues, traditional soil and water conservation (SWC) measures like hillside terracing, permeable rock dams, stone lines, earth basins, planting pits and earth mounds have been regularly employed in the Sahelian area. The Dogon Plateau is home to a broad variety of these measures, implemented to deal with the acute shortage of soil and water. As the population urgently needs support to preserve soil fertility and reduce soil erosion, SWC measures need to be improved and adopted more widely. However, most donors fund short-term projects without considering the maintenance that is needed to ensure SWC measures remain effective long-term.

The first lesson is that there is much to learn from the traditional ways of doing things and SWC projects should always begin by looking at what the people are doing for themselves. Secondly, the international cooperation actors should set up long-term funding programs improving the participation and inclusion of local communities. The final goal would be to ensure the stakeholders are not permanently dependent on international aids.

by Velio Coviello, Research Institute for Hydrogeological Protection (IRPI) and Italian National Research Council (CNR)

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.