GeoLog

Geomorphology

Imaggeo on Mondays: Small scale processes, large scale landforms

Imaggeo on Mondays: Small scale processes, large scale landforms

This picture was taken in a sea cliff gully landscape at the Portuguese coast. It shows the microrelief which small scale wash and erosional processes produce in these poorly consolidated sediments. These small scale landforms could be interpreted as initial stages of larger scale gully landforms, which can be seen in the back. This highlights the importance of regarding scales and scale linkages in the geosciences.

Description by Jana Eichel, as it first appeared on imaggeo.egu.eu.

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: Hole in a hole in a hole…

Imaggeo on Mondays: Hole in a hole in a hole…

This photo, captured by drone about 80 metres above the ground, shows a nested sinkhole system in the Dead Sea. Such systems typically take form in karst areas, landscapes where soluble rock, such as limestone, dolomite or gypsum, are sculpted and perforated by dissolution and erosion. Over time, these deteriorating processes can cause the surface to crack and collapse.

The olive-green hued sinkhole, about 20 m in diameter, is made up of a mud material coated by a thin salted cover. When the structures collapse, they can form beautiful blocks and patterns; however, these sinkholes can form quite suddenly, often without any warning, and deal significant damage to roads and buildings. Sinkhole formations have been a growing problem in the region, especially within the last four decades, and scientists are working hard to better understand the phenomenon and the risks it poses to nearby communities and industries.

Some researchers are analysing aerial photos of Dead Sea sinkholes (taken by drones, balloons and satellites, for example) to get a better idea of how these depressions take shape.

“The images help to understand the process of sinkhole formation,” said Djamil Al-Halbouni, a PhD student at the GFZ German Research Centre for Geosciences in Potsdam, Germany and the photographer of this featured image. “Especially the photogrammetric method allows to derive topographic changes and possible early subsidence in this system.” Al-Halbouni was working at the sinkhole area of Ghor Al-Haditha in Jordan when he had the chance to snap this beautiful photo of one of the Dead Sea’s many sinkhole systems.

Recently, Al-Halbouni and his colleagues have employed a different kind of strategy to understand sinkhole formation: taking subsurface snapshots of Dead Sea sinkholes with the help of artificial seismic waves. The method, called shear wave reflection seismic imaging, involves generating seismic waves in sinkhole-prone regions; the waves then make their way through the sediments below. A seismic receiver is positioned to record the velocities of the waves, giving the researchers clues to what materials are present belowground and how they are structured. As one Eos article reporting on the study puts it, the records were essentially an “ultrasound of the buried material.”

The results of their study, recently published in EGU’s open access journal, Solid Earth, give insight into what kind of underground conditions are more likely to give way to sinkhole formation, allowing local communities to better pinpoint sites for future construction, and what spots are best left alone. This study and further work by Al-Halbouni and his colleagues have been published in a special issue organised by EGU journals: “Environmental changes and hazards in the Dead Sea region.”

By Olivia Trani, EGU Communications Officer

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 modern cliff hides ancient dunes

Imaggeo on Mondays: A modern cliff hides ancient dunes

Ancient sand dunes exposed off a cliff face on the shoreline of Nova Scotia at the Islands Provincial Park. The juxtaposition of the high angled strata and flat lying layers above revels the drastic change in climate in Nova Scotia’s history; from vast sand dunes to a calm lake system, and presently the western coastline of the Atlantic Ocean.

Description by Robert Wu, as it first appeared on imaggeo.egu.eu.

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: How erosion creates natural clay walls

Imaggeo on Mondays: How erosion creates natural clay walls

The badlands valley of Civita di Bagnoregio is a hidden natural gem in the province of Viterbo, Italy, just 100 kilometres from Rome. Pictured here is the ‘wall,’ one of the valley’s most peculiar features, where you can even find the wooden structural remains of a trail used for agricultural purposes in the 19th and 20th centuries.

The photograph was taken by Chiara Arrighi, a post-doc research assistant at the University of Florence (Italy), in May last year after climbing roughly 200 metres from the bottom of the Chiaro creek valley. Trails in this region are not well traced or maintained, so she had to find her own way up among the chestnut woods. Once at the top, the trail becomes narrow and unprotected. “The inhabitants of the area still do not exploit this natural beauty as a tourist attraction,” said Arrighi. “In fact, nobody was on the trail, and the silence [was] unreal.”

Badlands are a typical geological formation, where grains of sand, silt and clay are clumped together with sedimentary rock to form layers, which are then weathered down by wind and water. The terrain is characterised by erosive valleys with steep slopes, without vegetation, separated by thin ridges.

Due to the slope’s steep angle and the clay’s low permeability, little water is able enter the soil. Instead water quickly flows across the surface, removing surface clay and carving into the slopes as it does so.

The morphological evolution of the clay slopes can be very rapid (for example, rock falls can occur quite suddenly after heavy rainfall) and occurs as a result of several physical mechanisms, such as mud flows, solifluction (slow movement of wet soil towards the bottom of the valley) and sliding.

During the evolution of the badlands, peripheral portions of the terrain made up of volcanic deposits (tuff cliffs) rose up from the landscape, bordered by nearly vertical slopes (called scarps). Many towns have been built on these erected hilltops, such as Civita di Bagnoregio.

By Chiara Arrighi and Olivia Trani

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/.