GeoLog

erosion

Imaggeo on Mondays: Natural Bridges Monument, Utah, USA

Imaggeo on Mondays: Natural Bridges Monument, Utah, USA

Slowly but surely, the force of water has carved out a beautiful landscape in the sandstones of the Colorado Plateau. Suspended over canyons, naturally formed bridges and arches are the starts of Utah’s first national monument. The geological and modern  history of the region is rich as Kimberly Galvez, a student of the University of Miami, describes below.

This image shows an overview of a portion of the Natural Bridges Monument in Utah, taken from the Colorado Plateau. In the lower center of the picture is the Sipapu Bridge, one of the 3 bridges within the national park.

The dominating sandstone comes from the Permian Cedar Mesa Formation that is part of the Colorado Plateau, a geologic province that extends through southern Utah and northern Arizona, northwest New Mexico, and western Colorado; with geologic units including the Lower Cutler Beds from the Pennsylvanian, Permian Organ Rock and Cedar Mesa Formation, Triassic Chinle and Moenkopi Formations, Jurassic Wingate Sandstone and the Quaternary alluvium.

Due to the regional uplift the Colorado Plateau experienced, meandering rivers progressively cut through the crossbedded sandstone – cross-bedding reflects the transport of sand by a flow of water over a river channel – of the Cedar Mesa Formation forming the bridges, leaving behind the exposed erosional surfaces carved out by the river.

Today, these bridges face many challenges: The region is still seismically active. Earthquake activity could lead to the collapse of (some of) the bridges and other small formations. Due to the low stability of the sandstone from the lack of anchoring from root structures, slope failures and slumps can be quite common and especially in the event of flash floods. Continuous wind patterns increase erosion and alter the exposed surfaces and the structure of the channel is constantly changing due to seasonal rainstorms.  Sediment transport and deposition, caused by streamflow, is a major factor in channel morphology and, therefore, the ecosystem of the Natural Bridges Monument.  The National Park Service constantly monitors the changes and issues that arise.

A final remark: Thanks to the entire group of the 2015 Annual AAPG Student Field Trip for making this photo possible. Members of the CSL – Center for Carbonate Research and the UM Student Chapter of AAPG for funds, and field trip leaders: Gregor Eberli and Donald McNeill.

By Kimberly C. Galvez, University of Miami – RSMAS

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: Erosion

Imaggeo on Mondays: Erosion

In mountainous regions precipitation – be that in the form of rain, hail or snow, for example – drives erosion, which means it plays an important part in shaping the way the landscape looks. Precipitation can directly wear away at hillsides and creates streams and rivers, which leave their mark on the scenery by cutting and calving their way through it.

Take for instance the hills in the arid coastal region of Pisco Valley, in Peru (pictured above). Contrary to what you might think having first looked at the photograph, very little erosion of rock happens here. The solid rock which makes up the undulating hills is a hard-wearing grantic rock (not dissimilar to the stone you might covet for your kitchen countertops).

Over time, wind-blown sediments have blanketed the granites. Loesses, as the deposits are known, are very soft and range between 20 and 60 cm in thickness. The channels which slice the hillside are carved into the loesses, not the granites which lie below.

Rain is such a rare thing in these parts that soil barely forms (Norton et al., 2015) and it’s impossible for plants to grow on the soft substrate, leaving the slopes exposed to the elements. When the infrequent rains do come, small scale gullies, only a few centimetres deep cut their way into the sediments, taking away material loosened by torrential rainfalls at high speeds.

References

Kevin P. Norton, Peter Molnar, Fritz Schlunegger, The role of climate-driven chemical weathering on soil production, Geomorphology, Volume 204, 1 January 2014, Pages 510-517, ISSN 0169-555X, http://dx.doi.org/10.1016/j.geomorph.2013.08.030.

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: The shrinking of Earth’s saltiest lake

One of the consequences of the rapid fall of the water level (>1 m per year), is that vast areas of salt-rich ground of the shrunken Dead Sea are prone to strong dissolution and mechanical erosion of the subsurface processes.

The Dead Sea is one of the saltiest lakes on Earth, located at the lowest point of the globe.  For centuries it has been known for the restorative powers of its muds and waters. Their hypersalinity means it is possible to easily float on the lake’s surface.

Bordering Israel, the West Bank and Jordan, it is a unique environment in an otherwise arid region.  Changing climate, which is seeing temperatures rise in the Middle East, and the increased demand for water in the region (for irrigation) mean the areas on the banks of the lake are suffering a major water shortage. As a result, the lake is shrinking at an alarming rate.

The changing geomorphology of the Dead Sea region is now the focus of a large international project (DESERVE) to address the resulting geohazards at the Dead Sea.

One of the consequences of the rapid fall of the water level (>1 m per year), is that vast areas of salt-rich ground of the shrunken Dead Sea are prone to strong dissolution and mechanical erosion of the subsurface processes. This leads to the widespread land subsidence and the development of sinkholes, which pose a major geological hazard to infrastructure, local population, agriculture and industry in the Dead Sea area, writes Djamil Al-Halbouni in an abstract presented at the EGU 2016 General Assembly.

Today’s Imaggeo on Monday’s image was taken in the purpose of investigating the sinkhole phenomenon along the coastline.

“Near-surface aerial photography offer valuable hints on possible processes that lead to the formation of huge depression zones, e.g. the ground and surface water flow, the existence of vegetation and water sources or simply the morphology,” explains Djamil.

Sets of images are then combined into digital terrain models to quantitatively estimate hazard potentials and development of sinkholes via repeated measurements.

Specifically, this image was taken by a camera on a helikite balloon from 150m altitude. It shows a canyon penetrating the whitish pure salt shoreline at the Jordanian coast. It also reveals, in its’ magnitude surprising for the scientists involved, round structures under the shallow water, which are interpreted as submarine springs and possible submarine sinkholes close to the shore.

 By Laura Roberts and Djamil Al-Halbouni of the German Research Center for Geosciences, Physics of the Earth, Potsdam, German

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: the rocks that look like Swiss cheese

Imaggeo on Mondays: the rocks that look like Swiss cheese

Over the course of centuries and millennia, the force of winds, seas, ice and rains, sculpt rock formations around the globe. From the world-famous glacier carved landscapes of Yosemite National Park, to the freeze-thawed hoodoos at Bryce National Park, through to the wind battered stone pillars of South China Karst, boundless geological formations have been transformed by the power of erosion and weathering.

When the force of winds and salty waters combine, their effect on the surface of rocks is quite unique. In some costal environments, a network of holes, of all shapes and sizes, puncture otherwise smooth and silky rocks. This form of weathering is aptly known as honeycomb weathering (though some of you might be more familiar with terms such as cavernous weathering, alveoli/alveolar weathering, stone lattice, stone lace or miniature tafoni weathering). Limestones, sandstones and granites are most affected.

Exactly how the interaction of the sea breeze and the salt in ocean waters results in the distinctive ‘Swiss cheese’ weathered pattern remains a bit of a mystery.  One of the front running theories proposes that it is the culmination of physical and chemical weathering.

Evaporation of leachate causes a deposition of the rocks minerals on its surface which leads to a decomposition of the rocks interior. Additionally salt weathering caused by oceanic brackish water as well as temperature changes support the formation of this feature,” explains Michael Grund, a researcher at Karlsruhe Institute of Technology.

In Corsican, Tafoni, means hole or perforated rock, so it is not surprising that this form of weathering sometimes takes its name after the Tafoni rock formation on the southern coast of Sardinia, where Michael snapped a superb example of the potholed intrusives which dominate the area.

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/.