GeoLog

sedimentology

Imaggeo on Mondays: how short-term storms can impact our landscapes

Imaggeo on Mondays: how short-term storms can impact our landscapes

In the Sierra de Aconquija, a mountain range in the southern Central Andes of Argentina, strong storms often come and go at a moment’s notice, but they can have a long-lasting impact on the Earth’s surface.

The thunderstorm cell featured in this photo formed in less than half an hour, giving all those nearby only a few minutes to take cover. Mitch D’Arcy, a geomorphologist and postdoctoral researcher at the University of Potsdam and the GFZ German Research Centre for Geosciences, had the opportunity to witness this storm (and snap this picture!) while carrying out field work in the area.

“It was a spectacular experience, pouring heavy rain onto a very localised part of the mountain range, but it was also a hazard because the storm was quickly moving towards us with a lot of lightning. Without any trees around, we were likely targets for lightning strikes!” said D’Arcy. Luckily, he and his colleagues were able to find shelter in their truck while the huge downpour passed over them.

These kinds of thunderstorms are short-lived, but have intense precipitation rates. In this case, the temperature dropped by 14 degrees Celsius, and the storm was accompanied by heavy hail and lightning. And while these natural hazards are transient, they can have a long-term impact on the region’s landscape. Severe storms are capable of triggering landslides and floods and can relocate large amounts of sediment and debris in a short period of time.

D’Arcy is part of an international research programme called StRATEGy (Surface processes, Tectonics and Georesources: The Andean foreland basin of Argentina), which looks into how past and present climate change makes a mark on the terrain of the Argentine Andes, among other topics.

This research is essential for understanding and predicting how human-caused climate change will alter weather patterns and impact surface processes (such as how quickly sediments are eroded and transported across landscapes), according to D’Arcy. Having a better understanding of these surface processes and their sensitivity to the climate could help scientists better inform the public about how to prepare for natural hazards, such as flooding, erosion and landslides.

D’Arcy notes that it’s also important to assess how climate and weather trends will impact the sedimentary record, since it is one of the only physical records that scientists can use to examine how the Earth’s surface has change through time.

“North-western Argentina is a fascinating place to study how climate change affects surface processes, because it has experienced pronounced and abrupt changes in hydroclimate through time,” said D’Arcy. Their research has found that even subtle changes in the region’s climate have produced large changes to the surface environment, impacting how rivers take shape and how sediments move.

For example, while the Sierra de Aconquija is a semi-arid environment today, more than 12,000 years ago it used to be much wetter as a result of global climate changes. In fact, back then the mountain range was covered in glaciers and many of the basins were filled with lakes.

“It’s really important that we understand how different landscapes function and how they react to changes in climate. When we look at places like the southern Central Andes in Argentina, we find that the landscape records interesting signatures of ancient climate changes in Earth’s past. However, one of the big questions we still don’t have a good answer to, is how important are these very intense but rare storms for shaping landscapes and creating the sedimentary record from the geological past,” said D’Arcy.

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: 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: Probing the Pliocene

Imaggeo on Mondays: Probing the Pliocene

The heights we go to for science…

This photograph shows a member of our team preparing to abseil down a cliff in the Charyn Canyon, in the Ili River basin of southeast Kazakhstan. The Charyn River and its tributaries, a branch of the Ili River north of the Tien Shan Mountains, have cut canyons up to 300 metres deep, carving through rocks of different geologic ages, some as old as 540 million years.

The name “Charyn” may derive from local Uighur or Turkic words for “ash tree” or “precipice” respectively, both of which are common in the area.

Charyn Canyon is presently characterized by a cold semi-arid climate, with dry summers and cold winters. However, these conditions are likely to have varied through time, becoming wetter, drier, warmer and cooler in response to major climate systems’ changing intensity and influence over the region.

Our research team investigates the past and present climate systems of the Cenozoic era, our current geological era which began 66 million years ago; the most recent 2.6 million years have been characterised by alternating ice ages and warmer so-called “interglacial” phases, and saw the evolution of humans. More specifically, we study climate systems in one of the most remote regions of Central Asia, known as the Eurasian Continental Pole of Inaccessibility. The area is a challenging place for climate research since it has no marine or ice core records, the most common calendars of ancient climate.

This region is poorly understood yet important within the global climate system, since it lies at the boundaries of the major northern hemispheric climate systems. These systems, such as the Siberian high pressure system and Asian monsoons, are likely to have shifted, expanded and contracted over time. These changes occur in response to factors like mountain uplift, and changes in the Earth’s orbital patterns and incoming solar radiation.

The aim of our study is to reconstruct climatic change over this period. By analysing various chemical and physical characteristics of the sediments, such as their age, magnetism, grain size and chemistry, we can reconstruct quantitative palaeoclimatic variability through time.

Here we focus on an 80-metre thick layer of sediment, which alternates between layers of river-transported gravels and wind-blown dust deposits, known as loess. Younger sedimentary layers have thicker dust deposits, reflecting a long-term aridification trend in the Ili Basin and, more broadly, Central Asia.

Our preliminary results from our fieldwork indicate that the canyon’s sediments represent an uninterrupted representation of the region’s climate from the Pliocene to early Pleistocene (from approximately 4.5 to 1 million years ago).

Achieving a comprehensive geological sampling of the Charyn Canyon was only possible by abseil. Our fieldwork, undertaken from May to June 2017, was a hot and dusty business, but ultimately a lot of fun. Definitely not for those with a fear of heights!

By Kathryn Fitzsimmons, Max Planck Institute for Chemistry, Germany and Giancarlo Scardia, São Paulo State University, Brazil

Imaggeo on Mondays: Angular unconformity

Imaggeo on Mondays: Angular unconformity

It is not unusual to observe abrupt contacts between two, seemingly, contiguous rock layers, such as the one featured in today’s featured image. This type of contact is called an unconformity and marks two very distinct times periods, where the rocks formed under very different conditions.

Telheiro Beach is located at the western tip of the Algarve; Portugal’s southernmost mainland region and the most touristic too.

The area, famous for its famous rocky beaches and great seefood, shows a spectacular Variscan unconformity between the highly-folded greywackes and shales of the Brejeira Formation (Moscovian-Carboniferous) and the horizontally placed red sandstones and mudstones of the Group Grés de Silves (of Late Triassic age: 237 and 201.3 million years old). There is a hiatus of about 100 million years between the two formations.

The Variscan period ranges from 370 million to 290 million year ago and is named after the formation of a mountain belt which extends across western Europe, as a result of the collision between Africa and the North American–North European continents.

The imposing sea cliffs produce a privileged place to observe the end of the Variscan Cycle and the beginning of the Alpine Cycle.

It is possible to visit the outcrop on foot, from the top of the cliffs to the beach, although the path is of high degree of difficulty. When going down to the beach one can begin to visualise the typical lithologies of the Grés de Silves. Toward its top you can see red to green Mudstones (dominant) intercalated with rare dolomites and immediately above the unconformity plane it is possible to observe the red sandstone with cross stratification. The highly-folded turbidites (a type of sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean) of the Brejeira Formation are located below the unconformity.

The folds feature chevron geometries (where the rocks have well behaved layers, with straight limbs and sharp hinges, so that they look like sharp Vs). The folding is the result of the final deformation phase of the Variscan compression.

The beds of sedimentary rocks show sedimentary structures attributed to sedimentation in a turbidic environment (turbititic currents), namely the Bouma sequence and sole marks like flute, groove and load casts.

                                                                                                     By André Cortesão, Environmental Engineer and Geoscientist collaborator of the University of Coimbra Geosciences Centre

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/