GeoLog

Stratigraphy, Sedimentology and Palaeontology

Imaggeo on Mondays: Civita di Bagnoregio – the dying town

Imaggeo on Mondays: Civita di Bagnoregio – the dying town

On top of a steep cliff standing out from the surrounding countryside, lies the small town of Civita di Bagnoregio, one of the most famous villages of Italy. It is often called the dying town, although more recently people have started to refer to it as fighting to live. What this little town is fighting against is the threat of erosion, as its walls are slowly crumbling down.

Located in central Italy, about a 100 km north of Rome, the town of Civita dates back to the Etruscan civilization, about 2500 years ago. It was most likely built on top of a hill for military reasons, since the 200 m of difference in height would provide perfect panoramic views. The city’s major development took place during the Middle Ages, and its well-preserved medieval character is one of the features that makes this city so magnificent nowadays. However, in 1695, a terrible earthquake demolished most of Civita by triggering a major landslide below, and forced people to move to the neighbouring village of Bagnoregio. This was not the only landslide that threatened the city. For centuries, Civita has been fighting against the natural degradation of the cliff, with recurring landslides slowly taking down the edges of the plateau, causing some of the medieval buildings to collapse and plummet into the ravine (Figure 1).

Figure 1. Evolution of the upper urbanised area of Civita di Bagnoregio from historical maps, showing many buildings destroyed by landslides during the past centuries. Credit: Margottini, C. & Di Buduo, G. Landslides (2017).

The geology of the plateau explains why this town is so susceptible to landslides (Figure 2, Delmonaco et al., 2004). The top of the plateau consists of a 20 m thick layer of consolidated rock formed from volcanic ash (ignimbrite), also known as tuff. The tuff was deposited by pyroclastic flows (rapid currents of volcanic debris and hot gas) related to the neighbouring Vulsini volcanic complex. This massive tuff layer overlies a more stratified section of pyroclastic deposits, roughly 70 m in thickness. These quaternary volcanic deposits lie above a bedrock of Plio-Pleistocene clay, which can be found all over the valley. This succession forms a classic setting for landslides. In the fragile clay deposits, slope instability is represented by mud flows and debris flows, while the upper, volcanic part of the plateau suffers from rock-falls, toppling and block-slides as it becomes unstable. Landslides can be dated back to 1373 AD, with 150 landslides documented by scientists who investigated the local geomorphology (Margottini and Di Buduo, 2016).

Figure 2. Geological profile of the study area. Credit: Giuseppe Delmonaco.

It seemed that the fate of Civita de Bagnoregio was to slowly disappear, but the city experienced a major turning point in 2013, when mayor Francesco Bigiotti decided to charge an entrance fee for people who wanted to visit the town. Tourists now pay a few euros to cross to the sloping footbridge towards the town. This proved to be a smart move, since people became more attentive and treated the site with more respect. The money raised by the entrance fee partly goes to preserving Civita’s fragile beauty and since 2015, the dying city received the UNESCO World Heritage status. This recognition of cultural heritage now leads to more investments from the regional government in order to preserve the historical site.

If you have the opportunity to visit the Civita, you will first enjoy a magnificent view on the town and the surrounding valley, before descending into the valley to cross the footbridge that provides the only gateway to the town. After a short climb towards the entrance, you’ll pass through an old arc, immediately bringing you back to medieval times. Then, all there is left to do is wander through the charming, quiet streets, observing the beauty of the classical quiet Italian village. Visit the Geology and Landslides museum, have lunch at one of the many authentic restaurants, or walk all the way to the end of the village, away from the other tourists. From there, a small trail leads into the countryside, where you can enjoy the magnificent views on the sharply eroded, clayey ridges in the surrounding badlands valley.

Previously referred to as the dying town, it now seems that there is some hope left after all for Civita di Bagnoregio. Something that will never change, however, is the interplay between mankind trying to survive in a hostile, but strategic environment of immense beauty, and nature that follows its own course of dismantling and eroding the existing relief.

By Elenora van Rijsingen, Ecole Normale Supérieure, Department of Geosciences, France

Conversations on a century of geoscience in Europe: Part 2

Conversations on a century of geoscience in Europe: Part 2

When you think about the last century of geoscience, what comes to mind? Perhaps Alfred Wegener’s theory of continental drift? Or Inge Lehmann’s discovery of Earth’s solid inner core?

Over the last 100 years, geoscientists have made incredible contributions to our understanding of the Earth, the solar system, and beyond. The science community has explored uncharted territory, challenged previously held conceptions, provided vital information to policymakers, worked to address societal challenges, and put forth paths for sustainability. Through the years, researchers have also worked to promote diversity, inclusion, transparency, and accessibility in the geosciences. Many Europe-based scientists have been at the forefront of these advances.

Inspired by the centennials of the American Geophysical Union (AGU) and the International Union of Geodesy and Geophysics (IUGG), which were both founded in 1919, we would like to highlight Europe’s role in shaping the geosciences and the great achievements of European geoscientists within the last century.

In this series of interviews, scientists across different disciplines and scientific fields reflect on the last 100 years of Earth, space and planetary sciences in Europe and share their perspectives on the future:


Karsten Gohl: Head of Geophysics Section at the Alfred Wegener Institute (AWI) Helmholtz Center for Polar and Marine Research

One of the broadest achievements in the geosciences in the last century is the transformation from individual discipline-oriented foci to an understanding of the interacting components of the entire Earth system in its complexity.

 

 

 

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Anny Cazenave: Director for Earth Sciences at the International Space Science Institute in Switzerland, and emeritus scientist at the Laboratoire d’Etudes en Géophysique et Océanographie Spatiales (LEGOS)

Current research in Earth sciences needs to account for the impacts of human activities on the Earth System… as well as for the impacts of natural systems on human societies.

 

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Mioara Mandea: Programme Manager for the Solid Earth Observation / Directorate of Innovation, Applications and Science at the Centre National d’Etudes Spatiales (French Space Agency)

A large number of European scientists has influenced my work over the last decades, and I would like to thank each and every one for support and guidance.

 

 

 

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Judith A. McKenzie: Professor em. of Earth System Sciences in the Geological Institute, Department of Earth Sciences at the ETH Zurich

Meeting these challenges from a geologic prospective will be essential for the survival of the quality of life that we have come to expect in Europe during the last century.

 

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Interviews by Olivia Trani, EGU Communications Officer

 

You can find more of our interviews on a century of geoscience in Europe here:

Part 1

 

Imaggeo on Mondays: An expedition to better understand Antarctic soils

Imaggeo on Mondays: An expedition to better understand Antarctic soils

A dramatic evening sky puts the frame to a photo taken during the Brazilian Antarctic expedition to James Ross Island in 2016. Brazilian palaeontologists and soil scientists together with German soil scientists spent over 40 days on the island to search for fossils and sample soils at various locations of the northern part of the island.

The island was named after Sir James Clark Ross who led the British expedition in 1842, which first charted locations at the eastern part of the island. James Ross Island is part of Graham Land, the northern portion of the Antarctic Peninsula, separated from South America by the stormy Drake sea passage.

Map of the Antarctic Peninsula featuring the James Ross Archipelago (Credit: The Scientific Committee on Antarctic Research, Antarctic Digital Database Map Viewer)

This photo was taken in the northern Ulu Peninsula, which is the northernmost part of the relatively large James Ross Island and the largest ice-free area in the Antarctic Peninsula region. The island’s characteristic appearance is formed by Late Neogene volcanic rocks (3-7 million years old) over fossil rich Late Cretaceous sandstones (66-120 million years old).

In the photo we are looking from a higher marine terrace at the Santa Martha Cove, the ‘home’ to the 2016 Brazilian Antarctic expedition, towards the steep cliffs of Lachman Crags, a characteristic mesa formed by Late Neogene lava flows. The Lachman Crags mesa, the Spanish word for tablelands, dominates the landscape of the northern part of the Ulu Peninsula. Above the cliffs visible in the photo, a glacier covered plateau stretches to the Northwest.

The marine terrace on which the tent is standing is comprised of a flat area that has been ice-free for approximately 6000 years and thus makes for a great model system to study soil development after glacial retreat. The ground is composed of a mixture of volcanic rocks and Cretaceous sandstones rich in all sorts of fossils, from fossilised wood to shark teeth, ammonites and reptile bones.

The strong winds that can start in Antarctica from one moment to the other and the very low precipitation led to the characteristic desert pavement, with stones sorted in a flat arrangement on top of the fine textured, deeply weathered permafrost soils. Although these soils host a surprisingly high number of microorganisms, most terrestrial life is restricted to wetter areas surrounding fresh water lakes and melt water streams. Thus lakes and snow meltwater-fed areas make for higher primary production of algae and mosses, fostering biodiversity and soil development by organic matter input.

As there are no larger bird rookeries on James Ross Island the only way sea-derived nutrients reach the Ulu Peninsula is by a rather grim feature:  dead seal carcasses that lie distributed across the lowlands (< 150 m asl) of the Ulu Peninsula. Carcasses fertilise the soils in their direct vicinity while slowly decomposing over decades, thus feeding small patches of lichens and mosses within the barren cold arid desert. The region is thus an illustration of the harsh Antarctic environment where even Weddell seals, animals that are well adapted for the living in dense pack ice during the polar night, die when losing track on land on the way to the water.

By Carsten Müller, Technical University of Munich Chair of Soil Science, Germany

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 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/.