GeoLog

landscape

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/.

Could beavers be responsible for long-debated deposits?

Could beavers be responsible for long-debated deposits?

Following her presentation at the European Geosciences Union General Assembly in Vienna, I caught up with geomorphologist and environmental detective Annegret Larsen from the University of Lausanne, Switzerland, about beavers, baffling sediments and a case she’s been solving for the past seven years.

Back in 2012 the German geomorphology community was seriously debating the source of buried black soils, a stark black layer of sediment found in floodplain deposits all over Europe. Such dark sediments are usually associated with organic, carbon-rich materials, like peat. But unlike the other dark deposits, these soils are low in organic carbon, leading to a wide spectrum of ideas about their origin.

“They’re almost everywhere, and many people have had big fights about them and where they come from. Fire might have played a role, or human impact, or a rising water table associated with changes in climate,” explains Larsen.

The soils themselves are quite variable. Some deposits are quite muddy, while some trap fragments of long-dead plants. “They look a little like the relic of a swamp, containing grassy vegetation, sticks, leaves and little nuts, and they’re mainly black,” said Larsen. At the University of Lausanne, Switzerland and the University of Manchester, UK, she and her colleagues have been studying the composition and chemistry of black soils in an effort to understand how they formed.

Recently, Larsen has uncovered a possible connection between the black soil deposits and European beaver habitats. She presented her findings at the annual EGU meeting earlier this month.

The accused: a European beaver. Credit: Per Harald Olson via Wikimedia Commons

The idea began to take shape while Larsen was driving within the Spessart region of Switzerland. During her travels, she had found the soil situated in environments where beaver populations had been dwelling for some 25 years.

“There are huge swamps, what we call beaver meadows. And the vegetation communities are just like the ones found in those deposits,” said Larsen.

This discovery led her to develop a field experiment with the aim to determine whether beavers could be responsible for these puzzling black deposits.

“It’s like a big mystery for me. To find out if the black floodplain soil really come from when there was a widespread beaver population, before humans eradicated the beaver, I need to understand what the beaver does nowadays, and that’s how I started the project.”

Larsen thinks the beaver-created landscapes change with age, and she has been keeping a close watch on four sites across Switzerland and Germany, where beaver communities have been established for up to 25 years.

The long-toothed mammals have striking impacts on the landscape, which differ depending on where they build their dam. Upstream architecture results in beaver cascades, a series of closely packed ponds, each separated by a beaver dam. Down river, efforts go into one ‘megadam’ that stretches across a slow, meandering section of the stream and cause it to spill out into a large swampy floodplain.

The cascades, Larsen describes, are pretty dynamic. “Sediment gets trapped behind each dam, then they get strained, breach and break, causing sediment to flush downstream. It’s collected by the next dam and that then overtops and then that breaks” and the process starts all over again.

One of Larsen’s field sites: the Distelbach beaver reach. Credit: Annegret Larsen

Beaver meadows begin as large expanses of water, ponds teeming with semi-aquatic vegetation. Over time, fine sediment gathers in the ponds. As the sediment builds up, the area becomes a swamp – a patchwork of shrubs, trees, running water and tough, grassy plants. “You definitely get an explosion in diversity, but it’s a complete change, the area becomes a wetland,” adds Larsen.

And the wetland contains plants that resemble those found in the buried floodplain soils.

“For me, it’s fascinating to think about how all our streams would have looked with a beaver in there: before humans impacted those streams, before humans eradicated the beaver, and before [humans] settled there. There must have been beavers everywhere. Every stream would have been a beaver stream. And a beaver stream looks totally different [to what we see today].”

With the deposits all over Europe, it isn’t hard to imagine that, in years past, beavers shaped the streams, swamps and landscapes of the continent. It’s feasible that these regions might have been swampy landscapes at one point in history.

So, are the beavers behind the black soils? “I think we’re on a good path to contribute to this discussion. It’s at least as reasonable as fire and climate,” she replies.

Larsen makes a strong case, but the jury, it seems, is still out.

By Sara Mynott, EGU Press Assistant

Imaggeo Photo Competition finalists 2019 – who will you vote for?

Imaggeo Photo Competition finalists 2019 – who will you vote for?

This year’s Photo Competition judging panel received more than 600 photo submissions, covering fields across the geosciences. The fantastic finalist photos are below and they are being exhibited in Hall X2 (basement, Brown Level) of the Austria Center Vienna – see for yourself!

Do you have a favourite? Vote for it! There is a voting terminal (also in Hall X2), just next to the exhibit. Voting closes by Thursday 11 April and the winners will be announced online on Friday!

Time flows as the climate is changing. Credit: Kasia Tokarska (distributed via imaggeo.egu.eu). A long-exposure look at Brúarfoss waterfall in Iceland.

 

Aurora show on the road. Credit: Junbin Zhao (distributed via imaggeo.egu.eu). Busy drivers pass by without noticing the beautiful northern lights’ show overhead.

Pulp ……eruption! Credit: Valerio Acocella (distributed via imaggeo.egu.eu). A close-up of a vent erupting blobs of blood-red basaltic magma during the Mt. Etna 2001 eruption, one of the most important of this volcano in the last century. This eruption marked a new cycle in the recent life of Etna and is also associated with flank instability threatening the lower inhabited eastern slope.

 

Temporary pond within ice fall of Fox Glacier. Credit: Stefan Winkler (distributed via imaggeo.egu.eu). A temporary pond of meltwater on the surface of Fox Glacier, Southern Alps, New Zealand. Due to the fast movement and the rough surface, there is not an established supraglacial or englacial meltwater system resulting in temporary ponds forming and subsequently draining during over several weeks to a few months.

 

43°29’S 147°08’E – Meet me at the lighthouse. Credit: Vytas Huth (distributed via imaggeo.egu.eu). Light pollution is an environmental hazard we often overlook. When I had the chance to view the Southern Hemisphere’s night sky with only the Antarctic Ocean in front of me, I realised how much we have already lost in the Northern Hemisphere and Europe. It almost seems as if the night is becoming extinct.

 

Something sticks out. Credit: Sophie von Fromm (distributed via imaggeo.egu.eu). While the windblown sand buries everything beneath, a lonely stick remains standing. Such sand storms occur quite frequently at the Gobabeb Training and Research Centre in the Namib Desert.

 

Coloured canyon curves. Credit: Nikita Churilin (distributed via imaggeo.egu.eu). The morning sunlight is reflecting in the grains of sand in the Lower Antelope Canyon and paint the canyon in unusual colours.

 

Humans’ route in harmony with nature. Credit: Anatolii Chernov (distributed via imaggeo.egu.eu). The Carpathian Mountains in Western Ukraine are a nice place to learn about structural geology and for relaxation. It is a pleasure to observe beautiful corners of the Earth, where people try to respect and cherish natural beauty.

 

Message from the deep. Credit: Katja Bigge (distributed via imaggeo.egu.eu). Stromboli volcano, the original example of Strombolian activity defined by small regular eruptions.

 

A frozen time capsule. Credit: Florian Konrad (distributed via imaggeo.egu.eu). The Schwarzmooskogel-Höhlensystem is located in the Totes Gebirge in Austria and consists of 17 individual caves with a total length of about 140km. Inside, it felt like time did not pass or just passed really slowly. The shapes that the ice had sculptured were endless and took our breath away.

The EGU General Assembly will take place from 07 to 12 April 2019 in Vienna, Austria. For the full session programme and more information on the General Assembly, see the EGU 2019 website and follow us on Twitter (#EGU19 is the official conference hashtag) and Facebook.