GeoLog

soil

Imaggeo on Mondays: Life between the arid mountains of Gansu, China

Imaggeo on Mondays: Life between the arid mountains of Gansu, China

Even within Earth’s more arid environments, you can find life!

This featured photo was taken near the Lanzhou Zhongchuan Airport, about 50 km away from Lanzhou city, the capital of Gansu province in Western China. The area lies in a region between the Qinghai-Tibet Plateau and the Loess Plateau, with an elevation ranging from 1,500 m to 2,200 m. The landscape is dominated by a network of ridges and valleys; the Loess Plateau in particular is known for its highly erodible soil.

The region is a typical temperate or semi-arid area receiving just 260-290 mm of precipitation annually with a potential evapotranspiration of about 1660 mm each year, according to the Gaolan and Yongdeng National Meteorological Stations. However, even in these dry conditions, you can still find pockets of agricultural plots nestled between the winding mountain ridges. Farmers in this region commonly rely on an agricultural method called terrace farming, where crops are grown on graduated platforms, resembling wide steps. Often used in dry mountainous environments, the practice not only creates a flat surface for farming, but also reduces soil erosion and efficiently conserves water. The terraced farms in this area are mainly distributed in the valley where lands are irrigated for wheat and maize production.

By Olivia Trani, Communications Officer, and Xiaoming Wang, State Key Laboratory of Cryospheric Science, Chinese Academy of Science, Lanzhou, China

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/.

GeoTalk: Severe soil erosion events and how to predict them

GeoTalk: Severe soil erosion events and how to predict them

Geotalk is a regular feature highlighting early career researchers and their work. In this interview we speak to Matthias Vanmaercke, an associate professor at the University of Liège in Belgium who studies soil erosion and land degradation across Europe and Africa. At the EGU General Assembly he received the 2018 Soil System Sciences Division Outstanding Early Career Scientists Award.

Thanks for talking to us today! Could you introduce yourself and tell us about your career path so far?

Hi! So I am Matthias Vanmaercke. I’m from Belgium. I’m studied physical geography at the University of Leuven in Belgium, where I also completed my PhD, which focused on the spatial patterns of soil erosion and sediment yield in Europe. After my PhD, I continued working on these topics but with a stronger emphasis on Africa. Since November 2016, I became an associate professor at the University of Liege, Department of Geography where I continue this line of research and teach several courses in geography.

At the 2018 General Assembly, you received a Division Outstanding Early Career Scientists Award for your contributions towards understanding soil erosion and catchment sediment export (or the amount of eroded soil material that gets effectively transported by a river system).

Could you give us a quick explanation of these processes and how they impact our environment and communities?

We have known for a long time that soil erosion and catchment sediment export pose important challenges to societies. In general, our soils provide many important ecosystem services, including food production via agriculture. However, in many cases, soil erosion threatens the long term sustainabilty of these services.

Several erosion processes, such as gully erosion, often have more direct impacts as well. These include damage to infrastructure and increased problems with flooding. Gullies can also greatly contribute to the sediment loads of rivers by directly providing sediments and also by increasing the connectivity between eroding hill slopes and the river network. These high sediment loads are in fact the off-site impacts of soil erosion and often cause problems as well, including deteriorated water quality and the sedimentation of reservoirs (contributing to lower freshwater availability in many regions).

Matthias Vanmaercke, recipient of the 2018 Soil System Sciences Division Outstanding Early Career Scientists Award. Credti: Matthias Vanmaercke.

What recent advances have we made in predicting these kinds of processes?

Given that we live in an increasingly globalised and rapidly changing world, there is a great need for models and tools that can predict soil erosion and sediment export as our land use and climate changes.

However, currently our ability to predict these processes, foresee their impacts and develop catchment management and land use strategies remains limited. This is particularly so at regional and continental scales and especially in Africa. For some time, we have been able to simulate processes like sheet and rill erosion fairly well. However, other processes like gully erosion, landsliding and riverbank erosion, remain much more difficult to simulate.

Nonetheless, the situation is clearly improving. For example, with respect to gully erosion, we already know the key factors and mechanisms that drive this process. The rise of new datasets and techniques helps to translate these insights into models that will likely be able to simulate these processes reasonably well. I expect that this will become feasible during the coming years.

 

What is the benefit of being able to predict these processes? What can communities do with this information?

These kinds of predictions are relevant in many ways. Overall, soil erosion is strongly driven by our land use. However, some areas are much more sensitive than others (e.g. steep slopes, very erodible soil types). Moreover, many of these different erosion processes can interact with each other. For example, in some cases gully formation can entrain landslides and vice versa.

Models that are capable of predicting these different erosion processes and interactions can strongly help us in avoiding erosion, as they provide information that is useful for planning our land use better. For instance, these models can help determine which areas are best reforested or where soil and water conservation measures are needed.

They also help with avoiding and mitigating the impacts of erosion. Many of these processes are important natural hazards (e.g. landsliding) or are strongly linked to them (e.g. floods). Models that can better predict these hazards contribute to the preparedness and resilience of societies. This is especially relevant in the light of climate change.

However, there are also impacts on the long-term. For example, many reservoirs that were constructed for irrigation, hydropower production or other purposes fill up quickly because eroded sediments that are transported by the river become deposited behind the dam. Sediment export models are essential for predicting at what rate these reservoirs may lose capacity and for designing them in the most appropriate ways.

At the Assembly you also gave a presentation on the Prevention and Mitigation of Urban Gullies Project (PREMITURG-project). Could you tell us a bit more about this initiative and its importance?

Urban mega-gullies are a growing concern in many tropical cities of the Global South. These urban gullies are typically several metres wide and deep and can reach lengths of more than one kilometre. They typically arise from a combination of intense rainfall, erosion-prone conditions, inappropriate city infrastructure and lack of urban planning and are often formed in a matter of hours due to the concentration of rainfall runoff.

Urban gully in Mbuji-Maji, Democratic Republic of Congo, September 2008. Credit: Matthias Vanmaercke

Given their nature and location in densely populated areas, they often claim casualties, cause large damage to houses and infrastructure, and impede the development of many (peri-)urban areas.  These problems directly affect the livelihood of likely millions of people in several countries, such as the Democratic Republic of Congo, Nigeria, and Angola. Due to the rapid growth of many cities in these countries and, potentially, more intensive rainfall, this problem is likely to aggravate in the following decades.

With the ARES-PRD project PREMITURG, we aim to contribute to the prevention and mitigation of urban gullies by better studying this problem. In close collaboration with the University of Kinshasa in the Democratic Republic of Congo (DRC) and several other partners and institutes, we will study this underestimated geomorphic hazard across several cities in DRC. With this, we hope to provide tools that can predict which areas are the most susceptible to urban gullying so that this can be taken into account in urban planning efforts. Likewise, we hope to come up with useful recommendations on which techniques to use in order to prevent or stabilise these gullies. Finally, we also aim to better understand the societal and governance context of urban gullies, as this is crucial for their effective prevention and mitigation.

Interview by Olivia Trani, EGU Communications Officer

April GeoRoundUp: the best of the Earth sciences from the 2017 General Assembly

April GeoRoundUp: the best of the Earth sciences from the 2017 General Assembly

This month’s GeoRoundUp is a slight deviation from the norm. Instead of drawing inspiration from popular stories on our social media channels and unique or quirky research featured in the news, we’ve rounded up some of the stories which came out of researcher presented at our General Assembly (which took place last week in Vienna). The traditional format for the column will return in May!

Major story

Artists often draw inspiration from the world around them when composing the scene for a major work of art. Retrospectively trying to understanding the meaning behind the imagery can be tricky.

This is poignantly true for Edvard Munch’s iconic ‘The Scream’. The psychedelic clouds depicted in the 18th Century painting have been attributed to Munch’s inner turmoil and a trouble mental state. Others argue that ash particles strewn in the atmosphere following the 1883 Krakatoa volcanic eruption are the reason for the swirly nature of the clouds represented in the painting.

At last week’s General Assembly, a team of Norwegian researchers presented findings which provide a new explanation for the origin of Munch’s colourful sky (original news item from AFP [Agence France-Presse): mother-of-pearl clouds. These clouds “appear irregularly in the winter stratosphere at high northern latitudes, about 20-30 km above the surface of the Earth,” explains Svein Fikke, lead author of the study, in the conference abstract.

“So far observed mostly in the Scandinavian countries, these clouds are formed of microscopic and uniform particles of ice, orientated into thin clouds. When the sun is below the horizon (before sunrise or after sunset), these clouds are illuminated in a surprisingly vibrant way blazing across the sky in swathes of red, green, blue and silver. They have a distinctive wavy structure as the clouds are formed in the lee-waves behind mountains”, writes Hazel Gibson (EGU General Assembly Press Assistant) in a post published on GeoLog following a press conference at the meeting in Vienna (which you can watch here).

With coverage in just over 200 news items, this story was certainly one of the most popular of the meeting. Read more about the study in the full research paper, out now.

What you might have missed

Also (typically) formed in the downside of mountains and in the conference spotlight were föhn winds. The warm and dry winds have been found to be a contributing factor that weakens ice shelves before a collapse.

Ice shelf collapse has been in the news recently on account of fears of a large crack in the Larsen C Ice Shelf generating a huge iceberg.  Though the exact causes for crack generation on ice shelves remain unclear, new research presented by British Antarctic Survey scientists at the conference in Vienna highlighted that föhn winds accelerate melting at the ice shelf surface.  They also supply water which, as it drains into the cracks, deepens and widens them.

Meanwhile, deep under ocean waters, great gouge marks left behind on the seafloor as ancient icebergs dragged along seabed sediments have been collected into an Atlas of Submarine Glacial Landforms, published by the Geological Society of London. The collection of maps sheds light on the past behaviour of ice and can give clues as to how scientists might expect ice sheets to respond to a changing climate.

Drumlins (elongate hills aligned with the ice flow direction) from the Gulf of Bothnia in the Baltic Sea. Credit: Atlas of Submarine Glacial Landforms/BAS

Closer to the Earth’s surface, groundwater also attracted its fair share of attention throughout the meeting. It’s hardly surprising considering groundwater is one of the greatest resources on the planet, globally supplying approximately 40% of the water used for irrigation of crops and providing drinking water for billions around the world. ‘Fossil’ groundwater, which accumulated 12,000 years ago was once thought to be buried too deep below the Earth’s surface to be under threat from modern contaminants, but a new study presented during the General Assembly has discovered otherwise.

Up to 85% of the water stored in the upper 1 km of the Earth’s outermost rocky layer contains fossil groundwater. After sampling some 10,000 wells, researchers found that up to half contained tritium, a signature of much younger waters. Their presence means that present-day pollutants carried in the younger waters can infiltrate fossil groundwater. The study recommends this risk is considered when managing the use of fossil waters in the future.

Links we liked

News from elsewhere

The spectacular end to the Cassini mission has featured regularly in this month’s bulletins.

During its 13 years in orbit, Cassini has shed light on Saturn’s complex ring system, discovered new moons and taken measurements of the planet’s magnetosphere. On September 15th,  the  mission will end when the probe burns up in Saturn’s atmosphere.

On 22 April, the final close flyby of Saturn’s largest moon, Titan, propelled the Cassini spacecraft across the planet’s main rings and into its Grand Finale series of orbits. This marks the start of the final and most audacious phase of the mission as the spacecraft dives between the innermost rings of Saturn and the outer atmosphere of the planet to explore a region never before visited; the first of 22 ring plane crossings took place on 26 April.You can watch a new movie which shows the view as the spacecraft swooped over Saturn during the dive here.

For an overview of highlights from the mission and updates from the ring-grazing orbits that began in November 2016 watch this webstream from a press conference with European Space Agency scientists at the General Assembly last week.

To stay abreast of all the EGU’s events and activities, from highlighting papers published in our open access journals to providing news relating to EGU’s scientific divisions and meetings, including the General Assembly, subscribe to receive our monthly newsletter.

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/.