GeoLog

GeoLog

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

NASA’s Juno mission reveals Jupiter’s magnetic field greatly differs from Earth’s

NASA’s Juno mission reveals Jupiter’s magnetic field greatly differs from Earth’s

NASA scientists have revealed surprising new information about Jupiter’s magnetic field from data gathered by their space probe, Juno.

Unlike earth’s magnetic field, which is symmetrical in the North and South Poles, Jupiter’s magnetic field has startlingly different magnetic signatures at the two poles.

The information has been collected as part of the Juno program, NASA’s latest mission to unravel the mysteries of the biggest planet in our solar system. The solar-powered spacecraft is made of three 8.5 metre-long solar panels angled around a central body. The probe (pictured above) cartwheels through space, travelling at speeds up to 250,000 kilometres per hour.

Measurements taken by a magnetometer mounted on the spacecraft have allowed a stunning new insight into the planet’s gigantic magnetic field. They reveal the field lines’ pathways vary greatly from the traditional ‘bar magnet’ magnetic field produced by earth.

Jupiter’s magnetic field is enormous. if magnetic radiation were visible to the naked eye, from earth, Jupiter’s magnetic field would appear bigger than the moon. Credit: NASA/JPL/SwRI

The Earth’s magnetic field is generated by the movement of fluid in its inner core called a dynamo. The dynamo produces a positive radiomagnetic field that comes out of one hemisphere and a symmetrical negative field that goes into the other.

The interior of Jupiter on the other hand, is quite different from Earth’s. The planet is made up almost entirely of hydrogen gas, meaning the whole planet is essentially a ball of moving fluid. The result is a totally unique magnetic picture. While the south pole has a negative magnetic field similar to Earth’s, the northern hemisphere is bizarrely irregular, comprised of a series of positive magnetic anomalies that look nothing like any magnetic field seen before.

“The northern hemisphere has a lot of positive flux in the northern mid latitude. It’s also the site of a lot of anomalies,” explains Juno Deputy Principal Investigator, Jack Connerney, who spoke at a press conference at the EGU General Assembly in April. “There is an extraordinary hemisphere asymmetry to the magnetic field [which] was totally unexpected.”

NASA have produced a video that illustrates the unusual magnetism, with the red spots indicating a positive magnetic field and the blue a negative field:

Before its launch in 2016, Juno was programmed to conduct 34 elliptical ‘science’ orbits, passing 4,200 kilometres above Jupiter’s atmosphere at its closest point. When all the orbits are complete, the spacecraft will undertake a final deorbit phase before impacting into Jupiter in February 2020.

So far Juno has achieved eleven science orbits, and the team analysing the data hope to learn more as it completes more passes. “In the remaining orbits we will get a finer resolution of the magnetic field, which will help us understand the dynamo and how deep the magnetic field forms” explains Scott Bolton, Principal Investigator of the mission.

The researchers’ next steps are to examine the probe’s data after its 16th and 34th passes meaning it will be a few more months before they are able to learn more of Jupiter’s mysterious magnetosphere.

By Keri McNamara, EGU 2018 General Assembly Press Assistant

Further reading

Connerney, J. E. P., Kotsiaros, S., Oliversen, R. J., Espley, J. R., Joergensen, J. L., Joergensen, P. S., et al. A new model of Jupiter’s magnetic field from Juno’s first nine orbits. Geophysical Research Letters, 45, 2590–2596. 2018

Bolton, S. J. et al. Jupiter’s interior and deep atmosphere: The initial pole-to-pole passes with the Juno spacecraft, Science, 356(6340), p. 821 LP-825. 2017

Guillot, T. et al. A suppression of differential rotation in Jupiter’s deep interior, Nature. Macmillan Publishers Limited, part of Springer Nature. All rights reserved., 555, p. 227. 2018

Imaggeo on Mondays: Corno Grande, tallest peak of the Apennines

Imaggeo on Mondays: Corno Grande, tallest peak of the Apennines

In the middle of the Apennines lays the Gran Sasso d’Italia mountain chain, a picturesque collection of mountains situated in the heart of Italy.

Featured here is one of the chain’s peaks, called the Corno Grande, meaning ‘Big Horn,’ coloured with a faint reddish light of a late-winter sunset. Sitting at 2,912 metres, this summit is easily the highest mountain in the Apennines.

The areas surrounding Corno Grande is enclosed in the Gran Sasso e Monti della Laga National Park, located in the hinterland of Italy’s Abruzzo region. The park, established in 1991, encompasses 2,015 square kilometres, making it one of the largest natural reserves in Europe.

Moreover, from an ecological standpoint, the region is one of the most biologically diverse areas in Europe, with more than 2,000 plant species, many of which can only be found in the park, and many rare animals.

The landscape that surrounds Corno Grande still shows traces of glacial erosion from the Quaternary Period, which began 2.6 million years ago. The region’s smooth highlands and U-shaped valleys are engravings of the slow glacial processes that occurred on these lands. The Corno Grande is even still host to a glacier today, as you can find the Calderone glacier, Western Europe’s southernmost glacier, beneath the mountain’s peak.

Sketch of the geodynamic setting of the Gran Sasso (Credit: Cardello and Doglioni, 2015)

The Apennine Mountains were built by a paradoxical geologic process, sometimes referred to as ‘syn-orogenic extension,’ where thickened crust spreads out while, at the same time, a belt of Earth’s crust is compressed, forming a chain of mountains. In the case of the Apennines, compression took place east of the range while extension occurred to the west.

“This synchronous processes of such different motions in the convergent belts is still an issue that must be unraveled for a better understanding of the mountain ridge formation,” said Alex Righetti, a PhD student studying marine geology at the Faculty of Sciences of the University of Lisbon, in Portugal, who captured this shot.

By Olivia Trani, EGU Communications Officer and Alex Righetti, FCUL

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/.

Geosciences Column: The best spots to hunt for ancient ice cores

Geosciences Column: The best spots to hunt for ancient ice cores

Where in the world can you find some of Earth’s oldest ice? That is the question a team of French and US scientists aimed to answer. They recently identified spots in East Antarctica that likely have the right conditions to harbor ice that formed 1.5 million years ago. Scientists hope that obtaining and analysing an undisturbed sample of ice this old will give them clues about Earth’s ancient climate.

The team published their findings in The Cryosphere, an open access journal of the European Geosciences Union (EGU).

Why study ancient ice?

When snow falls and covers an ice sheet, it forms a fluffy airy layer of frozen mass. Over time, this snowy layer is compacted into solid ice under the weight of new snowfall, trapping pockets of air, like amber trapping prehistoric insects. For today’s scientists, these air bubbles, some sealed off thousands to millions of years ago, are snapshots of what the Earth’s atmosphere looked like at the time these pockets were locked in ice. Researchers can tap into these bubbles to understand how the proportion of greenhouse gases in our atmosphere have changed throughout time.

As of now, the oldest ice archive available to scientists only goes back 800,000 years, according to the authors of the study. While pretty ancient, this ice record missed out on some major climate events in Earth’s recent history. Scientists are particularly interested in studying the time between 1.2 million years ago and 900,000 years ago, a period scientifically referred to as the mid-Pleistocene transition.

In the last few million years leading up to this transition, the Earth’s climate would experience a period of variation, from cold glacial periods to warmer periods, every 40,000 years. However, after the mid-Pleistocene transition, Earth’s climate cycle lengthened in time, with each period of variation occurring every 100,000 years.  

Currently, there isn’t a scientific consensus on the origin of this transition or what factors were involved. By examining old ice samples and studying the composition of the atmospheric gases present throughout this transition, scientist hope to paint a clearer picture of this influential time. “Locating a future 1.5 [million-year]-old ice drill site was identified as one of the main goals of the ice-core community,” wrote the authors of the study.  

The quest for old ice

Finding ice older than 800,000 years is difficult since the Earth’s deepest, oldest ice are the most at risk of melting due to the planet’s internal heat. Places where an ice sheet’s layers are very thick have an even greater risk of melting.

Mesh, bedrock dataset (Fretwell et al., 2013; Young et al., 2017) and basal melt rate (Passalacqua et al., 2017) used for the simulation. Credit: O. Passalacqua et al. 2018.

“If the ice thickness is too high the old ice at the bottom is getting so warm by geothermal heating that it is melted away,” said Hubertus Fischer, a climate physics researcher from the University of Bern in Switzerland not involved in the study, in an earlier EGU press release.

Last summer, a team of researchers from Princeton University announced that they had unearthed an ice core that dates back 2.7 million years, but the sample’s layers of ice aren’t in chronological order, with ice less than 800,000 years old intermingling with the older frozen strata. Rather than presenting a seamless record of Earth’s climate history, the core can only offer ‘climate snapshots.’

Finding the best of the rest

The authors of the recent The Cryosphere study used a series of criteria to guide their search for sites that likely could produce ice cores that are both old and undisturbed. They established that potential sites should of course contain ice as old as 1.5 million years, but also have a high enough resolution for scientists to study frequent changes in Earth’s climate.

Additionally, the researchers established that sites should not be prone to folding or wrinkling, as these kinds of disturbances can interfere with the order of ice layers.

Lastly, they noted that the bedrock on which the ice sheet sits should be higher than any nearby subglacial lakes, since the lake water could increase the risk of ice melt.

Magenta boxes A, B and C correspond to areas that could be considered as our best oldest-ice targets. Colored points locate possible drill sites. Credit: O. Passalacqua et al. 2018.

 

Using these criteria, the researchers evaluated one region of East Antarctica, the Dome C summit, which scientists in the past have considered a good candidate site for finding old ice. They ran three-dimensional ice flow simulations to locate parts of the region that are the most likely to contain ancient ice, based on their established parameters.

By narrowing down the list of eligible sites, the researchers were able to pinpoint regions just a few square kilometres in size where intact 1.5 million-year-old ice are very likely to be found, according to their models. Their results revealed that some promising areas are situated a little less than 40 kilometres southwest of the Dome C summit.

The researchers hope their new findings will bring scientists one step closer towards finding Earth’s ancient ice.

By Olivia Trani, EGU Communications Officer