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Rivers from a distant past

Logo http://tudelft.pageflow.io/rivers-from-a-distant-past

Tens of millions of years ago swirling rivers criss-crossed the plains of Wyoming, the least populous state in the United States. 

Today all that is left of these extensive river systems are thick layers of sand and clay, stacked on top of each other in what is known as the Bighorn Basin. 
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Armed with a hammer and a pickaxe, geologist Hemmo Abels studies the sediments left by rivers that once flowed across the plains of the United States.
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By means of painstaking detective work he gradually pieces together a picture of how these rivers changed over time, a process influenced in part by ancient climate change. The data he is gathering sheds light on our own subsoil when it comes to predicting the 3D architecture and character of our shallow to deep subsurface.
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Rivieren

The semi-arid area measures forty-by-a-hundred kilometres, some four times the size of the Veluwe national park in the Netherlands. 

'Fortunately the area I work in is smaller, some twenty by twenty kilometres, but it’s still a vast stretch of land,' Abels says. 'We spent the past decade collecting stratigraphic data, describing the sediments and determining the order and age of the layers.' 
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‘We are documenting river behaviour and the ways it changed over time. Did gullies become deeper or shallower? Did flooding occur more frequently or did it fall off? What types of soil were formed outside the riverbed?’ 

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Apart from fieldwork in the Bighorn Basin, Abels also conducts research in areas in Europe and Asia. He frequently puts away his pickaxe in favour of testing and refining his findings in computer models with the aid of numerical models of the river plains he is studying. ‘Which conditions can definitely be said to have been decisive in the formation of 35-meter-thick sandstone layers, and which played a minor role? A model is also a good tool to find out how field theory can inform applications needed to characterize our subsurface .’
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Klimaatverandering

Abels reconstructs the climate of the past and the effects of climate on rivers. ‘The effects of climate on river systems have been hugely under-researched.’ 

He is looking first of all at how climate change caused by shifts in the Earth’s axis and orbit affects river behaviour.
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He also studies periods in which abrupt global warming occurred and the ways it impacted everything from temperature and precipitation to erosion and sediment transport. ‘We can tell how climate variation influences a river system by studying the sediments that have remained. This knowledge can be directly applied to predict the kind of rock strata we will encounter in our own subsurface.’

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Abels’ research explains how unusually thick rock layers suddenly appear in the subsurface. ‘There is a 35-meter-thick sandstone layer in the Bighorn Basin, while seven meters is the norm. We can use the same methods in the Netherlands to predict where in the subsurface such anomalously thick sand bodies can occur and if these occur what is their character.’
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Veldwerk

Abels has been doing fieldwork in Wyoming every summer for the last ten years. What is daily life like in such a huge and sparsely populated area?
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Abels may be in the middle of nowhere but he isn’t alone. ‘I always have a team of colleagues with me. Then we have the volunteers who are all very handy with  a pickaxe.’ 

Meet Abels’ team, from left to right: Abels, Dirk-Jan Walstra of Deltares, and TU Delft colleagues Allard Martinius and Joep Storms.  
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A few small tents, a table and some chairs are all the team and the volunteers need. ‘We set up camp as near to the research area as possible.’ 

Although camping is not what it was ten years ago.. .


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Ten years ago the camp had no electricity. 

‘Now we have drones, computers and mobile phones and a generator to charge them. We have had mobile coverage for two years, and now it’s 4G no less. 

Abels is not altogether happy about this development. ‘In the past students would be dragged from their comfort zone pretty quickly. There is no moaning in a camp like this: you’re lucky to get a plate of food at night and cold water to wash with. And now everyone is looking at their phones at the end of the day instead of staring into the distance. ' 
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You know you’re in the wilderness as soon as you leave camp. There are rattlesnakes everywhere. ‘Rattlesnakes are more likely to bite when their body temperature goes down so the early mornings and evenings are when you really have pay attention.’ 

During the day they disappear into the undergrowth. But it pays to be vigilant even then. ‘Don’t just traipse through the bushes. And when you are climbing look first and then put your hand on the next stone. Walking and climbing are done at a slower pace than you are used to here.’
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The geologists spend most of their time in the camp or in the field. But once a week they do a big shop to get in the so-called ‘dry goods’. Trips to the village to buy supplies of water, fresh vegetables, fruit and ice for the cool boxes have to be organised more frequently. ‘If it gets hot each one of us will easily use four gallons of water a day.’
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Apart from fieldwork in the Bighorn Basin, Abels also conducts research in areas in Europe and Asia. But he is determined to return to Wyoming as often as possible. ‘We have gathered so much data there. This is not the end of what we can learn, it’s only the beginning. The knowledge that we have now is a basis for all kinds of deeper issues, issues that we can’t investigate in other places because we have to start from scratch again.’  
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Drone

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Last summer Abels flew a drone over the area for the first time. 'We use the photographs to make a 3D geological model.' 
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But the area is big even for a drone to cover. 'We will need many more flights in the years to come to fill in all the details.' 
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