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Finding fractures in the Outback

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Although they appear to be, these pillars are not remnants of a lost city. 

They are ancient sandstone shapes,  located slap bang in the middle of the outback in the Northern Territory of Australia. 



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About 1.4 billions years ago, the tops of these pillars were underneath shallow water. 

Slowly but steadily, because of heavy rains and extreme weather, the rocks eroded and gave rise to these dramatic shapes.

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Armed with a tent, a drone, hammers and compasses, a four-wheel drive and a few days of food and fuel, geologist Pierre-Olivier Bruna ventured far off the beaten track into this remote and exotic area.   

He was accompanied by his colleagues of TU Delft:  Jan Kees Blom, Giovanni Bertotti and master student Nassar Pragt.

The team, called NT-Work, was sponsored by the Dr Schürmannfonds Foundation.

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 Their purpose: to study the McArthur basin in the Lost City. 

The detailed structure of that basin is poorly understood. "The structural history is very incomplete as it did not receive much attention due to it's remote location."


 
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By means of painstaking field work the team gradually pieces together a picture of how the greater McArthur Basin formed over time to understand the large scale geological history. 
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Fracture networks

The team specifically investigated natural cracks in the rocks of the areas they visited. In geologist terms, they mapped fractures, which are any separations in a geologic formation that divide a rock into two or more pieces.

The team wondered: when were these fractures formed? Do these fractures intersect and hence, are they connected?  


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Why exactly are fractures so interesting from
a geologist's perspective? Bruna explains.

"Fractures can make a rock more permeable, which allows fluids to flow through the rocks. Looking at fractures thus tell us a lot  about how such a fluid would flow, whether it's water, like rainwater or groundwater, or potential hydrocarbons in the subsurface." 



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The team mostly mapped the visible parts of the rocks on the surface, which are called outcrops. Those visible cracks help geologists to predict the unseen geometry of those same rock formations far below the surface.  

"It's really hard to collect data about how fractures at depth are organised, because, well.. we can't just go underground and take a look. So we have to somehow derive information from the parts of the rock we actually can see with the naked eye!"  
 
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drone & 3D model

This year, the drone was a vital instrument to get a good overview of larger the area, it's inaccessible parts and it's fracture networks.  

"The pictures of the drone are actually bridging the gap between what we ourselves can do on the ground with manual field techniques, and high-altitude remote sensing methods."
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"Flying the drone was fun and easy to do", Bruna remembers. "But the terrain was not flat at all on most locations. And so it was hard to mount or dismount. Nassar had to catch the drone from mid-air many times!"


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The drone pictures actually allowed the team to construct their very own 3D map of the Lost City area after their return.

"This model gives us so many detailed information that we could never have measured on the spot or obtained otherwise!"

The team used a method called phtogrammetry to align all photos and stich them together in the right georeferenced way. Then they could reconstruct the topography of the area.


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And just because they can...
"....we can even simulate flying over the area once more, using our very own 3D model!"
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into the wild

Teammate Jan Kees Blom had been doing research in Australia for many years before he joined the NT-Work team. His experience was very useful, as travelling to this remote and sparsely populated area involved a lot of planning and preparations. 
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It takes three days by four-wheel drive to get to the Western Lost City. You'll need to cross crocodile creeks and drive through rough terrain on muddy roads.
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"Entering some outcrops is not easy at all. We had to work for it. Giovanni and Nassar had to pull and push at the same time for our jeep to be able to cross some farmer's land borders!"
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" Sometimes the road was not even recognizable - we had to stop many times to pull branches away to refind the track." 
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A lot of the planning went into making sure the team had enough food and, very vital, fuel for the days they were off grid. But in the Outback, unexpected events can cause delay. 

"We had anticipated to find a camp site and a fuel station in a place called Roper Bar. We arrived at 4:00 pm at a station that seemed unchanged since the end of WWII. But everything turned out to be shut down. So we took a dirt road to the next station an hour away, only to find that station had closed 3 hours earlier. Completely unplanned, we were forced to set up camp and wait for it to open at 9:00 in the morning."

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The team ran out of fuel one more time because of a detour they had to make. This time, fortunately, someone had given them a jerrycan which literally saved the trip.

 "It was quite a challenge to get the petrol into the car, tough. We actually had to cut one of our drinking bottles to be able to pour in the fuel without spilling it all."
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If you have a flat tyre in the bush, you need to try and fix it in order to always keep a spare. Luckily for the team, the ranger came to the rescue.

"Besides her official tasks, she dedicates a lot of her time to living remotely with repairs and maintenance on all kinds of vehicles, small engine power tools, water and power utilities. She really helped us out!"  
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After a great trip, it was time to return to the campus of Delft University of Technology. 

The team is already planning to revisit next year, to pick up where they left off. 

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The team would like to thank:
- Dr Schürmannfonds for sponsoring the research
- The geologists from the NTGS
(Northern Territory Geological Survey)
- The Northern Territory Government
(Aboriginal Area Protection Authority and the Rangers from the Nathan River Station)
- The Pastoral tenants and owners of the Broadmere station, Carpentaria Station and McArthur River station
- And all the friendly and helpful “Territorians” we met during our trip

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entering the area

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"My name is Dianne Chanot. I'm French and have become a Park Ranger at Nathan River Ranger Station in Limmen National Park.

We are a kind of jack-of-all-trades of the bush. To me, being park ranger really is the best job in the world, in the best possible "office"!

My main role is land management for this 12,000 square km park. I look after visitor infrastructure such as driving tracks and walking trails. I maintain facilities and assist in case of emergencies.

I conduct or participate in biodiversity surveys to try and protect native species as much as possible, and also take part in water and fish monitoring projects, or geology studies.

And we manage fire on park, like fighting wildfires, or more likely strategically burning at the appropriate time of the year to create a mosaic of burned landscape to protect infrastructure and fire-sensitive vegetation areas in the process. "
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