2023 Science Festival

Now I'll take you to visit the sites of the 2024 Olympic and Paralympic Games to see what will be hidden below the athletes' feet. I'm here with three researchers from the BRGM. Hello. Welcome. All three of you are geologists. I'll introduce you. On my left is Blandine Gourcerol. Hello. Next to you is Anne-Sophie Serrand. And we are delighted to welcome Nicolas Charles, on the far left. First we'll travel far from mainland France, to the South Pacific Ocean, to Tahiti, in French Polynesia, and more precisely, to the village of Teahupo'o, because an Olympic event is going to take place there. Blandine, what's going to happen in French Polynesia? All of the surfing events will take place in Teahupo'o, which is a very unique site. What's so special about it? Why will they be there? Teahupo'o has reef break waves, which are fairly regular, very powerful, tubing waves that will put all the athletes on an equal footing. They are extraordinary waves that are perfect for surfing. In the surf world, the waves there are famous, especially since American surfer Laird Hamilton rode a wave over 12m high there. I wouldn't want to be him. Hats off. So what explains the impressive waves at this particular spot? They're caused by the characteristics of Tahiti, where Teahupo'o is located. It's important to understand how an archipelago is formed. Tahiti is part of the Society Islands archipelago, a string of volcanic islands, one of which is Tahiti, which is also an extinct volcano. A string of islands is formed by a hot spot, an upwelling of magma that cracks through the Earth's crust... So the hot spot is underwater?

-Exactly.

-Inside the Earth's crust?

-Yes. It breaks through the oceanic crust. That creates a volcano. As the oceanic plate gradually moves away from the ridge, the volcano gradually moves away from the fixed hot spot, which continues to emit magma. It's as if you had a sheet of paper and made little holes in it while moving it around. You'd end up with lots of little holes. Exactly. So it creates a series of volcanoes that gradually go extinct. When those volcanoes go extinct, the plate gradually sinks down, because as volcanoes cool, their density increases. The volcanoes subside and then erode. You could call that the life cycle of an atoll. A volcanic island forms, and all around the island, fringing reefs form. So they form a sort of ring around it? Directly on the volcano wall. The shallow water and bright light make it possible to generate life. Over the course of the life of the island, it gradually erodes and subsides slightly. Then a lagoon is created between the coral reef, the lagoon and the island. That's the case of Tahiti. Further on in the life of an atoll, the island ends up disappearing. It gets totally submerged. But you still have the lagoon and the barrier reef. Then, when the oceanic plate sinks too far compared to the reef's vertical growth, the atoll starts to disappear. The volcano that was originally there completely disappears and only the reef will remain. But it dies at some point. What kind of timeframe is this? Does this mean that in a few years, we won't be able to surf there? This is on the scale of a few million years. That makes me feel better. So we can watch the Olympics and Paralympics. Can you explain how these waves are formed? We now understand that a reef formed. But why do we get these waves now? Tahiti is on a lagoon. There's an island, the lagoon and the barrier reef. When the wave arrives, it becomes more powerful when it hits the reef. It picks up more water as the water in the lagoon is drawn in by the power of the wave. So it kind of sucks it up? Totally. The two forces align, and that forms tubes. That's why you get such impressive waves. The reef is a mix of plants and animals, right? And minerals? The reef needs the rock face to grow on. There are very important interactions. It's a habitat for a number of fish. It's a place that is a very important ecosystem for the planet. You said it's a habitat for animals. But it's also helpful for the people on these islands. Why is that? A barrier reef, as the name suggests, creates a barrier for this island, protects the shore from storms and waves, protects the lagoon and its ecosystem and the mangroves found further inland, and prevents disruption of the ecosystem there. It's funny, because it sounds like the reef forms waves, but it also breaks them.

-Exactly.

-That's interesting. Let me turn to you, Nicolas. Here, closer to mainland France, we have no reef. So how can we protect ourselves and protect our coasts? That's a major issue with global warming. We know that the sea level is rising a few millimeters every year. Take the example of the Mediterranean coast, in Sète, where there are coastal beds, or thin coastal strips of sand. Experiments have been done on the seabed. They laid huge socks to break the swell, to reduce erosion on the coast. So there's research being done to minimize coastal erosion. Since we're in mainland France, we'll go to another Olympic and Paralympic site, a legendary venue that will host the equestrian, para-equestrian and pentathlon events. It's Versailles. It's a site with a particular landscape. Anne-Sophie, can you explain it? Versailles is gutter-shaped. It's in a gutter-shaped fold. In your field, you call it a syncline.

-Yes.

-We have a diagram. We'll show it and you can explain what we're seeing. Here you see the syncline. What do the different colors represent? They represent the different layers, the different geological formations that have been folded, as you can see here, into a gutter shape. That started around 40 to 50 million years ago, when, paradoxically enough, since it was far away, the Pyrenees formed. 40 million years ago, Iberia, or what is now Spain and Portugal, was where Brittany is. It started to turn and then pushed the bottom of France, creating a mountain range, the Pyrenees.

-We'll get to that. I'd like to understand how big this fold is. Is it the size of the gardens of Versailles? The whole city? How big is it? We have a part of the geological map of Paris here. It's on the scale of several kilometers. So it stretches over large distances.

-Dozens of kilometers. You said there's a link with the Pyrenees.

-Yes. When the Pyrenees were created, that caused folding a very long way from the Pyrenees. The effects of that Pyrenean collision went all the way to Normandy and near Paris. Take my sheet of paper example again. It's like colliding two sheets of paper and creating folds at the other ends.

-Yes. We can try it.

-I don't want you to damage your map.

-It's exactly the same principle.

-OK. Does the study of landforms have a name in geoscience? What's it called? It's called geomorphology. It describes the landscape in terms of folds and different landforms, including one type that Nicolas will talk about, the inlier, which gives us clues to understanding the geological history of the area. Do you study landforms? Yes. That's part of the studies we do as geologists. Now we'll visit a third site: the Butte Montmartre. We'll stay in the Paris region. Is that where the cycling event will be, Nicolas? It'll be part of one of the ascents in the cycling event. The Butte Montmartre is the highest point in Paris. It's 130m above sea level. It's 60 to 70m higher than the lowest point in Paris. So that's a bit of a climb. Like Anne-Sophie said, it's a unique landform. It's another geomorphological element. It's a typical structure called an inlier. It's a hill, a landform, that is isolated and reflects the forms that were around it but no longer exist because they have eroded. That erosion took place fairly recently, a few million years ago.

-Everything is relative. "Recently..." I think like a geologist. We look at long periods of time. What's unique about Montmartre... Everyone knows the Sacré-Coeur chapel. The basilica. The basilica sits on a foundation 40m deep. Why? Because of the nature of the ground below the hill. At the top of the hill, you have Fontainebleau sand, which is found higher up. There's a sample here. Fontainebleau sand, Anne-Sophie, at the Versailles site, is used in Olympic riding grounds. Can you find it all over Paris? Yes. It's mined around Fontainebleau for its very high-purity silica, especially for glassmaking. So knowledge of the Butte Montmartre made it possible to build the Sacré-Coeur basilica? Yes. To support it better, it's good to know what's going on deep below it, particularly...

-To adapt? Yes. You need fairly strong pillars to ensure the building's stability. But what's unique about the Butte Montmartre is that it was a quarry area. There was a lot of quarrying in the 19th century, and what was mined? This type of rock. What's that? It's a mineral: gypsum. Gypsum is used to make plaster. In scientific and English literature, you see the term "plaster of Paris," because historically, plaster was mined all over the Paris region.

-It still is.

-Is it still mined? Particularly around Roissy. That's a well-known source of gypsum.

-Is it found elsewhere in France?

-Yes. In the south of France. There are other deposits, but it's mostly mined in the Paris region. Let me go back to the Butte Montmartre. You said it's an inlier. It's a vestige. But what else is under the ground below Paris? Gypsum? Yes. Gypsum is found throughout the Paris region. On the Butte Montmartre, unfortunately, because of urbanization, we lost direct access to the outcrops. But you find them in the area I mentioned, near Roissy or Orly. Under Orly, there's gypsum. You need to see the continuity. Here's a map. There's a geological cross-section. It's like cutting a cake. You can see the different layers that emerge. You can see the continuity of the gypsum layer. Where does gypsum come from? Why is there so much in the Paris region now? This gypsum dates back to around 35 million years ago, at a time when... So very recently, for you. Yes, on a geological scale. The Earth is 4.5 billion years old, so that's very recent. 35 million years ago, the landscape was very different than it is today. There was a very shallow sea. That very shallow water caused a lot of evaporation. A bit like in a salt marsh, the gypsum mineral was left behind and is now mined. Can you describe the rock in front of you and what's inside it? Here we see very particular small formations, which are gypsum crystals. We call it "lark's foot" because it typically looks like the shape of a bird's foot. There are several types. This is what is typically mined in the big quarries in Paris, whether open-air or underground. There are real cathedrals. Anne-Sophie and I were lucky enough to visit them. You have arches underground that are a dozen meters high. We haven't talked about the other rocks in front of you. Can you describe them? They're volcanic rocks. We brought some lava. This is lava from Vesuvius. Why are they two different colors? It's their composition. They're a bit different. This one may have more magnesium than this one, which may have more iron. OK. And what about that one? That's a volcanic bomb.

-It's a...

-A volcanic bomb? What's that? It's when a strombolian eruption emits fragments that crystallize in the air. OK.

-What?

-It's defused.

-It's safe.

-I feel better now. Tell us more about your work at the BRGM. What do you work on? Do you work more on metals, Blandine? Yes. Metals and critical metals, especially lithium, which we we did a previous video on. What are you specifically interested in? We're trying to find out where the metals are that our society needs and look critically at their potential mining or in relation to mining criteria. Later we'll talk about materials and metals used in sports. Anne-Sophie, what are you working on at the BRGM? We do studies for industrial companies that have very specific problems sourcing certain metals or minerals, because metals and minerals are in everything. I challenge you to find something here that doesn't have an ounce of mineral in its composition. So we support industry, but we also support public policy. We help ministries and decentralized government agencies consider responsible sourcing of mineral raw materials. Nicolas, the BRGM plays a key role in finding climate change solutions. Yes. Through a range of disciplines. Here we have this reference document called a geological map. That's part of our work. We are France's leading geological mapping institution. We are a knowledge base for many other fields, like risk management at the regional level. This summer, we heard a lot about water management with the drought. In France, more than 2/3 of the water we consume from the tap comes from underground. So we need water specialists, or hydrogeologists. They were in great demand this year. They use our knowledge of what's underground from this reference document. It's all connected with global warming. We also look at long periods of time. The global warming we're experiencing is neither the first nor the last. The planet has experienced them throughout history. If we understand past climate changes, we can better understand how to mitigate and better adapt to this one in the future. 

BRGM AMBASSADOR WHAT DOES THE SCIENCE FESTIVAL MEAN TO YOU? 

The Science Festival is an opportunity to show what we do and make our work known to the public. So at the BRGM site, I do a piezometer workshop. It's a well that goes in the ground so you can see the water level. We measure the water level with a sensor. We put a camera in the well and we can see the water table, because the camera goes in the water. It's a chance to see the water flowing beneath our feet. It also gives us an opportunity to talk to people from different backgrounds and of different ages and sometimes even inspire teenagers and children to become scientists. 

WHAT CONNECTS YOUR RESEARCH TO "SCIENCE & SPORTS"? 

In terms of sports, what attracted me to caving was pushing yourself but also knowing your body, knowing your limits and listening to your body to know when to stop, when to eat and when to rest. 

DO YOU HAVE ANY STORIES ABOUT YOUR WORK AND SPORTS? 

We all have lots of stories, especially from working in the field. We have piezometers that we monitor regularly. I worked for several years in Picardy, in the former Picardy region, where we managed 113 piezometers. Each one has a story. After a few years, you know them by heart. They're like our children. We pamper and take care of them so they can give us data. We know their history and their owners. So we have a lot of stories about these piezometers. We also have a lot of stories from going out and doing field campaigns with our little sensors to measure as many wells as possible in one area to make a complete groundwater map. We go door-to-door, knocking on doors to ask if people have a well. So we meet a lot of people. Sometimes people don't even know they have a well in their backyard, but they're in our database. Sometimes we see really amazing wells in castles and even churches. You pick up stories along the way when you're out in the field.