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Geology of the Tour de France @geotdf.bsky.social · 24/07/2026

Alpe d'Huez day! Two years ago, Marjolein made this clip for the @le-tourdefrance.bsky.social Femmes about how the Alpe is folding without breaking! Enjoy the climb! And the spectacular folds...

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Geology of the Tour de France @geotdf.bsky.social · 14/07/2026

Three years ago, Marjolein Naudé made this clip about the Puy Mary, the Cantal volcano's highest peak not far from today's finish line. It was then the finish for a stage in the @letourfemmes.bsky.social! @uugeo.bsky.social

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Geology of the Tour de France @geotdf.bsky.social · 14/07/2026

Today's Tour de France stage ends at Le Lioran, at the top of the Cantal Volcano, Europe's larges stratovolcano. Two years ago, we made this clip there, our favorite :) How volcanism led to the invention of the bicycle! @vanhinsbergen.bsky.social @uugeo.bsky.social

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Geology of the Tour de France @geotdf.bsky.social · 20/05/2026

Carrara limestones are used for tiles and construction, are the standards for material science and isotope geochemistry (δ13C, δ18O). It's hard and homogeneous and excellent for architecture and art, such as the Pantheon or Michelangelo's David. And as subsurface for hard races!

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Geology of the Tour de France @geotdf.bsky.social · 20/05/2026

Marble originates as limestone that gets buried (here: to ~18 km depth) and heated (~500-600°C) by geological processes (Apennine mountain building), and then recrystallizes. Limestones are soft, compacted grains and fossils (right), marbles are hard, intergrown crystals (left).

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Geology of the Tour de France @geotdf.bsky.social · 20/05/2026

The Giro will pass Carrara today! The Carrara marble mines are Earth's largest. Since Roman times, some of the purest marbles in the world, used for iconic architecture and art, have been excavated in over 650 quarries.

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Geology of the Tour de France @geotdf.bsky.social · 10/03/2026

In case you wondered why GeoTdF is silent: we went incognito and trained to become pro. Today, we ended at nr 116 in Paris-Nice 😎 🦖 @teamvismaleaseabike.com @appysluijs.bsky.social

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Geology of the Tour de France @geotdf.bsky.social · 07/07/2025

And humans have used the dry North Sea to migrate from France to England and back during the last 800.000 years, depending on the climate state. And when there was enough ice, they could also walk to Ireland! No ferry needed. Or cycle, if they had invented the wheel.

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Geology of the Tour de France @geotdf.bsky.social · 07/07/2025

Well, dry, it was occupied by a tundra and a large river, that combined the Rhine, the Meuse, the Scheldt, and the Thames. These flowed towards the Bay of Biscay. Mammoths roamed the banks, and the vast tundras south of the ice caps of Scandinavia.

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Geology of the Tour de France @geotdf.bsky.social · 07/07/2025

OK, so we decided not do skip a GeoTdF year, but this stage is so boring that it's begging for some geo-info! We're riding along the North Sea coast towards Dunquerque. But even as recent as 20.000 years ago, there was no coast here! During the last ice age, the Channel was dry!

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Geology of the Tour de France @geotdf.bsky.social · 26/06/2025

OK, so we won't do a detailed GeoTdF this year, but we couldn't help ourselves...the geology of the Ventoux is quite clearly correlated with scenes during the climbs. For example, the famous 2016 incident that left Chris Froome running up with a broken bike - clearly geologically pre-determined.

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Geology of the Tour de France @geotdf.bsky.social · 10/05/2025

Eastern Albania is more mountainous, and consists of pieces of the former Greater Adria continent, pushed and piled up. And at the top lies one of the best preserved pieces of oceanic crust on land ('ophiolites') in the world: the Mirdita Ophiolite. But we'll stay west, and head for Italy next!

Geological cross section across western Albania, showing how pieces of Greater Adria crust are pushed and folded over each other

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Geology of the Tour de France @geotdf.bsky.social · 10/05/2025

This platform continues to the Greek Islands of Paxos, Lefkas, Kefallonia and Zakynthos. To the North and East of this platform was a deeper basin in which thin-layered limestones formed. You will see those, folded up and broken,in Albania. And later in Umbria and Marche, in northern Italy!

Thin-layered limestones in Albania, derived from an pushed-up sedimentary basin

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Geology of the Tour de France @geotdf.bsky.social · 10/05/2025

The last intact remnant of Adria lies below the Adriatic Sea, and on the Karaburun Peninsula in southwest Albania, and in Puglia, where the Giro will ride its first meters in Italy this year. These intact remnants are shallow marine limestones of the Apulian Platform in the south.

Karaburun Peninsula of southwest Albania

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Geology of the Tour de France @geotdf.bsky.social · 10/05/2025

Greater Adria was pulled down into subduction zones: both to the west, below Italy, and east, below Albania (and Greece and the Balkan). The sedimentary rocks that formed at the margins of Adria were scraped off and pushed up, making the Apennines and the Albanides/Hellenides/Dinarides

Cross section showing Adria diving below the Apennines in the west and the Albanides in the east

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Geology of the Tour de France @geotdf.bsky.social · 10/05/2025

The Giro d'Italia started in Albania, but the riders who are used to Italy will feel geologically right at home! Just like the Apennines, the Albanides (and the Dinarides to the North and Hellenides to the South) are made of rocks that were once part of the continent (Greater) Adria!

Paleogeographic map showing the outlines of the Greater Adria continent that once intervened Africa and Europe

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Geology of the Tour de France @geotdf.bsky.social · 20/03/2025

For those of you who are Tired Of All This Shit, we bring you: The relationship between volcanism and the invention of the bicycle! We made this clip, with @vanhinsbergen.bsky.social, for last year's Tour de France stage over the Cantal Volcano, and its highest remaining peak, Puy Mary ❤️🤠

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Geology of the Tour de France @geotdf.bsky.social · 08/03/2025

That continental edge was pushed below Corsica, 20 million years ago, and pulled back to the surface in the last 10 million years, when the Tyrrhenian Sea basin was formed. The limestones became marbles, the marbles became gravel, and now it’s the peloton that is under high pressure! Enjoy!

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Geology of the Tour de France @geotdf.bsky.social · 08/03/2025

Marble is a metamorphic rock: it was originally a limestone that was buried to 25 km depth or so, and heated up to a few hundred degrees. In the case of Tuscany, these limestones formed as reefs on the edge of the Adria continent.

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Geology of the Tour de France @geotdf.bsky.social · 08/03/2025

Strade Bianche day! The famous white gravel roads of Tuscany promise another epic battle on the bike. But where do the white gravels come from? Tuscany’s subsurface consists of marble: bright white crystals of calcium carbonate. These are famously mined in western Tuscany, in the Carrara quarries.

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Geology of the Tour de France @geotdf.bsky.social · 07/02/2025

The most spectacular rocks of the Semail Ophiolite are so-called 'pillow lavas'. These structures form when lava erupts below sea level: the lava quickly cools from the outside, but keeps flowing on the inside. Cut them, and you get a pile of pillows. Good for a rest day!

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Geology of the Tour de France @geotdf.bsky.social · 07/02/2025

In Oman, the Arabian continent went down into a subduction zone below oceanic crust, 80 million years ago, and scooped up the 'Semail' ophiolite. Along the race you see the magmatic rocks that formed at a spreading ridge, and rocks of the Earth's mantle that were below the ridge!

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Geology of the Tour de France @geotdf.bsky.social · 07/02/2025

An ophiolite is a piece of oceanic crust that is exposed above sea level. Oceanic crust forms at spreading ridges, and is normally many kilometers below sea level. But when subduction zones form in oceans, such as in the Philippines, oceanic crust may be uplifted and emerge.

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Geology of the Tour de France @geotdf.bsky.social · 07/02/2025

Geology of the Tour of Oman! - The peloton may think that they're riding through desert mountains this week, but for a geologist, they're riding through the deep ocean, and the mantle below that ocean! Oman is one of the favorite geo-destinations: the world's most beautiful 'ophiolite'. #Geoscience

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Geology of the Tour de France @geotdf.bsky.social · 28/01/2025

NW of Alula, the peloton will see dormant volcanoes of the Harat Uwayrid volcanic field of only 8-0.3 million years old. These are thought to relate to ‘plume’ volcanism, with calm basalt lava flows like on the Canary Islands! Familiar ground for those who trained on the #Teide !

Young intraplate volcano in western Arabia

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Geology of the Tour de France @geotdf.bsky.social · 28/01/2025

Sandstones of the next-younger Saq Formation is an Arabian lifesaver: these rocks are porous, and serve as the main aquifer (that is, a groundwater-bearing layer) of NW Arabia. These sandstones are rich in trace fossils: tracks in the sand made by ‘trilobites’that roamed the Cambrian sea floor!

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Geology of the Tour de France @geotdf.bsky.social · 28/01/2025

The Quweira Sandstonesare particularly resistant. These were were used for the famous settlements of Madain Saleh, not far from AlUla. This city was built in the 2nd century CE by the Nabateans, and has beautifully been preserved in the durable, hard rocks.

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Geology of the Tour de France @geotdf.bsky.social · 28/01/2025

The pro-cycling peloton is racing the Al'Ula Tour in Saudi Arabia this week, territory of spectacular cliffs of sandstones, deserts, and young volcanoes. The cliffs around AlUla formed in shallow seas, ~500 million years ago, but to the South Polar, as part of the supercontinent 'Gondwana'.

Geologist standing in front of a wind erosion-carved limestone cliff in the Al'Ula region of Saudi Arabia

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Geology of the Tour de France @geotdf.bsky.social · 20/01/2025

This causes earthquakes - mostly small ones, but in 1954 with a magnitude 5.4. The faults that push up Mt Lofty slip on average half a mm per year. And with this ongoing uplift, the Tour Down Under gets a little harder every year 😃!

Earthwuake map of Flinders Range, Adelaide

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Geology of the Tour de France @geotdf.bsky.social · 20/01/2025

But the ancient faults that cut these rocks were reactivated because the Australian plate is being squeezed between the Eurasia and the Pacific, and also interacting with India and Australia. The squeezing popped up the Flinders ranges, and the epic Mount Lofty, and this process continues today.

Map and cross section showing how Flinders Range is pushed up along faults

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Geology of the Tour de France @geotdf.bsky.social · 20/01/2025

the Adelaide region forms a rare exception: it's shaking! Australia consists mostly of rocks of billions of years old, which formed when ancient continents collided and long-forgotten mountain belts formed. The rocks around Adelaide are up to 900 million years old, when life was only microbial.

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Geology of the Tour de France @geotdf.bsky.social · 20/01/2025

And off we go with the 2025 geo-road cycling season 🥳🚴‍♀️🤠! The Tour Down Under brings the peloton to Adalaide, in the middle of the Australian plate. If you were afraid of earthquakes, you'd think this would be a safe place, as most earthquakes occur at plate boundaries. But you'd be wrong 😑.

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Geology of the Tour de France @geotdf.bsky.social · 07/12/2024

For the riders today, this is bad news. When the partitions are up, they provide some shelter to the wind. But during today's storm, they'll be down. Perfect conditions for some suffering. The organization is well prepared: behind the finish line, there is a puke station with plenty of buckets 😂.

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Geology of the Tour de France @geotdf.bsky.social · 07/12/2024

While the project became an enormous engineering success, it had ecological downsides. The dammed inlets turned from brackish to fresh water, affecting biodiversity. The final dam, of the Oosterschelde, is therefore contains open partitions that only during storms are shut.

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Geology of the Tour de France @geotdf.bsky.social · 07/12/2024

Following this disaster, the 'deltaworks' started: the inlets of the Zeeland estuary were dammed, dykes were raised. The project took decades and shortened the Dutch coastline by 700 km. All but one inlet are now dammed: only the Westerschelde, that leads to the Antwerp harbor, is still open.

Map showing the dams of the Zeeland estuary, that were built between 1960 and 1986

Photograph of the Oosterschelde dam and the artificial island Neeltje Jans, halfway.

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Geology of the Tour de France @geotdf.bsky.social · 07/12/2024

On February 1st, 1953, disaster struck. A storm surge led to multiple dike breaches, and an area of 150.000 hectare (370.000 acres) flooded. Nearly 2000 people drowned that night. 47000 cattle and 140000 poultry died. This was not the first flood, but it was the worst.

Map with the flooded area of the 1953 flooding.

picture showing a breached dam with high water flowing into the polders

Boy on a bike cycling through two feet of water in front of a flooded house

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Geology of the Tour de France @geotdf.bsky.social · 07/12/2024

The race will be held in Zeeland, a province in the SW of the Netherlands. Zeeland is an amalgamation of islands in an estuary, where the Meuse, Rhine, and Scheldt rivers meet the North Sea. And with the Dutch hobby of making polders, this land is especially vulnerable for floods.

Satellite image of zealand showing the waters of the estuary

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Geology of the Tour de France @geotdf.bsky.social · 07/12/2024

Today is the day of the Dutch Championships Headwind Cycling, where pro riders get beaten by the mailman! It will be a mild edition, with only a 6-7 Bft westerly wind, but the race parcours is chosen such that there is zero protection: the 9 km long Oosterschelde dam! A dam with a history.

Cyclists of a previous edition of the Headwind Cycling Championships, who nearly get blown off their city bikes

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Geology of the Tour de France @geotdf.bsky.social · 06/11/2024

Look what we found on the world wide web! So, get into gear, and start your geo-race!

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Geology of the Tour de France @geotdf.bsky.social · 29/10/2024

Normandy, Brittany and Mont Ventoux...just as we ran out of funding for clips 😭. Ow man, there's so much to tell there!

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Geology of the Tour de France @geotdf.bsky.social · 22/10/2024

For some reason, since the cycling season is over, a few hundred people started following GeoTdF on Bluesky! Maybe we should stop posting more often, it seems to work 😂. Welcome! And we’ll be back with Geo-Cycling stuff in January: the young thrusts of Mt. Lofty!

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Geology of the Tour de France @geotdf.bsky.social · 12/10/2024

What would the season's Grande Finale of @Il_Lombardia be without geology! You'll see the leaves falling over the folded and pushed up limestones - and dolomites of course, the name giver of the Italian Alps!

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Geology of the Tour de France @geotdf.bsky.social · 02/10/2024

Thanks Geological Society of South Africa, for inviting us to write about Geo-Sports in your Geobulletin! And for all of you out there interested, you can find our editorial, by Marjolein and Douwe here: gssa.pub/gb/content/i...

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Geology of the Tour de France @geotdf.bsky.social · 29/09/2024

Stefan Heuberger at ETH Züich explored the route for you and took pictures. In his blog on our website, he explains where the riders climb the remains of the majestic glaciers of the last ice age!

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Geology of the Tour de France @geotdf.bsky.social · 29/09/2024

Last day of the #Zurich2024 world championships, the men will have to show what they’re worth! And they’re lucky the race wasn’t 24000 years ago, because they’d had have to ski the entire thing back then 🥶

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Geology of the Tour de France @geotdf.bsky.social · 26/09/2024

It was the Last Glacial Maximum, around 24,000 years ago, that shaped most of the course today.Geologically speaking that was basically yesterday. It does give us the opportunity though to make geology even more visible during the long road races. #geology #cycling

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Geology of the Tour de France @geotdf.bsky.social · 26/09/2024

Ice ages and warmer periods shaped the landscape on our course. Most of it we can’t see anymore because time and erosion made them disappear under layers of sedimentation. Valleys that were once hundreds of meters deep are now filled in to form relatively flat roads for our riders. #zurich2024

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Geology of the Tour de France @geotdf.bsky.social · 26/09/2024

The road race takes us to beautiful geological sites along the route like drumlins, valleys, a tafelberg and gorgeous lakes. Stefan Heuberger of @eth-eaps.bsky.social at @ethzurich.bsky.social takes you on a tour to see but also shows you what you can’t see anymore.

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Geology of the Tour de France @geotdf.bsky.social · 22/09/2024

We also learn how the creation of the Alps tens of millions of years ago now comes in very handy when dealing with a nuclear problem. And how a boring tectonic situation makes that all possible. Enjoy the blog and the race!

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Geology of the Tour de France @geotdf.bsky.social · 22/09/2024

The riders will go fast but the Alps were the slow poke of mountain ranges. They took their time to form. The peaks that currently stand up to 4000 meters above sea level were once deep in the crust, covered by 10 km of rock. Most of that cover ended up in the foreland, as far as the Netherlands.

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