Gorges du Verdon

“One of the natural wonders of France… and of the Earth” (EAMartel)

A link in the history of the Alps ...

The tectonic deformations linked to the collision appear more and later towards the outside of the Alpine chain. At the end of the Tertiary era and the beginning of the Quaternary, between -7 and -2 million years ago, folds and thrusts deformed the region of Digne and Verdon. Sedimentary and tectonic assemblages are superimposed on each other.

The Gorges du Verdon were carved out of the limestone massifs of the Alpine chain which were massively displaced towards the south during this “eventful” period. The limestones of the gorges (dated from -150 to -135 million years ago, Upper Jurassic) therefore participated in this movement. They were themselves overlapped by other limestone sets.

In its course towards the Durance in the west, the Verdon has adapted to the deformations of the massifs. He dug his bed through an enormous pile of geological layers before reaching and notching the “lower” limestones, those of the current gorges. The notching work was facilitated and activated at a very precise moment in the history of the canyons around the Mediterranean: during the Messinian crisis.

This dramatic event begins around -6 million years ago. The coming together of the tectonic plates of Europe and Africa causes the bulging of the Gibraltar arc and interrupts the inflow of water from the Atlantic to the Mediterranean. The strong evaporation of Mediterranean waters is no longer compensated by this supply, the level of this sea drops by 1500 meters. This phenomenon ends 5,3 million years ago with the rupture of the Strait of Gibraltar. Indeed, this catastrophic event replenishes the Mediterranean in less than a century.

It was during this crisis that rivers and their tributaries cut deep canyons to reach low points, such as the sea and over-salty lagoons. When the sea returns to its normal level, deep erosion is no longer necessary, rivers and streams lose energy (less steep) and deposit the materials transported less and less far. The canyons are then gradually filled (from -5,3 to -2 million years).

Between -6 and -1 million years ago, these major events, the overlaps and the Messinian crisis, occur simultaneously and impact the Verdon sector. An aerial and underground karst network (see box on karst) was set up with the Messinian crisis. It evolved at the same time as the deformation of the limestone massifs occurred, which forced the water to force new passages. Then, during and after the clogging of the canyons, the alpine tectonic deformations continued and the then filled and inactive karst (we speak of paleokarst) of the Verdon was affected by faults.

The history of the Mediterranean canyons does not end there. In fact, the Quaternary ice ages also caused sea level drops in a much more modest way than during the Messinian crisis, water then being trapped in the polar caps and large glaciers.

The old karsts are reactivated and cleared of their sediments. In regions subject to alpine uplift, erosion was more intense there than downstream. This has encouraged the development of new networks superimposing on old networks and intersecting them. This is most likely the case with the current karst network of the Verdon.  

The debate on the Messinian history of the great gorges remains open and geologists are continuing their research in search of new clues.

What is certain is that the current landscape of the great gorges is a young landscape whose last model is inherited from the last glaciation, between -90 and -000 years.

Learn more about the karst

The name karst refers to a limestone region in Slovenia that served as a model to describe a certain type of landscape and aquifer. Karst regions exhibit particular forms of erosion and carbonate dissolution (chasms, galleries, underground networks, sinkholes). While there is a frequent lack of water on the surface, it is, on the other hand, abundant at depth since the water circulates in underground networks.

... in connection with 22 other geosites: Les siréniens de Castellane, Clue de Sisteron, Eaux-Tortes

The Gorges du Verdon are hollowed out of coral limestones dating from the end of the Jurassic (there are -150 to -145 million years ago). At the same time, at the future clue of Sisteron, the marine environment was deeper. Also, the limestones are less massive and contain many ammonites.

From the Eaux-Tortes site, it is possible to observe the thick limestone bars of the Séolanes. Like the Verdon, it is reef limestone. But unlike those of the Verdon, the Séolane reefs have not remained “in place” since the Upper Jurassic. They originally formed a reef platform east of Basse Provence. It is alpine history which led them to Ubaye!

What we can decipher from the current landscape

The route des crêtes and its many belvederes, the Martel path or even, for the more athletic, the Imbut hike, allow you to discover the great gorges of the Verdon and its famous white limestone from Provence ... 300 meters thick limestone notched by the Verdon!

On this site, fossils are rare. They may have disappeared due to natural phenomena of type dissolutions and recrystallizations. When the fossils are preserved, we can recognize corals of different types (branched, tabular…), large gastropods and lamellibranchs.

The limestones of the Verdon, 150 to 140 million years old, took place in a tropical environment. These are bioconstructed limestones, that is to say that they are living organisms, the corals, which built them until they formed a large barrier that sheltered areas of lagoons. This type of reef is particularly favorable to the formation of limestone massifs, whether by the accumulation and piling of coral remains (limestone skeletons) or the remains of other organisms with calcareous skeletons (macro or micro-organisms) .

A little anecdote?

Edouard Alfred Martel and Isidore Blanc, accompanied by members of their respective teams, were the first to explore the Gorges du Verdon as a whole in 1905.

Ten years before this famous exploration, the pharmacist Gustave Tardieu was already praising the gorges. He was the first to compare them to the great canyon of Colorado, and to give the name of "Styx" to the dreaded and famous gully which leads to the chaos of the Imbut.

The exploration of the Verdon led by Martel was not limited to the grand canyon. In 1905, they also explored about fifteen chasms including the Gros Aven de Canjuers.

Martel was already stressing the importance of the underground karst network. The waters of the Verdon, like those of its tributary Artuby, disappeared at certain points of their bed. These losses fed the resurgence of Fontaine l'Evêque downstream. Today it is filled and drowned under the waters of the Sainte-Croix-du-Verdon dam lake.