Four years ago, when sailing along the Dalmatian coast, we wondered as to why there were no rivers (see my blog C - 18 from 2019). There actually were. We just could not see them. Rain water washed out a wide cave system which drains water from the surface and carries it underground to the sea.
The Calanques are now a protected area and part of France's National Parks
We are going to visit a similar formation between Marseille and Cassis which is sited in the Parc National de Calanques. Rainwater is slightly acidic. When rain drops through the air, it acquires atmospheric gases such as carbon dioxide. As CO2 dissolves in the dropping rain, it forms carbonic acid and gives rain water a pH of 5.6. This is enough to erode even the best quality limestone. Just drop a bit of sparkling water on your marble kitchen top - actually do not do that. You create a permanent mark. That is why coke and red vinegar are the worst enemies of kitchen marble. One mistake and your beautiful stone is stained forever
The National Park des Calanques is unique as it protects also the continental shelf
The limestone plateau between Marseille and Cassis is about 250 million (Mesozoic) to 65 million (Jurassic) years old. It was laid down in the Tethys Sea that once separated the African Plate from the European Plate. It is full of maritime fossils – animals and plant s who once lived on the shallow sea floor. As African and European Plates began to move towards each other, they lifted the sea floor. The Plateau des Calanques was lifted above water a good 1.5 m years and is ever since exposed to erosion.
The now floded valleys are visible on this recent underwater map
Today, only part of this eroded landscape is visible. Half of the park was flooded at the end of the last ice age 10'000 years ago. The sea level rose by 130 meters. New comprehensive Ocean cartography shows the submerged river valleys and the karst fields hidden below the waves. This is the main reason the Parc National also covers the landscape below sea.
Scuba Divers doing Research on a Karst Field about 20 meters below Water
The part of the Calanques above sea level is the older part of the formation. Tunnels and arches have collapsed long since. What is left are steep and narrow valleys carved into the limestone plateau. Often their tongues are filled with sand and form tiny little beaches.
People swimming in one of the smaller Calanques. The white sand at the bottom is visible.
A few Calanques are different though .They started eroding when our globe was in the grip of four long ice ages with far lower sea levels. They erosion during one million year made them deep - they thus make excellent harbors for boats with a deep keel. The Calanque du Port Miou is an excellent example. Have not come across any other natural Yacht Harbor like it. Its narrow width makes it the ideal shelter for sail boats during the stormy winter season. No wonder it is always fully booked.
La Calanque du Port Miou - best natural Harbor I have ever seen