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Bonnet du Capelan

A cache by Ticaribou Send Message to Owner Message this owner
Hidden : 11/20/2009
Difficulty:
1 out of 5
Terrain:
1.5 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:

A volcanic neck: The "Bonnet du Capelan"


 



 

The Esterel range, is an old mountain (Hercynian type). It was constitued during Permian Era (-290 million years).The" Mont Vinaigre" is the highest peak (2015 ft).Before the formation of the Mediterranean sea, this piece of land was a part of Africa. During Tretiary Era, a part of Esterel was detached from the mainland. Corsica was borne.

290 million years ago, here, the Earth's crust was deeply cracked. Therefore, the lava spread all over this place and has created a red crimson layer called red porphyry. Sometimes this red porphyry was mixed with a blue one. Those rocks have colored the Esterel landscape. After this first volcanic activity, about 200 volcanoes have risen and the "Bonnet du Capelan" was one of them. During 30 million years, those volcanoes have belched basalt, sandstone and porphyry to create volcanic domes. During the Secondary Era ( Mesozoïc; - 150 million years), the "Bonnet du Capelan" and the others was eroded. The rain and the wind has exposed the volcanic neck of the "Bonnet du Capelan".

This volcanic neck called also volcanic plug was created when lava hardened within the vent when "Bonnet du Capelan" was active. When forming, a neck can cause an extreme build-up of pressure if volatile charged magma is trapped beneath. Sometimes, it can lead to an explosive eruption. Here, the neck was preserved and the erosion has removed surrounding rocks while the erosion-resist neck remained providing a distinctive landform called "Bonnet du Capelan". This geographic feature helped the celts to buid, many years ago, an oppidum above it.

Process of exhumation

 

 
     

Blue and Red Porphyry


 


Le massif de l'Esterel date de l'Ere Primaire.C'est un massif de type Hercynien.Le Mont Vinaigre est son point culminant(614m). Ce morceau de terre était attaché à l'Afrique avant la formation de la mer Méditerranée. Au Tertiaire une partie se détache et forme la Corse.

Il y a 290 millions d'années, ici, l'écorce terrestre se fissure profondément et laisse remonter à la surface une couche rouge pourpre: le porphyre rouge et une autre moins abondante le porphyre bleu. Après cette phase de volcanisme fissural, de vrais volcans vont s'édifier. A cette période se forme le Bonnet du Capelan. On pense qu'il existait près de 200 bouches volcaniques.Ces volcans étaient de type explosif strombolien.L'activité volcanique durera près de 30 millions d'années .Il en résulte une forte émission de basalte, de grès et de porphyre.Le Bonnet du Capelan va subir à l'Ere Secondaire (Mésozoïque, -150 millions d'années) une forte érosion.La pluie et le vent vont continuer leur action.Ils vont alors éroder les bords du dôme volcanique et faire apparaître un neck volcanique.

Ce neck représente la cheminée du volcan formée de roches magmatiques pétrifiées.Le neck du Bonnet du Capelan présente avec ses parois abruptes un réel avantage pour les peuples celto-ligures qui vont pouvoir y construire un oppidum.



You can log this Earthcache by submitting:

- a picture showing you or your GPS unit in front of the "Bonnet du Capelan"

and please answer the following tasks/research questions

- What is the other name of the red porphyry?

- What is the other name of the blue porphyry? (a part of this name comes from this Mountain)

- What is the height of the "Bonnet du Capelan"?


Pour valider cette Cache de la Terre:

- Merci d'envoyer une photo de vous ou de votre GPS unit devant le "Bonnet du Capelan"

et aussi de répondre à ces trois questions (pas sur le log mais par courriel):

- Quel est l'autre nom du porphyre rouge?

- Quel l'autre nom du porphyre bleu?

- Quelle est l'altitude du "Bonnet du Capelan"?



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