Êtes-vous un étudiant de l'EPFL à la recherche d'un projet de semestre?
Travaillez avec nous sur des projets en science des données et en visualisation, et déployez votre projet sous forme d'application sur Graph Search.
Concept
Stora Alvaret
Résumé
Stora Alvaret (ˈstûːra ˈâlːvarɛt; "the Great Alvar") is an alvar, a barren limestone terrace, in the southern half of the island of Öland, Sweden. Stora Alvaret is a dagger shaped expanse almost long and about at the widest north end. The area of this formation exceeds , making it the largest such expanse in Europe and comprising over one fourth of the land area of the island.
Because of the thin soil mantle and high pH levels, a great assortment of vegetation is found including numerous rare species. Stora Alvaret is not devoid of trees, contrary to a common misconception; in fact, it holds a variety of sparse stunted trees akin to a pygmy forest.
Stora Alvaret falls within UNESCO's Agricultural Landscape of Southern Öland, , which was designated World Heritage Site due to its extraordinary prehistory.
The limestone plain was created by glacial action from earlier ice age advances. The limestone formation itself was created about 500 million years ago in more southerly seas. Gradually hardening into limestone and drifting northward, the limestone of Stora Alvaret contains a rich fossil record of some of the marine creatures who contributed to it. For example, orthoceratites are found in some of the present day structures on the island.
Only as recently as 11,000 years ago did the first portions of the island of Öland emerge from the Baltic Sea, after the overpressure of the last glaciers was relieved by melting. Over the next several thousand years, more ice melted and the first wave of large mammals including humans migrated across the ice bridge from the mainland. Finally a thin soil mantle (only two centimetres at the deepest) was formed by plant colonisation of the bare limestone and some wind driven deposition, to create the alvar formation of the present. In many places the limestone has no soil whatsoever upon it.
The best known early paleolithic settlement occurs at Alby, situated on the east coast of the island, where excavations have revealed vestiges of wooden huts around a prehistoric lagoon.
Source officielle
À propos de ce résultat
Cette page est générée automatiquement et peut contenir des informations qui ne sont pas correctes, complètes, à jour ou pertinentes par rapport à votre recherche. Il en va de même pour toutes les autres pages de ce site. Veillez à vérifier les informations auprès des sources officielles de l'EPFL.