Island of the Possession

The island of the Possession is the principal island of the archipelago the sub-Antarctic of the islands Crozet, pertaining to the southern and antarctic Lands French.

Geography

With a surface of 150 km ², the island of the Possession is largest of the Archipel Crozet. It is also the only one to have a permanent base, the Base Alfred Faure, built in 1963, which lodges between 18 and 30 people for research tasks.

With the island of the East located 18 km at the east, beyond the channel of the Orcs, it form the Eastern group of the archipelago.

Volcanology

The volcanologic exploration of the island of the Possession was carried out in 1981 by Luc Chevallier (chart with the 1:50.000 with note, CNFRA n° 50).

The island is, as the island of the East, (see this monograph) a stratovolcano which was built during with less the 5 phases of activity.

Its eruptive center is currently localized in the West (Cape of Heroin) where faulted and rectified panels, worked by erosion marinades are in discordance with the general dip of the volcano. This the oldest phase 1 is made of hyaloclastites palagonitized interstratified with niveaus of marine fossils (pecten, mould) pilot of a under-watery activity.

The phase 2 is visible in the funds of valleys and corresponds to a subaerial activity of thick run basalts ending in a more explosive activity of pyroclastites. Annular networks of dykes entrelardent series 2 in its totality. This activity ranges between 9 and 1,3 million years is with Me-Pliocène and until Pleistocene.

The phase 3 settled after erosion of the surface of the lava of phase 2. It begin with a basal conglomerate followed by pyroclastites interstratified fine lava flows and sills becoming more abundant towards the end from the cycle. These products were brought by series of radial dykes centered on the West of the island. This phase proceeded between 1 and 0,5 million year (Pleistocene).

The phase 4 constitutes the entablatures of ten meters thickness crowning the plates. The lava comes from dykes gathered in a system of rift of direction NW-SE whose injections close to ten meters represent a major extension of the oceanic crust at that time. This phase was ruivie by one synchronous glacial period of that of the island of the East which in particular worked the tectono-glacial valley of Branloires.

The phase 5 is represented by cones of slags (Branca Mount for example and sutout the zone of the Mount of the Craters) aligned according to the dykes and fractures of the primitive volcano. It would have less than 100.000 years.

With regard to the petrology , the lava corresponds to a series of alkaline basalts and their derivatives emitted either under water (phases 1 and 2 partially) or to the free air (other phases). One notes lava coming from cumulats of a magmatic tank (ankaramites) and some lava of differentiation like the phonolite of the dome of Perugia (beginning phases 3).

The post-volcanic demonstrations are reduced to the Possession with a small thermo-mineral source which runs out with the favor of the faults of the graben of the valley of Branloires. The apparatuses of phase 5 result in classifying the island like a potentially active volcano.

See : Diagrammatic volcanologic chart and complementary data in J. Nougier and J.W. Thomson; Volcanoes off the Antarctic Punt and Southern Oceans. Res. Antarctic series vol.48, American Geophysical Union (1990).

History

The island of the Possession was discovered on January 24th 1772 by the French explorer Nicolas Thomas Marion-Dufresne. Julien Crozet, second on board Mascarin, was sent to ground where it carried out a ceremony of taking possession by depositing a bottle containing a parchment in the name of the king Louis XV. The island was then named island of the Taking possession.

External bonds

virtual Visit of the island of the possession

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