Tanna

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The island of Tanna, one of the largest islands of the Vanuatu archipelago (550 km2), belongs to the southern segment of the recent Vanuatu arch and is home to the active Yasur volcano.

It faces the North Loyalty basin, where recorded subduction speeds are rapid and reach 12 cm / year. Tanna Island is located about 130 km east of the Vanuatu Trench, about 40 km west of the Coriolis Trench and 127 km above the Yasur-level panel.

The first traces of volcanism are recorded in the Pliocene with the formation of the Green Hill massif in the north of the island, then the volcanic activity moved to the south with the construction in the middle Pleistocene of the Tukosmeru massif, which culminates Currently at 1084 m altitude.

Recent volcanic activity has been established in the southeast of the island since the Upper Pleistocene to form the Siwi rocks. The Yenkahe then formed an ancient volcanic cone, then very recently (probably less than 20,000 years ago) a paroxysmal eruption affected the island, leading to the deposit of Siwi ignimbrite, and the formation of a caldera d About 24 km2 along the Siwi fracture.

Since this event, the new arrival of magma has led to the progressive uplift of the Yenkahe resurgent block (3 x 6 km) at a high speed of 15.6 cm / year during the last millennium, and to the formation of slag cones Ombus and Yasur. The current volcanic activity of the island is focused on the strombolian cone of Yasur (360 m altitude) which has been building for about 800 years on the southwestern edge of the resurgent block of the Yenkahe. It is an asymmetrical cone with a summit crater 700 m in diameter and 200 m deep, sheltering 3 eruptive mouths. The historical activity of the Yasur, first recorded in 1774 by Captain Cook, is characterized mainly by strombolian eruptions in vulcanian. The frequency of eruptions is between 1 and 3 per minute during periods of high activity.

Ph. Bani et al. (2012) A. Beaumais et al. (2013).

(Back to the list of volcanoes of Vanuatu)

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© IRD/Ph. Bani et J-L. Froger.

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© IRD/Ph. Bani et J-L. Froger.

Guy

Docteur en Pharmacie, Biologiste Médical libéral à Marseille, France.

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