Geology
Easter Island is a volcanic high island, consisting mainly of three extinct coalesced volcanoes: Terevaka (altitude 507 metres) forms the bulk of the island, while two other volcanoes, Poike and Rano Kau, form the eastern and southern headlands and give the island its roughly triangular shape. Lesser cones and other volcanic features include the crater Rano Raraku, the cinder cone Puna Pau and many volcanic caves including lava tubes. Poike used to be a separate island until volcanic material from Terevaka united it to the larger whole. The island is dominated by hawaiite and basalt flows which are rich in iron and show affinity with igneous rocks found in the Galápagos Islands.
Easter Island and surrounding islets such as Motu Nui and Motu Iti form the summit of a large volcanic mountain rising over 2,000 metres (6,600 ft) from the sea bed. The mountain is part of the Sala y Gómez Ridge, a (mostly submarine) mountain range with dozens of seamounts. The range begins with Pukao and next Moai, two seamounts to the west of Easter Island, and extends 2,700 km (1,700 mi) east to the Nazca Ridge. The ridge was formed by the Nazca Plate floating over the Easter hotspot. The movement of Nazca and formerly the Farallon Plate over the hotspot has created a long underwater ridge, the Nazca Ridge, whose eastern end is being subducted under Peru. Only at Easter Island, its surrounding islets and Sala y Gómez does the Sala y Gómez Ridge form dry land.
Pukao, Moai and Easter Island were formed in the last 750,000 years and are the ridge's youngest islands. The most recent eruption was a little over 100,000 years ago.
In the first half of the 20th century, steam reportedly came out of the Rano Kau crater wall. This was photographed by the island's manager, Mr. Edmunds. According to geologists the last volcanic activity on the island occurred 10,000 years ago.
An alternative explanation for the islands is the activity of the Easter Fracture Zone.
Read more about this topic: Easter Island