Geography of Easter Island

Easter Island is one of the world's most isolated inhabited islands. Its closest inhabited neighbours are the Chilean Juan Fernandez Islands, 1,850 km (1,150 mi) to the east, with approximately 850 inhabitants.^{[citation needed]} The nearest continental point lies in central Chile near Concepción, at 3,512 kilometres (2,182 mi). Easter Island's latitude is similar to that of Caldera, Chile, and it lies 3,510 km (2,180 mi) west of continental Chile at its nearest point (between Lota and Lebu in the Biobío Region). Isla Salas y Gómez, 415 km (258 mi) to the east, is closer but is uninhabited. The Tristan da Cunha archipelago in the southern Atlantic competes for the title of the most remote island, lying 2,430 km (1,510 mi) from Saint Helena island and 2,816 km (1,750 mi) from the South African coast.

The island is about 24.6 km (15.3 mi) long by 12.3 km (7.6 mi) at its widest point; its overall shape is triangular. It has an area of 163.6 km² (63.2 sq mi), and a maximum elevation of 507 m (1,663 ft) above mean sea level. There are three Rano (freshwater crater lakes), at Rano Kau, Rano Raraku and Rano Aroi, near the summit of Terevaka, but no permanent streams or rivers.

Easter Island is a volcanic 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 m (6,600 ft) from the sea bed. The mountain is part of the Salas y Gómez Ridge, a (mostly submarine) mountain range with dozens of seamounts, formed by the Easter hotspot. 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 moving over the Easter hotspot.

Located about 350 km (220 mi) east of the East Pacific Rise, Easter Island lies within the Nazca Plate, bordering the Easter Microplate. The Nazca-Pacific relative plate movement due to the seafloor spreading, amounts to about 150 mm (5.9 in) per year. This movement over the Easter hotspot has resulted in the Easter Seamount Chain, which merges into the Nazca Ridge further to the east. Easter Island and Isla Salas y Gómez are surface representations of that chain. The chain has progressively younger ages to the west. The current hotspot location is speculated to be west of Easter Island, amidst the Ahu, Umu and Tupa submarine volcanic fields and the Pukao and Moai seamounts.

Easter Island lies atop the Rano Kau Ridge, and consists of three shield volcanoes with parallel geologic histories. Poike and Rano Kau exist on the east and south slopes of Terevaka, respectively. Rano Kau developed between 0.78 and 0.46 Ma from tholeiitic to alkalic basalts. This volcano possesses a clearly defined summit caldera. Benmoreitic lavas extruded about the rim from 0.35 to 0.34 Ma. Finally, between 0.24 and 0.11 Ma, a 6.5 km (4.0 mi) fissure developed along a NE–SW trend, forming monogenetic vents and rhyolitic intrusions. These include the cryptodome islets of Motu Nui and Motu Iti, the islet of Motu Kao Kao, the sheet intrusion of Te Kari Kari, the perlitic obsidian Te Manavai dome and the Maunga Orito dome.

Poike formed from tholeiitic to alkali basalts from 0.78 to 0.41 Ma. Its summit collapsed into a caldera which was subsequently filled by the Puakatiki lava cone pahoehoe flows at 0.36 Ma. Finally, the trachytic lava domes of Maunga Vai a Heva, Maunga Tea Tea, and Maunga Parehe formed along a NE-SW trending fissure.

Terevaka formed around 0.77 Ma of tholeiitic to alkali basalts, followed by the collapse of its summit into a caldera. Then at about 0.3Ma, cinder cones formed along a NNE-SSW trend on the western rim, while porphyritic benmoreitic lava filled the caldera, and pahoehoe flowed towards the northern coast, forming lava tubes, and to the southeast. Lava domes and a vent complex formed in the Maunga Puka area, while breccias formed along the vents on the western portion of Rano Aroi crater. This volcano's southern and southeastern flanks are composed of younger flows consisting of basalt, alkali basalt, hawaiite, mugearite, and benmoreite from eruptive fissures starting at 0.24 Ma. The youngest lava flow, Roiho, is dated at 0.11 Ma. The Hanga O Teo embayment is interpreted to be a 200 m high landslide scarp.