Geology of Chile - Pacific Islands

Pacific Islands

Easter Island is a volcanic high island, consisting of three extinct volcanoes: Terevaka (altitude 507 metres) forms the bulk of the island. Two other volcanoes, Poike and Rano Kau, form the eastern and southern headlands and give the island its approximately triangular shape. There are numerous lesser cones and other volcanic features, including the crater Rano Raraku, the cinder cone Puna Pau and many volcanic caves including lava tubes.

Easter Island and surrounding islets such as Motu Nui, Motu Iti are the summit of a large volcanic mountain which rises over two thousand metres from the sea bed. It is part of the Sala y Gómez Ridge, a (mostly submarine) mountain range with dozens of seamounts starting with Pukao and then Moai, two seamounts to the west of Easter Island, and extending 2,700 km (1,700 mi) east to the Nazca Seamount.

Pukao, Moai and Easter Island were formed in the last 750,000 years, with the most recent eruption a little over a hundred thousand years ago. They are the youngest mountains of the Sala y Gómez Ridge, which has been formed by the Nazca Plate floating over the Easter hotspot. Only at Easter Island, its surrounding islets and Sala y Gómez does the Sala y Gómez Ridge form dry land.

The Juan Fernández Islands are of volcanic in origin, and were created by a hotspot in the Earth's mantle that broke through the Nazca Plate to form the islands, which were then carried eastward off the hot spot as the Nazca Plate subducts under the South American continent. Radiometric dating indicates that Santa Clara is the oldest of the islands, 5.8 million years old, followed by Robinson Crusoe, 3.8-4.2 million years old, and Alexander Selkirk, 1.0-2.4 million years old. Robinson Crusoe is the largest of the islands, at 93 km² and the highest peak, El Yunque, is 916 meters. Alexander Selkirk is 50 km² ; its highest peak is Los Innocentes at 1319 meters. Santa Clara is 2.2 km², and reaches 350 meters.