Geography of Nauru - Geology of Nauru

Geology of Nauru

Nauru is a raised coral atoll positioned in the Nauru Basin of the Pacific Ocean, on a part of the Pacific Plate that formed at a mid oceanic ridge at 132 Ma. From mid Eocene (35mya) to Oligocene times a submarine volcano built up over a hotspot, and formed a seamount composed of basalt. The seamount is over 4300 meters high. This hotspot was simultaneous with a major Pacific Plate reorganisation. The volcano was eroded to sealevel and a coral atoll grew on top to a thickness of about 500 meters. Coral near the surface has been dated from 5 Mya to 0.3 Mya. The original limestone has been dolomitised by magnesium from sea water. The coral was raised above sea level about 30 meters, and is now a dolomite limestone outcrop which was eroded in classic karst style into pinnacles up to 20 meters high. To at least a depth of 55 meters below sea level, the limestone has been dissolved forming cavities, sinkholes and caves. Holes on the topside of the island were filled up by a phosphate layer up to several meters thick.

Anibare Bay was formed by the underwater collapse of the east side of the volcano. Buada Lagoon was formed by solution of the limestone when the sea level was lower, followed by collapse.

Nauru is moving at 104 mm per year to the north west along with the Pacific Plate.

Freshwater can be found in Buada lagoon, and also in some brackish ponds at the escarpment base in Ijuw and Anabar in the northeast. There is an underground lake in Moqua Cave in the southeast of the island.