Geology of Nauru
Encyclopedia
Pacific Plate
The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres, it is the largest tectonic plate....
that formed at a mid oceanic ridge at 132 Ma.
From mid Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
(35mya) to Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
times a submarine volcano
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
built up over a hotspot
Hotspot (geology)
The places known as hotspots or hot spots in geology are volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the mantle elsewhere. They may be on, near to, or far from tectonic plate boundaries. There are two hypotheses to explain them...
, and formed a seamount
Seamount
A seamount is a mountain rising from the ocean seafloor that does not reach to the water's surface , and thus is not an island. These are typically formed from extinct volcanoes, that rise abruptly and are usually found rising from a seafloor of depth. They are defined by oceanographers as...
composed of basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
. The seamount is over 4300 metres high. This hotspot was simultaneous with a major
Pacific Plate reorganisation. The volcano was eroded to sealevel and a coral
Coral
Corals are marine animals in class Anthozoa of phylum Cnidaria typically living in compact colonies of many identical individual "polyps". The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.A coral "head" is a colony of...
atoll
Atoll
An atoll is a coral island that encircles a lagoon partially or completely.- Usage :The word atoll comes from the Dhivehi word atholhu OED...
grew on top to a thickness of about 500 metres. Coral near the surface has been dated from 5 Mya to 0.3 Mya. The original limestone has been dolomitised by magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
from sea water. The coral was
raised above sea level about 30 metres, and is now a dolomite limestone outcrop which was eroded in classic karst
KARST
Kilometer-square Area Radio Synthesis Telescope is a Chinese telescope project to which FAST is a forerunner. KARST is a set of large spherical reflectors on karst landforms, which are bowlshaped limestone sinkholes named after the Kras region in Slovenia and Northern Italy. It will consist of...
style into pinnacle
Pinnacle
A pinnacle is an architectural ornament originally forming the cap or crown of a buttress or small turret, but afterwards used on parapets at the corners of towers and in many other situations. The pinnacle looks like a small spire...
s up to 20 metres high. To at least a depth of 55 metres 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
Phosphate
A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...
layer up to several metres thick.
Anibare Bay
Anibare Bay
Anibare Bay is a large bay located in the Anibare District of eastern Nauru island.-Physical features:It is bordered by capes to the north and south, in Ijuw and Meneng districts respectively.Its Anibare Beach is in excess of two kilometers long....
was formed by the underwater collapse of the east side of the volcano.
Buada Lagoon
Buada Lagoon
Buada Lagoon is a landlocked, slightly brackish, freshwater lake on the island Nauru. It is about .The average depth of lagoon is and maximum depth is ....
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
Buada Lagoon
Buada Lagoon is a landlocked, slightly brackish, freshwater lake on the island Nauru. It is about .The average depth of lagoon is and maximum depth is ....
, and also in some brackish ponds at the escarpment base in Ijuw
Ijuw
Ijuw is a district in the country Nauru, located in the north-east region of the island.-Location and features:It borders district Anabar to the north and Anibare to the south. Ijuw is a part of the constituency Anabar....
and Anabar in the northeast. There is an underground lake called Moqua Well
Moqua Well
The Moqua Well is a small underground lake, in Nauru.-Location:The well is located below the Nauruan Yaren district. The Moqua Well is not well known, one of a few attractions in Nauru.-Linguistic disambiguation:...
in Moqua Caves
Moqua Caves
The Moqua Caves are a geological feature in the Pacific island nation of Nauru.-Location:The caves are situated below Yaren, in the south of the island.This series of caves is located near to the Moqua Well.-See also:* Yaren* Geography of Nauru...
in the southeast of the island.