The Ngaoundéré Plateau is a highland area in the

Adamawa Region The Adamawa Region () is a constituent region of the Cameroon, Republic of Cameroon. It borders the Centre Region (Cameroon), Centre and East Region (Cameroon), East regions to the south, the Northwest Region (Cameroon), Northwest and West Re ...

Cameroon Cameroon, officially the Republic of Cameroon, is a country in Central Africa. It shares boundaries with Nigeria to the west and north, Chad to the northeast, the Central African Republic to the east, and Equatorial Guinea, Gabon, and the R ...

. It contains Tchabal Nganha, a large volcano, and many other recent volcanic structures.

Location

The plateau is between the forested south and

savannah A savanna or savannah is a mixed woodland-grassland (i.e. grassy woodland) biome and ecosystem characterised by the trees being sufficiently widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach th ...

north of Cameroon.

Ngaoundéré Ngaoundéré or N'Gaoundéré (Fula: N'gamdere, , 𞤲'𞤺𞤢𞤥𞤣𞤫𞥅𞤪𞤫𞥅) is the capital of the Adamawa Region of Cameroon. It had a population of 152,700 at the 2005 census. According to the film ''Les Mairuuwas – Maitre de l ...

, the capital of the Adamawa region, is located on the plateau. It lies over the Ngaoundere fault zone, which was reactivated in the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

. The Ngaoundere fault belongs the Central African Fault Zone. In this region the

asthenosphere The asthenosphere () is the mechanically weak and ductile region of the upper mantle of Earth. It lies below the lithosphere, at a depth between c. below the surface, and extends as deep as . However, the lower boundary of the asthenosphere i ...

upwells from a depth of about 190 km to about 120 km in a relatively narrow belt.

Formation

The plateau was formed by flows of

basaltic Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron ( mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90% ...

lavas that filled two broad valleys eroded into the

Precambrian The Precambrian ( ; or pre-Cambrian, sometimes abbreviated pC, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of t ...

basement, followed by further flows that built up the plateau. There are many

trachyte Trachyte () is an extrusive igneous rock composed mostly of alkali feldspar. It is usually light-colored and aphanite, aphanitic (fine-grained), with minor amounts of mafic minerals, and is formed by the rapid cooling of lava (or shallow intrus ...

and

phonolite Phonolite is an uncommon shallow intrusive or extrusive rock, of intermediate chemical composition between felsic and mafic, with texture ranging from aphanitic (fine-grained) to porphyritic (mixed fine- and coarse-grained). Phonolite is a var ...

plugs across the plateau, and lines of cinder cones from the most recent eruptions. The plateau contains Tchabal Nganha, a large

stratovolcano A stratovolcano, also known as a composite volcano, is a typically conical volcano built up by many alternating layers (strata) of hardened lava and tephra. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with ...

of basanitic to trachytic composition. Nganha is about 1,000 m high. It developed in four main events: eruption of numerous basaltic flows which form the bulk of the mountain; deposit of voluminous breccias, most of which were deeply eroded; eruption of trachytes and phonolites as thick flows; and finally basaltic activity in the summit area. Rocks date from 9.8 to 7 million years ago.

Related volcanic zones

Although considered by many geologists to be part of the Cameroon Volcanic Line, the

silicic Silicic is an adjective to describe magma or igneous rock rich in silica. The amount of silica that constitutes a silicic rock is usually defined as at least 63 percent. Granite and rhyolite are the most common silicic rocks. Silicic is the g ...

volcanism of the Ngaoundere plateau is younger (11-9 million years old) than silicic volcanism in the Western Highlands, with much more alkaline

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

s than in the western part of the line. This has been cited as evidence that the line is not caused by movement of the plate over a hotspot. To the east of Ngaoundere and Wakwa there is Quaternary volcanic activity consisting of scoria cones and lava flows, maars, and tuff cones. One lava flow in this area has been dated to 0.9 million years ago. Some of the volcanoes may be from the

Holocene The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...

period.

References

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