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The Comoros island chain in the Mozambique Channel is the result of the rifting of Madagascar away from Africa as well as "hotspot" mantle plume activity. The region is also impact by seismicity and deformation associated with the East African Rift system and the Comoros region is one of the best places in the world to study rift-hotspot interactions. The islands remain volcanically active.
The Comoros location in the Mozambique Channel is tectonically complex, due to the displacement of the Malagasarian microcontinent from the margin of the supercontinent Gondwana. [1]
From the Permian until the Early Jurassic, the Comoros region experienced Karoo rifting, on a northeast–southwest trend. During the Middle Jurassic and Early Cretaceous, an ocean basin, running north–south, formed along the Davie Ridge.
The volcanoes in the Comoros date to the recent past of the Pliocene, Pleistocene and Holocene period. The oldest volcano on the chain is 7.7 million years old, on Mayotte. Volcanoes are older further east. Anjouan is 3.9 million years old and Moheli is five million years old. Grande Comore is the youngest at only 10,000 years old. Some geologists have proposed that the Comoros is an example of one of 11 primary mantle plumes worldwide. [2]
The volcanoes produce alkali olivine basalt, although small amounts of phonolite and trachytic lava have also been found. Scoria and pozzolanic tuff is known from Grande Comore, Anjouan and Moheli.
The East African Rift System became active 22 to 25 million years ago in the Miocene and its offshore extent is the youngest. The rift system causes seismicity, extensional deformation and created the offshore Kerimbas Graben. [2]
Mount Karthala is an active volcano on Grande Comore, which erupted in April, 2005 and May, 2006.
There is very little mining in the Comoros, aside from the production of building material. In some cases, coral is mined to produce lime for concrete.
The Comoros archipelago consists of four main islands aligned along a northwest–southeast axis at the north end of the Mozambique Channel, between Mozambique and the island of Madagascar. Still widely known by their French names, the islands officially have been called by their Swahili names by the Comorian government. They are Grande Comore (Njazidja), Mohéli (Mwali), Anjouan (Nzwani), and Mayotte (Mahoré). The islands' distance from each other—Grande Comore is some 200 kilometers from Mayotte, forty kilometers from Mohéli, and eighty kilometers from Grande Comore—along with a lack of good harbor facilities, make transportation and communication difficult. Comoros are sunny islands.
The North American Plate is a tectonic plate covering most of North America, Cuba, the Bahamas, extreme northeastern Asia, and parts of Iceland and the Azores. With an area of 76 million km2 (29 million sq mi), it is the Earth's second largest tectonic plate, behind the Pacific Plate.
The Comoro Islands or Comoros form an archipelago of volcanic islands situated off the southeastern coast of Africa, to the east of Mozambique and northwest of Madagascar. The islands are politically divided between the Union of the Comoros, a sovereign country, and Mayotte, an Overseas Department of France.
Grande Comore is an island in Comoros off the coast of Africa. It is the largest island in the Comoros nation. Most of its population is of the Comorian ethnic group. Its population as of 2006 is about 316,600. The island's capital is Moroni, which is also the national capital. The island is made up of two shield volcanoes, with Mount Karthala being the country's highest point at 2,361 m (7,746 ft) above sea level. According to the 2009 revision of the constitution of 2002, it is governed by an elected Governor, as are the other islands, with the federal government being much reduced in power. The name Ngazidja is sometimes seen in the now nonstandard form Njazidja.
The Iceland hotspot is a hotspot which is partly responsible for the high volcanic activity which has formed the Iceland Plateau and the island of Iceland.
The East African Rift (EAR) or East African Rift System (EARS) is an active continental rift zone in East Africa. The EAR began developing around the onset of the Miocene, 22–25 million years ago. In the past it was considered to be part of a larger Great Rift Valley that extended north to Asia Minor.
The geology of Iceland is unique and of particular interest to geologists. Iceland lies on the divergent boundary between the Eurasian plate and the North American plate. It also lies above a hotspot, the Iceland plume. The plume is believed to have caused the formation of Iceland itself, the island first appearing over the ocean surface about 16 to 18 million years ago. The result is an island characterized by repeated volcanism and geothermal phenomena such as geysers.
The Anahim hotspot is a hypothesized hotspot in the Central Interior of British Columbia, Canada. It has been proposed as the candidate source for volcanism in the Anahim Volcanic Belt, a 300 km (190 mi) long chain of volcanoes and other magmatic features that have undergone erosion. This chain extends from the community of Bella Bella in the west to near the small city of Quesnel in the east. While most volcanoes are created by geological activity at tectonic plate boundaries, the Anahim hotspot is located hundreds of kilometres away from the nearest plate boundary.
The Bowie hotspot is a volcanic hotspot, located 180 kilometres (110 mi) west of the Queen Charlotte Islands in the Pacific Ocean.
The Hawai’i hotspot is a volcanic hotspot located near the namesake Hawaiian Islands, in the northern Pacific Ocean. One of the best known and intensively studied hotspots in the world, the Hawaii plume is responsible for the creation of the Hawaiian–Emperor seamount chain, a 6,200-kilometer (3,900 mi) mostly undersea volcanic mountain range. Four of these volcanoes are active, two are dormant; more than 123 are extinct, most now preserved as atolls or seamounts. The chain extends from south of the island of Hawaiʻi to the edge of the Aleutian Trench, near the eastern coast of Russia.
The postage stamps and postal history of the Comoro Islands is an overview of the postage stamps and postal history of the Comoro Islands, an Indian Ocean archipelago located on the south-east side of Africa.
The volcanology of Eastern Canada includes the hundreds of volcanic areas and extensive lava formations in Eastern Canada. The region's different volcano and lava types originate from different tectonic settings and types of volcanic eruptions, ranging from passive lava eruptions to violent explosive eruptions. Eastern Canada has very large volumes of magmatic rock called large igneous provinces. They are represented by deep-level plumbing systems consisting of giant dike swarms, sill provinces and layered intrusions. The most capable large igneous provinces in Eastern Canada are Archean age greenstone belts containing a rare volcanic rock called komatiite.
The Comoros forests is a terrestrial ecoregion which covers the Comoro Islands, which lie in the Mozambique Channel between Madagascar and East Africa. These include four main islands: Grande Comore, Anjouan and Mohéli, of the Union of the Comoros, and Mayotte, a department and region of France.
The Madagascar Plate or Madagascar block was once attached to the Gondwana supercontinent and later the Indo-Australian Plate.
The Erebus hotspot is a volcanic hotspot responsible for the high volcanic activity on Ross Island in the western Ross Sea of Antarctica. Its current eruptive zone, Mount Erebus, has erupted continuously since its discovery in 1841. Magmas of the Erebus hotspot are similar to those erupted from hotspots at the active East African Rift in eastern Africa. Mount Bird at the northernmost end of Ross Island and Mount Terror at its eastern end are large basaltic shield volcanoes that have been potassium-argon dated 3.8–4.8 and 0.8–1.8 million years old.
The geological deformation of Iceland is the way that the rocks of the island of Iceland are changing due to tectonic forces. The geological deformation explains the location of earthquakes, volcanoes, fissures, and the shape of the island. Iceland is the largest landmass (102,775 km²) situated on an oceanic ridge. It is an elevated plateau of the sea floor, situated at the crossing of the Mid-Atlantic Ridge and the Greenland-Iceland-Faeroe Ridge. It lies along the oceanic divergent plate boundary of North American Plate and Eurasian Plate. The western part of Iceland sits on the North American Plate and the eastern part sits on the Eurasian Plate. The Reykjanes Ridge of the Mid-Atlantic ridge system in this region crosses the island from southwest and connects to the Kolbeinsey Ridge in the northeast.
Noronha hotspot is a hypothesized hotspot in the Atlantic Ocean. It has been proposed as the candidate source for volcanism in the Fernando de Noronha archipelago of Brazil, as well as of other volcanoes also in Brazil and even the Bahamas and the Central Atlantic Magmatic Province.
As part of the Comoro Islands chain in the Mozambique Channel, the geology of Mayotte is virtually the same as the geology of the Comoros, the rest of the island chain which is independent of France. The island resulted from the rifting of Madagascar away from Africa as well as "hotspot" mantle plume activity, and is also impacted by seismicity and deformation associated with the East African Rift. However, because Mayotte is a part of France its geology is significantly more researched than that of other islands in the chain.
The plate theory is a model of volcanism that attributes all volcanic activity on Earth, even that which appears superficially to be anomalous, to the operation of plate tectonics. According to the plate theory, the principal cause of volcanism is extension of the lithosphere. Extension of the lithosphere is a function of the lithospheric stress field. The global distribution of volcanic activity at a given time reflects the contemporaneous lithospheric stress field, and changes in the spatial and temporal distribution of volcanoes reflect changes in the stress field. The main factors governing the evolution of the stress field are:
Intraplate volcanism is volcanism that takes place away from the margins of tectonic plates. Most volcanic activity takes place on plate margins, and there is broad consensus among geologists that this activity is explained well by the theory of plate tectonics. However, the origins of volcanic activity within plates remains controversial.
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