Ring of Fire
The Ring of Fire is a tectonic belt of earthquakes and volcanoes.
It is about long and up to about wide, and surrounds most of the Pacific Ocean.
The Ring of Fire contains between 750 and 915 active or dormant volcanoes, around two-thirds of the world total. The exact number of volcanoes within the Ring of Fire depends on which regions are included.
About 90% of the world's earthquakes, including most of its largest, occur within the belt.
The Ring of Fire is not a single geological structure. It was created by the subduction of different tectonic plates at convergent boundaries around the Pacific Ocean. These include: the Antarctic, Nazca and Cocos plates subducting beneath the South American plate; the Pacific and Juan de Fuca plates beneath the North American plate; the Philippine plate beneath the Eurasian plate; and a complex boundary between the Pacific and Australian plate. The interactions at these plate boundaries have formed oceanic trenches, volcanic arcs, back-arc basins and volcanic belts. The inclusion of some areas in the Ring of Fire, such as the Antarctic Peninsula and western Indonesia, is disputed.
The Ring of Fire has existed for more than 35 million years but subduction has existed for much longer in some parts of the Ring; many older extinct volcanoes are located within the Ring. More than 350 of the Ring of Fire's volcanoes have been active in historical times, while the four largest volcanic eruptions on Earth in the Holocene epoch all occurred at volcanoes in the Ring of Fire.
Most of Earth's active volcanoes with summits above sea level are located in the Ring of Fire. Many of these subaerial volcanoes are stratovolcanoes, formed by explosive eruptions of tephra alternating with effusive eruptions of lava flows. Lavas at the Ring of Fire's stratovolcanoes are mainly andesite and basaltic andesite but dacite, rhyolite, basalt and some other rarer types also occur. Other types of volcano are also found in the Ring of Fire, such as subaerial shield volcanoes, and submarine seamounts.
History
From Ancient Greek and Roman times until the late 18th century, volcanoes were associated with fire, based on the ancient belief that volcanoes were caused by fires burning within the Earth. This historical link between volcanoes and fire is preserved in the name of the Ring of Fire, despite the fact that volcanoes do not burn the Earth with fire.The existence of an orogenic belt of volcanic activity around the Pacific Ocean was known in the early 19th century; for example, in 1825 the pioneering volcanologist G. P. Scrope described the chains of volcanoes around the Pacific Ocean's rim in his book Considerations on Volcanos. Three decades later, a book about the Perry Expedition to Japan commented on the Ring of Fire volcanoes as follows: "They are in the line of that immense circle of volcanic development which surrounds the shores of the Pacific from Tierra del Fuego around to the Moluccas." An article appeared in Scientific American in 1878 with the title "The Ring of Fire, and the Volcanic Peaks of the West Coast of the United States", which outlined the phenomenon of volcanic activity around the boundaries of the Pacific. Early explicit references to volcanoes forming a "ring of fire" around the Pacific Ocean also include Alexander P. Livingstone's book "Complete Story of San Francisco's Terrible Calamity of Earthquake and Fire", published in 1906, in which he describes "... the great ring of fire which circles round the whole surface of the Pacific Ocean.".
In 1912, geologist Patrick Marshall introduced the term "Andesite Line" to mark a boundary between islands in the southwest Pacific, which differ in volcano structure and lava types. The concept was later extended to other parts of the Pacific Ocean. The Andesite Line and the Ring of Fire closely match in terms of location.
The development of the theory of plate tectonics since the early 1960s has provided the current understanding and explanation of the global distribution of volcanoes and earthquakes, including those in the Ring of Fire.
Geographic boundaries
There is consensus among geologists about most of the regions which are included in the Ring of Fire. There are, however, a few regions on which there is no universal agreement.. Indonesia lies at the intersection of the Ring of Fire and the Alpide belt. Some geologists include all of Indonesia in the Ring of Fire; many geologists exclude Indonesia's western islands.Some geologists include the Antarctic Peninsula and the South Shetland Islands in the Ring of Fire, other geologists exclude these areas. The rest of Antarctica is excluded because the volcanism there is not related to subduction.
The Ring of Fire does not extend across the southern Pacific Ocean from New Zealand to the Antarctic Peninsula or from New Zealand to the southern tip of South America because the submarine plate boundaries in this part of the Pacific Ocean are divergent instead of convergent. Although some volcanism occurs in this region, it is not related to subduction.
Some geologists include the Izu Islands, the Bonin Islands, and the Mariana Islands, other geologists exclude them.
Land areas
- Antarctica
- * Antarctic Peninsula
- * South Sandwich Islands
- Andes
- * Austral Volcanic Zone
- * South Volcanic Zone
- * Central Volcanic Zone
- * North Volcanic Zone
- Central America Volcanic Arc
- * Trans-Mexican Volcanic Belt
- North American Cordillera
- * Cascade Volcanic Arc
- * Aleutian Range
- ** Aleutian Islands
- ** Aleutian Arc
- Kamchatka Peninsula
- Kuril Islands
- Japan
- Ryukyu Islands
- Taiwan
- Philippine Mobile Belt
- Izu–Bonin–Mariana Arc
- * Izu Islands
- * Bonin Islands
- * Mariana Islands
- Tanimbar and Kai Islands
- Bismarck Archipelago
- Vanuatu
- Bougainville Island
- Solomon Islands
- Fiji
- Tonga Islands
- Kermadec Islands
- Taupō Volcanic Zone
Tectonic plate configurations
The Ring of Fire has existed for more than 35 million years. In some parts of the Ring of Fire, subduction has been occurring for much longer.The current configuration of the Pacific Ring of Fire has been created by the development of the present-day subduction zones, initially in South America, North America and Asia. As plate configurations gradually changed, the current subduction zones of Indonesia and New Guinea were created, followed finally by the New Zealand subduction zone.
Past plate configurations
Along the coast of east Asia, during the Late Triassic about 210 million years ago, subduction of the Izanagi plate was occurring, and this continued in the Jurassic, producing volcanic belts, for example, in what is now eastern China.The Pacific plate came into existence in the Early Jurassic about 190 million years ago, far from the margins of the then Paleo-Pacific Ocean. Until the Pacific plate grew large enough to reach the margins of the ocean basin, other older plates were subducted ahead of it at the ocean basin margins. For example, subduction has been occurring at the coast of South America since the Jurassic Period more than 145 million years ago, and remnants of Jurassic and Cretaceous volcanic arcs are preserved there.
At about 120 to 115 million years ago, the Farallon plate was subducting under South America, North America and north-east Asia while the Izanagi plate was subducting under east Asia. By 85 to 70 million years ago, the Izanagi plate had moved north-eastwards and was subducting under east Asia and North America, while the Farallon plate was subducting under South America and the Pacific plate was subducting under east Asia. About 70 to 65 million years ago, the Farallon plate was subducting under South America, the Kula plate was subducting under North America and north-east Asia, and the Pacific plate was subducting under east Asia and Papua New Guinea. About 35 million years ago, the Kula and Farallon plates had been subducted and the Pacific plate was subducting around its rim in a configuration closely resembling the outline of the present-day Ring of Fire.
Present-day plate configuration
The eastern parts of the Ring of Fire result from the collision of a few relatively large plates. The western parts of the Ring are more complex, with a number of large and small tectonic plates in collision.In South America, the Ring of Fire is the result of the Antarctic plate, the Nazca plate and the Cocos plate being subducted beneath the South American plate. In Central America, the Cocos plate is being subducted beneath the Caribbean plate. A portion of the Pacific plate and the small Juan de Fuca plate are being subducted beneath the North American plate. Along the northern portion, the northwestward-moving Pacific plate is being subducted beneath the Aleutian Islands arc. Farther west, the Pacific plate is being subducted at the Kamchatka Peninsula and Kuril arcs. Farther south, at Japan, Taiwan and the Philippines, the Philippine Plate is being subducted beneath the Eurasian plate. The southwest section of the Ring of Fire is more complex, with a number of smaller tectonic plates in collision with the Pacific plate at the Mariana Islands, the Philippines, eastern Indonesia, Papua New Guinea, Tonga, and New Zealand; this part of the Ring excludes Australia, because that landmass lies in the center of its tectonic plate far from subduction zones.
Subduction zones and oceanic trenches
If a tectonic plate's oceanic lithosphere is subducted beneath oceanic lithosphere of another plate, a volcanic island arc is created at the subduction zone. An example in the Ring of Fire is the Mariana Arc in the western Pacific Ocean. If, however, oceanic lithosphere is subducted under continental lithosphere, then a volcanic continental arc forms; a Ring of Fire example is the coast of Chile.The steepness of the descending plate at a subduction zone depends on the age of the oceanic lithosphere that is being subducted. The older the oceanic lithosphere being subducted, the steeper the angle of descent of the subducted slab. As the Pacific's mid-ocean ridges, which are the source of its oceanic lithosphere, are not actually in the middle of the ocean but located much closer to South America than to Asia, the oceanic lithosphere consumed at the South American subduction zones is younger and therefore subduction occurs at the South American coast at a relatively shallow angle. Older oceanic lithosphere is subducted in the western Pacific, with steeper angles of slab descent. This variation affects, for example, the location of volcanoes relative to the ocean trench, lava composition, type and severity of earthquakes, sediment accretion, and the amount of compression or tension. A spectrum of subduction zones exists between the Chilean and Mariana end members.