Ring Of Fire (MMA)

The Ring of Fire (also known as the Pacific Ring of Fire, the Rim of Fire, the Girdle of Fire or the Circum-Pacific belt) is a region around much of the rim of the Pacific Ocean where many volcanic eruptions and earthquakes occur. The Ring of Fire is a horseshoe-shaped belt about long and up to about wide.

The Ring of Fire includes the Pacific coasts of South America, North America, Russia's Kamchatka Peninsula, and some islands in the western Pacific Ocean. Although there is consensus among geologists about most areas included in the Ring of Fire, they disagree about the inclusion of a few areas, for example, the Antarctic Peninsula and western Indonesia.

The Ring of Fire is a direct result of plate tectonics: specifically the movement, collision and destruction of lithospheric plates (e.g. the Pacific Plate) under and around the Pacific Ocean. The collisions have created a nearly continuous series of subduction zones, where volcanoes are created and earthquakes occur. Consumption of oceanic lithosphere at these convergent plate boundaries has formed oceanic trenches, volcanic arcs, back-arc basins and volcanic belts.

The Ring of Fire is not a single geological structure. Volcanic eruptions and earthquakes in each part of the Ring of Fire occur independently of eruptions and earthquakes in the other parts of the Ring.

The Ring of Fire contains approximately 750–915 volcanoes (about two-thirds of the world's total) that have been active during the Holocene. The four largest volcanic eruptions on Earth in the Holocene epoch all occurred at volcanoes in the Ring of Fire. More than 350 of the Ring of Fire's volcanoes have been active in historical times.

Beside and among the currently active and dormant volcanoes of the Ring of Fire are belts of older extinct volcanoes, which were formed long ago by subduction in the same way as the currently active and dormant volcanoes; the extinct volcanoes last erupted many thousands or millions of years ago. 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 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 (e.g. Mount St Helens), which are 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 (e.g. Plosky Tolbachik), and submarine seamounts (e.g. Monowai).

The world's highest active volcano is Ojos del Salado (), which is in the Andes Mountains section of the Ring of Fire. It forms part of the border between Argentina and Chile and it last erupted in AD 750. Another Ring of Fire Andean volcano on the Argentina-Chile border is Llullaillaco (), which is the world's highest historically active volcano, last erupting in 1877.

About 76% of the Earth's seismic energy is released as earthquakes in the Ring of Fire.
About 90% of the Earth's earthquakes and about 81% of the world's largest earthquakes occur along the Ring of Fire.

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 a 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 he Japanese Islandsare 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." (''Narrative of the Expedition of an American Squadron to the China Seas and Japan, 1852–54''). 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 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. (See: ). Indonesia lies at the intersection of the Ring of Fire and the Alpide belt (which is the Earth's other very long subduction-related volcanic and earthquake zone, also known as the Mediterranean–Indonesian volcanic belt, running east–west through southern Asia and southern Europe). Some geologists include all of Indonesia in the Ring of Fire; many geologists exclude Indonesia's western islands (which they include in the Alpide belt).

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 (the Pacific–Antarctic Ridge, the East Pacific Rise and the Chile Ridge) 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
* Sunda Arc
* Lesser Sunda Islands
* Tanimbar and Kai Islands
* Bismarck Archipelago
* Vanuatu
* Bougainville Island
* Solomon Islands
* Fiji
* Tonga Islands
* Kermadec Islands
* Taupō Volcanic Zone

Volcanoes in the central parts of the Pacific Basin, for example the Hawaiian Islands, are very far from subduction zones and they are not part of the Ring of Fire.

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 (by about 115 million years ago) in South America, North America and Asia. As plate configurations gradually changed, the current subduction zones of Indonesia and New Guinea were created (about 70 million years ago), followed finally by the New Zealand subduction zone (about 35 million years ago).

Past plate configurations

Along the coast of east Asia, during the Late Triassic about 210 million years ago, subduction of the Izanagi Plate (the Paleo-Pacific 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 it 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 the 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.

Oceanic trenches

Oceanic trenches are the topographic expression of subduction zones on the floor of the oceans. Oceanic trenches associated with the Ring of Fire's subduction zones are:

*Peru–Chile Trench
*Middle America Trench
*Aleutian Trench
*Kuril–Kamchatka Trench
*Japan Trench
*Ryukyu Trench
* Izu–Bonin Trench
*Mariana Trench
*Yap Trench
*Philippine Trench
* Tonga Trench
*Kermadec Trench
*Hikurangi Trench

Gaps

Subduction zones around the Pacific Ocean do not form a complete ring. Where subduction zones are absent, there are corresponding gaps in subduction-related volcanic belts in the Ring of Fire. In some gaps there is no volcanic activity; in other gaps, volcanic activity does occur but it is caused by processes not related to subduction.

There are gaps in the Ring of Fire at some parts of the Pacific coast of the Americas. In some places, the gaps are thought to be caused by flat slab subduction

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