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 tectonic belt, about long and up to about wide, which circumscribes the Pacific Ocean. It contains between 750 and 915 volcanoes, around two-thirds of the world total, and 90% of the world's earthquakes, including 81% of its largest, take place 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 inclusion of some areas in the Ring of Fire, such as the Antarctic Peninsula and western Indonesia, is disputed. The interactions at these plate boundaries have formed oceanic trenches, volcanic arcs, back-arc basins and volcanic belts.
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 (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).
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 [the Japanese Islands] 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." (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 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.