A Belt of 900 Volcanoes Around One Ocean
Picture a chain about 40,000 km long and up to about 500 km wide, wrapped around most of the Pacific Ocean. That is the Ring of Fire. It holds between 750 and 915 active or dormant volcanoes, around two-thirds of the world total. The exact count depends on which regions you include.
It is also the planet's busiest earthquake zone. About 90% of the world's earthquakes happen here, including most of the largest ones. The next busiest region, the Alpide belt, gets only about 5-6%.
Here is the twist: the Ring of Fire is not one single structure. It is many separate plate boundaries that happen to circle the same ocean. It has existed for more than 35 million years, and more than 350 of its volcanoes have been active in historical times.
Why a Volcano Belt Is Named After Fire
The name is a leftover from an old idea. From Ancient Greek and Roman times until the late 18th century, people believed volcanoes were caused by fires burning inside the Earth. Volcanoes do not actually burn anything with fire, but the name stuck.
Scientists noticed the pattern long before they could explain it. In 1825, the volcano expert G. P. Scrope described chains of volcanoes around the Pacific rim. A book about the Perry Expedition to Japan in the 1850s spoke of an "immense circle" of volcanoes around the Pacific. A 1906 book about the San Francisco earthquake used the phrase "the great ring of fire".
In 1912, geologist Patrick Marshall drew the "Andesite Line" in the southwest Pacific, which closely matches the Ring. The full explanation only arrived with the theory of plate tectonics in the early 1960s.
Plates Diving Under Plates
The Ring of Fire exists because of subduction. Around the Pacific, ocean plates are being pushed down beneath their neighbours. The Nazca and Cocos plates slide under South America. The Pacific plate dives beneath the Aleutian Islands and Kamchatka. Where they sink, the seafloor forms deep oceanic trenches, including the Mariana Trench.
What grows on top depends on what is above. When an ocean plate sinks under another ocean plate, a curved chain of volcanic islands forms, like the Mariana Arc. When it sinks under a continent, a line of volcanoes rises along the coast, like in Chile.
The angle matters too. Older seafloor dives more steeply. The Pacific's ridges, where new seafloor is made, sit much closer to South America than to Asia. So young seafloor slides under South America at a shallow angle, while old seafloor plunges steeply in the western Pacific.
The Ring Has Holes in It
Despite its name, the ring is not complete. In parts of the south Pacific, between New Zealand and Antarctica, the plates pull apart instead of colliding, so there is no subduction belt there. There are also gaps along the Americas, such as in northern Mexico and southern California, partly because of the San Andreas Fault.
Some famous volcanoes are not part of it at all. Hawaii sits in the middle of the Pacific, far from any subduction zone, so it does not count. Australia is left out too, because it lies in the centre of its own plate.
Geologists even argue about the edges. Indonesia sits where the Ring meets the Alpide belt. Many experts place its western islands, home to Krakatoa and Toba, in the Alpide belt instead. The Antarctic Peninsula and some Pacific island chains are also disputed.
Record Quakes, Lava Lakes and Rich Soil
The Ring holds some huge records. The four largest volcanic eruptions of the last 11,700 years all happened here, and so did twenty of the twenty-five largest. The largest earthquake ever recorded, the 1960 Valdivia earthquake in Chile, measured 9.4-9.6.
Some stories sound unreal. Villarrica in Chile is one of only five volcanoes in the world known to have an active lava lake in its crater. In 1993, Lascar in Chile dropped ash on Buenos Aires, more than 1,600 km away. Japan holds about 10% of the world's active volcanoes and records as many as 1,500 earthquakes a year.
There is a bright side underground. Weathered volcanic ash forms soils called andosols, which are full of volcanic glass. The Ring of Fire is the world's main home for this soil, and it is usually quite fertile.
