Ring of Fire
The Ring of Fire runs for about 25,000 miles around the Pacific Ocean, in a band that reaches up to roughly 500 kilometres wide. Geologists also call it the Pacific Ring of Fire, the Rim of Fire, the Girdle of Fire and the Circum-Pacific belt. About 90% of the world's earthquakes happen inside it. Why does one ocean carry so much of the planet's shaking? How old is this pattern, and who first noticed it? And what changes when a mountain, an island or a whole country is counted in, or left out?
Until the late 18th century, writers going back to Ancient Greece and Rome pictured volcanoes as the vents of fires burning inside the Earth. That belief survives in the name Ring of Fire, even though volcanoes do not actually set the ground alight.
In 1825 the pioneering volcanologist G. P. Scrope described chains of volcanoes along the rim of the Pacific in his book Considerations on Volcanos. About three decades later, a book on the Perry Expedition to Japan, covering 1852-54, put the idea more grandly. Narrative of the Expedition of an American Squadron to the China Seas and Japan placed the Japanese Islands "in the line of that immense circle of volcanic development". That circle, it said, surrounds the Pacific shores from Tierra del Fuego around to the Moluccas.
In 1878 Scientific American ran an article titled "The Ring of Fire, and the Volcanic Peaks of the West Coast of the United States." It outlined volcanic activity along the boundaries of the Pacific. In 1906 Alexander P. Livingstone published Complete Story of San Francisco's Terrible Calamity of Earthquake and Fire. He wrote of "the great ring of fire which circles round the whole surface of the Pacific Ocean."
In 1912 the geologist Patrick Marshall introduced the term Andesite Line for a boundary between islands in the southwest Pacific. Those islands differ in volcano structure and lava types. The concept was later extended to other parts of the ocean, and the line closely matches the Ring of Fire. The real explanation for all of it arrived only with the theory of plate tectonics, developed from the early 1960s.
Around the Pacific, the Antarctic, Nazca and Cocos plates are all forced beneath the South American plate. This is the secret of the ring. It is not one geological structure but the sum of many plates sinking at convergent boundaries, a process called subduction. The Pacific and Juan de Fuca plates slide beneath the North American plate, and the Philippine plate dives under the Eurasian plate. In Central America, the Cocos plate goes under the Caribbean plate.
The eastern edge of the ring comes from a few large plates colliding. The western edge is more tangled. Along the north, the northwestward-moving Pacific plate sinks beneath the Aleutian Islands arc, and farther west it descends at Kamchatka and the Kuril arcs. In the southwest, smaller plates meet the Pacific plate at the Mariana Islands, the Philippines, eastern Indonesia, Papua New Guinea, Tonga and New Zealand. Australia is left out, because that landmass sits in the middle of its own plate, far from any subduction.
The Mariana Arc in the western Pacific shows what happens when one patch of ocean floor sinks beneath another: a curving chain of volcanic islands. The coast of Chile shows the other case. There, ocean floor sinks beneath a continent and builds a volcanic continental arc.
The angle of descent depends on age. The older the sinking ocean floor, the steeper it plunges. The Pacific's mid-ocean ridges lie much closer to South America than to Asia, so the ocean floor reaching the South American coast is younger. It dives at a shallow angle there, while the older western Pacific floor plunges more steeply. That difference shapes how far volcanoes sit from the trench, what the lava is made of, and what kind of earthquakes strike. Chile and the Marianas mark the two ends of a whole spectrum.
Each subduction zone leaves a trench on the ocean floor. The list for the ring has fourteen entries, from the Peru-Chile Trench and the Aleutian Trench to the Mariana, Tonga and Kermadec trenches, plus the Hikurangi Trough. The Kuril-Kamchatka Trench, which runs along Kamchatka's Pacific coast, reaches 10500 metres.
About 210 million years ago, in the Late Triassic, the Izanagi plate was sinking beneath the coast of east Asia. Its descent continued through the Jurassic and produced volcanic belts, including some in what is now eastern China.
The Pacific plate itself did not yet exist. It came into being in the Early Jurassic, about 190 million years ago, far from the edges of the ocean basin. Until it grew large enough to reach those edges, older plates were consumed ahead of it. Along the coast of South America, subduction has been going on since the Jurassic, more than 145 million years ago. Remnants of Jurassic and Cretaceous volcanic arcs are still preserved there.
The cast of plates kept changing. Between 120 and 115 million years ago, the Farallon plate was sinking under South America, North America and north-east Asia, while the Izanagi plate was sinking under east Asia. By 85 to 70 million years ago, Izanagi had moved north-eastwards and was descending beneath east Asia and North America. Farallon still fed South America, and the Pacific plate had begun to sink under east Asia. Between 70 and 65 million years ago, the Kula plate took over beneath North America and north-east Asia. By about 35 million years ago, both Kula and Farallon had been consumed. The Pacific plate then sank around its whole rim, in an outline close to the modern ring.
The present subduction zones appeared in stages. By about 115 million years ago they existed in South America, North America and Asia. The zones of Indonesia and New Guinea formed about 70 million years ago. Many older, extinct volcanoes lie inside the ring today, because subduction began in places long before the ring took its final shape. The youngest piece is the New Zealand zone, which formed about 35 million years ago.
Indonesia sits where the Ring of Fire meets the Alpide belt, the Earth's other very long zone of subduction-related volcanoes and earthquakes. The Alpide belt runs east-west through southern Asia and southern Europe. Some geologists place all of Indonesia in the Ring of Fire. Many exclude the western islands, which they count in the Alpide belt instead. News media and popular science writing often include the western islands, and with them Krakatoa, Merapi, Tambora and Toba. The eastern islands, including Sulawesi and Halmahera, are more widely accepted as part of the ring.
At the far south of the map, the Antarctic Peninsula and the South Shetland Islands split opinion. Deception Island is one of the volcanoes there, and it owes its existence to rifting in the Bransfield back-arc basin. Mount Erebus and the volcanoes of Victoria Land are not related to subduction, so they are left out. The same goes for the Balleny Islands between Antarctica and New Zealand. Geologists also disagree about the Izu Islands, the Bonin Islands and the Mariana Islands, with some including them and others not.
The Hawaiian Islands lie in the central Pacific, very far from any subduction zone, so they are not part of the ring. The ring also does not stretch across the southern Pacific from New Zealand to the Antarctic Peninsula or to the tip of South America. The plate boundaries there, the Pacific-Antarctic Ridge, the East Pacific Rise and the Chile Ridge, are pulling apart instead of colliding.
Even within the accepted ring there are gaps. Flat slab subduction is thought to explain the three gaps between the four sections of the Andean Volcanic Belt. In northern Mexico and southern California, a divergent boundary in the Gulf of California and the San Andreas Fault interrupt the pattern. Farther north, in northern British Columbia, Yukon and south-east Alaska, volcanoes exist but are caused by continental rifting, not subduction.
Depending on which regions a geologist counts, between 750 and 915 volcanoes, active or dormant, belong to the Ring of Fire. That is around two-thirds of the world's volcanoes. More than 350 of them have erupted in historical times.
The four largest eruptions of the Holocene epoch, the last 11,700 years, all happened at ring volcanoes. They came from Fisher Caldera in Alaska in 8700 BC and Kurile Lake in Kamchatka in 6450 BC. The other two were Kikai Caldera in Japan in 5480 BC and Mount Mazama in Oregon in 5677 BC. Twenty of the twenty-five largest eruptions of the same period also happened here.
Most of Earth's active volcanoes with summits above sea level stand in the ring. Many are stratovolcanoes such as Mount St. Helens, built up when explosive eruptions of tephra alternate with flows of lava. The lava is mainly andesite and basaltic andesite, with dacite, rhyolite and basalt turning up less often. Plosky Tolbachik is a shield volcano, and Monowai is a submarine seamount.
The Andes hold some of the ring's records. Ojos del Salado, on the border of Argentina and Chile, rises 6893 metres and is the world's highest active volcano; it last erupted in AD 750. Nearby on the same border, Llullaillaco at 6739 metres is the highest historically active volcano, and it last erupted in 1877.
Villarrica in Chile is one of only five volcanoes known to hold an active lava lake in its crater. Melting snow and ice there often trigger lahars, as in the eruptions of 1964 and 1971. In 1993 Lascar, in the northern Chilean Andes, produced pyroclastic flows reaching 8.5 kilometres northwest of its summit. Its ash fell on Buenos Aires, more than 1600 kilometres away.
Sangay in Ecuador has a history of roughly 500,000 years of instability. Two earlier versions of the mountain were destroyed in huge flank collapses, and the debris still litters the surroundings. It has been a UNESCO World Heritage Site since 1983.
The Alpide belt, which stretches from central Indonesia to the northern Atlantic by way of the Himalayas and southern Europe, is the next most seismically active region. It accounts for 5-6% of earthquakes. From 1900 to the end of 2020, however, most earthquakes of magnitude 8.0 or higher struck inside the Ring of Fire. They are presumed to be megathrust earthquakes at subduction zones.
Four of the most powerful earthquakes since modern seismological equipment and magnitude scales arrived in the 1930s happened here. The 1960 Valdivia earthquake in Chile measured 9.4-9.6 and is the largest ever recorded. The 1964 Alaska earthquake, known as the Good Friday earthquake, measured 9.2. The 2011 Tohoku earthquake and tsunami in Japan measured 9.0-9.1. The 1952 earthquake at Severo-Kurilsk in Kamchatka measured 9.0.
Japan records as many as 1,500 earthquakes a year, and magnitudes of 4 to 6 are not uncommon. Minor tremors rattle buildings somewhere in the country almost daily. The 1923 Great Kantō earthquake killed 130,000 people. The Great Hanshin earthquake of the 17th of January 1995 killed 6,434. On the 11th of March 2011, a magnitude 9.0 earthquake struck, the biggest in Japan's history and the fifth largest on record according to the US Geological Survey. Undersea earthquakes also expose the Japanese coast to tsunamis.
Chile has seen strong shaking in recent years, tied to the subduction of the Nazca plate. A magnitude-8.8 earthquake hit central Chile on the 27th of February 2010. On the 1st of April 2014, a magnitude 8.2 earthquake struck northern Chile after a run of moderate to large shocks. Many aftershocks followed, including a magnitude 7.6 event on the 2nd of April.
The Cascadia subduction zone is a fault about 680 miles long, running 50 miles off the Pacific Northwest coast from northern California to Vancouver Island. A magnitude-9 earthquake struck there in 1700. We know of it through scars that its tsunami left on the coast and through Japanese records, since tsunami waves cross the Pacific. Geological evidence suggests great earthquakes at least seven times in the last 3,500 years, a return time of 400 to 600 years.
Unlike most subduction zones, Cascadia has no oceanic trench. The uplifted coast ranges and heavy sediment from the Fraser, Columbia and Klamath rivers help hide it. Meanwhile the outer margin is slowly compressed, like a giant spring awaiting release.
At 8:32 am on the 18th of May 1980, an earthquake shook Mount St. Helens and its weakened north face slid away. For two months before that, earthquakes and steam venting had followed an injection of magma at shallow depth, which raised a huge bulge on the north slope. With the face gone, the partly molten, gas-rich rock inside lost pressure and exploded into a very hot mix of pulverized lava and older rock. That blast raced toward Spirit Lake faster than the sliding face itself. It was the most significant eruption in the contiguous 48 US states in recorded history, rated VEI 5. It exceeded the 1915 eruption of California's Lassen Peak.
On the 15th of July 1888, Mount Bandai in Japan suffered a large earthquake after a week of seismic activity. A tremendous noise and a large explosion followed. Eyewitnesses counted about 15 to 20 more explosions, and the last was projected almost horizontally to the north. The collapse of Ko-Bandai sent a debris avalanche that buried several villages and formed several large lakes. The eruption closely resembled the one at Mount St. Helens nearly a century later.
The 1991 eruption of Mount Pinatubo in the Philippines is the second-largest of the 20th century. Successful forecasts of its climactic phase led to the evacuation of tens of thousands of people, which saved many lives. Even so, pyroclastic flows, ash deposits and later rain-driven lahars destroyed thousands of houses. In Guatemala, the 1902 eruption of Santa Maria had a volcanic explosivity index of 6 and ejected an estimated 5.5 cubic kilometres of magma. In Mexico, the 1982 eruption of El Chichón killed about 2,000 people and left a caldera 1 kilometre wide, which filled with an acidic crater lake.
On the 24th of December 1953, a lahar destroyed the Tangiwai rail bridge in New Zealand moments before a Wellington to Auckland express was due, and 151 people on the train died. The lahar came from Mount Ruapehu, whose warm acidic crater lake refills between major eruptions. If a tephra dam holds the lake back until the water rises past its normal outlet, the dam can collapse and release a surge. Ruapehu's major eruptions have been about 50 years apart, in 1895-1945 and 1995-1996. In 2000 the ERLAWS system was installed on the mountain to detect such a collapse and alert the authorities.
Volcanic ash weathers into andosols, also known as andisols, and the Ring of Fire is the world's main home for them. These soils contain large proportions of volcanic glass and typically have good fertility.
Not every eruption has happened yet. The Auckland volcanic field on New Zealand's North Island holds at least 40 volcanoes and is currently dormant. Its most recent activity came about 600 years ago at Rangitoto Island, which erupted 2.3 cubic kilometres of lava. The field is likely to erupt again within "hundreds to thousands of years", a very short span in geological terms.
Updated
Common questions
What is the Ring of Fire?
The Ring of Fire is a tectonic belt of earthquakes and volcanoes that surrounds most of the Pacific Ocean. It is also called the Pacific Ring of Fire, the Rim of Fire, the Girdle of Fire and the Circum-Pacific belt.
How long is the Ring of Fire?
The Ring of Fire is about 25,000 miles long and up to roughly 500 kilometres wide. It circles most of the Pacific Ocean.
How many volcanoes are in the Ring of Fire?
The Ring of Fire contains between 750 and 915 active or dormant volcanoes, around two-thirds of the world total. The exact number depends on which regions are included, and more than 350 have erupted in historical times.
What causes the Ring of Fire?
The Ring of Fire is caused by the subduction of different tectonic plates at convergent boundaries around the Pacific Ocean. It is not a single geological structure, and these plate interactions formed its trenches, volcanic arcs and volcanic belts.
Which are the biggest earthquakes in the Ring of Fire?
The 1960 Valdivia earthquake in Chile, magnitude 9.4-9.6, is the largest ever recorded. The 1964 Alaska earthquake (9.2), the 2011 Tohoku earthquake in Japan (9.0-9.1) and the 1952 Severo-Kurilsk earthquake in Kamchatka (9.0) are also among the most powerful.
Is Indonesia part of the Ring of Fire?
Indonesia lies where the Ring of Fire meets the Alpide belt, so its status is debated. Many geologists include the eastern islands but exclude the western islands, such as Sumatra and Java, which they count in the Alpide belt.
Why are the Hawaiian Islands not in the Ring of Fire?
The Hawaiian Islands lie in the central Pacific, very far from any subduction zone. For that reason they are not part of the Ring of Fire.
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