Plate Tectonics and the Ring of Fire | National Geographic Society (2023)

TheRing of Fireis a string ofvolcanoes and sites ofseismicactivity, or earthquakes, around the edges of the Pacific Ocean. Roughly 90% of allearthquakes occur along the Ring of Fire, and the ring is dotted with 75% of allactive volcanoes on Earth.

The Ring of Fire isn’t quite a circular ring. It is shaped more like a 40,000-kilometer (25,000-mile)horseshoe. A string of 452 volcanoes stretches from the southern tip of South America, up along thecoastof North America, across theBering Strait, down through Japan, and into New Zealand. Several active anddormant volcanoes in Antarctica, however, “close” the ring.

Plate Boundaries

The Ring of Fire is the result ofplate tectonics.Tectonic plates are huge slabs of the Earth’scrust, which fit together like pieces of a puzzle. The plates are not fixed but are constantly moving atop a layer of solid andmoltenrockcalled themantle. Sometimes these platescollide, move apart, or slide next to each other. Most tectonic activity in the Ring of Fire occurs in thesegeologically active zones.

Convergent Boundaries

Aconvergent plate boundaryis formed by tectonic plates crashing into each other. Convergent boundaries are oftensubduction zones, where the heavier plate slips under the lighter plate, creating a deeptrench. This subduction changes thedensemantle material intobuoyantmagma, which rises through the crust to the Earth’s surface. Over millions of years, the rising magma creates a series of active volcanoes known as avolcanic arc.

If you were to drain the water out of the Pacific Ocean, you would see a series of deep ocean trenches that runparalleltocorresponding volcanic arcs along the Ring of Fire. These arcs create bothislands andcontinentalmountain ranges.

The Aleutian Islands in the U.S. state of Alaska, for example, run parallel to the Aleutian Trench. Both geographic features continue to form as the Pacific Platesubducts beneath the North American Plate. The Aleutian Trench reaches a maximum depth of 7,679 meters (25,194 feet). The Aleutian Islands have 27 of the United States’ 65 historically active volcanoes.

TheAndes Mountainsof South America run parallel to the Peru-Chile Trench, created as the Nazca Plate subducts beneath the South American Plate. The Andes Mountains include the world’s highest active volcano, Nevados Ojos del Salado, which rises to 6,879 meters (over 22,500 feet) along the Chile-Argentina border. Many volcanoes in Antarctica are so geologically linked to the South American part of the Ring of Fire that some geologists refer to theregionas the “Antarctandes.”

Divergent Boundaries

Adivergent boundaryis formed by tectonic plates pulling apart from each other. Divergent boundaries are the site ofseafloor spreadingandrift valleys. Seafloor spreading is the process of magma welling up in the rift as the old crust pulls itself in opposite directions. Cold seawater cools the magma, creating new crust. The upward movement and eventual cooling of this magma has created high ridges on the ocean floor over millions of years.

TheEast Pacific Riseis a site of major seafloor spreading in the Ring of Fire. The East Pacific Rise is located on the divergent boundary of the Pacific Plate and the Cocos Plate (west of Central America), the Nazca Plate (west of South America), and the Antarctic Plate. In addition to volcanic activity, the rise also has a number of hydrothermal vents.

Transform Boundaries

Atransform boundaryis formed as tectonic plates slidehorizontally past each other. Parts of these plates get stuck at the places where they touch.Stressbuilds in those areas as the rest of the plates continue to move. This stress causes the rock to break or slip, suddenlylurching the plates forward and causing earthquakes. These areas of breakage or slippage are calledfaults. The majority of Earth’s faults can be found along transform boundaries in the Ring of Fire.

The San Andreas Fault, stretching along the central west coast of North America, is one of the most active faults on the Ring of Fire. It lies on the transform boundary between the North American Plate, which is moving south, and the Pacific Plate, which is moving north. Measuring about 1,287 kilometers (800 miles) long and 16 kilometers (10 miles) deep, the fault cuts through the western part of the U.S. state of California. Movement along the fault caused the 1906 San Francisco earthquake, which destroyed nearly 500 city blocks. The earthquake and accompanying fires killed roughly 3,000 people and left half of the city’sresidents homeless.

Hot Spots

The Ring of Fire is also home tohot spots, areas deep within the Earth’s mantle from which heat rises. This heatfacilitates the melting of rock in thebrittle, upper portion of the mantle. The melted rock, known as magma, often pushes through cracks in the crust to form volcanoes.

Hot spots are not generally associated with the interaction or movement of Earth’s tectonic plates. For this reason, manygeologists do not consider hot spot volcanoes part of the Ring of Fire.

Mount Erebus, the most southern active volcano on Earth, sits over the eruptive zone of the Erebus hot spot in Antarctica. Thisglacier-covered volcano has alava lakeat itssummit and has been consistentlyerupting since it was first discovered in 1841.

Active Volcanoes in the Ring of Fire

Most of the active volcanoes on The Ring of Fire are found on its western edge, from the Kamchatka Peninsula in Russia, through the islands of Japan and Southeast Asia, to New Zealand.

Mount Ruapehu in New Zealand is one of the more active volcanoes in the Ring of Fire, with yearly minor eruptions, and majoreruptions occurring about every 50 years. It stands 2,797 meters (9,177 feet) high. Mount Ruapehu is part of the Taupo Volcanic Arc, where the dense Pacific Plate is subducting beneath the Australian Plate.

Krakatau, perhaps better known asKrakatoa, is an island volcano in Indonesia. Krakatoa erupts less often than Mount Ruapehu, but much morespectacularly. Beneath Krakatoa, the denser Australian Plate is being subducted beneath the Eurasian Plate. Aninfamouseruption in 1883 destroyed the entire island, sendingvolcanic gas,volcanic ash, and rocks as high as 80 kilometers (50 miles) in the air. A new island volcano, Anak Krakatau, has been forming with minor eruptions ever since.

Mount Fuji, Japan’s tallest and most famous mountain, is an active volcano in the Ring of Fire. Mount Fuji last erupted in 1707, but recent earthquake activity in eastern Japan may have put the volcano in a “critical state.” Mount Fuji sits at a “triple junction,” where three tectonic plates (the Amur Plate, Okhotsk Plate, and Philippine Plate) interact.

The Ring of Fire’s eastern half also has a number of active volcanic areas, including the Aleutian Islands, the Cascade Mountains in the western U.S., the Trans-Mexican Volcanic Belt, and the Andes Mountains.

Mount St. Helens, in the U.S. state of Washington, is an active volcano in the Cascade Mountains. Below Mount St. Helens, the Juan de Fuca plate is being subducted beneath the North American Plate. Mount St. Helens lies on a particularly weak section of crust, which makes it moreproneto eruptions. Its historic 1980 eruption lasted 9 hours and covered nearby areas in tons of volcanic ash.

Popocatépetl is one of the most dangerous volcanoes in the Ring of Fire. The mountain is one of Mexico’s most active volcanoes, with 15 recorded eruptions since 1519. The volcano lies on the Trans-Mexican Volcanic Belt, which is the result of the small Cocos Plate subducting beneath the North American Plate. Located close to theurban areas of Mexico City and Puebla, Popocatépetl poses a risk to the more than 20 million people that live close enough to bethreatened by adestructiveeruption.

Fast Fact

Cooling RingThe Pacific Plate, which drives much of the tectonic activity in the Ring of Fire, is cooling off. Scientists have discovered that the youngest parts of the Pacific Plate (about 2 million years old) are cooling off and contracting at a faster rate than older parts of the plate (about 100 million years old). The younger parts of the plate are found in its northern and western parts—the most active parts of the Ring of Fire.

Fast Fact

Jolting Japan
The island nation of Japan lies along the western edge of the Ring of Fire, and is one of the most tectonically active places on Earth. As much as 10% of the world’s volcanic activity takes place in Japan.

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