The Ring of Fire

Close your eyes and picture a real-world volcano.

Where are you on the globe?

You might be at one of Italy’s famous spewers, Etna or Vesuvius. You might be in Hawaii on Mauna Kea or Mauna Loa. Maybe you went to Africa’s High Point, Kilimanjaro.

Or, likely, you’re in one of many spots where continental land meets the Pacific Ocean. Perhaps you’re near a major city, such as Tokyo or Seattle, where Mount Fuji and Mount Rainier sit like ever-present sentinels.

In fact, if you asked a computer to pick a random active volcano, two out of every three times you would end up on continental land very close to the Pacific Ocean in a region known as the Ring of Fire.

The Ring of Fire - graphic by Gringer

Also known as the Rim of Fire, the Girdle of Fire, or the Circum-Pacific Belt, the majority of the world’s active volcanoes inhabit this swath of Earth’s surface. About 40,000 miles long and 310 miles wide at the broadest point, the band sports between 750-915 volcanoes (the inexact number occurs because of a geological dispute about the definition of the region). Most scientists agree that the Ring contains the Pacific sides of South America and North America, portions of Russia, Japan, a slew of Pacific islands, and New Zealand. A few adventurous geologists include western Indonesia and Antarctica.

Why is this stretch so volcanic?

Though explorers and scientists noticed the magmatic properties of the Ring by the early 19th century, the definitive understanding of the phenomenon did not emerge until the 1960s. The answer is plate tectonics.

(Aside: that evidence for and recognition of plate tectonics did not occur until the second half of the 20th century feels incredible)

Plate tectonics is the mechanism of continental drift. The rigid outer shell of our planet – the lithosphere – contains the crust and the upper mantle. This section of the planet is fractured into plates. Depending on the definition, seven or eight major plates exist, in addition to a number of smaller “platelets.” These chunks move around on Earth’s surface, riding a fluid-like layer called the asthenosphere.

The tectonic plates of the Earth - graphic by M. Bitton

Because the plates move on a crowded dancefloor, they inevitably interact with other plates.

Geologists identify three types of plate boundaries/interactions. A divergent boundary occurs when plates move away from each other; at these borders, new crust forms as magma fills the rifts. When two plates slide past each other, we call them transform boundaries. Though these two can cause interesting fireworks, they are not responsible for the Ring of Fire.

Our volcanic band exists because of convergent boundaries. At these meetings, the plates plow into each other. This type of boundary – when it features two continental plates – can form massive mountains. The Himalayas are still growing because the Indian Plate is smashing into the Eurasian Plate. When an oceanic plate meets a continental plate, however, things can get crazy. The lithosphere in the ocean is denser than its counterpart on land. When the two converge, the oceanic lithosphere is forced below the continental lithosphere in a process called subduction.

Subduction zones become volcano factories. As the lithosphere is subducted, it melts as it reaches the upper levels of the mantle, allowing it to become magma. Magma is less dense than the layers above it, so it rises toward the surface. When too much magma accrues in a region, a volcano goes boom.

A prototypical subduction zone - graphic by Booyabazooka

Volcanoes can exist in non-convergent spots, such as the Hawaiian hotspot, but the world’s biggest and baddest live at these types of locations. The four largest volcanic eruptions during the Holocene – the most recent geological epoch – happened somewhere on the Ring. Expand the list and 20 of the top 25 belong to the Ring.

In addition to massive eruptions in the distant past, the Ring is responsible for some of recorded history’s biggest calamities and explosions. Mt. St. HelensTambora’s Year Without a Summer led to the creation of the novel FrankensteinKrakatoa’s detonation caused the loudest sound ever heard.

The Ring of Fire is named for volcanoes (even though volcanoes technically aren’t burning), but it produces another major type of activity, too: earthquakes.

More than three-quarters of the planet’s seismic energy is released in the Ring of Fire. Specifically, 90% of Earth’s earthquakes happen on the band! More than 81% of the worst earthquakes also transpire in the region.

Global earthquake distribution - graphic by USGS
Global map of subduction zones - graphic by Gavin P. Hayes

The Ring of Fire has existed in its current format for about the last 35 million years. That’s plenty of time for extensive volcanic destruction across the region but the shortest of periods in geological terms. 

The Pacific Plate currently moves northwestward about three or four inches each year. Each inch of that plate that subducts eventually becomes magma. The complete subduction – if current trends continue – will take tens or hundreds of millions of years, so it’s likely the Ring of Fire will continue to be a prominent feature of the Earth’s surface while humans inhabit it.

Though we can revel in their majesty and beauty, these volcanoes can also pose significant risks to population centers and the global climate. And that doesn’t even touch the temblors.

Kambalny, an active volcano in Russia's Kamchatka Peninsula - Daniel Läubli
Mount Fuji - photo by Marion & Christoph Aistleitner

Further Reading and Exploration

Ring of Fire – National Geographic

What is the “Ring of Fire”? – U.S. Geological Survey

Ring of Fire – Encyclopedia Britannica

Introduction to Subduction Zones: Amazing Events in Subduction Zones – USGS

Where do earthquakes occur? – USGS

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