Pacific Ring of Fire

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The Ring of Fire, more formerly known as the circum-Pacific seismic belt, is a name used to describe an incredibly long string of volcanoes, and an earthquake zone, that stretches around much of the Pacific Ocean.

At around 40,000 km (29,000 miles) in length, it includes the volcanoes along the Andes Mountains, the western side of North America, the Aleutian Islands, the islands of Japan and south-east Asia, and New Zealand.

An Uninterrupted Path of Volcanoes from South America to New Zealand

The majority of it is formed by a line of subduction faults, where one tectonic plate is forced under another, creating conditions that are ripe for volcano formation.

Three-quarters of the Earth’s volcanoes are located along the Ring of Fire, and 90% of all earthquakes around the world occur at these tectonic plate boundaries, many of which are among the most destructive ever recorded. 

The Cascadia Subduction Zone, located in the U.S. Pacific Northwest and southwestern British Columbia, has hosted magnitude ≥8.0 megathrust earthquakes in the geologic past, a future earthquake is imminent, and the potential impacts could cripple the region. Subduction zone earthquakes represent some of the most devastating natural hazards on Earth.
The Cascadia Subduction Zone, located in the U.S. Pacific Northwest and southwestern British Columbia, has hosted magnitude ≥8.0 megathrust earthquakes in the geologic past, a future earthquake is imminent, and the potential impacts could cripple the region. Subduction zone earthquakes represent some of the most devastating natural hazards on Earth. Image: USGS, public domain.

At a subduction plate boundary, two tectonic plates collide with one another, resulting in the heavier plate (usually a lower, oceanic one) being dragged underneath. As the plate is plunged down into a layer of the mantle beneath named the asthenosphere, it comes under great pressure from both the weight of the plate above and the hot mantle itself. The melting of the plate forces magma upward through cracks in the Earth’s crust, which erupts explosively as a volcanic eruption.

Since the majority of the Pacific Ocean is surrounded by these types of tectonic plate boundaries, this explains why an almost uninterrupted path of volcanoes occurs from South America along to New Zealand. 

Tectonic Processes in the Pacific

The tectonic processes around the Pacific have shaped its surrounding continental edges, and explain the reason for many of the islands along the side of the western and northern Pacific. Although the Andes Mountain Range is primarily the result of subduction-related uplift, volcanoes have also shaped the range, including peaks such as Copahue, the Nevados de Chillán group and many others in Ecuador and Colombia.

In late November 2013, volcanic activity along the western fringe of the Pacific "Ring of Fire" gave rise to a little island.
In late November 2013, volcanic activity along the western fringe of the Pacific “Ring of Fire” gave rise to a little island. Image: NASA

The Cascade Range in the Pacific Northwest also consists of a number of volcanoes, including Mount St. Helens and Mount Rainier.

Additionally, entire island chains and countries owe their existence to the Ring of Fire; large parts of the Aleutian archipelago, Japan, the Philippines and New Zealand are the result of volcanic action. 

Distribution of Volcanoes Around the Ring of Fire

The distribution of volcanoes around the Ring of Fire is not evenly distributed, and there are various sections along it where volcanic and seismic activity is more pronounced than in other places.

The greatest example of this is Japan, which sees a higher concentration of volcanic eruptions and earthquakes than is usual for the rest of the ring. This is due to the meeting of not two, but three tectonic plates: the Pacific, Philippine and Eurasian plates.

Map showing the Pacific Ring of Fire.
Map showing the Pacific Ring of Fire. Source: USGS, public domain.

The Pacific and Philippine plates are subducted underneath the Pacific plate, creating a greater amount of magma that can reach the surface than normally occurs at a subduction zone. This unusual situation also results in Japan experiencing a notably higher proportion of large earthquakes than other similar-sized parts of the Ring of Fire.

Around 20% of the world’s earthquakes with a magnitude over 6 occur within and adjacent to the archipelago. 

There are also a few gaps along the Ring of Fire where there is very little to no volcanic activity, but strong earthquakes often occur. The most notable of these gaps is in the southwestern United States, throughout central and southern California.

This is because there is no subduction plate boundary here, but instead a transform fault, where the Pacific and North American tectonic plates slip past each other. This is named the San Andreas Fault, and is caused by the Pacific plate moving north-westward and the North American plate drifting south-eastward.

View of the San Andreas Fault looking southeast along the surface trace in the Carrizo Plain, north of Wallace Creek. Elkhorn Rd. meets the fault near the top of the photo. Photo: Scott Haefner, U.S. Geological Survey. Public domain.
View of the San Andreas Fault looking southeast along the surface trace in the Carrizo Plain, north of Wallace Creek. Elkhorn Rd. meets the fault near the top of the photo. Photo: Scott Haefner, U.S. Geological Survey. Public domain.

Therefore, there is very little volcanic activity in this region, as there is no tectonic plate to subduct, and the plates do not pull away from each other in opposite directions. Strong earthquakes, however, are still a regular occurrence along the San Andreas Fault, including the 6.9 magnitude Loma Prieta earthquake, which struck the San Francisco Bay Area in 1989, and the 6.0 magnitude Parkfield earthquake in 2004.

Catastrophic Volcanic Eruptions and Earthquakes

The Ring of Fire has been responsible for many of the world’s most catastrophic volcanic eruptions and earthquakes. The 1991 eruption of Mount Pinatubo was not only the second-largest eruption of the 20th Century, but was particularly disruptive as it affected many densely populated areas along the western side of Luzon, the largest island in the Philippines.

The eruption was responsible for producing catastrophic pyroclastic flows, devastating mudflows and a large ash cloud that spread hundreds of miles across, depositing as far away as Vietnam and the Malay Peninsula. 847 people were killed in the eruption, and 10,000 people were left homeless.

Another example is the 1985 eruption of Mount Ruiz in Colombia; although it was not as large as Pinatubo, the Ruiz eruption caused the ice and snow covering to quickly melt, forcing a torrent of mud, ash and water to tumble down the volcano. Devastatingly, 25,000 people were killed by this catastrophe. 

Many of the world’s most catastrophic earthquake disasters have also occurred along the Ring of Fire. The Kobe earthquake in 1995 had a magnitude of 6.9; as it struck a highly-populated urban area, more than 6,000 people unfortunately lost their lives in the disaster.

In New Zealand, a 7.1 magnitude earthquake hit the city of Christchurch in 2010, followed by a number of particularly bad aftershocks that struck periodically until December 2011. These caused a great deal of destruction to the infrastructure in Christchurch, and unfortunately resulted in 180 deaths.

Tsunami damage in Natori, Japan, 2011. Photo: Bruce Jaffe, USGS Pacific Coastal and Marine Science Center. Public domain.
Tsunami damage in Natori, Japan, 2011. Photo: Bruce Jaffe, USGS Pacific Coastal and Marine Science Center. Public domain.

Many earthquakes around the Pacific have also caused a great number of tsunamis, including the devasting Tōhoku earthquake and tsunami that struck eastern Japan in March 2011. The huge wave caused countless devastation, including three nuclear meltdowns; almost 20,000 people lost their lives in the disaster. 

References

National Geographic Society. (2014, December 8). Kobe earthquakehttps://www.nationalgeographic.org/thisday/jan17/kobe-earthquake/

Newhall, C., Hendley II, J. W., & Stauffer, P. H. (2005, February 28). The cataclysmic 1991 eruption of Mount Pinatubo, Philippines, fact sheet 113-97. U.S. Geological Survey Publications Warehouse. https://pubs.usgs.gov/fs/1997/fs113-97/

Plate tectonics: Subduction zones. (n.d.). VolcanoDiscovery. https://www.volcanodiscovery.com/geology/subduction-zones.html

Ring of Fire. (n.d.). Encyclopedia Britannica. https://www.britannica.com/place/Ring-of-Fire

The World’s Most Active Earthquake Zone Is the Closest Place on Earth to Unraveling World-shaking Geophysical Mysteries. (n.d.). The University of Tokyo. https://www.u-tokyo.ac.jp/en/whyutokyo/wj_001.html

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