What is the Pacific Ring of Fire?

SBS World News takes a look at why a cluster of natural disasters happen in the surrounds of the Pacific Ocean.

What is the Ring of Fire?
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The Ring of Fire stretches for 50,000 kilometres around the rim of the Pacific Ocean.

Its edges mark a ring of high volcanic and seismic activity.

The majority of the Earth’s volcanic activity and earthquakes happen along this belt which stretches from the southern tip of South America to the coast of North America across the Bering Strait and down to Japan, south east Asia and New Zealand.

Despite its name, the Ring of Fire is actually horseshoe shaped.

It gets its fiery name from the amount of active volcanoes which lie within it. When viewed from space it almost resembles a ring circling the Pacific Ocean.

 

 

How is a volcano formed?
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There are two main ways volcanoes can form. One is a hot spot volcano which is located in a region where the underlying Earth’s mantle is hotter than the surrounding areas.

This allows rocks to melt to generate magma. This may or may not occur on tectonic plate boundaries (see below). Hawaii and Antarctica are considered examples of hot spots.

The other type of volcano forms through the subduction process. The majority of the volcanoes in the Ring of Fire are considered subduction zone volcanoes.

These occur when two tectonic plates converge on one another, and one of the plates is dense enough to slide beneath the other and dive into the Earth’s interior.

Volcanoes produced by the subduction process are typically called stratovolcanoes. You need an element of subduction to be able to form majority of volcanoes on Earth.

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What are tectonic plates and why are they important?
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Tectonic plates make up the exterior, relatively rigid shell that covers the Earth’s surface.

The meeting points of each plate are called boundaries. When tectonic plates move against each other they cause earthquakes and eruptions of magma, which can form volcanoes. 

The key plates in the Ring of Fire are either oceanic or continental plates. Volcanic and seismic activity typically occurs when an oceanic plate comes into contact with a continental plate through the subduction process (see above).

Another instance of plate interaction is known as a transform boundary.

This is when plates slide against each other in a horizontal slip motion. The San Andreas Fault is an example of this. Volcanoes do not form on transform faults but earthquakes do occur.

Watch: The Pacific Ring of Fire explained.

 

Active, Dormant and Extinct volcanoes: What’s the difference?
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A volcano doesn’t need to have erupted recently to be defined as a volcano. Geoscience Australia Senior Seismologist Professor Phil Cummins said the term volcano refers to the process of formation and whether it was formed as a result of volcanic eruption.

The words active, dormant and extinct are often used to describe volcanoes, but definitions for their use are bit vague.

An active volcano is one that erupts regularly, as would be the case for any volcano that has erupted historically.

A dormant volcano is an active volcano that has not erupted recently but may erupt in the future, such as one for which there is no historical knowledge of an eruption but there is geologic evidence pointing to an eruption in the past 10,000 years.

An extinct volcano is one that is expected to never erupt again, such as a volcano that has not erupted in the past 10,000 years.

 

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How many tectonic plates are in the Ring of Fire?
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There are key major and minor plates which impact activity in the Ring of Fire.

These start with the most southern, the Antarctic Plate, the Indian-Australian Plate, the Philippine Plate, the Amur Plate, the Okhotsk Plate, the Eurasian Plate, the North American Plate, the Juan de Fuca Plate, and the Caribbean Plate, which lie just outside the Ring of Fire.

The Pacific Plate, the Cocos Plate, the South American Plate and the Nazca Plate are the oceanic plates that lie within the Ring of Fire.

Professor Cummins said the distinction between a major and minor plate is determined by its size.

“There are various tectonic processes that can cause a plate to split into smaller plates,” he said.

A hot spot is something that can cause a plate to split in two. 

What is a lahar?
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A lahar is a volcanic mudflow, a mix of rock and water, which can occur with or without eruption.

They occur typically when a landscape has been covered by loose volcanic material and they pick up material as they travel, causing destruction to whatever is in its path.

Where are the Ring of Fire’s danger zones?
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The Aleutians

The Aleutians are the most northern part of the pacific Ring of Fire. They are an island chain in Alaska that consists of more than 300 small volcanic islands. These form an arc in the northern Pacific Ocean which stretches from the Alaskan Peninsula to far eastern Russia. The Aleutians separate the Bering Sea from the Pacific Ocean and they were created by the Pacific Plate subducting beneath the Northern American Plate.

The East Pacific Rise

This is the ocean ridge which divides the Pacific Plate from the Antarctic, Nazca and Cocos Plates. It stretches from the coast of Central America to South America and is home to submarine volcanoes, islands, trenches, and hydrothermal vents.

One of the most famous locations is the Black Smokers near the Galapagos Islands off the South American west coast, considered the first hydrothermal vents discovered on Earth.

The San Andreas Fault

This is the most famous transform boundary (see above) in the world, the San Andreas Fault is found along the south west coast of California in the United States.

It slices the area in two from Cape Mendocino to the Mexican border. As a result San Diego, Los Angeles and Big Sur are found on the Pacific Plate and San Francisco, Sacramento and Sierra Nevada are on the North American Plate.

Mount Erebus

Where fire meets ice at the most active volcano in Antarctica. Mount Erebus sits on Ross Island, a hot spot in Antarctica for volcanoes. Hot spots originate deep within the Earth’s mantle, where conditions allow heat to rise and create volcanic activity.

Mount Ruapehu

Located in Taupo on New Zealand’s North Island, Ruapehu is considered one of the more active volcanoes in the Ring of Fire.

The volcano sits on the Australian Plate, above the Pacific Plate that subducts beneath it. Every year Ruapehu experiences eruptions. Fortunately these are mostly minor but major eruptions do occur every 50 years or so.

Anak Krakatau 

Found in Indonesia, Krakatau erupts less often than New Zealand’s Mount Ruapehu but typically with more fury. In 1883 an eruption of Krakatoa almost destroyed the original Krakatoa island entirely.

This eventually led to the formation of Anak Krakatau the ‘child of Krakatoa’, another island volcano that has experienced regular minor eruptions ever since. The area lies above where  the Australian Plate subducts beneath the Eurasian Plate.

Mount Fuji

Mount Fuji is Japan’s tallest and most widely known mountain. It’s also an active volcano which sits above three tectonic plates, which meet at a point known as a ‘triple junction’ - The Amur Plate, Okhotsk Plate and the Philippine Plate. 

Major Ring of Fire catastrophes
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Some major cataclysmic events have happened within the Pacific Ring of Fire since the 1800s.

These include the major eruption of Indonesia’s Krakatoa in 1883 and Mount St Helens in 1980, along with Chile’s 1960 and Alaska’s 1964 earthquakes.

More recently we saw the 2011 quakes in Japan and New Zealand and the devastating quake and tsunami in the Indian Ocean in 2004.

Mount St. Helens roars to life in this Oct. 17, 1980 file photo sending a plume of smoke and ash skyward. The plume was estimated to be 50, 000 feet.
Are we crazy to live near volcanoes?
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According to Professor Phil Cummins, there are many reasons why volcanic areas are attractive places to live.

As large scale catastrophes are typically infrequent, he said the agricultural and tourism benefits can justify why so many people choose to live near volcanoes such as Japan’s Mt Fuji, Bali’s Mt Agung and New Zealand’s Mt Ruapehu.

“Volcanoes can be very attractive as they offer fertile soil, usually for a very long period between eruptions. It’s good for farming and the pressure to populate these areas can be pretty irresistible,” he said. 

Even though eruptions are difficult to predict, Professor Cummins said that many communities are able to manage the risks when it comes to residential proximity.

Residents on edge as Mexican volcano spews lava and ash after earthquake (September 2017).

Australia: Earthquakes and volcanoes
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Being situated between two of the Ring of Fire’s highly active regions; New Zealand and Indonesia, Australia has relatively low earthquake and volcanic activity.

Thee continent has many volcanoes, majority of which are not active. The only known active volcano on the Australian mainland is Mount Gambier in South Australia, which is said to have erupted as little as 5000 years ago, however the likelihood of another eruption any time soon is considered low.

Australia also has a low earthquake risk, however Professor Cummins warned low risk also meant low tolerance and preparedness for an earthquake event.

He noted the 1989 Newcastle 5.4 magnitude earthquake, considered one of Australia’s biggest natural disasters. The quake led to changes in building practices in the country and a greater knowledge of the impact of earthquakes in populated areas.

“There are no active plate boundaries in Australia, but quakes do occur in response to the buildup of stress in the Earth’s crust,” Professor Cummins said.

“We’ve seen fairly large quakes in the west and there’s no reason why a quake couldn’t occur in the east.

“The risk we face is much lower than New Zealand and the level of hazard is much lower, but our tolerance for impact is also pretty low.”