Volcanism
Volcano
A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. The process is called Volcanism and has been ongoing on Earth since the initial stages of its evolution over 4 billion years ago.
Volcanoes are Earth’s geologic architects. They’ve created more than 80 percent of our planet’s surface, laying the foundation that has allowed life to thrive. Their explosive force crafts mountains as well as craters. Lava rivers spread into bleak landscapes. But as time ticks by, the elements break down these volcanic rocks, liberating nutrients from their stony prisons and creating remarkably fertile soils that have allowed civilizations to flourish.
There are volcanoes on every continent, even Antarctica. Some 1,500 volcanoes are still considered potentially active around the world today; 161 of those—over 10 percent—sit within the boundaries of the United States.
But each volcano is different. Some burst to life in explosive eruptions, like the 1991 eruption of Mount Pinatubo, and others burp rivers of lava in what’s known as an effusive eruption, like the 2018 activity of Hawaii’s Kilauea volcano. These differences are due to the chemistry driving the molten activity. Effusive eruptions are more common when the magma is less viscous, or runny, which allows gas to escape and the magma to flow down the volcano’s slopes. Explosive eruptions, however, happen when viscous molten rock traps the gasses, building pressure until it violently breaks free.
Formation of Volcanoes
- The majority of volcanoes in the world form along the boundaries of Earth’s tectonic plates—massive expanses of our planet’s lithosphere that continually shift, bumping into one another.
- When tectonic plates collide, one often plunges deep below the other in what’s known as a subduction zone.
- As the descending landmass sinks deep into the Earth, temperatures and pressures climb, releasing water from the rocks.
- The water slightly reduces the melting point of the overlying rock, forming magma that can work its way to the surface—the spark of life to reawaken a slumbering volcano.
- Not all volcanoes are related to subduction,
- Another way volcanoes can form is what’s known as hotspot volcanism.
- In this situation, a zone of magmatic activity—or a hotspot—in the middle of a tectonic plate can push up through the crust to form a volcano.
- Although the hotspot itself is thought to be largely stationary, the tectonic plates continue their slow march, building a line of volcanoes or islands on the surface. This mechanism is thought to be behind the Hawaii volcanic chain.
Location of Volcanoes
- Some 75 percent of the world’s active volcanoes are positioned around the ring of fire, a 25,000-mile long, horseshoe-shaped zone that stretches from the southern tip of South America across the West Coast of North America, through the Bering Sea to Japan, and on to New Zealand.
- This region is where the edges of the Pacific and Nazca plates butt up against an array of other tectonic plates. Importantly, however, the volcanoes of the ring aren’t geologically connected. In other words, a volcanic eruption in Indonesia is not related to one in Alaska, and it could not stir the infamous Yellowstone supervolcano.
Reasons for Concentration of volcanoes along the Ring of Fire
The Ring of Fire is a string of volcanoes and sites of seismic activity, or earthquakes, around the edges of the Pacific Ocean. Roughly 90% of all earthquakes occur along the Ring of Fire, and the ring is dotted with 75% of all active 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 the coast of North America, across the Bering Strait, down through Japan, and into New Zealand. Several active and dormant volcanoes in Antarctica, however, “close” the ring.
Plate Boundaries
The Ring of Fire is the result of plate tectonics. Tectonic plates are huge slabs of the Earth’s crust, which fit together like pieces of a puzzle. The plates are not fixed but are constantly moving atop a layer of solid and molten rock called the mantle. Sometimes these plates collide, move apart, or slide next to each other. Most tectonic activity in the Ring of Fire occurs in these geologically active zones.
Convergent Boundaries
A convergent plate boundary is formed by tectonic plates crashing into each other. Convergent boundaries are often subduction zones, where the heavier plate slips under the lighter plate, creating a deep trench. This subduction changes the dense mantle material into buoyant magma, 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 a volcanic arc.
If you were to drain the water out of the Pacific Ocean, you would see a series of deep ocean trenches that run parallel to corresponding volcanic arcs along the Ring of Fire. These arcs create both islands and continental mountain 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 Plate subducts 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.
The Andes Mountains of 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 the region as the “Antarctandes.”
Divergent Boundaries
A divergent boundary is formed by tectonic plates pulling apart from each other. Divergent boundaries are the site of seafloor spreading and rift 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.
The East Pacific Rise is 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
A transform boundary is formed as tectonic plates slide horizontally past each other.
Parts of these plates get stuck at the places where they touch. Stress builds in those areas as the rest of the plates continue to move. This stress causes the rock to break or slip, suddenly lurching the plates forward and causing earthquakes.
These areas of breakage or slippage are called faults. 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’s residents homeless.
The Ring of Fire is also home to hot spots, areas deep within the Earth’s mantle from which heat rises. This heat facilitates the melting of rock in the brittle, 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, many geologists 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. This glacier-covered volcano has a lava lake at its summit and has been consistently erupting 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 major eruptions 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 as Krakatoa, is an island volcano in Indonesia. Krakatoa erupts less often than Mount Ruapehu, but much more spectacularly. Beneath Krakatoa, the denser Australian Plate is being subducted beneath the Eurasian Plate. An infamous eruption in 1883 destroyed the entire island, sending volcanic 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 more prone to 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 the urban areas of Mexico City and Puebla, Popocatépetl poses a risk to the more than 20 million people that live close enough to be threatened by a destructive eruption.
Volcanic Landforms
Volcanic landforms are divided into extrusive and intrusive landforms based on weather magma cools within the crust or above the crust. Rocks formed by either plutonic (cooling of magma within the crust) or volcanic (cooling of lava above the surface) are called ‘Igneous rocks’.
Effects of Volcanism
Destructive effects of volcanism:
- Volcanism can be a greatly damaging natural disaster. The damage is caused by advancing lava which engulfs whole cities. Habitats and landscapes are destroyed by lava flows.
- Showers of cinders and bombs can cause damage to life.
- Violent earthquakes associated with volcanic activity and mud flows of volcanic ash saturated by heavy rain can bury nearby places.
- Sometimes ash can precipitate under the influence of rain and completely cover the surrounding regions.
- Health concerns after a volcaniceruption include infectious disease, respiratory illness, burns, injuries from falls, and vehicle accidents related to the slippery, hazy conditions caused by ash.
- Further effects are the deterioration of water quality, fewer periods of rain, crop damages, and the destruction of vegetation.
- In coastal areas, seismic sea waves called tsunamis are an additional danger which are generated by submarine earth faults where volcanism is active.
Positive effects of volcanism:
- Volcanism creates new landforms like islands, plateaus,volcanic mountains etc. For example: Deccan plateau, Mt. Vesuvius.
- The volcanic ash and dust are very fertile for farms and orchards.
- Volcanic rocks yield very fertile soil upon weathering and decomposition.
- Although steep volcano slopes prevent extensive agriculture, forestry operations on them provide valuable timber resources.
- Mineral resources, particularly metallic ores are brought to the surface by volcanoes. Sometimes copper and other ores fill the gas bubble cavities. The famed Kimberlite rock of South Africa, source of diamonds is the pipe of an ancient volcano.
- Lava rock is extensively used as a source of crushed rock for concrete aggregate or rail road ballast, and other engineering purposes
- In the vicinity of active volcanoes, waters in the depth are heated from contact with hot magma giving rise to springs and geysers. The heat from the earth’s interior in areas of volcanic activity is used to generate geothermal electricity.
- Countries producing geothermal power include USA, Russia, Japan, Italy, New Zealand and Mexico.
- At many places volcanic landforms attract heavy tourist traffic. At several places national parks have been set up centred around volcanoes.
Measures to mitigate volcanic disasters
- One of the most effective ways of reducing the risk of a volcanic eruption is having an evacuation plan. This involves ensuring evacuation strategies are in place along with emergency shelter and food supplies being planned for.
- Based on monitoring data, exclusion zones can be set up to ensure people are evacuated from areas likely to be affected before an eruption.
- Local people can also be educated about actions they can take to reduce the risk of loss of life or injury.
- People are taught that if they are unable to be evacuated what they should do to protect themselves, e.g. go indoors to avoid falling ash and rock.
