Volcano

A volcano is a vent or fissure 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. Volcanoes are most often found where tectonic plates are diverging or converging. Because most of Earth's plate boundaries are underwater, many volcanoes are found beneath the ocean, like those along the Mid-Atlantic Ridge and the Ring of Fire.

Volcanoes can also form in places where the Earth's crust is stretching and thinning, such as in the East African Rift and the Rio Grande rift. Some volcanoes form far from plate boundaries due to mantle plumes rising from deep within the Earth, creating hotspots like the Hawaiian hotspot.

Volcanoes are classified as active, dormant, or extinct. Active volcanoes have erupted recently and might erupt again, while extinct ones no longer have a magma source. Dormant volcanoes have not erupted for a very long time but might still become active.

Large volcanic eruptions can change Earth's climate. Ash and droplets of sulfuric acid from eruptions can block sunlight, cooling the troposphere and sometimes leading to volcanic winters that affect food supplies around the world.

Other planets also have volcanoes. For example, Venus and Mars both have many volcanic features. Scientists have even suggested a broader definition of "volcano" that includes processes like cryovolcanism on other worlds.

Etymology and terminology

The word volcano comes from the early 17th century, based on the name of Vulcano, a volcanic island in the Aeolian Islands of Italy. This name was inspired by Vulcan, the god of fire in Roman mythology.

The activity and processes linked to volcanoes are known as volcanism, and the scientific study of these activities is called volcanology.

Plate tectonics

Main article: Plate tectonics

The theory of plate tectonics explains how Earth's outer shell, called the lithosphere, is broken into large and small pieces called plates. These plates slowly move because of heat from deep within Earth. Most volcanoes form where these plates meet — either coming together or moving apart.

When plates move apart, new crust forms between them, often creating underwater volcanoes. When plates come together, one plate can dive beneath another, melting and forming magma that may erupt as volcanoes. There are also places called hotspots, where hot material from deep inside Earth rises to create volcanoes, such as the Hawaiian Islands.

Volcanic features

Further information: Types of volcanoes

A volcano needs a place to store melted rock called magma, a path for the magma to move up, and an opening to let the magma out as lava. The material that comes out, like lava and ash, builds up around the opening to form a volcano shape, often a mountain.

Volcanoes look different depending on many things. Some have steep sides made from thick, slow-moving lava, while others have broad, gentle slopes. Lava and ash can come out from many places on a volcano, not just the top. There are many kinds of volcanoes, including ones made mostly of ash, big flat ones called shield volcanoes, and even ones that form under water or ice. Some volcanoes are very big and can affect the whole world when they erupt.

Erupted material

The material that comes out during a volcanic eruption can be grouped into three main types:

1. Volcanic gases, which are mostly steam, carbon dioxide, and sulfur compounds like sulfur dioxide or hydrogen sulfide
2. Lava, which is magma that reaches the surface and starts to flow
3. Tephra, which are solid pieces of different sizes thrown into the air

Volcanic gases change from volcano to volcano. Water vapour is usually the most common, followed by carbon dioxide and sulfur dioxide. Other gases include hydrogen sulfide, hydrogen chloride, and hydrogen fluoride.

Lava’s behavior depends on its composition. Lava with lots of silica (a type of mineral) is thick and doesn’t flow easily. This type of lava can trap gases inside, leading to explosive eruptions. Lava with less silica is thinner and flows more easily. These different types of lava create various landforms and shapes on the Earth’s surface.

Tephra forms when magma bursts apart due to fast-expanding gases. Small pieces, called volcanic ash, can spread far from the volcano and settle on the ground.

Main article: Volcanic gas

Main article: Lava flow

Main article: Tephra

Volcanic eruptions

Main article: Volcanic eruption

Volcanoes can erupt in many different ways. Some eruptions are gentle, while others are very powerful. One way to measure how powerful an eruption is called the volcanic explosivity index, which ranges from quiet lava flows to huge eruptions that can cover large areas with ash.

Different types of eruptions include Hawaiian eruptions, which are gentle and produce flowing lava, and Plinian eruptions, which are very powerful and can create tall eruption columns and dangerous flows of hot rock and gas. Other types include Strombolian, Vulcanian, and Peléan eruptions, each with its own unique features and power.

Volcanic activity

Volcanoes can be very active, sometimes erupting several times a year, or they may only erupt once every tens of thousands of years. Scientists describe volcanoes as erupting, active, dormant, or extinct, though these terms can overlap and aren't always used the same way by all experts.

An erupting volcano is one where we can see magma, or melted rock, coming out. An active volcano shows signs like earthquakes, swelling ground, or extra gases, even if it's not erupting right now. Dormant volcanoes aren't showing these signs but could become active again in the future. Extinct volcanoes are ones scientists think won't erupt again because they no longer have a supply of magma. However, it can sometimes be tricky to tell if a volcano is truly extinct or just dormant for a very long time.

Decade volcanoes

Main articles: Lists of volcanoes and Decade Volcanoes

The Decade Volcanoes are 16 special volcanoes chosen for study because of their history of big eruptions and their closeness to where people live. They were named to support efforts to reduce natural disasters. These volcanoes are found around the world, including places like Russia, Mexico, Italy, Colombia, the United States, Indonesia, and Japan.

Scientists watch some of these volcanoes closely using special tools to better understand when they might erupt again. This helps keep people safe by giving early warnings.

Volcanoes and humans

Hazards

Main article: Volcanic hazard

Volcanic eruptions can be very dangerous to people. There are many types of eruptions, such as steam explosions, ash clouds, and fast-moving flows of hot rock and gas. These can hurt people and damage things. Volcanic gases can rise high into the sky and change the weather, sometimes making it colder for years. Ash from eruptions can also be bad for airplanes, as it can damage their engines.

Benefits

Even though eruptions can be dangerous, volcanoes also give us useful things. The rocks from volcanoes, like tuff, are soft and easy to shape, and people have used them to build things for thousands of years. Soil made from volcanic ash is very rich and helps plants grow well. Volcanoes also provide heat that can be used to make electricity. Many people visit volcanoes as tourists, which helps local economies.

Safety considerations

Near places where people live, scientists watch volcanoes very closely. They try to warn people before an eruption happens. Because of this, many lives have been saved. For example, before the big eruption of Mount Pinatubo in 1991, people were told to leave, and this helped save many lives. It is important for everyone to know what their local authorities do to keep people safe from volcanoes.

Volcanoes on other celestial bodies

See also: List of extraterrestrial volcanoes, Volcanism on the Moon, Volcanism on Mars, Volcanism on Io, and Volcanism on Venus

Our Moon doesn’t have large, active volcanoes today, but it does show signs of past volcanic activity. You can see this in the dark patches called maria, as well as in long, narrow valleys known as rilles and small rounded hills called domes.

The planet Venus has a surface covered mostly with a dark rock called basalt, showing that volcanoes helped shape it long ago. Scientists think Venus may have gone through a big change on its surface about 500 million years ago. There are wide spreads of melted rock called lava flows, and some kinds of volcanic activity happen there that we don’t see on Earth.

On Mars, there are several huge, extinct volcanoes, including Arsia Mons, Ascraeus Mons, Hecates Tholus, Olympus Mons, and Pavonis Mons. Though these volcanoes have been quiet for millions of years, spacecraft have found clues that Mars might have had volcanic activity more recently than we thought.

Jupiter’s moon Io is the most active volcano place we know of in our solar system. It has many volcanoes that burst out hot, glowing rocks and gases. Another moon of Jupiter, Europa, shows a different kind of volcanic activity called cryovolcanism, where water freezes on its cold surface.

The moon Triton of Neptune and the moon Enceladus of Saturn also show cryovolcanism, where icy mixtures burst out and freeze again. Scientists think other faraway worlds might have similar icy volcanic activity too.

History of volcano understanding

People have noticed volcanoes for a very long time. Ancient stories from many cultures often linked volcanoes to gods or supernatural events. For example, some traditions tell of gods living inside mountains or using fire to escape danger.

Over time, people tried to explain volcanoes in different ways. Some thought they were caused by winds or fires deep inside the Earth. It wasn't until much later that scientists began to understand the real reasons behind volcanic eruptions, tying them to the movement of Earth's plates and the heat from the planet's interior.