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 word volcano is derived from the name of Vulcano, a volcanic island in the Aeolian Islands of Italy whose name in turn comes from Vulcan, the god of fire in Roman mythology. The study of volcanoes is called volcanology, sometimes spelled vulcanology.

On Earth, volcanoes are most often found where tectonic plates are diverging or converging, and most are found underwater.

The Stromboli stratovolcano off the coast of Sicily has erupted continuously for thousands of years, giving rise to its nickname “Lighthouse of the Mediterranean”

For example, a mid-ocean ridge, such as the Mid-Atlantic Ridge, has volcanoes caused by divergent tectonic plates whereas the Pacific Ring of Fire has volcanoes caused by convergent tectonic plates.

Volcanoes can also form where there is stretching and thinning of the crust’s plates, such as in the East African Rift and the Wells Gray-Clearwater volcanic field and Rio Grande Rift in North America.

Large eruptions can affect atmospheric temperature as ash and droplets of sulfuric acid obscure the Sun and cool the Earth’s troposphere. Historically, large volcanic eruptions have been followed by volcanic winters which have caused catastrophic famines.

Plate tectonics:

According to the theory of plate tectonics, Earth’s lithosphere, its rigid outer shell, is broken into sixteen larger and several smaller plates. These are in slow motion, due to convection in the underlying ductile mantle, and most volcanic activity on Earth takes place along plate boundaries, where plates are converging (and lithosphere is being destroyed) or are diverging (and new lithosphere is being created).

Divergent plate boundaries: At the mid-ocean ridges, two tectonic plates diverge from one another as hot mantle rock creeps upwards beneath the thinned oceanic crust. The decrease of pressure in the rising mantle rock leads to adiabatic expansion and the partial melting of the rock, causing volcanism and creating new oceanic crust.

Most divergent plate boundaries are at the bottom of the oceans, and so most volcanic activity on the Earth is submarine, forming new seafloor. Black smokers (also known as deep sea vents) are evidence of this kind of volcanic activity. Where the mid-oceanic ridge is above sea level, volcanic islands are formed, such as Iceland.

Aerial view of the Barren Island, Andaman Islands, India, during an eruption in 1995. It is the only active volcano in South Asia.

Cordillera de Apaneca volcanic range in El Salvador. The country is home to 170 volcanoes, 23 which are active, including two calderas, one being a supervolcano. El Salvador has earned the epithets endearment La Tierra de Soberbios Volcanes, (The Land of Magnificent Volcanoes).

Convergent plate boundaries:

Subduction zones are places where two plates, usually an oceanic plate and a continental plate, collide. The oceanic plate subducts (dives beneath the continental plate), forming a deep ocean trench just offshore.

In a process called flux melting, water released from the subducting plate lowers the melting temperature of the overlying mantle wedge, thus creating magma. This magma tends to be extremely viscous because of its high silica content, so it often does not reach the surface but cools and solidifies at depth. When it does reach the surface, however, a volcano is formed.

Thus subduction zones are bordered by chains of volcanoes called volcanic arcs. Typical examples are the volcanoes in the Pacific Ring of Fire, such as the Cascade Volcanoes or the Japanese Archipelago, or the Sunda Arc of Indonesia.

Map showing the divergent plate boundaries (oceanic spreading ridges) and recent sub-aerial volcanoes (mostly at convergent boundaries)

Stratovolcanoes (composite volcanoes):

Stratovolcanoes (composite volcanoes) are tall conical mountains composed of lava flows and tephra in alternate layers, the strata that gives rise to the name. They are also known as composite volcanoes because they are created from multiple structures during different kinds of eruptions. Classic examples include Mount Fuji in Japan, Mayon Volcano in the Philippines, and Mount Vesuvius and Stromboli in Italy.

Ash produced by the explosive eruption of stratovolcanoes has historically posed the greatest volcanic hazard to civilizations. The lavas of stratovolcanoes are higher in silica, and therefore much more viscous, than lavas from shield volcanoes. High-silica lavas also tend to contain more dissolved gas.

Cross-section through a stratovolcano (vertical scale is exaggerated):
1. Large magma chamber
2. Bedrock
3. Conduit (pipe)
4. Base
5. Sill
6. Dike
7. Layers of ash emitted by the volcano
8. Flank
9. Layers of lava emitted by the volcano
10. Throat
11. Parasitic cone
12. Lava flow
13. Vent
14. Crater
15. Ash cloud


A supervolcano is a volcano that has experienced one or more eruptions that produced over 1,000 cubic kilometers (240 cu mi) of volcanic deposits in a single explosive event. Such eruptions occur when a very large magma chamber full of gas-rich, silicic magma is emptied in a catastrophic caldera-forming eruption. Ash flow tuffs emplaced by such eruptions are the only volcanic product with volumes rivaling those of flood basalts.

The material that is expelled in a volcanic eruption can be classified into three types:

Volcanic gases, a mixture made mostly of steam, carbon dioxide, and a sulfur compound (either sulfur dioxide, SO2, or hydrogen sulfide, H2S, depending on the temperature)
Lava, the name of magma when it emerges and flows over the surface
Tephra, particles of solid material of all shapes and sizes ejected and thrown through the air.

Volcano and Human:

Volcanic eruptions pose a significant threat to human civilization. However, volcanic activity has also provided humans with important resources.

Solar radiation graph 1958–2008, showing how the radiation is reduced after major volcanic eruptions

Sulfur dioxide concentration over the Sierra Negra Volcano, Galapagos Islands, during an eruption in October 2005

Schematic of volcano injection of aerosols and gases

Volcanoes on other celestial bodies:

There are several extinct volcanoes on Mars, four of which are vast shield volcanoes far bigger than any on Earth. They include Arsia Mons, Ascraeus Mons, Hecates Tholus, Olympus Mons, and Pavonis Mons. These volcanoes have been extinct for many millions of years, but the European Mars Express spacecraft has found evidence that volcanic activity may have occurred on Mars in the recent past as well.

Olympus Mons (Latin, “Mount Olympus”), located on the planet Mars, is the tallest known mountain in the Solar System.

Jupiter’s moon Io is the most volcanically active object in the Solar System because of tidal interaction with Jupiter. It is covered with volcanoes that erupt sulfur, sulfur dioxide and silicate rock, and as a result, Io is constantly being resurfaced. Its lavas are the hottest known anywhere in the Solar System, with temperatures exceeding 1,800 K (1,500 °C). In February 2001, the largest recorded volcanic eruptions in the Solar System occurred on Io.

The Tvashtar volcano erupts a plume 330 km (205 mi) above the surface of Jupiter’s moon Io.

Europa, the smallest of Jupiter’s Galilean moons, also appears to have an active volcanic system, except that its volcanic activity is entirely in the form of water, which freezes into ice on the frigid surface. This process is known as cryovolcanism, and is apparently most common on the moons of the outer planets of the Solar System.

Where are most volcanoes located?

Pacific Ocean
Sixty percent of all active volcanoes occur at the boundaries between tectonic plates. Most volcanoes are found along a belt, called the “Ring of Fire” that encircles the Pacific Ocean. Some volcanoes, like those that form the Hawaiian Islands, occur in the interior of plates at areas called “hot spots.”

What is volcano explain?

A volcano is an opening in the earth’s crust through which lava, volcanic ash, and gases escape. … Beneath a volcano, liquid magma containing dissolved gases rises through cracks in the Earth’s crust.

What is the number 1 volcano in the world?
The most active volcanoes in the world

Kilauea volcano on Hawaii is the world’s most active volcano, followed by Etna in Italy and Piton de la Fournaise on La Réunion island.

13 thoughts on “Volcano

  1. Thanks for an interesting read. Here from the lovely, Tim Dittmer’s site.
    I was in Bali shortly before the eruption of Mt. Agung. It was quite the adventure with the island on alert, but I learned a lot about volcanoes on that trip. 🙂

    Eventually it did erupt about a month after I returned home, and has stayed active, erupting many more times since 2017 when I was there.

    Liked by 1 person

    • Yes, there is another volcano in Indonesia called Krakatoa. In August 1883, the eruption of the main island of Krakatoa killed more than 36,000 people, making it one of the most devastating volcanic eruptions in human history. Krakatoa is a small volcanic island in Indonesia, located about 100 miles west of Jakarta.

      Liked by 1 person

    • I think ,you should also read a article about Machu Picchu which I have posted. You will find it really interesting. I have embedded a song and movie which are filmed in Machu Picchu.


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