Geology And Geophysics
Formation of a volcano

How are Volcanoes Formed

Formation of a volcano
Jose Juan Gutierrez's image for:
"How are Volcanoes Formed"
Caption: Formation of a volcano
Image by: Worldtraveller
© public domain

A volcano is a geological fracture or opening in the Earth's crust caused by tremendous internal forces, such as pressure and temperature inside the Earth. These dynamic internal forces push magma and gases up through a volcano's vent. Once these volcanic materials reach the surface of the Earth, they break down, condense or harden around a volcano's vent. Over many thousands or millions of years, the collection of lava forms steep-sided cones known as volcanoes. Since the formation of the Earth, volcanoes have been erupting molten material due to intense pressure build-up in the Earth’s interior, and they have produced the configuration of the varied landscapes that are part of the planet. Volcanoes are often formed where tectonic plates converge or diverge (for instance along Mid-Ocean Ridges and subduction zones).

 How a volcano is formed?

The Earth’s crust contains various sections of rock known as tectonic plates. Tectonic plates are like puzzle pieces that, moving constantly against each other. Volcanoes often form along where plate tectonics make contact. The friction produced melts the Earth’s crust, creating magma. Extremely heated magma creates pressure and slowly rises to the surface through the fractures between the tectonic plates. Over time it finds its way out through a volcanic vent. When the magma spews out of the vent, it is called lava. Most volcanoes are created along divergent tectonic plates in mid-ocean ridges.

Where are volcanoes found?

Most volcanoes are formed on the ocean floor, while other volcanoes may be formed at subduction zones, which is the region where one oceanic plate sinks underneath one continental plate. The friction produces magma. The magma rises due to pressure and heat, and when it reaches the surface of the Earth, then, a volcano is born. Mt. Etna in Italy was formed in this way. Other volcanoes may form near or in the middle of tectonic plates, including hotspots and Island Arcs. Some others may form on continental land, such as in the Continental Rifts.

While most volcanoes occur at mid-ocean ridges; however, there are some volcanoes that form on land. Some volcanoes form away from the point of tectonic contact, and are known as hotspots. They are formed from rising magma intrusions known as mantle plumes. Hotspots are magma chambers regions that are stationary under the Earth’s crust. When a mantle plume gives rise to a volcano over hotspot, the displacement of the continental plate moves the new formed volcano, and exposes new parts of the tectonic plate for more volcano formations. This process of volcano creation is known as volcanic chains. An example of this type of formation is the Hawaiian Islands.

What volcanoes do

The damage that volcanic eruption produces is often measured by volume and density. Distance attenuates the damage that lavas and pyroclastic flows might produce.  Lahars and debris drag everything along their path, rarely permitting survival in the proximities of the volcano; however, in isolated spots, some organisms may survive. Tephra deposits become thinner at larger distances, and biota survival is possible. The 1980 Mt. St. Helens eruption demonstrates that some plant species, such as rhizomatous are likely to survive. And other species may survive on soil blocks and wads. While blasts may produce minimum damage to plants that grow on or below the ground, tephra impacts can severely damage mosses, lichens, mat formers, low herbs and other plants incapable of thriving through thick deposits.

Volcanic eruptions affect people in varied ways. Pyroclastic flows, which are mixtures of hot gases, volcanic fragments, pumice, ash, ice and glass shards, can move at high speeds (100-200 km/h, 60-120 miles/ h) and reach long distances. Volcanic plums can worsen existent respiratory problems. Lahars, which are mixtures of rock and debris, can flow down the slopes of a volcano at speeds of 100 km/h (60 miles/h). A lahar killed 23,000 people in Armero, Colombia in 1985. According to, the positive side of volcanic eruptions is that they produce rich soils for farming.

More about this author: Jose Juan Gutierrez

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