A volcano is a rupture in the Earth’s (or another celestial body’s) crust that allows hot lava, volcanic ash, and gases to escape from a magma chamber located beneath the surface. 1 On Earth, volcanoes are the result of the action between the major tectonic plates. These sections of the Earth’s crust are rigid, but sit atop the relatively viscous upper mantle. The hot molten rock, known as magma, is forced up to the surface – where it becomes lava. In short, volcanoes are found where tectonic plates are diverging or converging – such as the Mid-Atlantic Ridge or the Pacific Ring of Fire – which causes magma to be forced to the surface. Volcanoes occur when material significantly warmer than its surroundings is erupted onto the surface of a planet or moon from its interior. On Earth, the erupted material can be liquid rock ("lava" when it's on the surface, "magma" when it's underground), ash, cinders, and/or gas. There are three reasons why magma might rise and cause eruptions onto Earth’s surface.
The Earth's life, water and atmosphere would not exist without volcanoes. 2 Volcanoes are important for many reasons, including benefiting nearby plants with nutrient-rich ash, providing rare species with habitats that are inaccessible to humans and livestock, and enriching the atmosphere with gases. Volcanic gases released from vents since the Earth's formation are responsible for the atmosphere and oceans. While meteorites and comets also brought gases that helped build the atmosphere of the Earth, volcanic activity was probably the primary source of these gases. Over 80 percent of the surface of the Earth comes from volcanic activity. Volcanic eruptions produce everything from plains and hills to mountains and plateaus. Volcanic deposits are also used as building materials. Volcanoes continue to play an important role by adding to the Earth's water supply and forming new islands. Volcanic eruptions may slow climate change by releasing aerosols that help block sunlight into the Earth's stratosphere.
Volcanic eruptions result in ash being dispersed over wide areas around the eruption site. And depending on the chemistry of the magma from which it erupted, this ash will be contain varying amounts of soil nutrients. While the most abundant elements in magma are silica and oxygen, eruptions also result in the release of water, carbon dioxide (CO²), sulfur dioxide (SO²), hydrogen sulfide (H²S), and hydrogen chloride (HCl), amongst others. 3
In addition, eruptions release bits of rock such as potolivine, pyroxene, amphibole, and feldspar, which are in turn rich in iron, magnesium, and potassium. As a result, regions that have large deposits of volcanic soil (i.e. mountain slopes and valleys near eruption sites) are quite fertile.
Volcanoes also play a vital role in periodically cooling off the planet. When volcanic ash and compounds like sulfur dioxide are released into the atmosphere, it can reflect some of the Sun’s rays back into space, thereby reducing the amount of heat energy absorbed by the atmosphere. This process, known as “global dimming”, therefore has a cooling effect on the planet.
Outgassing and Atmospheric Formation
The most beneficial aspect of volcanoes is the role they play in the formation of a planet’s atmosphere. Us terrestrial organisms depend on them for everything from the air we breathe, to the rich soil that produces our food, to the geological activity that gives rise to terrestrial renewal and biological diversity.
Another Benefit for Life in Earthquakes
Volcanoes may have helped create life on Earth