A volcano is an opening in the crust of a planet or a vent from the planet's core, through which magma (molten rock found below the surface of the earth), hot ash, gas or steam can extrude to the surface. When magma erupts from a volcano, it is called lava. Volcanoes are one of the most destructive forces on Earth and cause many natural disasters.
Formation of Volcanoes
Volcanoes are created via three main tectonic processes. As tectonic plates move, shift, and bump against each other, one plate is subducted under the other; forming a subduction zone. This is why the majority of the world’s volcanoes are formed along the boundaries of the Earth’s tectonic plates.
In the subduction zone, the crust heats up and is melted into magma and gases. This can happen up to 100 miles below the earth. Magma then resides in pools or magma chambers, which are usually found in the Earth’s crust. This is where the volcanic eruptions take place.
Volcanoes can also be formed when the plates drift away from each other. The magma pushes up in the gap, forming lava. These types of volcanoes are mostly found on the ocean floor. One of the most well-known examples is the Mid-Atlantic Ridge.
Volcanoes can also form over ‘hotspots’, which are stationary points in the mantle, weakened by thermal plumes. Magma rises from within the Earth’s mantle through these points to the surface. This process is how the Hawaiian Islands are continuously formed.
National Geographic - How Volcanoes Form
Volcanoes are described in terms of their activity, and can be:
- “Active”- the volcano erupts frequently and has a lot of associated activity
- “Dormant”- the volcano is temporarily inactive, but not fully extinct
- “Extinct”- the volcano is not likely to ever erupt again.
There are 3 main categories of volcanoes that can be produced in these environments, which all have different shapes and types of eruptions.
A shield volcano is a large, broad volcano with gently dipping sides. They take this form because of the non-viscous, basaltic lava that flows up through the crust, forming layers that slowly build into a volcano.
In a sense, these volcanoes are constantly erupting, but the eruptions are very rarely explosive, unless there is an edition of volatile material to the magma chamber. These are known as effusive eruptions, shown by the 2018 activity of Hawaii's Kilauea volcano. The Hawaiian Islands can be classed as Shield volcanoes.
Lava Enters the Pacific Ocean in Hawaii
Composite volcanos, or stratovolcanos, form a ‘classic’ volcano shape; looking like steep-sided, mountains with a large crater at the summit. They are usually symmetrical, built from the various volcanic deposits they extrude.
Due to the viscosity of the lava produced in these environments, eruptions are more sporadic, but also more explosive than those of a shield volcano. These explosive eruptions can occasionally be devastating, such as in the case of Mt St Helens, Washington when it erupted in 1980.
Mount St. Helens Erupting
Cinder cone volcanoes are extremely common, although erupt very little in terms of lava. They are usually small, with one main vent, and can even form on the side of larger volcanoes as extra vents.
A typical eruption from a cinder cone throws a lot of glassy, obsidian fragments into the air which then fall back to earth to form the cone of the volcano. A typical cinder cone volcano is Paricutin, in the volcanic field of west-central Mexico.
Overview of Ores & Minerals Found in Volcanic Environments
A mineral is a solid material, which occurs naturally on Earth, with definitive boundaries around chemical and physical properties. An ore is a type of that rock that contains minerals (usually metals) that are of economic value. Ores are extracted through mining and are then refined to take out the valuable element or elements. It must be noted that ores can be native minerals themselves.
Many of the most important metals that are mined on Earth have their origins, either directly or indirectly, in volcanic environments. For example, a volcanic rock may not ever reach the Earth’s surface, and so will cool slowly under the crust in plutonic environments. This allows large crystalline deposits of metals to precipitate out in minable quantities.
For example, Bauxite is an ore that contains aluminium, which, in some locations, can be found in the volcanic rock basalt. Basalt typically is produced from shield volcanoes. Aluminium is also used in everyday things such as cars, light bulbs, drinking cans, and kitchen utensils.
Other metals formed in volcanic environments include gold silver, lead, copper, and zinc. These are associated with magmas found deep within the roots of extinct volcanoes.
Sources and Further Reading
This article was updated on the 20th March, 2019.