Volcano Eruption: A Spectacular But A Deadly Phenomenon of Nature

What is a Volcano?

A volcano is a crack in the crust of a planet, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber beneath the surface.

Volcanoes are most commonly found where tectonic plates are diverging or converging on Earth, and the majority are found underwater. The Mid-Atlantic Ridge, for example, 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 the crust's plates are stretching and thinning, as in the East African Rift and the Wells Gray-Clearwater. Upwelling diapirs from the core-mantle boundary, 3,000 kilometers (1,900 miles) deep in the Earth, are thought to cause volcanism away from plate boundaries. This results in hotspot volcanism, such as the Hawaiian hotspot. Volcanoes are rarely formed when two tectonic plates slide past each other.

As ash and droplets of sulfuric acid obscure the Sun and cool the Earth's troposphere, large eruptions can affect atmospheric temperature. Large volcanic eruptions have historically been followed by volcanic winters, which have resulted in catastrophic famines.

Volcanoes can be found on planets other than Earth. Mercury, for example, has pyroclastic deposits caused by explosive volcanic activity.

Tectonics Plate

The Earth's lithosphere, its rigid outer shell, is divided into sixteen larger and several smaller plates, according to plate tectonics theory. These are moving slowly due to convection in the underlying ductile mantle, and most volcanic activity on Earth occurs along plate boundaries, where plates are converging (and destroying the lithosphere) or diverging (and new lithosphere is being created).

Plate Boundaries 

Divergent: Two tectonic plates diverge at the mid-ocean ridges as hot mantle rock creeps upwards beneath the thinned oceanic crust. The decrease in pressure in the rising mantle rock causes adiabatic expansion and partial melting, resulting in volcanism and the formation of new oceanic crust. Because most divergent plate boundaries are at the ocean's bottom, most volcanic activity on Earth is submarine, forming new seafloor. This type of volcanic activity is evidenced by black smokers (also known as deep sea vents). Volcanic islands, such as Iceland, form where the mid-oceanic ridge rises above sea level.

Convergent: Subduction zones are areas where two plates collide, usually an oceanic plate and a continental plate. The oceanic plate subducts (dives beneath the continental plate), resulting in the formation of a deep ocean trench just offshore. Water released from the subducting plate lowers the melting temperature of the overlying mantle wedge, resulting in magma formation. Because of its high silica content, this magma is extremely viscous and rarely reaches the surface, instead cooling and solidifying at depth. When it does reach the surface, however, it creates a volcano. Subduction zones are thus bounded by volcanic arcs, which are chains of volcanoes.

Volcano Types

Active

Volcanoes still having a supply of magma are generally classified as active and erupt more frequently. The recent eruption of Mauna Loa in Hawaii and the Merapi volcano in Indonesia are an example of it. 

Dormant

As the word suggests the magma supply is not disconnected and might erupt without any sign of warning. Mount Fuji in Japan & Mount Kilimanjaro in Africa are examples of it

Extinct

Volcanoes whose magma supply is cut off and there is no chance of future eruption are termed as extinct volcanoes. Mount Thielsen in Oregon & Mount Slemish in Antrim.

How do Volcanoes Erupt?

Deep within the Earth, temperatures are so high that some rocks slowly melt and form magma, a thick, flowing substance. Magma rises and collects in magma chambers because it is lighter than the solid rock around it. Some of the magma eventually makes its way to the Earth's surface via vents and fissures. Lava is a term used to describe erupted magma.

Certain volcanic eruptions are explosive, while others are not. The explosiveness of an eruption is determined by the composition of the magma. Gases can easily escape from thin and runny magma. This type of magma flows out of the volcano when it erupts. The eruptions of Hawaii's volcanoes are a good example. Lava flows rarely kill people because they move slowly enough that people can avoid them. When magma is thick and sticky, gases cannot easily escape. Pressure builds up until the gases violently escape and explode. The Mount St. Helens eruption in Washington is a good example. The magma blasts into the air and breaks apart into pieces known as tephra in this type of eruption. Tephra can range in size from tiny ash particles to boulders the size of a house.

Volcanic eruptions can be deadly and explosive. They can shoot hot tephra clouds from the side or top of a volcano. These raging clouds tear down mountainsides, destroying nearly everything in their path. The ash that erupted into the sky has fallen back to Earth in the form of powdery snow. Ash blankets can suffocate plants, animals, and humans if they are thick enough. Mudflows form when hot volcanic materials mix with water from streams or melted snow and ice. Lahars (mudflows) have buried entire communities near erupting volcanoes.