What is a Volcano.

The word volcano refers to a place (fissure or vent) where molten rock (magma), gasses or other debris erupts from the interior of the earth. The origin of the word volcano is associated with a Roman god of fire Vulcan.  According to Roman mythology, he was thought to carry his iron smelting activities on an active volcano named Vulcano at Lipari Island in Italy (Upton, 1565).
A progressive study of volcanoes, how they are formed and diversity of their formations has helped many scholars and other populations at large understand them better. Most of volcanic activities have been associated with destruction but most of spectacular and beautiful landforms have been as a result of volcanic activities (Williams, 14).
There are three elements involved in a volcanic system i.e.
A vent which is a point through which the volcanic material erupts to form a much or less symmetrical cone shaped structure called edifice.
The conduit which is the passage way of the magma to the surface. This is connected to the magma chamber. Due to instability of some eruptions, there develops some fractures from sides of the cone towards the central vent. These fractures act as passages of flank eruptions on the sides of edifice to form parasitic cones. At some times volcanic gases escapes through these vents hence earning the name of fumaroles.
A reservoir which holds the magma deep in the crust of the earth.
Volcanoes are formed through a process called volcanism. Underneath the earths crust, there are molten rocks called magma. For an eruption to occur, there must be a change in pressure at the reservoir so as to overcome the resistance pressure produced by the earth crust. Such changes are brought up by activities like earthquakes, plate tectonics, melting of glacier, changes in tides and rainfall (Williams, 19).  On reaching the earths surface, this liquid magma is called lava.  Other solid materials consisting of rocks, ash, cinders which are fragments of lava and light- weight rocks called pumice which resulting from explosive volcanic eruptions are known as tephra.
Volcanic activities are not limited to earths surface as they do also occur on other planets. Undersea volcanic activity produces landforms known as Submarine or Underwater volcanoes.
How it occurs.
 The origin of a volcano is when molten rock material also known as magma and associated gases finds their way into the surface of the earth. Rocks beneath the earths crust are held under great pressure and very high temperatures hence existing in a semisolid state and at a slightest opportunity the magma spews out to balance the pressure.
Volcanoes exist in three stages in their life cycle
Active stage, which is an early stage and eruptions are frequent.
Dormant stage, when the eruption becomes less frequent (sleeping stage).
Extinct stage, when there has been no eruptions in n a long historic time. They are however grouped according to the way they appear on the surface of the earth. The resulting mound of volcano is called cone which consists of lava and rocks exuded from the crust by the molten magma (Scarth, 26). Other constituents are ash and cinders (small lava fragments) The prominent shape and size of cone is dictated by the type of eruption and cones material
 There are of three major types which are defined by their form and composition
1. Composite Volcanoes (Stratovolcano)
This appears as a cone shaped mountain whose slopes are smooth, steep and bare.  Active ones have a prominent plume of smoke from one central vent. Lava emitted is usually thick and solidifies fast before flowing for a long distance. At times, alternate layers of lava and ash are formed. Example is Mt. Kilimanjaro in Tanzania and Vesuvius in Italy.  In case of a violent explosion the top part is blown off leaving a huge crater like depressions called a caldera. Other calderas are formed by subsidence when the supply of magma is depleted. This forms a good site for a lake i.e. Crater Lake in USA (Morton, 35). Other examples are Arenal and Irazu volcanoes in Costa Rica.
Shield or Lava cone volcanoes.
This type of volcano is mainly made of fluid lava flow and appears as a large volcanic dome structure with long gentle slopes. At times this kind of volcano can have multiple vents producing lavas flows. A good example of this is Mauna Loa in Hawaii.
3.  Ash Cinder cone Volcanoes.
This type of volcano is produced through accumulation of loose pieces of magma known as scoria that fall and accumulates around the vent after a moderate explosive activity. Examples include Volcano De Fuego in Guatemala and Paricutin in Mexico. Other landforms produced by fissure eruptions that covers a large area and its features are lava plateaus, When water comes into contact with hot rocks underneath on its way out it results to a hot springs and geysers. The main difference between hot spring and a geyser is the pressure in which hot water exits the ground (Chester, 1567). For a geyser, water is ejected explosively. Hot springs are common in Iceland and geysers are found along the floor of the Great Rift Valley in East Africa.
Although many volcanoes are known to start on earth, there are many more volcanoes that start at the bottom of the ocean. These are known as Submarine or Underwater volcanoes. Most of these eruptions occur along the plate tectonic lines where plate movements are common. This is however not limited to the deep waters as it can occur on shallow waters ejecting magma and other contents on surrounding land (Upton, 76). There are about 5,000 active underwater volcanoes. Every year, underwater volcanoes accounts for more than 75 of the total lava that erupts. The eruption of a submarine volcano is very different from surface volcano due to the unlimited supply of water to cool the hot lava.
Upon eruption, a shell of lava solidifies immediately around the lava forming what is known as pillow lava. These volcanoes are responsible for formation of islands i.e. Hawaiian islands. There has been a great handicap in study of submarine volcanoes due to the environment which they occur in. It is worth noting at this point that the biggest submarine volcano is in Hawaii (Scarth, 92). It is also actually taller than the tallest mountain on the earth surface, Mt Everest if measured from the sea floor.
In general therefore, Volcanoes are caused by pressure that builds below the earth crust and it is forced to erupt by magma through weak points of the earth surface. When the magma inform of lava cools it forms rocks. The volcanoes are very active and it is very dangerous for lives of any living organism. If there is likelihood of volcano formation then the area of formation should be cleared completely so that there are no cases of injuries or death. Mountainous areas are the most areas that are affected by volcanoes and people should take care when living in such areas. The topic of volcanoes has been covered comprehensively by the author.


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