By ARILESERE FATIU .O Matric Number: 04/25OC013Department of Science Education (Edu-Tech) University of Ilorin
Volcano, mountain or hill are formed by the accumulation of materials erupted through one or more openings (called volcanic vents) in the earths surface. The term “volcano” can also be referred to as vents themselves. Most volcanoes have steep sides, but some can be gently sloping mountains or even flat tablelands, plateaus, or plains. The volcanoes above sea level are the best known, but the vast majority of the worlds volcanoes lie beneath the sea, formed along the global oceanic ridge systems that crisscross the deep ocean floor. According to the Smithsonian Institution, 1,511 above-sea volcanoes have been active during the past 10,000 years, 539 of them erupting one or more times during written history. On average, 50 to 60 above-sea volcanoes worldwide are active in any given year; about half of these are continuations of eruptions from previous years, and the rest are new.
A volcano is an opening, or rupture, in a planetssurface or crust, which allows hot, molten rock, ash,and gases to escape from below the surface. A Volcano can also be referred to as vents asmention in the introduction above. Volcanic activitysuch as the extrusion of rock tends to form mountainsor features like mountains over a period of time.
All volcanoes are formed by the accumulation of magma (moltenrock that forms below the earths surface). Magma can erupt throughone or more volcanic vents, which can be a single opening, a cluster ofopenings, or a long crack, called a fissure vent. It forms deep withinthe earth, generally within the upper part of the mantle (one of thelayers of the earth’s crust), or less commonly, within the base of theearths crust. High temperatures and pressures are needed to formmagma. The solid mantle rock must be melted under conditionstypically reached at depths of 80 to 100 km below the earth’s surface.Once tiny droplets of magma are formed, they begin to rise becausethe magma is less dense than the solid rock surrounding it. Theprocesses that cause the magma to rise are poorly understood, but itgenerally moves upward toward lower pressure regions, squeezinginto spaces between minerals within the solid rock.
As the individual magma droplets rise, they join to form ever-larger blobs and move toward the surface. The larger the risingblob of magma, the easier it moves. Rising magma does notreach the surface in a steady manner but tends to accumulate inone or more underground storage regions, called “MagmaReservoirs”, before it erupts onto the surface. With eacheruption, whether explosive or non-explosive, the materialerupted adds another layer to the growing volcano. After manyeruptions, the volcanic materials pile up around the vent orvents. These piles form a topographic feature, such as ahill, mountain, plateau, or crater, that we recognize as a volcano.Most of the earths volcanoes are formed beneath theoceans, and their locations have been documented in recentdecades by mapping of the ocean floor.
Three different types of materials may erupt from an active volcano.These materials are :1. Lava: is magma that breaks of the earth the surface and erupts from a volcano2. Tephra or pyroclastic : is made of rock fragments formed by explosive shattering of sticky magma, and3. Gases: are primarily in the form of steam and are released from volcanoes during eruptions. Gases come from the magma itself or from the hot magma coming into contact with water in the ground. Volcanic plumes can appear dark during an eruption because the gases are mixed with dark coloured materials such as tephra.The type and amount of the material that erupts from an activevolcano depends on the composition of the magma inside the volcano.Below are the diagram of each of the following volcanic materials.
Volcanoes come in different shapes andsizes, depending on the makeup of themagma, the style of the eruption, and how oftenthey erupt. The major types of volcano are:cinder cones;composite volcanoes (also knownstratovolcanoes);shield volcanoes;calderas andplateaus.