PRESENTED BY GOWRI V PRABHU
Volcano refer to the eruption of hot molten lava from below the surface of earth.
A volcano is a vent in the earth’s crust through which Lava, Steam, ashes etc. are expelled.
RING OF FIRERING OF FIREA zone along the edge of Pacific Ocean that has
many Volcanoes and Earthquakes.The horseshoe shaped 40,000 kilometre long
belt is characterized by higher volcanic activity. The Ring of Fire is a string of volcanoes that
runs around the edge of the Pacific Ocean.
•A string of 452 volcanoes stretches from the southern tip of South America, up along the coast of North America, across the Bering Strait, down through Japan, and into New Zealand
HOW ARE THEY FORMED ?• When tectonic plates collide and go through the
process of subduction, it sets the foundation for a volcano. The overlapping of the tectonic plates causes the magma to break through the crust, which is the cause of a volcanoes' birth.
• When temperature and pressure rises, the rock melts and moves through the surface and crust, and releases gases and magma, volcanic eruption occurs.
The narrow opening of a volcano is called Vent. The upper part of vent is a cup shaped depression called Crater.
The rock material ejected during volcanic activity is deposited on surface of Earth. It is called Lava.
Pyroclastic Flow is fluidized mixture of solid to semi-solid fragments.
It is characterized by hot expanding gases that flows down the flank of volcanic edifice.
• Pyroclastic flows are mixtures of hot gas, ash and other volcanic rocks travelling very quickly down the slopes of volcanoes. They are one of the most dangerous hazards posed by volcanoes.
Viscosity - the property of a fluid that resists the force tending to cause the fluid to flow
Magma - molten material beneath or within the earth's crust, from which igneous rock is formed
Lava - the molten, fluid rock that issues from a volcano or volcanic vent
Ash - the powdery residue of matter that remains after burning
Caldera - A large crater formed by volcanic explosion or by collapse of a volcanic cone.
DEFINITIONSDEFINITIONS
VOLCANOES CAN BE IN ONE OF THREE PHASES: ACTIVE, DORMANT, AND EXTINCT. Active volcanoes are ones that have erupted in the
past 10,000 years, and that are likely to erupt again. An example is Mt. Saint Helens in U.S.A.
Dormant volcanoes are ones that have not erupted in the past 10,000 years, but still have the possibility, though unlikely. An example is Mt. Rainier in the U.S.A.
Extinct volcanoes are one which no eruption has occurred within historic times and future occurrences are highly improbable . An example is Mt. Ashitaka in Japan.
HOTSPRINGS AND GEYSERSHOTSPRINGS AND GEYSERS•A natural spring of mineral water at a temperature of 21°C (70°F) or above, found in areas of volcanic activity is called Hotspring.
• A hot spring that intermittently sends up fountain like jets of water and steam into the air is known as a Geyser.
There are three major types of volcanoes:
Shield volcanoes
Composite volcanoes
Cinder cone volcanoes
SHIELD VOLCANOES• The magma inside a shield volcano is
rich in iron and magnesium and is very fluid.
• Since the magma is very fluid, the lava coming out of the volcano tends to flow great distances.
• When shield volcanoes erupt, the flowing lava gives the volcano the shape of a gently sloping mountain.
COMPOSITE VOLCANOES• The magma inside a composite
volcano is rich in silica and much thicker than magma from a shield volcano.
• Gases get trapped inside this thicker magma.
• Eruptions from composite volcanoes can be flowing lava or explosions. The explosive eruptions come from the trapped gases and produce cinders and ash.
CINDER CONE VOLCANOES• The magma inside a cinder cone
volcano has large amounts of gas trapped in it.
• Eruptions from cinder cone volcanoes are violent and explosive because of all the gas trapped in the magma.
• The large amounts of hot ash and lava thrown out of the vent fall to the ground forming the cone shape that these volcanoes have.
CAUSES OF VOLCANIC ACTIVITYCAUSES OF VOLCANIC ACTIVITY
•When a part of the earth's upper mantle or lower crust melts, magma forms. A volcano is essentially an opening or a vent through which this magma and the dissolved gases it contains are discharged.
SEVERAL PROCESSES ASSOCIATED SEVERAL PROCESSES ASSOCIATED WITH MECHANISM OF VOLCANISMWITH MECHANISM OF VOLCANISM
• A gradual increase of temperature with increasing depth at the rate of one deg. Celsius for every 32 minutes.
• Gases and Vapours are formed due to heating of water, which reaches underground through percolation.
• The ascent of magma forced by vast volume of gases and water vapour.
• The occurrence of Volcanic Eruption
EFFECTS OF VOLCANIC ERUPTIONSEFFECTS OF VOLCANIC ERUPTIONS
•The effects of volcanic eruptions can be divided into primary and secondary effects.
•The primary effects are immediate and come from the eruption itself.
•The secondary effects result from the primary effects.
Volcanic gases: All magma contains dissolved gases. These gases are mainly steam, carbon dioxide and compounds of sulphur and chlorine.
Lava flows: These are streams of molten rock.Pyroclastic flows - These are high speed
avalanches of hot ash, rock fragments and gas which move down the sides of a volcano. These flows occur when the vent area or ash column collapses.
Lahars - These are mixtures of water, rock, ash, sand and mud that originate from the slopes of a volcano. Lahars often happen because of heavy rainfall erodingvolcanic deposits.
Landslides - Heat from cooling magma can cause hydrothermal alteration of the rocks, turning sections of them into clay. This weakens the rocks and increases the risk of slope failures.
Flooding - Explosive eruptions can change the surface areas around a volcano and disrupt drainage patterns, leading to long-term flooding.
Other secondary effects include:
Food / water supply interrupted.Homelessness.Businesses forced to close.Cost of insurance claims.Unemployment.Long-term issues with the tourism
industry.
•Volcanoes are caused when molten rock (magma) flows out onto the earth’s surface through fissures that are caused due to the movement of plates
•Though volcanic eruptions are threats to human life, the areas
where the eruptions have taken place are useful too. They have
helped to create beautiful Hawaiian Islands.
•These areas are rich in minerals.
• Volcanic Eruption cause heavy damage to human life and
property.
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