Volcanoes-Types, Causes and Effects
A volcano is a vent on the surface of the earth from which hot molten magma,solid rock pieces,ash and other gases are erupted and spread on the surface of the earth. When volcanoes erupt, they present the scene of bursting and burning of a mountain.
A volcano has a vent or pipelike opening through which gases and other materials erupt. This pipe remains connected with the magma chamber inside the earth.
Causes of Volcanic Eruptions
According to geologists and other scientists, following could be the causes of volcanic eruptions:
- Crustal Disturbances: The crustal disturbances are closely related to volcanic eruptions. Folding and faulting lessens the pressure on the underlaid rocks. It causes the formation of magma due to melting of solid rocks. This rising magma on finding weakness in the earth crust breaks it open to erupt on the surface of the earth as a volcano.
- Weak Zones in the Earth Crust: The parts of the earth where two tectonic plates collide against or drift apart from each other are considered very weak. For example- African and Eurasian plates lie to the east of mid atlantic ridges and to their west lies the American plate. These plates are drifting apart from each other. Against this, the American plate is colliding against the East Pacific plate near Andes mountain ranges and going under the East Pacific plate. The edges of the plate while being drawn under the East Pacific plate are being melted to form magma which erupts on the surface. It is on this account that volcanic eruptions take place on the mountain ranges of Andes and Rockies.
- Magma Saturated with Gases: The magma, in the interior of the earth is often found saturated with gases like carbon dioxide, Hydrogen sulphide and also in small quantities nitrogen, chlorine gas and other explosive materials. These gases together with water vapour makes the magma highly explosive. On account of the pressure exerted by these gases, magma is thrown out as lava on the surface of the earth.
In this manner, volcanoes act as safety valves of hidden energy of the earth. The accumulated energy deep inside the earth finds its way out on the surface through a volcanic eruption and calmness returns to the interior for a while.
Types of Volcanoes
Based on the frequency of eruption, there are three types of volcanoes:
- Active Volcanoes: These are volcanoes which erupt frequently. Generally their vent remains open. Mount Etna of Italy, Cotopaxi in Equador are some examples.
- Dormant Volcanoes: These volcanoes may not have erupted during known geological period but there is a possibility of their erupting any time. In other words, they may lie dormant awaiting active eruption anytime. Sometimes gases and steam comes out of them. They cause great destruction of life and property once they become active again. Visuvious Volcano of Italy is an example.
- Extinct Volcanoes: These volcanoes have exhausted their energy and have not erupted during the known geological period. The vent of these volcanoes remains closed with solidified lava. The formations such as craters may be filled with water and crater lakes may be formed. The slopes of these landforms may be covered with vegetation. Popa in Myanmar is an example of extinct volcano.
On the basis of nature of eruption and form developed on the surface, they are classified into following types:
- Shield Volcanoes: These are made up of basalt, a type of lava that is very fluid when erupted. They become explosive when water gets into the vent. They develop into a cinder code. Hawaiian volcanoes are examples of this category.
- Composite Volcanoes: These volcanoes are explosive and along with lava, they erupt large quantities of ashes and pyroclastic material. This material form layers near the vent opening. Mount Fuji in Japan, Mount Rainier in USA are examples.
- Caldera: These are the most explosive volcanoes. When they erupt they tend to collapse on themselves rather than building any tall structures. These collapsed depressions are called calderas. Yellowstone, Mount Mazama are examples.
- Flood Basalt Provinces: Lava of these volcanoes flows for long distances and form basalt provinces. They cover broad regions with lava surfaces. Deccan Traps of India, Siberian Traps are examples of flood basalt provinces.
- Mid-Oceanic Ridge Volcanoes: These occur in the oceanic areas. The central portion of mid oceanic ridge experience frequent eruptions.
Effects of Volcanic Activity
The volcanic eruption is the most dangerous phenomenon. Their sudden eruption causes great upheaval on the surface of the earth. Hundreds of tonnes of burning rocks, dust and ash are thrown up in the sky. The clouds of smoke rise up several kilometers in the atmosphere. A huge river of molten lava flows down the slopes. Everything that comes in its way- trees, animals, humans and their houses and factories are engulfed in flames and lapped up in the fiery flowing river. Effects of volcanoes include:
- Volcanoes make several types of landforms. Fujiyama mountain in Japan and Malwa plateau in India are the result of volcanic activity.
- Regur soils are formed on lava plateaus. These soils are highly fertile for growing cotton.
- At many places near the volcanoes, sulphur, boric acid and pumice are found.
- Many minerals come to the surface with volcanic eruptions. Silver, Zinc, Copper and other metals are also obtained. Iron ore deposits in Sweden are of volcanic origin.
- Volcanoes are sources of hot water springs. Many skin diseases are cured by bathing in this water.
- Crater lakes made by volcanoes are of great use in irrigation.
- Volcanoes also helps in knowing about the interior of the earth. The molten magma which comes out of the volcanoes can be studied to understand the materials found inside the earth.
- They cause enormous loss to life and property and submerges a vast area causing destruction of vegetation.
Have you ever seen a volcanic eruption?
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