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What is a Volcano?

21-NOV-2014 11:15

    A volcano is a region on the Earth’s surface where hot lava, gases and volcanic ash erupt through the earth’s crust. Literally, the word volcano comes from the name of the Roman God of Fire, Vulcan. These volcanoes exist on the Earth because its crust is divided into 17 solid tectonic plates which float on extremely hot and soft layer in the Earth’s mantle. Hence, on this planet, volcanoes are usually found where tectonic plates are diverging or converging.

    Hawaii’s Mauna Loa is the largest volcano on this planet. Mt. St Helens in USA is the most active volcano. Olympus Mons on the planet Mars is the largest volcano in the Solar System.

    Types of Volcanoes

    The volcanoes are classified on the basis of their frequency of eruption.

    1. Active Volcanoes are those that erupt regularly. One example of the active volcano is Kilauea, the famous Hawaiian volcano, which has been continuously erupting since 1983, and has the longest lava lake. Another example is Mount Yasur, in Vanuatu, which has been erupting continuously for over 800 years.
    2. Extinct volcanoes are those that are not expected to erupt again, because the volcano does not consist of magma. Some extinct volcanoes are found on the Hawaiian-Emperor Seamount Chain in the Pacific Ocean. Hohentwiel, Shiprock and Zuidwal volcanoes in Netherlands are also examples of extinct volcanoes.
    3. Dormant volcanoes are those that have erupted in historical times but are now inactive. Volcanoes may remain dormant for a long period of time. For instance, Yellowstone has a recharge period of approximately 700,000 years.

    Effects of Volcanoes

    • There are various types of volcanic eruptions:
    • Phreatic eruptions are steam-generated eruptions
    • Explosive eruption of lava with high silica level
    • Effusive eruption of lava with low silica level
    • Pyroclastic flow is a fast-moving current of hot gas and rock
    • Debris flow
    • Carbon dioxide emission

    All these volcanic eruptions can cause hazard to human life, as these activities are accompanied by earthquakes, hot springs, geysers and mud pots. In 1815 AD, the eruption of Mount Tambora leads to global climate abnormalities popularly known as the “Year Without a Summer”. As a result of this volcanic activity, agricultural crops and livestock died in most of the regions of the Northern Hemisphere. This is the considered the worst famines of the 19th century.

    Weathering and Erosion

    The Solar System

    Standard Time and Time Zones

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