Volcanic Eruptions

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Lesson 2- Why do Volcanoes Erupt?
8:34 — by Erin Cawley

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Key Questions

  • Its acidity.
    That is the amount of silica dissolved in the magma.

    An "acid" volcano is explosive.
    A basic volcano lets its distructive lava gently flow out of the caldera.

    In the first case one finds all sorts of quartz crystals within the solidified lava. In the second one gets basalts, diorites, and other basic rocks.

    Hawaiian volcanoes are basic ones.
    The ones on the margin of the Pacific Fire Belt tend to be acid and explosive (think of Krakatoa).

    But this is only a general rule. Since volcanoes all have a personality and a life expectation. They are young and acid; old and basic and eventually phase out into "solfataras".
    In this moribund stage (that may last a few thousand years), all activity ceases except for geyser, fumaroles and thermal sources.

  • Answer:

    Volcanic eruptions are classified on base of their "Eruptive Styles"


    Geological research shows that....
    1. Some volcanoes erupt Clouds+Ashes+Debris, with very small amount of Lava.
    2.Some volcanoes erupt Lava, with very minor amount of Clouds+Ashes+Debris.

    Which type of material will be erupted by Volcanoes, totally depend upon its "Eruptive Styles".

    There are 2 types of eruptive styles of volcanoes.

    a) Effusive eruption:
    These eruptions produce mainly (Lava Flows), Lava flows are mainly of Basalt, having very low viscosity.
    Such type of eruptions result in the formation of "Shield Volcanoes".

    b) Explosive eruption:
    These eruptions produce clouds and avalanches of Pyroclastic debris.
    Such type of eruptions yield "Cinder-Cone Volcanoes" & "Composite Volcanoes"

  • Strato-volcanoes have cones composed alternately of lava flows and ash deposits. This implies that eruptions alternate between relatively peaceful ones entailing lava flows, and somewhat explosive ones that produce ash.