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VOLCANISM (Basic Terms (Pluton Used to describe all forms of igneous…

- - - - Sill (Concordant)
        Flat sheet like igneous intrusion
        E.g Greart Whin Sill of N.E. England
      - Dyke (Disconcordant)
        Thin wall like igneous intrusion
        They are the most commonly found intrusive forms in the western Maharashtra area.
        E.g. Cleveland Dyke of Yorkshire, England
      - Batholith ( Disconcordant)
        Huge igneous intrusion of great depth
        Covering large area (more than 100 sq. km)
        Irregular in shape
        Intrudes across the layers of country rocks.
        Appear on the surface only after the denudational processes
        remove the overlying materials.
        It lies often at the centre of major mountain ranges like Himalayas.
        They are the cooled portion of magma chambers
        It cools very slowly resulting in very coarse grained granite like structure
      - Lopolith (Concordant)
        Saucer shaped igneous intrusion in a syncline
        E.g. Bushveld lopoliths of Transvaal, South Africa
      - Phacolith (Concordant)
        Lens shaped igneous intrusion in a syncline or over an anticline
        They have a definite conduit to source beneath in the form of magma chambers.
        Eg. Corndon Hill in Shropshire, England
      - Laccolith (Concordant)
        Lens shaped igneous intrusion with a flat base( or mushroom shaped ), and connected by a pipe-like conduit from below ,that forces the overlying strata into a dome
        Eg. Laccoliths of Karnataka Plateau
    - - Batholith
        Huge igneous intrusion of great depth
        
        Stock
        Collective term for all smaller size igneous intrusion
      - Concordant
        Follow the existing bedding planes of country rocks.
        
        Disconcordant
        Breaks right through existing bedding plane
  - - - Plug (Spine)
        A plug is a tower/pillar of hard rock left by volcano.
        It is inherently a weak structure.
      - Crater
        It is a funnel( bowl) shaped depression, usually round with steep sides
        It may result into a lake called crater lake.
      - Scoria
        It refers to bubble filled stones ejected from a volcano.
        Eg. Pumice stone
      - Cinder cone
        Small cone shaped hill usually less than 450m height.
        It has a truncated top.
        It is the result of accumulation of large quantities of cinder thrown out during moderately explosive eruption.
      - Caldera
        It is very large basin shaped crater .
        They are found at the tops of volcanoes where the original crater has collapsed.
        The basin , which is many times larger than the original volcanic vent, may be flooded to produce a lake or,
        the flat floor may contain a number of small volcanic cones produced by volcanic activity after the collapse.
        Eg. Lake Toba in Sumatra
      - Strato-volcano (Composite cone)
        Found in highest and most common volcanoes
        It has alternate layers of lava and ash.
        It is conical in shape with steep sides.
        Eg. Mt. Stromboli ( Lighthouse of the Mediterranean)
        Mt. Fuji
      - Parasitic cone
        From the main conduit of volcanic cone, subsidiary pipe/dike may reach the surface as feeders to parasitic cones.
      - Large igneous province or Flood basalt
        This region in geological past experienced numerous fissure type eruptions of basaltic lava
        Eg. Deccan trap
        Weathering of lava has resulted in black cotton soil which is one of the finest examples of a parent material controlled soil .
        Trap in Swedish means a step like formation .
    - - Lava
        Molten material which gets properly solidified.
      - Ash
        Sand sized volcanic material
      - Dust
        Extremely fine volcanic material
      - Cinders
        Half burnt material
      - Tephra
        These are fragments thrown into air by volcanic eruption.
        Larger fragments are called Volcanic bombs.
        Smaller chunks are called Lapilli.
      - Pyroclastic materials
        They include molten material into air that may solidify in flight or at surface and solid lava fragments of various sizes.
      - Lahar
        Volcanic ash and dust with water makes mud flow.
        Lahar refers to torrential mudflows of wet volcanic materials.
        These are very dangerous mass movements.
      - Aa
        It is a Hawaiian word for jagged ( angular) ,chunky ( blocky) lava.
        This formation is a result of more viscous lava.
      - Pahoehoe
        It is a Hawaiian word used for ropy lava formation.
        It is the result of lava which is less viscous.
        Lava may cool quickly to develop a thin skin.
        If the lava continues to flow underneath, the surface wrinkles into rope like coils called Pahoehoe.
      - Gases
        Eg. nitrogen compounds, sulphur compounds and minor amounts of chlorene, hydrogen and argon