Volcanism & Volcanic Landforms

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Types of Volcano
Characteristic of Magma/Lava
Basic/Basaltic lava
Acidic/Andetile lava
  • Less viscous & High fluid
  • Cover large area, flow quietly,   not explosive.
  • Iron + Mg high
  • Si – Poor Composition (Dark in   Colour)
  • Form Shield or Dome
  • More viscous
  • Cover small area, loud explosion  
  • Iron + Mg high
  • Si – Rich Composition (Light in   Colour).
  • Cone is therefore steep-sided.
  • Form spine or plug   at the crater. (Ex: Mt. Pelee in Martinique)
Mode of Eruption
Fissure Eruption type
Central Eruption type
  • Acquire Ocean floor/Crust
  • Rather than volcanic cone   volcanic plateaus. It creates in flood basalt
  • Acquire in Continental – Mostly   central eruptive.
  • Volcanic Mt or Cones
Frequency of Eruption
Active
Dormant
Extinct
  • More frequency volcanic   eruption.
  • Ex: Stromboli (light house of   mediterian sea), Etma, Baran island (only active volcano in India).
  • Once/long back eruptive, may be   future eruption possible.
  • Ex: Vesurious.
  • Once erupted but no future eruption   or No eruption in history but having features of volcano.
  • Ex: Mt. Kenya, Mt. Kilimanjaro   (Highest point in Africa), Narkondam island (India).
  • Krakatava – Between java & Sumathra island, Belive as dormant but it erupted in 1883.
  • Lake toba (Indonesia) – Only after it erupted it known as active volcano.
  • Mt. Krakatau & Mt  Vesivius – thought extinct, but both erupted most violently.
Landforms associate with volcano
  • Magma while solidify within the crust as plutonic rock resulting in intrusive landforms.
  • Magmas that reachs the surface and solidify, form extrusion landforms.
  • Rocks formed by either plutonic or volcanic activity are called igneous rock.
Extrusive
  • High fluid biuld up lava domes or shield volcanoes.
  • Less fluid lava exploded more violently from ash & cinder cones with large craters & steep slope.
  • Lava solidify after some distance, confined in valley, form lava tongues & lava-dammed lakes. Minor features lava bridge & lava tunnels.
  • Composite cones often called strato-volcanies – common volcano.
  • Coarser fragmental rock collectively called Pyroclasts. Includes lapilli, scoria, pumica & volcanic bombs.
  • New eruption added new layer.
  • Mt. Stromboli, frequently eruption – lighthouse of the Mediterranean.
Instrusive
  • Common intrusive landforms
    • Sills (horizontal) – Ex: Great Whin Sill of N.E.England.
    • Dykes (Vertical) – Ex: Cleveland dyke of Yorkshire.
  • Other types
    • laccolith – dome-shaped at upper & base fed by pipe like conduit from below. (Ex: Henry Mountains, in Utah U.S.A)
    • Lopolith – saucer shape. (Ex: Bushveld lopoliths of Transvaal, South Africa).
    • Phacolith – lens-shaped, crest of an anticline or bottom of Syncline. (Ex: Corndon Hills in Shropshire, England).
    • Bathilith – huge mass of igneous rock, usually granite. (Ex: Wicklow Mountains of Ireland, upland of Britanny,France).
Types of volcano based on shape and Nature
Shield Volcano
Cinder Cone Volcano
Composite Volcano
Lava Dome
  • Lava basis
  • Highest & largest.
  • Dome shape.
  • Central eruptive.
  • Barring the basalt flows.
  • Explosive if somehow water gets   into the vent.
  • Ex: Hawaii (US), Mt. Mauna
  • Relatively small
  • Cone like shape
  • Absence of lava eruption   domination of Pyroclastic material.
  • More dangerous
  • Acid lava
  • Presence of parasite cone.
  • Explosive eruption with large   quantities of pyroclastic material and ashes
  • Also called strata volcano.
  • Ex: Stromboli, Krakatuo
  • Lava domes are formed when erupting lava is too thick to   flow and makes a steep-sided mound as the lava piles up near the volcanic   vent. They are built by slow eruptions of highly viscous lava.

Carter & Caldara
  • Carter – Mouth of the Volcano.
  • Caldara – Also mouth of the Volcano (Enlarged carter/ crater within crater).
  • Water collect in Crater & Caldara form Crater & Caldara lake. Ex: Lake Toba in Sumatra.
Distribution
Pacific Ring of Fire or Circum Pacific Belt
  • Greatest concentration is probably that in the Circum-Pacific region.
  • Popularly ‘Pacific Ring of Fire’ (2/3 of World Volcano).
  • Atlantic coast – few active volcano & many dormant, extinct volcano.
  • Mediterranean region associated with Alpine folds.
  • In Africa, volcano along East African Rift.
  • West Africa – Mt. Cameroon only active volcano.
Geysers and Hot Springs
  • Geysers are fountain of hot water & superheated stream.
  • Emitted an explosive, often triggered off by gases seeping out of heated rock.
  • Three major areas
    • Icerland, the Rotorua district of North Island, new Zealand & Yellowstone park of USA.
  • Hot springs or thermal spring – water rises to the surface without any explosion. Contains Dissolved mineral & Medical value.

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