Geography Grade 9 icse

• what are active volcanoes?

  those that erupt in lava, gas, ash, cider, pumice etc in the recent historic periods.
• there are about 500 active volcanoes. name a few of them. 


  Mt. St Helna (USA), Mt Etna in Italy, Mt Stromboli, Mt Mauna Loa in Hawaii.
• What are Dormant Volcanoes?

  They are those that have erupted in the past but are likely to erupt afer being inactive for a long period of time.
• Name a few Extinct Volcanoes

  Mt Kilimanjaro in Africa, Mt Elburz in Europe, Mt Kenya, Mt Aconcagua in South America
• Name a few Dormant Volcanoes

  Mt Vesuvius standing 4000 feet above the Bay of Naples and some volcanoes in the West Indies, Philippines and Japan
• What are extinct Volcanoes? Those that were active in the remote geological periods.
• A volcano is a vent or narrow opening in the Earth's crust connected by a conduit to an underlying magma chamber through which magma, lava, rock fragments, ash, steam and other gases are emitted from the interior of the Earth
• Types of volcanoes based on frequency and intensity of eruption:

  • Active volcanoes
  • Dormant (Sleeping) volcanoes
  • Extinct volcanoes
• Active volcanoes have erupted in recent historic periods, with about 500 active volcanoes in the world. Examples include Mt. Stromboli, Mt. Etna in Italy, Mauna Loa in Hawaii.

  Dormant volcanoes have erupted in the past and are likely to erupt again after remaining inactive for a long period of time. Examples include Mt. Vesuvius, volcanoes of Japan, Philippines, etc.
• Two types of volcanic eruptions:

  1. Eruption through a point/opening on the Earth's surface (Conical Volcano)

  2. Eruption along a long narrow fissure in the crust (Shield Volcano or Lava Plateaus)
• Composite cones are cinder cones that grow into large volcanic hills with alternating layers of lava and ash. They are formed due to an explosive eruption followed by eruption of lava. Parasite cones develop on the slopes of the volcano when the main vent grows too high
• Two types of landforms formed due to the constructive effects of volcanoes:

  • Extrusive landforms
  • Intrusive landforms
• Lava plateaus are formed when magma erupts quietly through narrow fissures or cracks, spreading and cooling down as a sheet of lava. Examples include Deccan trap region or Deccan Plateau (India), Columbia plateau (Western USA), Antrim plateau (Northern Ireland)
• Extrusive landforms are formed by the solidification of lava on the surface of the Earth. Different extrusive landforms in a volcanic region include:

  • Volcanic cone (Cone-shaped hill)
  • Lava cones (Based on composition of lava)
  • Lava Plateaus (Due to Fissure eruptions)
• Differences:

  • Crater: Formed when a volcano erupts explosively, blowing up a portion of the summit to form a depression
  • Caldera: Formed when the summit of a volcano blows up during a violent explosion, forming a large depression
• Differences:

  • Acid Lava: Highly viscous, solidifies near the vent to form steep dome-shaped hills
  • Basic Lava: Hottest lava, fluid, solidifies away from the vent forming broad summit with gentle slopes (lava shields or shield volcanoes)
• Sills are intrusive landforms of horizontal shape, while dykes are intrusive landforms of vertical form. Sills solidify between layers of sedimentary rocks, forming terraces or benches on hill slopes. Dykes form long narrow ridges and are of igneous origin
• Batholiths are gigantic intrusions of coarse-grained igneous mass formed when a huge reservoir of magma cools and solidifies in an irregular shape, forming the core of old mountains
• Constructive effects of volcanoes:

  • Formation of igneous rocks
  • Providing valuable nutrients for the soil through lava and ash
  • Attracting tourists and boosting the economy
  • Releasing heat for harnessing geothermal energy
• Destructive effects of volcanoes:

  • Loss of life and property
  • Release of gases and smoke causing pollution
  • Disruption of air traffic by ash and dust
  • Creation of mudflows called Lahars when rainwater or melting snow mix with volcanic ash and mud
• A crater lake is formed when a caldera is filled with water, such as Lake Nukuru in Kenya
• Important volcanic zones:

  • The Circum-Pacific Belt or Ring of Fire
  • Mid-World Mountain Belt