Volcanic features

• Volcanic Features


  These are features formed by volcanic activity. There are 2 types: Intrusive and Extrusive
• Types of Volcanic Features

  • Intrusive
  • Extrusive
• Intrusive Volcanic Features


  • Formed due to magma cooling beneath the earth's surface
  • Volcanic features beneath the Earth's Surface
• Intrusive Volcanic Features


  • Batholiths
  • Laccoliths
  • Phacoliths
  • Sills
  • Dykes
• Batholiths


  Large dome-shaped reservoirs of cooled Magma, located deep within the earth's crust. If the overlying rocks are denudated, they form steep sided rounded hills or uplands on exposure on the earth's surface.
• Batholiths


  • Become a round top hill over time
  • Example: Canadian Shield
• Laccoliths


  Smaller reservoirs of magma/molten-rock material forming a bulge or dome shape in the rest of the rock strata. These are usually connected to batholiths.
• Laccoliths


  • Become a conical hill over time
  • Example: Paricutin (Mexico)
• Phacoliths


  Smaller reservoirs of magma
• Sills


  Strips of molten rock material positioned horizontally between rock strata and is parallel to it.
• Sills


  • Become an scarp/escarpment or outcrop over time
  • Example: Great Whim Sill (Northern England), Palisades Sill (New Jersey, USA)
• Dykes


  Strips of molten rock material positioned vertically or diagonally cutting across rock strata
• Dykes


  • Become a spring waterfall or ridge over time
  • Example: Devils Tower (USA) - ridge, Angel Falls (Venezuela) - waterfall, Banff Upper Hot Springs (Canada) - spring
• Extrusive Volcanic Features


  Formed by lava and ash at the surface of the earth
• Extrusive Volcanic Features


  • Ash and Cinder Cone
  • Shield Volcanoes
  • Composite/Strata volcanoes
  • Caldera
  • Volcanic Plugs
  • Lava Plateaus
  • Geysers
  • Hot Springs
  • Fumeroles
• Ash and Cinder Cones


  Formed from fragmented particles such as cinders, ash and dust and lava ejected from a single vent. They are symmetrical in shape. They are formed from ACIDIC LAVA and have a bowl-shaped crater.
• Ash and Cinder Cones


  • Cinder cones: formed from explosions within the pipe/vent, have wider crater than ash cones, ejected materials deposited in layers
  • Ash cones: have a gentler gradient than cinder cones, consist of finer materials
  • Example: Mt Misery in Nevis
• Shield Volcanoes


  Formed from the accumulation of BASIC/ BASALTIC LAVA. Their sides are broad and gentle and their crater wide.
• Shield Volcanoes


  • Example: Mauna Loa, world's largest volcano in Hawaii
• Composite/Strata Volcanoes


  Comprise of alternate layers of lava flows, ash and cinder and may rise to over 2,500meters. They are steep with symmetrical sides. And created with BASALTIC/BASIC LAVA.
• Composite/Strata Volcanoes


  • Example: Fuji Yama in Japan
• Caldera


  A large steep-sided basin-shaped volcanic crater or depression. VISCOUS LAVA (ACID LAVA) hardens and plugs the vent of a volcano leading to the build-up of pressure inside. A violent eruption consequently occurs in which the crater is blown off explosively. The top of the volcano then collapses into the underlying magma forming an enlarged crater called a caldera.
• Caldera


  • Calderas usually develop several smaller vents or new cones. Water may collect in the caldera forming crater or caldera lakes.
  • Example: The top of Mt. Somma was blown off forming a caldera, Crater lake in Oregon
• Lava/Basalt Plateaus


  A plateau is an extensive relatively flat upland. It is a wide flat plateau made from fluid BASIC LAVA. The basic lava may flow far distances from long fissures forming this broad plateau.
• Lava/Basalt Plateaus


  • Basic lava sometimes escape through long fissures instead of a central vent. Or basic lava may cover the hills and valleys of pre-existing landscapes, producing a wide flat plateau.
  • Example: Deccan Plateau in India, Great plains of the Snake Basin
• Volcanic Plugs


  A steep semicircular pinnacle in the vent or pipe of the volcano. It is short lived and subjected to erosion, created by Acidic Lava solidifying in the vent of a composite volcano blocking/plugging it and them as the volcano becomes dormant it erodes leaving only the hardened lava.
• Volcanic Plugs


  • Example: Mt. Pele'e in Martinique