Volcanic Features

• Batholiths


  A large body of igneous rock formed beneath the earth's surface by the intrusion and solidification of magma
• Batholiths


  • They are large magma chambers deep below the earth's surface
  • When the magma solidifies behind large igneous rocks
  • When the earth's surface erodes down these rocks are exposed, they are often dome shaped
• Batholiths


  • Half dome, Yosemite
• Laccolith


  When viscous magma moves up a dyke but is too thick to penetrate the surface, this creates a bulge in the surrounding landscape
• Laccolith

  • Henry mountains, Utah
• Dykes


  • They are vertical intrusions which cut across the layers of rock (the strata)
  • They often occur in groups which are known as dyke swarms
  • They form when magma rises into an existing fracture or creates a new crack by forcing its way through the rock and then solidifying
  • The igneous rock is more resistant than the surrounding rock leading to it being exposed through erosion
• Dykes


  • Devils stairsteps, Colorado
• Sills


  They are horizontal intrusions which go between the different layers of rock (between the strata)
• Hot springs


  A spring that is produced by the emergence of geothermally heated groundwater
• Hot springs


  • Blue Lagoons, Iceland
• Flood Basalts


  • Types of volcanic feature that doesn't necessarily form near a plate boundary
  • Rising magma plumes generate flood basalts
  • Major outpouring of basaltic lava over time
  • Can be 100s of miles in length and miles thick
• Flood Basalts


  • Columbia river basalt
  • Deccan Plateau, India
• Fumaroles


  • An opening in the earth's crust which emits steam and gasses (e.g. CO2, SO2)
  • Continue 1000s of years after the volcano has become extinct
• Geysers


  • Geysers result from the heating of groundwater by shallow bodies of magma
  • In addition, to a heat source geysers need a constant supply of water and an underground plumbing system that holds the water as it heats up
  • An eruption cycle starts with the conduit being filled with super-heated water from below. The water is much hotter than normal boiling point and some of it eventually turns to steam
  • Cooler shallow groundwater starts filling the chamber from above mixing with the hot water and raising the water level
  • Filling the plumbing system can take anywhere from seconds to days
  • As the water rises the pressure at the bottom increases due to the weight of the liquid above, boiling is suppressed by the cool water and increased pressure
  • The hot water below is still heating the water above it and so the temperature increases
  • Superheated steam from below rises and condenses in the cooler water above, warming it until the entire conduit is close to boiling point
  • Pressure of the expanding steam in the system throws the water out of the geyser and into the air forming an eruption