Themes of the Day:

• Forms of Intrusive Igneous Bodies
• Types of Volcanoes

Forms of Igneous Bodies

• Intrusive forms:
  • magma body, country rock, xenolith
  • pluton, stock, batholith
  • sill, dike
  • volcanic neck - e.g., Devils Tower, WY, Shiprock, NM
• Extrusive forms:
  • volcanoes, lava flows

Types of Volcanoes

• Profile of a volcano, and types of eruption dictated by composition of the magma (lava) - Types of Igneous Rocks
• Main types of volcanoes and volcanic products:
  • Shield Volcanoes - low viscosity basaltic magmas - lava lakes and flows common - not explosive - flood basalts and submarine pillow lavas are basaltic, too - e.g., Mauna Loa, Hawaii
  • Cinder Cones - variable composition, often basaltic - usually a single batch of magma - steep cones formed by cinders piled around vent at angle of repose - e.g., Paricutin, Mexico, Wizard Island, Crater Lake, Oregon
  • Composite Volcanoes (Stratovolcanoes) - interayered lava flows and pyroclastic deposits - ranges from intermediate to felsic in composition (andesite-dacite-rhyolite) - in volcanic arcs above subduction zones - e.g., Mount Cleveland, Alaska
  • Dome Volcanoes - similar in composition and often genetically related to composite volcanoes - usually more viscous (more silicic) magma type (dacite/rhyolite) - pyroclastic flows abundant - explosive eruptions common
  • Continantal Calderas - in continental regions the result of the largest types of volcanic eruptions - large, shallow, silicic magma chambers empty catastrophically with unparalleled violence; roof of magma chamber collapses into emptied portion of magma chamber
  • Difference in Scale
• Crater vs. Caldera
• USGS Photo Glossary of Volcanic Terms - lots of good illustrations of volcanoes and volcanic features

Virtual Volcanic Field Trip (time permitting)

• Volcano Observatories
  Choose Volcano Observatory Hawaiian Alaska Cascades Long Valley Caldera Yellowstone Popocatépetl Colima Montserrat PHIVOLCS Volc. Survey Indonesia Merapi