Chapter 9
Volcano an opening in Earth s crust through which molten rock, gases, and ash erupt and the landform that develops around this opening.
3 Conditions Allow Magma to Form: Decrease in pressure (lowers the melting temperatures of materials in asthenosphere) Takes place along rift valley at midocean ridge (lithosphere is thinner and exerts less pressure) Increase in temperature (causes materials in asthenosphere to melt) Occurs at a hot spot Increase in the amount of water (lowers the melting temperatures of materials in asthenosphere) Occurs at subduction boundaries
Where are volcanoes found? Mid-ocean ridges where plates move apart (Occurs at.. ). Divergent Boundaries
Where are volcanoes found? At subduction boundaries where plates are forced under other plates.
Where are volcanoes found? Over hot spots
Characteristics of magma/lava: Types of Magmas: Felsic Intermediate Mafic Ultra mafic
High Silica rocks are called Felsic Igneous Rocks and are light in color.
Silica-Rich, or Felsic Lavas Igneous rocks and lava that have a Silicate composition of 65% or more are considered to be Felsic.
Low Silica rocks are called Mafic Igneous Rocks, and are dark in color.
Mafic Rocks
Silica-Poor, or Mafic Lavas Igneous rocks and lava that have a Silicate composition of 45-50% or less are considered to be Mafic.
Igneous rocks that have a Silicate composition of 50-65% are considered to be Intermediate or Andesitic (named after a rock made from a mixture of Mafic magma and minerals from Felsic country rock ).
High Silica content causes Felsic Magma to be thick, or viscous, and slow -flowing.
Felsic Dome
Felsic Dome
Low Silica content causes Mafic Magma to be thin or low-viscosity, and fast-flowing.
Lava Flows/Eruptions:
Pahoehoe lava basaltic lava with high temperatures and quickly flowing. Lava has smooth, ropelike surface. (Mafic lava flow)
Aa lava cooler basaltic lava, moves a bit slower. Lava has rough jagged surfaces.
Pillow lava lava that flows underwater. Lava has rounded, pillowlike shape.
Pyroclastic flow- dense, superheated cloud of solid fragments and ash it is a VIOLENT eruption!
Tephra or Ash Deposits
Volcanic Landforms
Shield Volcano broad base volcano with gentle sloping sides - (basaltic lava builds up sides because of low viscosity and lava flowing long distances before hardening). Eruption is fast moving, non explosive.
Cinder Cones a smaller type of volcano, can form in groups and on sides of larger volcanoes. Molten lava is thrown into the air from a vent and as it falls the lava breaks into fragments which accumulate into a cone-shaped mound. Eruption involves lava thrown into the air.
Capulin Mtn., New Mexico is a Cinder Cone (we did the topographic profile of this earlier in year)
Composite Volcano (also know as Stratovolcano) a taller, steep volcano. Eruption is lava and pyroclastic material. (lava and Tephra)- Felsic Mt. St. Helens in Washington Mt. Shasta in California Mt. Fuji in Japan
Do Volcanoes Exist Anywhere Outside of Earth? - Yes! Moon maria, are the dark lower areas of basaltic lava flows on the moon. (occurred ~ 3-4 bya) The moon is cold now and no longer volcanically active.
Do Volcanoes Exist Anywhere Outside of Earth? - Yes! Mars has shield volcanoes (Olympus Mon, the larges volcano in the solar system). Volcanic activity is relatively recent (about 20-60mya), scientist wonder if erupts are still taking place, or if they will take place in future.
Do Volcanoes Exist Anywhere Outside. of Earth? - Yes! Venus has more than 1,600 large volcanoes, most are shield volcanoes. Scientist think volcanic activity here may still be active and that s why surface temperatures are so high there
Do Volcanoes Exist Anywhere Outside of Earth? - Yes! Io (Jupiter s 3rd largest moon) is one of the most volcanically active places in the solar system. Scientist believe that lavas on Io may resemble those of early Earth.
Name that picture: Cinder Cone Composite/Stratovolcano Pahoehoe Lava Shield Volcano Aa Lava Pillow Lava