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Intro to volcanoes
Transcript of Intro to volcanoes
Lava - exists above the surface Volcano - opening (vent) in earth’s surface where lava, ash, and gasses are expelled Volcano -- the vent where magma, ash and gas are expelled onto the surface of the Earth. Two types of Magma
Mafic (MAF ik) also called Basaltic magma-- Dark colored -- Rich in magnesium and iron
Makes up oceanic crust and continental
Runny often resulting in quiet eruptions
Felsic (FEL sik) also called Granitic magma-- Light Colored -- Rich in silicates
Makes up continental crust
sticky, often resulting in explosive eruptions. Eruptions can be quiet or explosive. Why? Quiet Erupions -- Small amount of trapped gasses occur in magma. Associated with malfic magma and shield volcanoes.
Example: Hawaii -- Mt. Kileaua Explosive Eruptions -- Large amounts of trapped gasses occur in magma. Often associated with Felsic Magma and cinder cone or composite volcanoes.
Example: Mt. St. Helens Pyroclastic material (tephra)-- The rock that formes during an eruption.
Classified by the size of particles Types of pyroclastic material:
Largest -- Volcanic blocks
64mm or less -- lapilli (luh PIL ie)
2mm or less -- Volcanic ash
0.25mm or less -- Volcanic dust What does the volcano look like? Depends on the cone
There are three types of cone to look for: Calderas -- This large depression in the ground is formed when the magma chamber partially empties collapsing the earth above. Shield -- Broad, wide area formed from quiet eruptions where lava flows have layered the land. These types are often formed over Hot Spots. Example -- Hawaii Composite -- Forms the largest volcanic mountains. Sometimes called stratovolcanoes.
Formed from alternating layers of pyroclastic material (tephra) and lava flows. These volcanoes are often formed over Convergent boundaries. Cinder -- Steep sides with a concave top. Formed from explosive eruptions and made mostly from pyroclastic material (tephra). These volcanoes are often formed over Divergent boundaries. Backup -- Remember lava forms Igneous rock. Igneous rock that forms below
ground is intrusive, igneous rock that is formed above ground is extrusive. most are dormant (not active)
-over 600 are active
-most are located on the “ring of fire”