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Volcanoes. Formed at Plate Boundaries Ring of Fire!

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Presentation on theme: "Volcanoes. Formed at Plate Boundaries Ring of Fire!"— Presentation transcript:

1 Volcanoes

2 Formed at Plate Boundaries Ring of Fire!

3 Some Volcanoes form at Hot Spots Examples: Hawaii and Yellowstone

4 3 Types of Volcanoes Shield Volcano Composite (Strato) Volcano Cinder Cone Volcano

5 Types of lava and eruptions Mafic Lava: Rich in magnesium and poor in silica. Erupts generally quietly and is not viscous (flows easily. Dark color. (Example: Mauna Loa in Hawaii). Felsic Lava: Rich in silica and poor in magnesium. Erupts violently with pyroclastic flows and ash. Light color. Very viscous. (Example: Mt. Vesuvius and Mt. St. Helens.)

6 Shield Volcano Broad with gently sloping sides. Quiet eruptions with mafic lava Usually the lava hardens into Basalt, which makes up the ocean floor. Largest volcano Example: Mauna Loa in Hawaii

7 Cinder Cone Volcano Very steep slopes More felsic and explosive eruptions. The cinders of volcanic rock (scoria, pumice) are deposited to form a cone. Example: Mauna Kia in Hawaii

8 Composite Volcano/Stratovolcano Tall and steep Alternating layers of lava flows and pyroclastic material (ash). Mostly explosive eruptions due to felsic magma though some quiet lava flows. Very Viscous lava Examples: Mt. Fuji in Japan and Mt. St. Helens in Washington State.

9 Calderas Yellowstone is an example of a caldera type eruption

10 Volcanoes from Rifting Plates When plates diverge, magma can rise up and form a rift-volcano. Examples: Mid-Atlantic Ridge and African Rift Valley.

11 Flood Basalts: Well that’s weird. 17-12 Million Years ago, miles long rifts in Washington and Oregon erupted huge flows of basalt. Called Flood Basalts. Geologists not really sure why it happened.

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