Volcanoes

Formed at Plate Boundaries

Ring of Fire!

Some Volcanoes form at Hot Spots

• Examples: Hawaii and Yellowstone

3 Types of Volcanoes

• Shield Volcano• Composite (Strato) Volcano• Cinder Cone Volcano

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.)

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

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

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.

Calderas

Yellowstone is an example of a caldera type eruption

Volcanoes from Rifting Plates

• When plates diverge, magma can rise up and form a rift-volcano.

• Examples: Mid-Atlantic Ridge and African Rift Valley.

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.