Transcript Volcanoes Formed at Plate Boundaries Ring of Fire! Some Volcanoes form at Hot Spots • Examples: Hawaii and Yellowstone.

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.