Download Volcanoes I

Volcanoes I
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Title Slide: Volcanoes I
Slide 2: What Are Volcanoes?
•Volcanoes are breaks in the earth’s crust where magma, gases, and pyroclastic debris
erupts through to the surface.
•As pressure builds, the magma is forced up and carves through solid rock, creating a
central vent.
Slide 3: Magma
•Magma is a molten mixture of rock forming substances (liquid rock), gases, and water
vapor.
•When it reaches the surface it is called lava.
Slide 4: Structure
Volcanoes vary in structure. Some of which include:
•Cracks in the earth's crust where lava erupts
•Domes
•Shields
•Mountain-like structures with a crater at the summit
Slide 5: Where Volcanoes Occur
Most volcanoes form at plate boundaries, most often:
•Convergent boundaries- Where the plates are coming together, one subducts beneath the
other
•Divergent boundaries-Where the plates of the crust and mantle are pulling apart
allowing magma to rise to fill the gaps
Slide 6: Where Volcanoes Occur
Other volcanoes can form at hotspots, places in the mantle where high temperatures melt
rock. This creates a plume of magma which rises to the Earth’s surface.
Slide 7:Hot Spots
•Can occur in the middle of plates.
•The plate moves over a stationary hot spot.
•An chain of islands is formed over millions of years as the plate drifts over the hot spot.
•An example is the Islands of Hawaii
Slide 8: Types of Volcanoes
Volcanoes do not all look alike. Their shape is based on what type of materials they
erupt. There are three main types of volcanoes:
•Cinder Cone
•Composite (Strato-) Volcano
•Shield Volcano
Slide 9: Cinder Cone
•Erupt explosively, forming as the cinders pile up around the vent
•Tend to be very small
•Very rapid growth, but usually less than 500 meters high.
Slide 10: Cinder Cone Volcano
•This forms steep, cone shaped volcanoes.
•Often form on or near larger volcanoes.
•An example is Lassen Volcanic Park in California
Slide 11: Composite Volcano
•Explosive, erupt with molten lava, solid rock, and ash building in alternating layers
•The layers form into symmetrical cones, and the slopes are steep.
•Much larger than Cinder Cones
•Can develop secondary cones
Slide 12: Composite Volcano
•The crater may change form rapidly
•Also called stratovolcanoes
•Can be quiet or explosive
•Most dangerous type to humans and the environment!
•An example is Mount St. Helens
Slide 13: Mount St. Helens
•Located in Washington
•8,364 feet high
•Erupted in 1980 after being dormant since 1857
Slide 14: Shield Volcano
•Built by repeated lava flows from quiet eruptions.
•Has highly fluid lava that spreads, hardens and accumulates in layers
•Gently rises
•Has a wide, steep-sided central depression
Slide 15: Shield Volcano
•They look like a warriors shield.
•Builds up a broad, gently sloping volcanic mountain with a circular base.
•Largest type of volcano
•An example is Hawaii’s Mauna Loa
Slide 16: Parts of a Volcano
•Magma chamber - a large underground pocket formed by the rising magma.
•Pipe - narrow, almost vertical crack in the crust that carries the magma to the surface.
Slide 17: Parts of a Volcano
•Vent - point on surface where the magma leaves the pipe.
•Side Vent - sometimes lava will exit from cracks in the side of a volcano.
•Crater - bowl shaped area that forms around the vent.