Chapter 10Volcanoes

What is A Volcano?

• A VOLCANO is an opening in Earth’s surface that often forms a mountain when layers of lava & ash erupt

• After many thousands or even millions of years, magma reaches earth’s surface and flows out through an opening called a VENT.

• The steep walled depression around a volcano’s vent is the CRATER.

Magma vs. Lava

Magma – molten material inside a volcano

Lava – molten material on earth’s surface

Draw & Label the parts of a Volcano

Where do volcanoes occur?

1. Where plates move APART

AKA: Divergent plate boundaries

2. Where plates move TOGETHER

AKA: Convergent plate boundaries

Where do volcanoes occur?

3. HOT SPOTS areas of earth that melt

rock & force magma upward

Pacific Ring of Firearea around the pacific plate where earthquakes & volcanoes are common

Active vs. Dormant• Most of Earth’s volcanoes are DORMANT, which

means they are not currently active

• There are more than 600 active volcanoes in the world

• The most active volcano in the world is Kilauea in Hawaii

VIDEO

• how volcanoes form

Eruptions• Eruptions can either be quiet or explosive.

• Two factors to determine the type of eruption:

1. Amount of water vapor and other gases trapped in the magma.

2. Whether the magma is basaltic or granitic.

Trapped Gases• Gases like water vapor and carbon dioxide are

trapped in magma by the pressure of the surrounding magma.

• As magma nears the surface, pressure is reduced.–Gas escapes easily = quiet eruption–Gas trapped under high pressure = explosive

eruption

Magma Composition

• Basaltic Magma – contains less silica, very fluid, and produces quiet, nonexplosive eruptions.– Example: Kilauea, Hawaii

• Granitic Magma – contains a lot of silica, very thick, and high water content. Gets trapped in vents causing pressure to build up resulting in explosive violent eruptions.– Example: Mount Saint Helens

VIDEOS

• Kilauea Eruption

• Mount Saint Helen Eruption

TYPE 1: SHIELD VOLCANO

• Broad volcano• Gently sloping sides• Quiet Eruption

Hawaiian Islands

TYPE 2: CINDER CONE VOLCANO

• Explosive eruptions throw lava into the air• Lava then cools & hardens into TEPHRA

- steep, smooth sides- loosely consolidated

Paricutin, Mexico

TYPE 3: COMPOSITE VOLCANO

• Vary between quiet & explosive eruptions• Lava & tephra is repeated over & over

Mount Saint Helens

Brain Pop

http://www.brainpop.com/science/earthsystem/volcanoes/