Volcanoes

What is a Volcano?

• A volcano is an opening in Earth’s crust through which molten rock, rock fragments and hot gases erupt.

How do volcanos erupt?

• A volcano may erupt violently or gently.• A violent eruption can cause tremendous

destruction even is not much molten rock reaches the surface.

• A gentle eruption can pour out rivers of molten lava that flow long distances

What is magma?

• A major portion of all magma is silica.• Magma also contains gases that expands as

the magma rises.• Magma rises toward the Earth’s surface as

long as it is less dense then the surround rock.• Once the magma stops rises, it collects in

areas called magma chambers.

What is magma?

• Magma collects in a Magma Chamber before erupting through a volcano.

• When magma erupts. It is called lava.• Lava is magma that has reached Earth’s

surface.

During an eruption

• What looks like smoke rising from a volcano is actually a mixture of ash and gases.

• Volcanic gases can mix with rock fragments and stay near the ground. – The mixture forms a pyroclastic flow

• Which is a dense cloud of superhot gases and rock fragments that races downhill.

LAB ACTIVITYWhat happens when a volcano erupts?

• Materials– Empty film canister– Effervescent antacid tablet– Water

Everyone must wear their safety googles

Procedure

• Add water to an empty film canister until it is ¾ filled.

• Drop an antacid tablet in the water and put the lid on the canister.

• Observe what happens.

Answer the following questions:

• What happened to the water and to the canister lid?

• What caused the changes you observed?

• How might the events you observed be similar to the eruption of a volcano?

Where do most volcanoes form?

• Volcanoes are common along tectonic plate boundaries where oceanic plates sink beneath other plates.

• Volcanoes are also common along tectonice boundaries where plates pull apart, allowing magma to rise from the mantle.

• The volcanoes around the Pacific Ocean form a belt called the Ring of Fire.

The Ring of Fire

Subduction zones

Name the plate

What are the different kinds of volcanoes?

Volcanoes do not all look alike. Their shape is based on what type of materials they erupt. There are three main kinds, or shapes, of volcanoes.

Classify Volcanoes• Composite • Cinder • Shield

• Active • Intermittent

• Dormant • Extinct

ShieldVolcanoes

Volcanoes that build up from many slow, steady, flows of hot lava, are called shield volcanoes. This kind of volcano is low and broad with gently sloping sides. They look like a warriors shield.

Cinder Cone Volcanoes

Cinder cone volcanoes form when solid rock and ash shoot up into the air and fall back around the volcano opening.

The cinder cone volcano has steeply sloped sides.

Composite Volcanoes

Composite volcanoes, erupt with molten lava, solid rock, and ash. The layers pile up much like layers of cake and frosting. The layers form into symmetrical cones, and the

slopes are steep.

Pictures, Images, and information From:Soames Summerhays/Photo Researchers, Inc.

Kraft-Explorer/Photo Researchers Inc.Masao Hayashi-Dung/Photo Researchers Inc.

Why Do Volcanoes Blow Their Tops? By Melvin and Gilda Bergerwww.usgs.gov/education/learnweb/volcano/index.html

Label a Volcano

Using the labels given find the correct part.Check yourself on the next slide.

Parts of a Volcano

Where are the Volcanoes?

Count the total

amount of active

volcanoes.

Active Volcanoes of the World

70

60

50

45

40

20

12

600

204

50Indonesia

Central America

Europe

Japan

Africa

Iceland

Italy

Ring of Fire

South America

North America