Volcanoes8th grade Physical Science

How are Volcanoes Formed?

O Gases force magma, melted rock in the Earth to rise. If magma breaks through the Earth’s surface, a volcano is formed.

Three Different Types of Volcanoes

O Shield VolcanoO Composite Cone VolcanoO Cinder Cone Volcano

Shield VolcanoO They release relatively fast-moving

less gassy lava, and tend to have less explosive eruptions than other types of volcanoes.

O People often walk fairly close to these erupting volcanoes.

O They usually form large, broad volcanoes.

Mount Bachelor in Oregon

Composite Cone Volcano

O These volcanoes have explosive eruptions as a result of more gassy magma.

O They are formed from layers of lava and ash.

O Composite Cones are also known as stratovolcanoes.

Mount St. Helens in Washington

Cinder Cone VolcanoO These are the smallest and most

common volcanoesO They are formed from explosive

eruptions that shoot small pieces of magma and ash into the air.

O The magma then cools and hardens as it falls back to the Earth, forming a cinder cone.

O In many cases, cinder cones form on the sides of a larger volcano.

Mt. Etna in Italy

Active VolcanoO Active volcanoes is one that has

erupted since the last ice age approximately in the past 10,000 years.

Dormant VolcanoO Dormant volcanoes would then be

one that hasn’t erupted in the past 10,000 years, but it is expected to erupt again.

Extinct VolcanoO Extinct Volcanoes would be one that

nobody expects to ever erupt again.

Two Types of EruptionsO More gassy eruptionsO Less gassy eruptions

More Gassy EruptionsO Explosive and violent eruption and

magma shoots out of the volcano.

Less Gassy EruptionsO More quiet eruption. The magma just

flows smoothly out of the volcano.

Ring of FireO Many volcanic eruptions have

occurred worldwide.