VolcanoesChapter 5

S6E5: Convection currents cause plate

movement which causes geologic activity such as

volcanoes.

What is a VOLCANO?

A weak spot in Earth’s crust where magma comes up to the surface

Where are most of Earth’s major volcanoes located?

• In belts around the Earth’s continents and oceans along plate boundaries

• One major belt is known as the Ring of Fire, located around the rim of the Pacific Ocean

Volcanoes at Divergent Boundaries

• May form in the ocean at mid-ocean ridges

• May form on continents at rift valleys

Example:Great Rift Valley in East Africa

Volcanoes at Converging Boundaries

Form where 2 plates collide:Oceanic ContinentalOceanic Oceanic

The resulting volcanoes create a string of islands called an

Island Arc

Examples of Island Arcs: The Aleutian Islands

Another Example of an Island Arc: The Carribean Islands

Volcanic Hot Spots

• A volcano forms above a Hot Spot when magma erupts through the crust and reaches the surface

Oceanic Hot Spot:The Hawaiian Islands

Continental Hot Spot: Yellowstone National Park, Wyoming, USA

Volcanic eruption vary depending on the viscosity of the magma

• What is viscosity?

–The resistance of a liquid to flow. The greater the viscosity, the thicker the flow

–Depends on the amount of silica (from 50% - 70%)

Quiet Eruption • Volcano erupts quietly

• Low silica magma has low viscosity and flows easily

• Example: The Hawaiian

Islands

Explosive Eruption

• Volcano erupts violently

• High silica magma, high viscosity, thick and sticky, does not flow – builds up pressure

• Example:

Mt Saint Helens

• Mount St. Helens about noon on May 18, 1980

after being dormant for 123 years.

Pyroclastic Flow

• Volcano erupts violently

• Hurls out a mixture of hot gases, ash, cinders, & bombs

• Example: Mayon Volcano, Philippines

Three Main Types of Volcanoes:

1. Shield Volcano

2. Cinder Cone Volcano

3. Composite Volcano

Shield Volcano

• Gradual, build-up of lava

• Wide, gently sloping mountain

• Example: Hawaiian Islands Notice the shapes of the shields??? Hummm…

Cinder Cone Volcano

• Erupts violently, producing ash, cinders, and bombs

• Loose materials build up around the vent in a steep cone-shaped mountain

• Example: Pariciutin, Mexico• https://www.youtube.com/watch?v=g4-rrixcz6w

Cinder Cone Volcano

Composite Volcano

• Lava alternates with layers of ash in explosive eruptions

• Tall, cone-shaped mountain• Examples: Mt. Fuji, Japan and

Mt. Saint Helens, Washington, USA

Composite Volcanoes

Mt. Saint Helen’s Before & After eruption

Comparing Shield & Composite Volcanoes

Comparing the shapes

of Volcanoes!

Check out this volcano link…

• http://mail.colonial.net/~hkaiter/volcanoes.html

What is a Caldera?Huge hole left by the collapse of a

volcanic mountain

Geothermal Activity

• Hot springs & geysers are types of geothermal activity often found in areas of past or present volcanic activity

What are hot springs?• They form when groundwater is heated by

nearby magma or hot rock deep underground

Which one is a geyser?

https://www.youtube.com/watch?v=wE8NDuzt8eg

Seriously, what is a geyser?

A fountain of water and steam that erupts from the ground

• Example: Old Faithful at Yellowstone National Park

It erupts ‘faithfully’ every 33 – 93 minutes

Experimenting with Volcanic Eruptions

• Volcano Info…build & erupt a volcano…have fun!

• http://kids.discovery.com/games/build-play/volcano-explorer

• http://kids.discovery.com/games/pompeii/pompeii.html