Download Volcanoes

Volcanoes
Chapter 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  Continental
Oceanic  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…
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
Comparing Shield & Composite
Volcanoes
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
Cinder Cone Volcano
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?
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/pompeii/pompeii.html