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Chapter 4
Lesson 2
Earthquakes
And
Volcanoes
Earthquakes
o
Earthquake – sudden movement of Earth’s crust
o
The actual place underground where the rocks
break producing vibrations is called the focus
o
The place on the surface directly above the focus
is called the epicenter
http://www.geo.uib.no/jordskjelv/index.php?topic=earthquakes&lang=en
http://www.geo.uib.no/jordskjelv/index.php?topic=earthquakes&lang=en
http://www.geo.uib.no/jordskjelv/index.php?topic=earthquakes&lang=en
San Andreas
Fault
Seismic Waves
Originate at the focus and travel outward in all
directions
Magnitude – the measure of the amount of
energy released by an earthquake

Aftershocks: Are adjustments in the crust
after in earthquake
Volcano – opening in the Earth’s crust
• Eruption –
outpouring of
melted rock,
ash, and gases
• Lava – magma
that reaches the
Earth’s surface
• Crater – a
• depression
around a vent
Ring of Fire The ring around the Pacific
Ocean that has most of the world’s
volcanoes
Volcanoes
Quiet
lava
flows
• Dike – magma that hardens in a vertical
crack
• Sill – magma that hardens between
horizontal layers of earth
• Laccolith – magma in a sill that pushes
upward
• Batholith – large, underground magma
formation
Types of Volcanoes
• Shield Volcano
a) Built from layers of
lava
b) Non-explosive
eruptions
c) Not very steep, but
can be big
Types of Volcanoes
•
Cinder Cone
Volcano
a) Built from
pyroclastic material
b) Moderately
explosive, short
eruptions
c) Small in size, steep
slopes
Types of Volcanoes
•
Composite
Volcanoes
a) Most common type
b) Explosive eruptions
and lava flow
c) Built from
pyroclastic material
AND lava
Mt. St. Helen before the explosive eruption
Volcanoes
Mt. St. Helen after the eruption
• Island chain – line of
volcanic mountains
• Hot spot – stationary pool of
magma
• Island arc – volcanic
islands that are made my subducting
ocean floor plates
Mid-Plate Hotspots