Chapter 4Lesson 2

EarthquakesAnd

Volcanoes

o Earthquake – sudden movement of Earth’s crust

o The actual place underground where the rocks break producing vibrations is called the focusfocus

o The place on the surface directly above the focus is called the epicenterepicenter

Earthquakes

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

Originate at the focus and travel outward in all directions

Magnitude – the measure of the amount of energy released by an earthquake

AftershocksAftershocks: Are adjustments in the crust after in earthquake

Seismic Waves

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

VolcanoesVolcanoes

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

VolcanoesVolcanoes

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 HotspotsMid-Plate Hotspots