Earthquakes and Volcanoes.ppt

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Earthquakes and Volcanoes

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Earthquakes

• An earthquake is the shaking and

trembling that results from the sudden movement of part of the Earth’s crust.

• The most common cause of earthquakes

is faulting.

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Seismic Risk Map of the U.S.

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San Andreas Fault

• The San Andreas fault extends 960 km

from Mexico to the north of California.

• The land to the west is moving north. The

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Tsunamis

• Earthquakes which occur on the ocean

floor produce giant sea waves called tsunamis.

• Tsunamis can travel at speeds of 400 to

500 miles per hour.

• As they approach the coast, they can

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Focus

• The focus is the underground origin of an

earthquake.

• Most faults occur between the surface and

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Epicenter

• Directly above the focus, on the Earth’s

surface is the epicenter.

• During an earthquake, the most violent

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Seismic Waves

• There are three main types of seismic

waves.

• Primary

• _Secondary

• _Surface

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Primary Waves

• Seismic waves that travel fastest are P

waves. They travel through solids, liquids and gases.

• P waves are push-pull waves.

• _{They move at different speeds depending}

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Secondary Waves

• S waves travel through solids but not

liquids or gases.

• S waves cause particles to move from side

to side. They move at right angles to the direction of the wave.

• Seismic waves that do not travel through

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Surface Waves

• The slowest moving seismic waves are

called surface waves or L waves.

• L waves cause most of the damage.

• _{L waves originate on the Earth’s surface at}

the epicenter. They move along the

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The Seismograph

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The Richter Scale

• 1-10

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Predicting Earthquakes

• Scientists have identified warning signals

the help predict earthquakes with greater accuracy.

• Sometimes slight changes in the tilt of the

Earth’s surface can be detected.

• Some scientists believe animals behavior

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Formation of a Volcano

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Volcano

• _{The opening from which lava erupts is the}

vent. Volcanoes often have more than one vent.

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Volcanic Eruptions

• During volcanic eruptions, many rock

fragments are blown into the air.

• The smallest particles are called volcanic

dust. (less than 0.25 mm)

• Volcanic Ash ( 0.25 -5mm) falls to the

Earth and forms small rocks.

• Volcanic bombs (a few cm to several

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Types of Volcanoes

• Different types of volcanic eruptions form

different types of volcanoes.

• Cinder cones

• _{Shield volcanoes}

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Three Types

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Cinder Cones

• Volcanoes made mostly of cinders and

other rock particles that have been blown into the air are called cinder cones.

• Because the material is loosely arranged,

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Cinder Cone Volcano

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Shield Volcanoes

• Volcanoes composed of liquid flows are

called shield volcanoes. A dome-shaped mountain is formed such as Mauna Loa (4km over sea level) in the Hawaiian

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Shield Volcanoes

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Composite Volcanoes (also called

Stratovolcanoes)

• Volcanoes built up of alternating layers of

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Mount Vesuvius

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Mount Vesuvius

• Images of victims in eruption of Vesuvius in 79 AD. Most died as a result of

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Composite Volcano

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Crater

• There is often a funnel-shaped pit or

depression at the top of a volcanic cone. This pit is called a crater.

• If the crater becomes very large as a result

of the collapse of its walls, it is called a caldera. A caldera may also form when

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Volcanic Crater

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Volcanic Activity

• An active volcano is one that erupts wither

continually or periodically

• A volcano that has been known to erupt

within modern times but is now inactive is classified as a dormant volcano

• A volcano not known to have erupted

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Volcano and Earthquake Zones

• Most major earthquakes and volcanic

eruptions occur in three zones of the

world. Scientists believe that there is a

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Ring of Fire

• One major earthquake and volcano zone

extends nearly all the way around the edge of the Pacific Ocean. This zone goes through New Zealand, the

Philippines, Japan, Alaska and along the western coasts of North and South

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Mediterranean Zone

• A second Major earthquake and volcano

zone is located near the Mediterranean Zone and extends across Asia into India. Many countries in the zone, including Italy, Greece and Turkey, have violent

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Mid-Atlantic Ridge Zone

• The third major earthquake and volcano

zone extends through Iceland and to the middle of the Atlantic Ocean. There is

under the ocean a long range of volcanic mountains called the Mid-Atlantic Ocean Range. Scientists believe that the volcano and earthquake activity are due to the

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Earthquake Belts

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