Movements of the Earth’s CrustHarcourt Science

Unit DChapter 1

Mrs.Strand6th grade Lockwood Middle School

What are the Earth’s Layers?

• Terms:– Crust– Mantle– Core– Lithosphere– Asthenosphere– Plate Tectonics

What are the Earth’s Layers?

Earth’s Plates & How they move

QuickTime™ and aTIFF (Uncompressed) decompressor

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Look in book pg D8 for names

http://science.enotes.com/images/earth/woes_02_img0118.jpg

Changes to the Earth’s Surface

• Erosion– Wind– Water– Glacier

• Falling Space Material– Meteorites

How the Earth’s Plates Move

• Terms:– Divergent boundary– Convergent boundary– Transform fault boundary– Mid-ocean Ridge– Rift– Sea-floor Spreading

How Earth’s Plates Move

• Divergent Boundary– Mid-ocean ridges– May also occur on continents (Africa)

QuickTime™ and aTIFF (Uncompressed) decompressor

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How Earth’s Plates Move

• Convergent Boundaries– Crust is absorbed at convergent boundaries

• 1. Ocean plate collides with another ocean plate– Causes deep trenches (mariana trench in the Phillipines)

• 2.Continental plates collide– Forms some of the highest mountains in the world

(himalayas)• 3. Oceanic plate collides with a continental plate

– Forms mountains and volcanoes– 80% of volcanoes and 90% of earthquakes occur on

convergent boundaries.

How Earth’s Plates MoveTransform Fault Boundaries

• Two plates move past each other in opposite directions.

• Most occur in oceanic crust.• San Andreas fault• Earthquakes are common along

these boundaries• Mountains are very common

Earth’s Surface Changes Over Time

http://www.ucmp.berkeley.edu/geology/anim4.html

Earthquakes and Volcanoes

• Terms:– Earthquake– Focus– Epicenter– P wave– S wave– Surface Wave – Richter Scale– Volcano

Earthquakes & Volcanoes

• Plate movements cause earthquakes– One million earthquakes each year. Only about

200 earthquakes cause damage.• Earthquake waves

– P waves= faster, “push-pull” motion– S waves= slower, vibrations at 90° to the

direction of travel– Surface waves= travel only at the earth’s

surface and are the slowest waves

Earthquakes & Volcanoes

• Earthquake Measurement

The Modified Mercalli Scale expresses the intensity of an earthquake's effects in a given locality in values ranging from I to XII.

The Richter scale is logarithmic so that a recording of 7, for example, indicates a disturbance with ground motion 10 times as large as a recording of 6.

Two ways toMeasureEarthquakes:

Earthquakes & Volcanoes

• How volcanoes form:– Along convergent boundaries

Earthquakes & Volcanoes

• Types of Volcanoes• Among the different kinds of volcanoes are:

• * shield volcanoes Unlike the composite volcanoes which are tall and thin, shield volcanoes are tall and broad, with flat, rounded shapes.

• * cinder cones Cinder cones are simple volcanoes which have a bowl-shaped crater at the summit and only grow to about a thousand feet, the size of a hill. They usually are created of eruptions from a single opening.

• * composite volcanoes They are built of alternating layers of lava flows, volcanic ash, cinders, blocks, and bombs.

http://www.windows.ucar.edu/tour/link=/earth/interior/volcanos_general.html

Earthquakes & Volcanoes

• Hot Spot VolcanoesHot spots are areas in the earths mantle which, for unexplained reasons, are hotter than the surrounding mantle.

The Hawaiian Islands are recent volcanoes produced by a hot spot that has given birth to countless volcanic islands, which over time have sunk into the sea to become atolls and seamounts.

Hot spot volcanoes can show us how plates have moved in the past by leaving a trail of islands or atolls. This map of the Hawaiian_Emperor seamount chain shows us which way the plate was moving throughout history