I. Changes to the Earth’s Surface Chapter 9
A. The Earth’s surface is constantly changing.
II. Earth’s crust
A. The Earth is made of 3 layers
1. Crust
2. Mantle
3. Core
B. The crust is the top layer of the Earth
C. Landforms are natural features on the Earth’s surface.
1. Mountains rise 600 meters above the land around them.
2. Plains are flat land.
3. Plateaus are flat land on high ground.
4. Peninsulas are landforms along coasts.
III. Weathering affects landforms
A. Weathering is the gradual wearing away or changing of rock and soil caused by water, ice, temperature changes, wind, or living things.
B. The Earth under goes weathering all the time.
C. Two types of weathering
1. Physical weathering causes the size of a rock to change.
a) Causes
(1) Water
(2) Ice
(3) Temperature changes
(4) Living things
2. Chemical weathering causes the size and the material of the rock to change.
a) Chemicals cause rock to change into different material.
b) Acid rain
(1) Rainwater mixes with carbon dioxide to form a weak acid.
(2) When it rains the acid combines with rock material to form a new chemical.
c) Animals and plants give off chemicals that cause weathering.
IV. Weathered materials move
A. Erosion is the movement of weathered materials by water, ice, gravity, and wind.
1. Rainwater moves soil down a mountain.
2. Streams carry weathered material a long way.
3. Waves change the shape of the coastline.
4. Glaciers slide and wear away rock.
5. Water running downhill forms canyons and valleys.
B. Deposition is the laying down of rock, soil, or other materials building up parts of the Earth’s surface.
1. Delta
a) A fan-shaped area of land that builds up where a river flows into an ocean.
b) The river slows down and deposits large amounts of eroded material to form a delta.
2. Dunes
a) Wind deposits grains of sand in deserts to form dunes.
C. Rapid forms of erosion
1. Gravity and landslides
a) Gravity pulls all objects from higher to lower ground.
b) Rapid downhill movement of rock or soil is a landslide.
2. Gravity and avalanches
a) Avalanches are large amounts of snow or ice that fall rapidly down a mountain.
b) Strong winds, earthquakes, and explosions can start an avalanche.
D. Controlling erosion and deposition
1. Grow plants on hills to slow erosion.
2. Farmers can plow hilly areas in steps called terraces.
3. At the shore barriers are built to stop large waves from carrying sand away from the beach.
4. People may limit deposition by digging out deposited material from waterways so ships can pass.
V. Volcanoes
1. Volcanoes form at a weak spot in the Earth’s crust.
2. Magna boils to the surface
3. Volcano erupts
4. Magma is called lava on the surface.
5. Rock and ash cover the Earth’s surface.
6. Two types
a) Violent eruptions
(1) Blows off its top
(2) Steep sides
b) Quiet eruptions
(1) Lava oozes out slowly
(2) Forms gentle slopes
7. Active volcanoes have frequent eruptions
8. Dormant volcanoes have not erupted for a long time
9. Mount St. Helens in Washington erupted in 1980.
10. The Earth’s surface can change rapidly.
VI. Earthquakes
A. Plates move suddenly causing the Earth’s crust to shake.
1. Plates are very large pieces of the Earth’s crust and mantle.
2. Volcanoes form along places were the plates come together.
3. Faults are breaks or cracks in rocks where the crust can move.
B. The focus of the earthquake is where the plates start to move.
C. Epicenter is the point on the Earth’s surface directly above the focus.
D. Underground waves of energy travel from the focus point.
E. Greatest damage is caused near the Epicenter.
VII. Effects
A. Volcanic ash can reduce the amount of sunlight on the Earth, causing cooler temperatures.
B. Earthquakes can cause tsunamis that destroy coastal areas and landslides that damage buildings and roads.
C. Earthquakes and volcanoes cause rapid changes in the Earth’s surface.