6th Grade Science-Chapter 3

Chapter 3, Lesson 1 Notes

*The process that breaks down rock and other substances is called weathering.

*Once the rock is broken down, the smaller pieces can be removed by wind, water, ice, or gravity.

*Erosion is the process by which bits of broken rock are carried away.

*In the cycle of erosion, the process moves material called sediment, which consists of small particles of rock or soil, or the remains of plants and animals.

*Deposition occurs where the agents of erosion deposit, or lay down, sediment.  Deposition changes the shape of land.

*Weathering, erosion, and deposition act together in a cycle that wears down and build up Earth’s surface.

*The type of weathering in which rock is physically broken into smaller pieces is called physical weathering.

*Chemical weathering is the process that breaks down rock through chemical changes.

*The natural agents of physical weathering include freezing and thawing, release of pressure, plant growth, actions of animals, and abrasion.

*Abrasion refers to the wearing away of rock by rock particles carried by water, ice, wind, or gravity.  Water seeps into cracks in rocks and freezes and expands.  The ice forces the rock apart.  Wedges of ice in rocks widen and deepen cracks in the process called frost wedging.

*The agents of chemical weathering include water, oxygen, carbon dioxide, living organisms, and acid rain.  For example, the oxygen gas in air combines with iron in the presence of water in a process called oxidation.  The product of oxidation is rust.  Rust makes rock soft and crumbly.

*The most important factors that determine the rate at which weathering occurs are the type of rock and climate.  Some rocks weather more easily because they are permeable.

*Permeable means that a material is full of tiny, connected air spaces that allow water to seep through it.

Chapter 3, Lesson 2 Notes

*Topography is the shape of the land.  An area’s topography may be flat, sloping, hilly, or mountainous.  The topography of an area includes the area’s elevation, relief, and landforms.

*The height above sea level of a point on Earth’s surface is its elevation.  The difference in elevation between the highest and lowest parts of an area is its relief.

*The Rocky Mountains include huge mountains separated by deep valleys.  These areas have high relief, or great differences in elevation.

*There are many different landforms.  A landform is a feature of topography, such as a hill or valley, formed by the processes that shape Earth’s surface.  Different landforms have different combinations of elevation and relief. 

*Landforms vary greatly in size and shape.  Three major types of landforms are plains, mountains, and plateaus.

*A plain is a landform made up of nearly flat or gently rolling land with low relief.  A plain that lies along a seacoast is called a coastal plain.  A plain that lies away from the coast is called an interior plain.

*The broad interior plains of North America are called the Great Plains. 

*A mountain is a landform with high elevation and high relief.  A mountain’s base can cover an area of several square kilometers.

*A mountain range is a group of mountains that are closely related in shape, structure, area, and age.

*A landform that has high elevation and a more or less level surface is called a plateau.  The Columbia Plateau in Washington State is an example.

*A large area of land where the topography is made up mainly of one type of landform is called a landform region.  The Great Plains and Rocky Mountains are examples of major landform regions.

*Other terms used to describe landform regions include uplands, which are regions of hilly topography, and lowlands, which are regions of plains with low elevations.

Chapter 3, Lesson 3 Notes

*Gravity is the force that pulls everything toward the center of Earth.  It pulls rock down slopes.  It can cause sections of rock to fall off cliffs.  It can also cause movement of a large amount of sediment.

*Gravity causes mass movement, any one of several processes that move sediment downhill.  Mass movement can be rapid or slow.  And erosion and deposition both take place during a mass movement event.

*The different types of mass movement include landslides, mudflows, slumps, and creep.

*A landslide occurs when rock and soil slide quickly down a steep slope.

*A mudflow is the rapid downhill movement of a mixture of water, rock, and soil.  Mudflows often occur after heavy rains in a normally dry area.

*In the type of mass movement known as a slump, a mass of rock and soil suddenly slips down a slope.  Unlike a landslide, the material in a slump moves down in one large mass.

*Creep is the very slow downhill movement of rock and soil.  Creep may tilt vertical objects like telephone poles and tree trunks at unusual angles.