Weathering, Erosion and Deposition

Weathering

• Weathering is the wearing away of rock and can be chemical or mechanical These mountains in Costa Rica were mechanically weathered by abrasion.

• Abrasion is weathering by grinding action.

These mountains in Salt Lake City, Utah, were also weathered by abrasion.

More examples of weathering on the Pacific

Coast of Costa Rica are shown by these sea stacks

out in the ocean. They were formed as ocean waves

weathered away part of the

rocks seen here.

Another example of how weathering

forms landscapes is the creation of a

horn. This is a peak of a mountain that has been formed by the weathering away of

rock by glaciers.

1. Mechanical Weathering

• Process by which rocks are broken down into smaller pieces by physical forces.

• Types of Mechanical weathering– Ice wedging– Plant roots– Abrasion– Burrowing of animals (animal action)– Temperature changes (freezing and thawing)

Frost Wedging

PLANT ROOTS

Abrasion

Animal Action (Burrowing)

Chipmunks live in dens in the soil and search the litter for seeds and nuts.Plant roots break up

the soil and hold it in place.

Earthworms break up the soil, making it easier for plant roots to spread and for air and water to enter the soil. They create waste which makes soil more fertile by adding nitrogen.

Bacteria are decomposers that break down animal and plant remains and wastes.

How decomposers enrich soil and make it fertile: mechanical weathering.

Freezing and Thawing(temperature changes)

Chemical Weathering• the process that breaks down rock through

chemical changes.• The agents of chemical weathering:– water- water dissolves rock over time– oxygen- combines with iron to form rust

(oxidation)– carbon dioxide- dissolves in water to form

carbonic acid– living organisms- plant roots secrete acids– acid rain- from the burning of fossil fuels

Water

• Water weathers rock by dissolving it.

Oxygen

• Iron combines with oxygen in the presence of water in a processes called oxidation.

• The product of oxidation is rust.

Carbon Dioxide

• CO2 dissolves in rain water and creates carbonic acid.

• Carbonic acid easily weathers limestone and marble.

Living Organisms

• Lichens that grow on rocks produce weak acids that chemically weather rock.

Acid Rain

• Compounds from burning coal, oil and gas react chemically with water forming acids.

• Acid rain causes very rapid chemical weathering.

2 factors that determine the rate of weathering:

• rock type- Rock that is permeable (has holes that let water in), weathers faster than rock that is impermeable. The mineral content of rock also determines how fast a rock weathers.

• climate- Rock weathers faster in warm, humid climates.

Karst Topography• A type of landscape created by chemical

weathering of limestone • Located in rainy regions where there is

limestone near the surface, characterized by sinkholes and caves.

View brainpop animation: http://www.brainpop.com/science/weather/weathering/

Erosion

• Erosion is the movement of sediment by water, wind or ice.

• In this picture taken in Oregon, a gully has been created by a stream that has cut a path through soft sediment after a strong rainfall.

Erosion

• Erosion has caused this bank in Squaw Creek to be cut away by the weathering of the river, forming a landform that simulates a partial cave on the left side of this picture.

Erosion

• Here, erosion by longshore drift, has caused a lagoon to form along this beach in Costa Rica.

Mass Movement

• http://www.phschool.com/atschool/phsciexp/active_art/mass_movement/index.html

Waterfalls

• http://www.classzone.com/books/earth_science/terc/content/visualizations/es1305/es1305page01.cfm?chapter_no=visualization

View brainpop video and name 3 types of erosion and how they change land: http://www.brainpop.com/science/earthsystem/erosion/

Deposition

•Definition: deposition is the settling out of sediment that has been eroded.

DepositionDeposition is the adding of sediment in an area as it settles out and forms new landforms. In this picture, taken in Squaw Creek, near Sisters, Oregon, rocks have

been deposited along the bank of the river after heavy rains.

Deposition

• In this picture, also taken in Squaw Creek, a sandbar has been formed by sediment that has been washed down the river. This might also be considered a spit.

Deposition

• In this picture, salt has been deposited in the Great Salt Lake, Utah. You can see the salt deposits. They appear as white areas on the edge of the water.

Landforms

• http://www.classzone.com/books/earth_science/terc/content/visualizations/es1205/es1205page01.cfm?chapter_no=visualization

Erosion Control Methods:

• These native plants were left undisturbed on the beach in Costa Rica, so that they would hold in the sand and prevent erosion on the beach. This is an example of permanent erosion control.

other examples of erosion control:

silt fencing

terracing

River Formation

• A river is a natural stream of freshwater that is larger than a brook or creek. Rivers are normally the main channels or largest tributaries of drainage systems. Typical rivers begin with a flow from headwater areas made up of small tributaries, such as springs. They then travel in meandering paths at various speeds. Finally, they discharge or flow out into desert basins, into major lakes, or most likely, into oceans.

Erosion and Deposition• Meanders are formed

by the weathering of one bank of a river and the deposition of the weathered sediment on the opposite bank of the river. This creates a loop-like bend in a river, such as this one. This view was taken from an airplane over a mountain range in the midwest.

•changes in a meandering river• http://www.classzone.com/books/earth_science/

terc/content/visualizations/es1306/es1306page01.cfm?chapter_no=visualization

• formation of an oxbow lake:• http://www.cleo.net.uk/resources/

displayframe.php?src=309/consultants_resources%2F_files%2Fmeander4.swf

The world's longest river is the Nile River in Africa, which runs 4,187 miles (6,739 kilometers) from its source in Burundi to the Mediterranean Sea.

•

• Every river has a point of origin- it is the highest point in the water basin.

• Gravity- is important; rivers almost always flow downhill watercourse.

• Some rivers start from springs, especially in humid climates. Springs occur as groundwater rises to Earth's surface and flows away.

• Other rivers originate from lakes, marshes, or runoff from melting glaciers located high in the mountains. Some rivers have their beginnings in huge glaciers.

Steps to River Formation1) Precipitation (rainwater or snow ) is the source of the water for most

rivers. 2)When a heavy rain falls on ground that is steeply sloped or is already

saturated with water, water runoff trickles down Earth's surface rather than being absorbed- this is called surface runoff.

3) After it travels a short distance, the water begins to run in small parallel rivulets called rills.

4) As these rills pass over fine soil or silt, they begin to dig shallow channels, called gullies. This is the first stage of erosion. A gully only has water in it when it rains.

5) A stream is formed when gullies join together. It is a channel along which water is continually flowing down a slope. Streams rarely dry up.

6) A stream grows larger as it gets water from tributaries. A tributary is a stream that flows into a larger stream.

Visual steps to river formationRills

gullies

River System

Notes quiz1. Examples of mechanical weathering area) ice wedging, animal actions, oxidationb) plant growth, ice wedging, abrasionc) freezing and thawing, burrowing, acid rain

2. Examples of chemical weathering are• a) acid rain, oxidation, living organism• b) freezing and thawing, animal actions,

oxidation• c) burrowing, carbon dioxide, abrasion

3. Deposition isa) the movement of sediment or rockb) the settling out of sediment or rockc) the breaking down of sediment or rock

4. A meander is• a) a small river that runs into a larger river• b) a loop-like bend in a river• c) a lake that has been cut off from a river

• 8) Rills in soil run together to form __________ that only have water in them when it rains.

• 9) What forms when gullies join together?• a) a rill• b) a stream• c) a tributary

• 10) What is the original source of water of most rivers? (1st step in river formation)