Background Information
Weathering
- Rocks are broken down into progressively smaller pieces by the effects of weather
- These pieces do not move to a new location, they simply break down, but remain next to one another
- Often rocks are broken down so much that they become dirt
- Products of weathering: clay, sand, rock fragments, and soluble substances
- These pieces do not move to a new location, they simply break down, but remain next to one another
- Often rocks are broken down so much that they become dirt
- Products of weathering: clay, sand, rock fragments, and soluble substances
Physical Weathering
- Takes place when rocks are broken down without any change in the chemical nature of the rocks.
- The rocks are essentially torn apart by physical force, rather than by chemical breakdown.
- Types:
- Swiftly moving water
- Plant Roots
- Constant freezing, and thawing of water
- Salt wedging- as water leaves rocks, the salt is left behind and salt deposits build up, creating pressure that can cause rocks to split and weaken
- Temperature changes- as temperatures heat up, the rocks themselves expand somewhat; as the temperatures cool down, rocks contract slightly; the effect can be the weakening of the rock itself
- The rocks are essentially torn apart by physical force, rather than by chemical breakdown.
- Types:
- Swiftly moving water
- Plant Roots
- Constant freezing, and thawing of water
- Salt wedging- as water leaves rocks, the salt is left behind and salt deposits build up, creating pressure that can cause rocks to split and weaken
- Temperature changes- as temperatures heat up, the rocks themselves expand somewhat; as the temperatures cool down, rocks contract slightly; the effect can be the weakening of the rock itself
Chemical Weathering
- Takes place in almost all types of rocks; smaller rocks are more susceptible because they have a greater amount of surface area
- Chemical reactions break down the bonds holding the rocks together, causing them to fall apart, forming smaller and smaller pieces
- The most common types of chemical weathering are oxidation, hydrolysis and carbonation.
- Chemical reactions break down the bonds holding the rocks together, causing them to fall apart, forming smaller and smaller pieces
- The most common types of chemical weathering are oxidation, hydrolysis and carbonation.
Physical vs. Chemical Weathering
- One way to understand the difference between physical weathering and chemical weathering is to imagine two pieces of paper that are the same size. The first piece of paper is torn into tiny pieces. Then the second one is burned.
- Tearing up the piece of paper is an example of physical disintegration. Even though the paper is shredded into tiny pieces, the physical properties of the paper have not changed.
- By contrast, burning the second piece of paper is an example of chemical decomposition. That is because burning the paper leaves a new composition of ashes
- Tearing up the piece of paper is an example of physical disintegration. Even though the paper is shredded into tiny pieces, the physical properties of the paper have not changed.
- By contrast, burning the second piece of paper is an example of chemical decomposition. That is because burning the paper leaves a new composition of ashes
Erosion
- Takes place when materials in the landscape are moved from one location to another
- Examples: dust is blown off the side of a cliff face by wind, or as silt is carried downstream by a river
- Once rocks have been broken down by weathering and by mass wasting, the final fate of all materials is to be carried away to another location by erosion.
- Examples: dust is blown off the side of a cliff face by wind, or as silt is carried downstream by a river
- Once rocks have been broken down by weathering and by mass wasting, the final fate of all materials is to be carried away to another location by erosion.
Water Erosion
- The most influential force in erosion is water. Water’s ability to move materials from one location to another, along with the fact that it is found everywhere along the surface of the earth, make it a superb tool for erosion.
- Rain carries away bits of soil and slowly washes away rock fragments.
- Rushing streams and rivers wear away their banks, creating larger and larger valleys.
- In a span of about 5 million years, the Colorado River cut deeper and deeper into the land in what is now the U.S. state of Arizona. It eventually formed the Grand Canyon, which is more than 1,600 meters (1 mile) deep and as much as 29 kilometers (18 miles) wide in some places. - Waves constantly crash against shores. They pound rocks into pebbles and reduce pebbles to sand. Water sometimes takes sand away from beaches. This moves the coastline farther inland.
- The Cape Hatteras Lighthouse was built in 1870, on theOuter Banks, a series of islands off the coast of the U.S. state of North Carolina. At the time, the lighthouse was nearly 1,000 meters (3,300 feet) from the ocean. Over time, however, the ocean eroded most of the beach near the lighthouse. By 1999, the surf endangered the structure. Many people thought it would collapse during a strong storm. The lighthouse was moved 880 meters (2,900 feet) inland.
- Rain carries away bits of soil and slowly washes away rock fragments.
- Rushing streams and rivers wear away their banks, creating larger and larger valleys.
- In a span of about 5 million years, the Colorado River cut deeper and deeper into the land in what is now the U.S. state of Arizona. It eventually formed the Grand Canyon, which is more than 1,600 meters (1 mile) deep and as much as 29 kilometers (18 miles) wide in some places. - Waves constantly crash against shores. They pound rocks into pebbles and reduce pebbles to sand. Water sometimes takes sand away from beaches. This moves the coastline farther inland.
- The Cape Hatteras Lighthouse was built in 1870, on theOuter Banks, a series of islands off the coast of the U.S. state of North Carolina. At the time, the lighthouse was nearly 1,000 meters (3,300 feet) from the ocean. Over time, however, the ocean eroded most of the beach near the lighthouse. By 1999, the surf endangered the structure. Many people thought it would collapse during a strong storm. The lighthouse was moved 880 meters (2,900 feet) inland.
Wind Erosion
- Serious problem in many parts of the world. It is worse in arid and semiarid regions. Wind erosion is a major problem on about 75 million acres of land in the United States. About 5 million acres are moderately to severely damaged each year.
Causes automobile accedents, fouls machinery, and imperils animal and human health.
Sand dunes, dust bowels, dessert hills
Causes automobile accedents, fouls machinery, and imperils animal and human health.
Sand dunes, dust bowels, dessert hills
Ice Erosion
- As glaciers move, they pick up everything in their path, from tiny grains of sand to huge boulders.
- The rocks carried by a glacier rub against the ground below, eroding both the ground and the rocks. Glaciers grind up rocks and scrape away the soil. Moving glaciers gouge out basins and form steep-sided mountain valleys.
- Several times in Earth's history, vast glaciers covered parts of the Northern Hemisphere. These glacial periods are known as ice ages. Glaciers carved much of the northern North American and European landscape.
- Today, in places such as Greenland and Antarctica, glaciers continue to erode the earth. These ice sheets, sometimes more than a mile thick, carry rocks and other debris downhill toward the sea.
- The rocks carried by a glacier rub against the ground below, eroding both the ground and the rocks. Glaciers grind up rocks and scrape away the soil. Moving glaciers gouge out basins and form steep-sided mountain valleys.
- Several times in Earth's history, vast glaciers covered parts of the Northern Hemisphere. These glacial periods are known as ice ages. Glaciers carved much of the northern North American and European landscape.
- Today, in places such as Greenland and Antarctica, glaciers continue to erode the earth. These ice sheets, sometimes more than a mile thick, carry rocks and other debris downhill toward the sea.
Deposition
- The process by which rocks, sand and sediment are deposited by the forces of erosion.
- Landforms produced by deposition
- In the desert and beach, the deposition patterns of the wind creates sand dunes.
- Streams create deltas when they deposit sand and sediment at their mouths, where the water slows to meet the ocean.
- The waves of the ocean create beaches as they deposit sand over time.
- Deposition and Egyptian Civilization- The action of the Nile river in ancient Egypt is one of the best examples of how deposition can positively affect human society. Each year, the Nile river flooded, depositing silt over the lands closest to its banks. Because of this fertile soil, the farmland could produce bountiful crops. In this way, the process of deposition was important to the flowering of ancient Egyptian civilization.
- Landforms produced by deposition
- In the desert and beach, the deposition patterns of the wind creates sand dunes.
- Streams create deltas when they deposit sand and sediment at their mouths, where the water slows to meet the ocean.
- The waves of the ocean create beaches as they deposit sand over time.
- Deposition and Egyptian Civilization- The action of the Nile river in ancient Egypt is one of the best examples of how deposition can positively affect human society. Each year, the Nile river flooded, depositing silt over the lands closest to its banks. Because of this fertile soil, the farmland could produce bountiful crops. In this way, the process of deposition was important to the flowering of ancient Egyptian civilization.
Erosion and People
- Erosion is a natural process, but human activity can make it happen more quickly.
- Trees and plants hold soil in place. When people cut down forests or plow up grasses for agriculture or development, the soil washes away or blows away more easily. Landslides become more common. Water also rushes over exposed soil rather than soaking into it, causing flooding.
- Erosion control- the process of reducing erosion by wind and water.
- Erosion and sedimentation controls include a wide range of temporary and permanent measures. Planting vegetation is one of the best ways to stabilize soils and minimize erosion. Sedimentation ponds are used to capture storm runoff and allow sediment to settle to the pond's bottom, and silt fences are used to contain water runoff and minimize sedimentation in nearby streams. As the picture to the right shows, silt fences do not always work.
- Trees and plants hold soil in place. When people cut down forests or plow up grasses for agriculture or development, the soil washes away or blows away more easily. Landslides become more common. Water also rushes over exposed soil rather than soaking into it, causing flooding.
- Erosion control- the process of reducing erosion by wind and water.
- Erosion and sedimentation controls include a wide range of temporary and permanent measures. Planting vegetation is one of the best ways to stabilize soils and minimize erosion. Sedimentation ponds are used to capture storm runoff and allow sediment to settle to the pond's bottom, and silt fences are used to contain water runoff and minimize sedimentation in nearby streams. As the picture to the right shows, silt fences do not always work.