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Chapter 5: Weathering and Erosion

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1 Chapter 5: Weathering and Erosion

2 Weathering Weathering is the chemical and physical breakdown of rocks at or near Earth’s surface. This occurs when rocks are exposed to air, water, pressure changes, and the actions of living things. Weathering is the reason most landscapes look the way they do. Weathering affects buildings and roads too.

3 What’s an example of weathering that you encounter everyday if you drive in a car or ride the bus?
Potholes! Potholes are areas of road that have been broken apart by physical weathering.

4 Types of Weathering

5 Chemical Weathering Chemical weathering is the breakdown of a rock through a change in mineral or chemical composition. Chemical Weathering = Change in Composition

6 Chemical Weathering Oxidation is a type of chemical weathering.
This is when oxygen combines with another chemical. When iron rusts, this is oxidation.

7 Chemical Weathering Another form of chemical weathering is from water.
Acids from decaying organic matter mixes with the water creating acidic water. This acidic water can dissolve rocks. Water can also combine with carbon dioxide creating carbonic acid (soda). This easily dissolves limestone and marble.

8 Physical Weathering The break down of rock into smaller pieces without chemical change is physical weathering. Physical Weather = Pieces of the original

9 Physical Weathering Frost action breaks up rocks. When water freezes, its volume expands. After the water expands inside the rocks, the rocks begin to crack. Over a long winter, the cracks grow and the rock eventually crumbles

10 Physical Weathering Another type of physical weathering has to due with pressure. If the pressure on a rock is reduced, by man made or natural forces, the rock has room to expand and crack.

11 Physical Weathering Abrasion is another type of physical weathering where rock particles grind against other rock. These rocks can be moved by ice, gravity, running water, or air. These rocks are usually rounded.

12 Factors Affecting the Rate and Type of Weathering

13 Exposure The rate and type of weathering depend on the exposure of the rocks to air, water, and the actions of living things. The closer a rock is to the surface of Earth the faster it will weather.

14 Exposure The amount of energy from the sun (solar energy) on the north and south side of a mountain affect the temperature and moisture, which in turn affects weathering. This causes different soil properties on opposite sides of the mountain.

15 Particle Size When rocks are smaller the amount of surface area per unit volume exposed to weathering is greater. What this means to us: A smaller rock weathers faster What dissolves faster, a sugar cube or granulated sugar?

16 Mineral Composition The minerals that make up the rocks have different properties that affect weathering. Calcite found in limestone and marble weather quickly in slightly acidic water. Quartz does not dissolve easily, so it is usually weathered physically into sand.

17 Climate Chemical weathering occurs more in warm, wet climates.
Chemical Weathering = Warm, Wet Climate (CW, WC) In cold climates frost action is the most common form of weathering.

18 Soil formation

19 Soil Formation Soil is a mixture of rock particles and organic matter on Earth’s surface that supports rooted plants. Why is sand not considered soil?

20 Organic Material & Soil Formation
Plant roots widen cracks in rocks.

21 Organic Material & Soil Formation
Plants drop leaves that decay and release acids that dissolve rocks. Dead leaves and other organic materials that provide nutrients in the soil is called humus.

22 Soil Formation Soil can form where bedrock was before.
Over time soil develops in horizontal layers with distinct layers. This soil has similar properties to it’s parent soil. The most important factor in the the type of soil formed is the climate.


24 Soil Formation Soil can be moved by moving water, wind, or a glacier.
Already formed soil is directly transported. Sediments are transported by erosion and the deposited sediments become the parent material for soil.

25 NYS Soil Formation The soil in NYS came from sediments deposited (left behind) from glaciers in the last ice age Most soil in NYS is considered immature soil.

26 0:39 0:38 0:40 0:41 0:43 0:42 0:37 0:36 0:31 0:30 0:32 0:33 0:35 0:34 0:44 0:45 0:54 0:53 0:55 0:56 0:58 0:57 0:52 0:51 0:47 0:46 0:48 0:49 0:50 0:29 0:28 0:08 0:07 0:09 0:10 0:12 0:11 0:06 0:05 End 2:00 0:01 0:02 0:04 0:03 0:13 0:14 0:23 0:22 0:24 0:25 0:27 0:26 0:21 0:20 0:16 0:15 0:17 0:18 0:19 0:59 1:00 1:40 1:39 1:41 1:42 1:44 1:43 1:38 1:37 1:32 1:31 1:33 1:34 1:36 1:35 1:45 1:46 1:55 1:54 1:56 1:57 1:59 1:58 1:53 1:52 1:48 1:47 1:49 1:50 1:51 1:30 1:29 1:09 1:08 1:10 1:11 1:13 1:12 1:07 1:06 1:02 1:01 1:03 1:04 1:05 1:14 1:15 1:24 1:23 1:25 1:26 1:28 1:27 1:22 1:21 1:17 1:16 1:18 1:19 1:20 2:00

27 Erosion

28 Erosion Erosion is the process of weathering rocks that are transported as sediments. Sediments that are moved from their original location are evidence of erosion. Proof that this occurs can be seen in muddy streams, beaches, along rivers, and in soil.

29 Transporting Systems of Erosion

30 Transporting Systems of Erosion
Erosion involves a system which must include these things: An agent of erosion stream, glacier, wave, current, wind or human activity The sediment being moved A driving force Usually gravity

31 The Driving Force Gravity is usually the driving force.
Rocks in higher elevations have potential energy (stored energy waiting to be used). When the rocks fall, the potential energy is converted into kinetic energy.

32 Gravity Erosion Gravity is the driving force behind erosion.
It causes sediments to flow downhill by running water, glaciers, and underwater currents. Gravity can also act on its own pulling rocks and sediments down hill in mass movement. Mass movement is usually referred to as a land slide.

33 Mass Movement This is sometimes called direct gravity erosion.
There are two forces working against each other in a mass movement. Gravity forcing the rocks down Friction trying to keep the rocks in place Ever heard, every action has an equal and opposite reaction……. This is what is going on here.

34 Mass Movement Mass movement is caused a reduction in the frictional force. This means: something has to change and there is nothing forcing the rocks/dirt to stay where they are. This is usually caused by a large about of rain, an earthquake, waves, and road building activities.

35 Running Water Erosion and Streams
Something as small as a few raindrops can be an agent of erosion. During rainstorms small amounts of water often find a channel of a temporary stream valley called a rill or gully.

36 Running Water Erosion and Streams
If a channel of running water exists it is considered a stream. A smaller stream that flows into a larger stream is called a tributary. If water flows through this channel for the major part of the year it is considered a permanent stream

37 Running Water Erosion and Streams
Streams carry sediments in multiple ways. Dissolved minerals are carried in solution. Clay sized particles are suspended in the water aka they float around in the water. Larger solid sediments are carried by rolling along the stream bottom. This is why they are rounded. The rounding of the rocks is called stream abrasion.

38 Running Water Erosion and Streams
Streams carve deeper channels. The channel is V-shaped. Rivers cause V-shaped valleys. The area of land drained by any stream is called its watershed. Watersheds can range in size from a book to an entire continent. A landmass that divides watersheds in called a divide. The Rocky Mountains divide the USA into two main watersheds, toward the Pacific Ocean and toward the Atlantic Ocean.

39 Stream Velocity Three factors in determining stream velocity.
The slope of the stream or gradient. The volume of water in the stream. Shape of the stream bed.

40 Stream Velocity If a large amount of water touches the stream bed, there is more friction, causing a slow down in the stream velocity. If less water touches the surface of the stream, there is less friction and a higher velocity.

41 Stream Velocity Water does not move at equal velocities throughout a stream. When the stream is straight, the maximum velocity is in the center. When the stream curves, the maximum velocity is the outside of the curve.

42 Stream Velocity Stream velocity also varies with depth.
The highest velocity is just below the surface has. The velocity is the lowest at the bottom of the stream. The surface of the stream has a slower velocity due to air friction.


44 Stream Velocity A stream with a greater velocity can carry larger sediments. Use the table in the ESRT to answer questions on sediment size.

45 Evolution of a Stream Streams change over time.
The picture on the your packet shows a stream in various parts of its evolution. 1. This stream starts in the finger lake. Finger lakes are bodies of water in U-Shaped valleys carves by glaciers and often partly dammed at one end by a pile of glacially deposited sediments.

46 Evolution of a Stream 2. The stream then down cuts a narrow V-shaped valley. There is usually a steep slope and many abrupt changes in elevation resulting in waterfalls and rapids.

47 Evolution of a Stream 3. As the stream grows larger, it begins to shift its course in a series of bends, this is called meanders. This creates a flood plain because the water may flow out of the stream.

48 Evolution of a Stream 4. At the end of a stream, it cuts a wide valley and an equally wide flood plain. Sediments are deposited in the valley, creating a delta.

49 Wind Erosion When sediments the size of sand or smaller are near solid surface, they can be moved by wind. Arid (dry) areas, such as deserts and lake and ocean coastlines are the most common places where loose sediments are available for wind erosion.

50 Wind Erosion There are two parts to wind erosion
Deflation: Wind blows away the loose sediments, lowering the land surface. Sandblasting/Abrasion: Wind blows sand against other objects causing abrasion.

51 Glacial Erosion Glaciers are a naturally formed mass of ice and snow that moves downhill on land under the influence of gravity. Glaciers behave like water in their movements.

52 Types and Features of Glacial Erosion
When a glacier moves over land, the rocks and anything under it freeze into the ice and are dragged along. These rocks create drag marks on the ground they move over. These gouging and sanding actions produce glacial grooves and glacial parallel scratches.

53 Types and Features of Glacial Erosion
These gouging and sanding actions produce glacial grooves and glacial parallel scratches. The direction of the glacial grooves and scratches on bedrock shows the direction of former glacial movements.

54 Types and Features of Glacial Erosion
Sediments are carried on glaciers on or near the surface of the glacier. The pieces of rock carried by a glacier can be the size of a house.

55 Types and Features of Glacial Erosion
These sediments can be carried hundreds of miles. These transported rocks are usually made of very different minerals. They are called erratics. A glacier creates a U-shaped valley.

56 Wave and Current Erosion
When wind transfers energy to the surface of water (lake or ocean) it creates waves. When waves enter shallow waters the wave drags on the bottom of the shore and the wave becomes unstable. Water rushes toward the shore as breaking waves.

57 Wave and Current Erosion
There is a lot of energy in a crashing wave. Waves arrive at an angle to the shore because they are bent, concentrating the energy into other locations. These areas of high energy are usually eroded away over time.


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