Module #13 - Weathering and Erosion

INSTRUCTIONS FOR TODAY

1. Video of the Day: How the Earth Was Made: 25 Strangest Geological Formations on Planet Earth (8 min.)

Be sure to make point form notes from this video in your digital video journal. Please make sure this document is SHARED with Mr. Durk.

2. Read the following information below in Part 1: Background and Terminology. Follow all hyper-links to external websites for activities, demonstrations and videos (if applicable). Copy only KEY information (i.e. the highlighted terms) to your notebook (in google docs). The multiple choice question provided below are for your understanding ONLY.

3. Today, you have two choices for completing Module #13:

Option #1: Complete the Weathering Webquest (see below) and complete. Send your answers using google docs to Mr. Durk using the ugcloud.ca. You will need to record your answers on a separate google doc.

Weathering Webquest

Weathering Webquest LINK (NOTE: This is a flash animation, so it must be completed on a desktop or chromebook)

Option #2: Erosion or Mass Movement: Case Study: Piktochart. Find a particular place in the world that is experiencing severe erosion (coastal, soil, etc.) or a famous mass movement. Create a Piktochart highlighting the issues, locations, and specific characteristics of this erosion / mass movement. You are required to use the website provided, which will mean that you will need to create an account and learn how to use the software.

DUE DATE: Submit all components to Mr. Durk before Module #14 (Tuesday May 3rd)

Part 1: Background and Terminology

Weathering

Weathering is the breakdown of any rock in situ (without movement). We can classify all types of weathering into two general categories: chemical and physical.

Chemical Weathering

The three main agents of chemical weathering are dissolution, plant decay and oxidation. In each case, rock reacts with water, gases or acids to cause breakdown. Some landform features associated with chemical weathering include caves and karst topography. In general, the softer the rock type, the easier it is chemically weathered.

Karst Topography, mountains created by chemical weathering

Credit: U.S. Geological Society/photo by Monroe, W.H.

Physical Weathering

As the name suggests, this type of weathering does not involve any chemicals. There are many different types of physical weathering and they often have a greater visual effect on the landscape than chemical weathering.

Thermal Expansion

Thermal expansion, also known as onion-skin weathering occurs in deserts where hot days and cool night’s causes stress on the outer layers of rocks. The stresses then cause the outer layers to peel off.

Freeze Thaw

Freeze Thaw weathering, also known as frost wedging occurs when liquid water enters cracks in exposed rocks and is then frozen. Water expands up to 9% of its volume when frozen so this added pressure begins to crack the rock. As this process of freeze thaw continues, the cracks expand and eventually pieces of the rock may fall off.

Pressure Release

Pressure release weathering occurs when material such as soil is eroded from the surface and exposes rock. The decrease in pressure on the rock causes it to expand, and then break down.

Salt Crystal Growth

Similar to freeze thaw weathering, salt crystal growth occurs when crystal of salts, within the cracks of rocks expand. This type of weathering is normally associated with arid environments and coast lines.

Biotic Weathering

A final type of weathering and probably one of the most interesting is biotic weathering that occurs when living organisms cause the break down of rock. This may be from the chemicals produced by lichens or mosses or by pressure exerted on rock by tree and plant roots.

Erosion

Erosion is the process of the movement of solid material (rock, soil, mud, etc.) by agents such as wind, water ice. It may also occur when materials move downslope, due to gravity.

Causes of Erosion

• amount and intensity of precipitation

• texture of the soil

• gradient of the slope

• ground cover

• land use

Types of Erosion

Gravity Erosion

This type of erosion moves rock and sediment downslope due to the force of gravity. It is also known as mass wasting, which we will look at on the next page.

Water Erosion

here are many types of water erosion depending on the intensity of rainfall. Splash erosion is caused by the impact of raindrops on soil. Sheet erosion occurs when heavy rain on bare soil carries sediment downslope. When there is more rain falling then can be absorbed, surface runoff occurs. This can produce gullying features. Finally streams and rivers cause downward erosion on high slopes forming a V pattern. In flatter areas the river will erode laterally (side to side).

River Erosion

Reproduced with the permission of the Minister of Public Works and Government Services Canada, 2006

Courtesy of Natural Resources Canada, Geological Survey of Canada

Shoreline Erosion

As the name suggests, this type of erosion occurs along coastlines. Continued wave action on both hard and soft coastlines will eventually cause sediment and rock to erode. This type of erosion can be increased with tidal actions. You will look more at features created by shoreline erosion in further activities.

Ice Erosion

Ice erosion is caused by the movement of glaciers, both alpine and continental. Glaciers break up the rock and transport it leaving a variety of features behind including: drumlins, morraines, and others. Again, you will study glacial features later in this unit.

Wind Erosion

This type of erosion is also known as eolian erosion. Sediment is commonly entrained by winds and is transported, but at high velocities, wind can also transport rocks. Vegetation can often impede or stop wind erosion.

Mass Wasting

This type of erosion is also known as slope movement occurs when soil, rock and or sediment move downslope under the force of gravity.

Types of Mass Wasting

Creep

This is a long term process. It occurs as small movements of soil or rock gradually moving downslope over time. In general, the steeper the slope the faster the creep.

Landslides

This happens when a large section of land slides during one movement. There is usually a well defined zone of sliding. It may also be known as a rock slide or a slump.

Flows

This occurs when excess water air and or ice causes the movement of rock and soil to exhibit a fluid behaviour. This can include avalanches, mudflows, debris flows and earth flows.

Topples and Falls

This last type of mass wasting occurs when blocks of rock fall away from a slope.

Causes of Mass Wasting

Soil and rock only as long as the gravitational forces are not stronger than fictional forces. Certain factors are able to reduce the frictional force, which causes the gravitational force to become stronger, creating mass wasting. Examples of these factors include:

• seismic shaking

• increased pressure from structures

• increased soil moisture

• reduction of roots from vegetation

• undercutting of the slope

• weathering by frost heave

Questions: For your own understanding ONLY.

• 1. Which of the following is not a type of erosion?

  2. a) wind

  3. b) rain

  4. c) ice

  5. d) acid

• 1. Answer

  2. This type of physical weathering occurs because of differences in temperature daily.

  3. a) pressure release

  4. b) freeze thaw

  5. c) thermal expansion

  6. d) salt crystal growth

• 1. Answer

  2. Salt crystal weathering is mostly likely to occur in what environment?

  3. a) coastal areas

  4. b) tundra

  5. c) jungles

  6. d) mountainous

• 1. Answer

  2. Splash erosion involves the action of:

  3. a) rivers

  4. b) lakes

  5. c) raindrops

  6. d) waterfalls

• 1. Answer

1. Which is not a cause of mass wasting:

   1. a) wind

   2. b) increased moisture

   3. c) earthquakes

   4. d) frost heave

• 1. Answer