Weathering and Erosion

Mrs. Degl 4

Weathering, Erosion, Deposition, and Landscapes

Weathering – the mechanical and chemical processes that change objects on Earth’s surface over time.

Weathering breaks down the rocks, erosion moves the particles, and deposition drops the sediments in another location.

Erosion – the removal of weathered material from one location to another; the sediments are transported by wind, gravity, glaciers, man, and running water.

Deposition – the process whereby these sediments are released by their transporting agents (dropped).

Weathering – responsible for limited changes in Earth’s surface – dissolving, crumbling or weakening a rock.

Can take thousands of years.

Two forms – physical and chemical

Erosion – responsible for large scale changes in the form of the Earth.

Rivers, valleys, and canyons are created by the erosion of weakened or disintegrated rock.

Can take thousands of years or minutes.

Water is a major factor in weathering.

Rain splashes mud

Puddles form

Water flows along surface, moving downhill.

Little water paths become rills.

Rills deepen into creeks, then streams, and finally, rivers.

Water digs deeper channels and carries more earth and rock from shores and bottom.

Stream

Large river

13

There are two primary types of weathering:Chemical and Physical

1. Physical Weathering – the breakdown of rocks and minerals into smaller pieces without a change in chemical composition.

Causes of physical weathering:1. Freeze/thaw2. Wedging by plant roots3. Day/Night temperature fluctuations4. Loss of thin surface of rocks by exfoliation or

abrasion5. Gravity causing rocks to fall from heights and then

breaking into pieces6. Animals, including people, digging into rocks

Freezing & Thawing

When water in the cracks of rocks freezes it expands causing the crack to enlarge or get bigger. The ice melts & refreezes over & over, breaking the rock apart.

Result of Freezing & Thawing

Mrs. Degl 16

Wedging by plant roots

Day/Night Temperature fluctuations

Exfoliation

Abrasion, wind erosion

Gravity

Old Man in the Mountain, NH before May 5, 2003

After May 5, 2003

Animal actions

• Physical weathering exposes new surfaces and pieces.

• New surfaces can be physically or chemically weathered

22

23

2. Chemical Weathering – Decomposition of rock material due to the chemical reaction of compounds in the rock with chemicals in the environment.

Not all rocks are composed of the same chemicals or minerals, so chemical weathering affects different rocks differently.

24

Chemical weathering occurs at the surfaces of rocks.

When physical weathering results in freshly exposed rock surfaces, agents of chemical weathering have new material to decompose.

Mrs. Degl 25

Chemical Weathering occurs when elements and minerals in rocks react with chemicals from the environment. The rock breaks down at the same time as it changes chemical composition. The end result is different from the original rock. There are 3 main types of chemical weathering:

1. Oxidation – oxygen combines with the elements in the rock and it reacts. This the scientific name for rust.

2. Hydration – water reacts with the minerals in rocks and can dissolve certain minerals.

3. Carbonation – carbon dioxide dissolves in water to form carbonic acid. This makes acid rain which chemically weathers (dissolves) rocks. Other acids, like sulfuric acid, also combine with water to make acid rain.

26

Chemical Weathering: H2O + CO2 H2CO3

water + carbon dioxide carbonic acid

Statue created in 1702, Germany

Picture on left, taken 1908 (after 206 years) Picture on right, taken 1969 (61 years later)

Mrs. Degl 27

2. Particle Size – Larger particles weather slower and smaller particles weather at a faster rate.

There are 4 factors that effect the rate of weathering:1. Surface Area (exposure) - Exposing more surface area will increase the rate of weathering.

3. Chemical Composition (what a rock is made of) – Certain rocks and minerals are naturally weaker than others, while others are more resistant (stronger). 4. Climate – Warmer, moister climates have the most weathering. Heat & water speed up all chemical reactions. This is the most important factor in weathering.

Mrs. Degl 28

Erosion (transport)There are 5 main agents of erosion:1. *Running Water*2. Glaciers3. Wind4. Gravity 5. Man

Weathering has to happen before erosion. The rocks have to be broken into smaller sediments before they can be eroded away.

Wind Erosion

Glacier

Mrs. Degl 29

Mount Rushmore There is a pile of weathered material at the bottom. It is slowly being eroded down hill by gravity. It will not be there forever!!

Water, wind, or gravity exert a force on the soil material, causing it to move.

When erosion occurs on a slope, soil is washed from the slope. The steeper the slope, the more erosion can occur.

Obstacles like rocks and vegetation can slow the progress of erosion or divert the path of the erosion.

 

30

Investigation 1

• CaCO3 + 2HCl CaCl2 + CO2 + H2O Calcium Hydrochloric Calcium Carbon Water

carbonate acid chloride dioxide

GAS Marble – consists mostly

of the mineral calcium carbonate (CaCO3)

31

32

Mantle Convection and Plate Tectonics

33

Hot mantle rises, cools at surface and sinks.

Crust floats on mantle. New crust material comes from rising mantle, pushes old crust away.

Mantle Convection and Plate Tectonics

34

Plate Tectonics Over Geologic Time

35

Wind erosion

Sandstone 36

Sand grains carried by strong and consistent winds act as abrasives capable of sculpting solid rock.

Wind erosion

Dust Bowl in Texas, 1935 37

Soil erosion in cultivated farmlands can result in devastating dust storms.

Water erosion

Cannon Beach, Oregon 38

Water erosion

39

Factors that influence water erosion

40

• Rainfall intensity and runoff – heavy bursts of hard rain cause more soil erosion than light rain. Heavy rains can saturate soil and create puddles that flow with gravity and start erosion

Factors that influence water erosion

41

• Slope gradient – water erosion is more likely on steeper surfaces, water moves very quickly down the side of a steep hill

• Vegetation – plant roots can absorb water, hold soil, leaves and branches absorb energy of raindrops

Rock Cycle

• http://www.classzone.com/books/earth_science/terc/content/investigations/es0602/es0602page02.cfm Interactive rock cycle

42

Mrs. Degl 43

Soil forms from the weathering of the rock below it. The solid rock below is called Bedrock. The rock is exposed to wind, rain etc… The rock breaks down over time to form soil. Soil has different layers called Soil Horizons.

O- Horizon = the very thin surface covering (not really a layer)A – Horizon (TOPSOIL) = dark surface soil that contains a lot of living material and dead plant/animal remains (humus). This is the layer with all of the nutrients needed to grow plants.B-Horizon (SUBSOIL) = lighter colored soil with less nutrients and more clayC-Horizon (REGOLITH) = larger rock fragments that sit on top of the unweathered bedrock

Soil

• Soil is the product of weathering and erosion.

44

What do you see in the soil?

45