1. Weathering & Erosion

2. Earth’s Changing Surface
Earth is a constantly changing body affected by natural forces:
On the Inside:
Plate Tectonics = moving of Earth’s Plates driven by convection currents
Earthquakes & Volcanoes
On the Outside:
Weathering & Erosion

3. Weathering & Erosion
Weathering is the process of breaking down or dissolving the earth’s rocks.
Mechanical Weathering
Chemical Weathering
Erosion is the process of moving particles of rock from one locations to another.
Water
Glaciers
Wind
No rock is heard enough to resist the forces of weathering and erosion. Together they shape Earth’s topography.

4. Weathering
The interaction of the lithosphere (rock) with the atmosphere (air) and hydrosphere (water) results in weathering.
Driven by climate, combination of temperature and precipitation.
Hot & humid = greater amount of weathering
Cool & Dry = reduced amounts of weathering

5. Physical Weathering
The type of weathering in which rock is slowly, mechanically broken down into smaller pieces.
Changes the size and shape of the rock but not is composition.
Factors:
Freezing and Thawing
Plant & Animal Actions
Abrasions

6. Freezing and Thawing
In colder climates, water seeps into cracks and freezes.
The freezing water expands, making the crack bigger – frost action.

7. Growth of Plants
As plants grow, their roots move into the cracks of rocks.
As roots grow, cracks become larger.
Roots grow into
cracks and make
them bigger.

8. Animal Actions
As animals dig burrows in the ground they loosen and break apart rocks in the soil.

9. Abrasion
Wind, water and ice carry smaller sand and rock particles that act like sandpaper on other rock surfaces.
Glacial Abrasion
Wind Abrasion

10. Chemical Weathering
The process of weathering that changes the rock’s size, shape AND composition.
Produces rock particles that have a different mineral makeup from the rock that it came from.
Agents:
Water
Oxygen
Carbon dioxide
Acid rain

11. Water
The universal solvent that dissolves substances, solutes, into solution.
As a rock is covered by water, minerals leave the rock by dissolving out.
Creates spaces in the rock that can weaken it and cause it to break apart.

12. Oxygen
Oxygen reacts easily with other substances changing their properties.
Oxygen (O) + Iron (Fe) = Iron oxide (Fe2O3), rust

13. Carbon Dioxide
Does not contribute to chemical weathering until dissolved in water.
Water (H2O) + Carbon Dioxide (CO2) = (H2CO3) carbonic acid
Carbonic acid dissolves calcite,
found in limestone. Causes caves
and caverns; Howe Caverns

14. Acid Rain
Acid rain comes mostly from the burning of coal by power plants in the Midwest.
Sulfur oxides rise into the air combining with water to form sulfuric acid.
Lowers the pH of water and bedrock killing off living organisms.
pH of lemon juice

16. Soil Formation
The formation of soil is a slow and complex process through the processes of weathering mixing with organic matter.
Can be hundreds to thousands of years, years, in hard rock areas.
Can takes less time, 20 years, in softer bedrock areas of shale and sandstone.

17. Soil Formation Partially weathered Rock Unweathered Rock Immature Soil
Top Soil
Top Soil
Partially weathered
Rock
Subsoil
Unweathered
Rock
Partially
weathered
Rock
Unweathered
Rock
Unweathered
Rock
Immature Soil
Mature Soil

18. Soil Horizons Horizons: O Horizon – organic material
Decayed plants and animals,
humus
A Horizon – topsoil
Humus, clay and minerals
B Horizon – subsoil
Clay but little humus
C Horizon – bedrock
Partly weathered rock

19. Soil Composition
Soil – a mixture of rock particles (sand, silt and clay), minerals, decayed organic material (humus), air and water formed from weathered rock.

20. Soil Texture
Soil texture depends on the size of individual soil particles that make it up.
Gravel – 2mm and larger
Sand – less than 2mm
Silt – less than 1/16mm
Clay - less than 1/256mm

21. Erosion
The movement of rock particles from one location to another, Erosion, in a downhill motion toward their lowest possible location; sea level.
Agents of Erosion:
Water
Glaciers
Wind

22. Erosion by Water
Water is always moving downhill due to the force of gravity.
The greatest force of erosion.
Wears down mountains to hills
Carves out valleys
Changes the direction of river flow.

23. Erosion by Glaciers
Glaciers are formed from accumulated snow, compacted into ice and being pulled downhill by the force of gravity.
Begin to form when snow reaches approximately 150ft in depth.
Act as bulldozer, moving large amounts of rock and soil over time, till.
Material deposited after a glacier stops moving, moraine.

25. Erosion by Wind
A major force of physical weathering, wind is also a contributor to erosion.
Creates and transports rock particles.