1. Constructive & Destructive Forces on Landforms
5-3.1

2. Two Types of Forces
Destructive Forces: processes that destroy landforms.
2 types: Slow (weathering) and Fast (Erosion)
Ex. landslides, volcanic eruptions, earthquakes, floods
Constructive forces: forces that build up an existing landform or create a new one.
Caused by: water, gravity, wind and glaciers.
Ex: deposition, landslides, volcanic eruptions, floods

3. Weathering
Weathering Pictures
Weathering: a slow, destructive force that breaks rocks into smaller pieces called sediments. Can by physical (mechanical) or chemical.
Keywords:
wear down, break
apart

4. Mechanical weathering: the breaking of rock into smaller pieces by forces due to gravity, ice, plant roots, or other physical forces.

5. Mechanical Weathering:
Rock is physically broken into smaller pieces
Small pieces have same composition as the original rock
Very slow

6. Mechanical Weathering:
Caused by…(Agents)
Freezing and Thawing
Release of Pressure
Growth of Plants
Animals
Abrasion – Grinding away of rock by other rock particles that are carried by water, ice, wind, or gravity

7. Chemical Weathering: the changing of materials in a rock by chemical processes. Rock particles have different mineral make-up than original rock

8. Chemical Weathering: Caused by…(Agents) H2O  MOST important
Oxygen (O2)
Carbon Dioxide (CO2)
Living organisms
Acid Rain  very rapid

9. Agent Type Description
Mechanical
Rock particles wear away rock
Chemical
Forms from coal, oil, and gas burning
Freezing/Thawing
Breaks rock by ice wedging
Carbon Dioxide
Forms carbonic acid in water
Weathers marble and limestone
Burrowing in the ground breaks rock
Plant growth
Roots pry apart cracks in rock
Living Organisms
Produce weak acid that weathers rock
Oxygen
Causes rust on some rock
Sun or forest fire causes rock to crack

10. Rates of Weathering: Type of rock Climate
Minerals that make up the rock determine how fast it weathers
Climate
Occurs faster in wet climates & at high temperatures

11. Erosion
Grand Canyon Video
Erosion: the destructive movement of materials away from one place by wind, water, ice and gravity.
Wave Erosion- caused by water
Wind Erosion (Dust Storm)

12. Landslides
Landslides: occur when gravity quickly pulls rock and dirt downhill.

13. Floods
Floods: a great flow of water over an area that is usually dry land.

14. Erosion & Deposition
Deposition: the placing of materials in a new place (constructive force).
Ex. Sandbars

15. Water Erosion & Deposition
River Delta- Deposits of sediment at the mouth of the Mississippi River creating new land called a delta.

16. Wind Erosion & Deposition
Sand Dunes- sand is moved by wind
Desert Sand Dunes
Ocean Sand Dunes

17. Mass Movement: Caused by gravity Process that moves sediment downhill
4 types
Landslide - Slump
Mudslide - Creep

18. Landslide: Most destructive
When rock & soil slide quickly down a steep slope

19. Mudflow: Rapid downhill movement of H2O, rock, and soil
Often occurs after heavy rains

21. Slump:
A mass of rock & soil suddenly slips down a slope (in a large mass/clump)

23. Creep:
Very slow downhill movement of rock & soil

25. Volcanic Eruptions
Volcano: an opening in the Earth’s crust through which steam, lava and ashes erupt.
Cause both destructive and constructive changes to landforms.

26. Mount St. Helens Mount St. Helens Video Saint Helen’s Before
Saint Helen’s After

27. Volcanoes can be constructive, but also destructive…

28. Earthquakes
Earthquakes: the shaking of Earth’s surface caused by the release of energy along a fault.
San Andreas Fault, California

29. Effects of Weathering on Mountain Ranges
Moraine Lake, Rocky Mountains (younger mts.)
Appalachian Mountains
Older mountains
Effects of weathering
Rounding, softening of edges