1. Weathering & Erosion

2. Weathering
Process of chemically changing or physically breaking down rock.
Water, ice, wind, & gravity weather rock.
Weathering happens on the surface.

3. Erosion
Erosion = process that wears down and carries away rock and soil fr. one place to another
Agents of Erosion (What’s doing the erosion?):
Water – streams, rivers, oceans, glaciers
Wind
Gravity
End product of erosion = SOIL or SEDIMENT

4. TYPES OF Weathering
1. Mechanical: physically break down rocks into smaller fragments.
A. Frost wedging
B. Unloading
C. Biological activity
2. Chemical: Chemical reactions dissolve minerals in rock
Acidic water

5. A Mechanical Weathering: Frost Wedging
Expanding ice
and expands
Common in mountainous regions; Mid-latitudes w/ winter season (freezing and thawing required)
Talus = piles of rock at the base of a mt. or cliff produced by f.wedging

7. Frost wedging produces rock spires

8. Frost wedging produces smaller rock pieces with MORE SURFACE AREA for CHEMICAL WEATHERING TO WORK.

9. 2. Examples or Mechanical Weathering
Unloading & Exfoliation: Igneous rock are exposed b/c of uplift and erosion.
Unloading:
Outer layers of rock expand (b/c under less pressure; not buried anymore)
Exfoliation: Outer layers “shed” and break loose.
Produce domes; Usually granite

10. 2. Examples or Mechanical Weathering
Unloading & Exfoliation: Produces …
Domes and Exfoliation Scabs

11. 3. Examples or Mechanical Weathering Biological Activity: Plant Roots
Shippensburg, PA, 1999
Shippensburg, PA, 2005

12. Chemical Weathering:
Chem. Rxns break down rock when gases dissolve in water.
Gases that Dissolve in Water
From
Reacts how?
Oxygen
photosynthesis
Reacts with metals in minerals to form oxides
Carbon dioxide
Many sources
Carbonic acid reacts with minerals
Sulfur dioxide
Air pollution, volcanoes
Sulfuric acid reacts with minerals
Nitrogen dioxide
Nitric acid reacts with minerals
Acids in water react faster with carbonates (limestone, marble) than silicates (as in granite)

13. Examples of Chemical Weathering
Red rock layers formed by iron reacting w/ oxygen
Iron reacts w/ oxygen to make blue soil.
Caves form when limestone is dissolved by acidic water
ACIDIC RAIN WATER will dissolve calcium containing rocks (limestone, & marble). This is how caves are made.
2. Oxidation (chemical reactions w/ O2) of Iron containing rocks (Makes rust)

14. Chemical Weathering of Granite
Quartz: Most resistant (unchanged)  larger particles  transported shorter distances (makes up beach sand)
Feldspar: Weathers to clay minerals  clay = smaller particle size = transported by rivers out to sea  deposited in ocean

15. Chemical Weathering of Silicate Minerals
Some things dissolve:
Sodium(Na), Potassium (K), Magnesium (Mg) dissolve in acidic water  become part of gound water.
Iron (Fe) reacts w/ O2  iron oxide (rust/red rocks)
Si, O, Aluminum = resistant to chem. Weath (don’t dissolve in acids)  bcm smaller clay minerals.
Clay = Si, O, Al minerals

16. Weathering & Climate

17. Chemical Weathering & Climate
Carbonic acid weathers rock and particles usually end up on the bottom of the ocean floor..
Carbonic acid forms when CO2 is dissolved in water. This CO2 comes from the ATMOSPHERE.
More chemical weathering = More CO2 removed fr. Atmosphere.
When “NEW” land is exposed to Earth’s surface, weathering rates increase; temps. Decrease.
Mt. Building exposes new land.
Mt. Building = Cooling Climate

18. Rates of Weathering depend on…
Temperature –
Warmer temps. Increase Chem. Weathering
Alternating freezing & warm temps. increase Mechanical Weathering.
Availability of Water – More water, more weathering
Type of Rock – Calcium containing rocks (limestone, calcite, marble) are prone to chemical weathering

19. Mass Movements= Transfer of rock and soil downslope due to gravity.
Weathering weakens & breaks apart rock; gravity moves rock downslope to a valley.
Streams at base of valley carry sediments away.

20. Types: Based on 1). Material 2). Speed
Rockfalls: Rocks fall freely thru. air down very steep slopes (esp. where mt. were blasted to make road); Fast; freeze-thaw loosens rock.

21. Mass Movements
Slides: Block of material moves suddenly along flat inclined surface; FAST
Rockslide/Landslide/ Mudslide
Mt. regions
After heavy rain or melting (destabilizes soil)

22. Mass Movements
Slumps: Block of material moves down curved surface (forms steps) (not fast; not far)
Oversteepened slopes w/ thick accumulation of clay (that gets heavy after rains)

23. Mass Movements
Flows: Fast moving material w/ lg. amount of water, moving downslope (Muddy w/ debris)
Semiarid mts. (no veg. to hold down soil after heavy rains)
Base of snow. peaked volcanoes
Very destructive

24. Mass Movement Earthflow: Slow moving flows
Hillsides in wet regions
“Tongue” shaped pile
Creep: Slowest; few mm or cm/year; freeze-thaw separates and move soil.

25. TYPES OF MASS MOVEMENT:

26. Types of Mass Movement (aka, mass wasting)

27. More rain means greater chance of mass movement

28. Triggering Mass Movements
Water: Heavy Rainfall/Snow
Soil gets saturated (pore spaces filled); rock/soil layers get very heavy  Gravity pulls downhill
Oversteepened Slopes
More than 40 degree angle; Stream cuts base of cliff; people blast base of mountains for road/housing construction
Removal of Vegetation
No roots to hold down soil; No roots to absorb water
Earthquakes/Volcano Eruptions

29. Videos Landslides (National Geographic)
Mudflow (Austria)
Mudflow (Austria):
Rockfall (Cornwall cliffs)
Rockfall (Yosemite)
Rockslide

30. Creep
Slope
Landslide

31. A. B. C. D.