Weathering & Erosion
Weathering
• Process of chemically changing
or physically breaking down rock.
• Water, ice, wind, & gravity
weather rock.
• Weathering happens on the
surface.
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
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
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
Frost wedging produces rock spires
Frost wedging produces smaller rock pieces with MORE
SURFACE AREA for CHEMICAL WEATHERING TO
WORK.
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
Examples or Mechanical Weathering
Unloading & Exfoliation: Produces …
Domes and Exfoliation
Scabs
Examples or Mechanical Weathering
Biological Activity: Plant Roots
Shippensburg, PA, 1999
Shippensburg, PA, 2005
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
Air pollution, volcanoes Nitric acid reacts with
minerals
Acids in water react faster with carbonates (limestone,
marble) than silicates (as in granite)
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
1. 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)
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
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
Weathering & Climate
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
Rates of Weathering depend on…
1. Temperature –
• Warmer temps. Increase Chem.
Weathering
• Alternating freezing & warm temps.
increase Mechanical Weathering.
2. Availability of Water – More water, more
weathering
3. Type of Rock – Calcium containing rocks
(limestone, calcite, marble) are prone to
chemical weathering
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.
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.
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)
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)
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
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.
TYPES OF MASS MOVEMENT:
Types of Mass Movement (aka, mass wasting)
More rain means greater chance of mass movement
Triggering Mass Movements
1. Water: Heavy Rainfall/Snow
Soil gets saturated (pore spaces filled); rock/soil
layers get very heavy  Gravity pulls downhill
2. Oversteepened Slopes
More than 40 degree angle; Stream cuts base of cliff;
people blast base of mountains for road/housing
construction
3. Removal of Vegetation
No roots to hold down soil; No roots to absorb water
4. Earthquakes/Volcano Eruptions
Videos
• Landslides (National Geographic)
• http://video.nationalgeographic.com/video/environment/environmentnatural-disasters/landslides-and-more/landslides/
• Mudflow (Austria) http://www.youtube.com/watch?v=ARkBJdsZw4w
• Mudflow (Austria): http://www.youtube.com/watch?v=VMJiibdVYjE
• Rockfall (Cornwall cliffs)
http://www.youtube.com/watch?v=QdsxtCtX5nk
• Rockfall (Yosemite)
http://www.youtube.com/watch?v=H0YhlqP1BgE
• Rockslide http://www.youtube.com/watch?v=ZVYGJYnJTi0
Creep
Slope
Landslide