Transcript Topic 9 Weathering and Erosion

Topic 9 Weathering and
Erosion
Weathering: The chemical and physical
breakdown of rock
Types of Weathering
Chemical Weathering:Breakdown of rock forms new substances
A) Oxidation: Minerals combine with O2 to form
different minerals
Reaction Rim: Outer layer of oxidation
Chemical Weathering Continued
B) Dissolving: Water removes minerals from rocks
C) Acids: Carbonic acid from rain enters the ground
and reacts with rocks
Physical Weathering: breaking rocks into smaller
pieces without changing what
they are.
A) Temperature Change: Rocks may break when exposed
to rapid temp. change.
B) Root pry: Roots break rock as it grows
C) Frost Action: The expansion of water due to freezing in
the cracks of rocks
D) Abrasion: Rocks grinding past each other and wear down
-Water abrasion rounds and smoothes
-Wind abrasion causes pitting
Factors Affecting the Rate and Type of
Weathering
1) Exposure: The closer to the surface the higher the rate
What is the relationship between depth and rate of weathering?
Inverse
2) Particle Size: Greater surface area = more weathering
Surface area is the amount of exposed surface
Relationship (Surface area vs. weathering) Direct
3) Mineral Composition: Hard minerals are more resistant
to weathering
Resistant minerals
Quartz
Olivine
Feldspar
Weak Minerals
Calcite
Mica
4) Climate: Warm and moist = Chemical Weathering
Cold and moist = Physical
Soil Formation
Soil: Weathered rock and organic material
Residual Soil: Formed in place (same minerals as
bedrock)
Transported Soil: Formed somewhere else (different
minerals than bedrock)
Why doesn’t NYS have mature soil?
Erosion: Transport of weathered material
Parts of an Erosional System
1) Agent: Thing that does the moving
2) Sediment: Weathered material
3) Force: Force that causes motion
2 Primary Forces of Erosion
The sun causes unequal heating of the Earth and winds
Gravity causes rivers to flow and particles to fall
Gravity Erosion
Indirectly: Causes water and ice to flow
Directly: Sediments fall downhill
What are the two Forces involved? Gravity and Friction
When does gravitational erosion take place?
G>F
Angle of Repose: Angle which particles naturally settle (35)
Types of Gravitational Erosion From
Fastest to Slowest
1) Rock Fall: Rocks fall off cliffs
2) Mudflow: Soil becomes saturated and flows
3) Debris flow: Composed of dirt and
other materials
4) Soil Creep: Gradual downhill movement of soil
Running Water Erosion and Streams
Stream: Running water confined to a channel
Tributary: Small stream that feeds larger
Methods of Stream Erosion
1) Solution: Dissolved material
2) Suspension: Particles are carried by the stream
Muddy water is evidence
3) Saltation: Rolling and bouncing along bottom
Watershed: Area drained by one stream or river
Stream load: Total amount of sediment in a stream
What shape are valleys formed by rivers?
4 Factors that Affect Stream Velocity
1) Gradient: Change in elevation / distance
Relationship: Direct
2) Discharge: Amount of water flowing past a certain spot in a
given amount of time
Relationship: Direct
How do tributaries affect this? They increase discharge
3) Channel Shape: Semicircle channel have most velocity
What is the determining factor or force? friction
4) Position in the Stream: Just below the surface and at
the outside of bends is fast
Relationship Between Velocity and Particles Carried
How fast does a
stream have to travel
to carry particles that
are cobble sized?
How fast does
a stream have
to travel to
carry particles
that are .2cm in
diameter?
Evolution of a Stream
Age
Gradient
Erosion
Discharge
High
High
High
Load
Features
Young
High
Waterfalls,
rapids
Low
Meanders,
oxbows, flood
plains
Mature
Low
Low
Low
Features of a Mature River
Meanders: Series of bends and turns
Flood plain: Wider valley that becomes flooded
Delta: Fan of sediments at the end of a river
Oxbow Lake: Lake formed from a meander cut-off
How Flood Plains Work
Formation of an Oxbow Lake
Listening Questions From Mark Twain’s
“Life on the Mississippi”
1) The width of the United States is about 3,000 miles; Mississippi River is
4,300 miles long. How can the river be longer than the U.S. is wide?
2) Why does the Mississippi have such a large discharge (volume)?
3) What is the depth of the Mississippi at its deepest and where does this
occur?
4) Why has the Mississippi been called the “Great Sewer?”
5) Explain how a river can shorten itself by over 30 miles?
6) How can river shortening be disastrous to towns along the
Mississippi?
7) Contrast what the Mississippi does to the land at its source and its
mouth?
Watershed Drainage Patterns are Determined by
The Geology and Landscape Features of a Region
Wind Erosion
Where does wind erosion take place? Most commonly in
warm dry climates
How does it happen? Particles are moved by wind
2 Main Types of Wind Erosion
1) Deflation: Particles are moved to desert base level
Desert Pavement: Large particles left behind don’t move
2) Sandblasting: Sand and wind blast rocks
Features: Pitting and frosting
Formations from sandblasting:Arches, mushroom rocks
Why is only the bottom eroded? Wind can only raise
particles 2m
Glacial Erosion
Why are glaciers important to NYS? They once covered
NYS
Two Types of Glaciers
1) Continental: Huge ice sheets
2) Alpine: Mountain glaciers
What direction do glaciers move? Downhill
How do they recede? Melting > Accumulation
Where do glaciers have the greatest velocity?
Where there is less friction
Evidence of Glaciers
1) Glacial plucking: Glaciers pull rocks from earth
2) Glacial grooves (striations): Scratches made from
glaciers (show direction)
3) Erratics: Random rocks left from glaciers
4) U-shaped valleys: Broad U valleys
How have glaciers affected NYS?
1) Soil:
Immature soil (scraped to PA)
2) Lakes: Finger lakes carved by glaciers
How long ago were the glaciers here? 10,000 yrs.
Wave and Current Erosion
What happens to beach sediments? Abrasion rounds
and smoothes
What rock material is left on the beaches? Quartz
Features of Wave and Current Erosion
Beachfronts: Steep slopes and cliffs
Long-shore Drift: Waves come in at an angle and
move sediment down shore
Bays: Small body of water connected to a larger
Sandbars: Ridge of sand formed just off the shore
Spits: Type of bar that forms from re-entrance