Download Weathering, Erosion, Deposition

Weathering, Erosion, Deposition
Weathering
• The breakdown of rocks into smaller particles
Types of Weathering
• Physical
• Chemical
Physical Weathering
• Does not change the composition of the rock
• Dominates in cold/ moist climates
• Creates more surface area
Frost Wedging
• Occurs in climates with freezing and thawing
temperatures
– Ex pot holes
Root action
• Roots grow into and under rocks
• Roots pry the rock apart
– Ex. Cracks in the sidewalk
Abrasion
• Bumping and rubbing of rocks as they collide
• Rocks become smaller, smoother, rounder
Exfoliation
• Surface of the rock peels off
– Unloading- caused by uplift and exposure of rock
that was once deep underground
– Decreases pressure on the rocks
Chemical Weathering
• Changes the composition of the rocks
• Dominates in warm moist climates
• Occurs on the surface of rock materials
Types of chemical weathering
• Oxidation
• Carbonation
• Hydration
oxidation
• Iron atoms combine with oxygen to form iron
oxide (rust)
carbonation
• Carbonic acid in rain causes minerals to
dissolve
– Marble gravestones
hydration
• Water weakens the rock and the rock
crumbles
– Feldspar becomes clay
Composition of rocks
• Weaker, less resistant rocks weather away
faster than other rocks
• In the diagram, shale (layer A) is less resistant
than the other rocks
Factors that Effect Weathering
Factor
Physical Weathering
Chemical Weathering
Climate
Cold and moist
Warm and moist
Exposure
-Creates more
surface area where
weathering can
occur
-longer exposure
means more
weathering
-occurs on the
surface where the
rock is exposed to
the atmosphere or
hydrosphere
Composition
- Weaker rocks are
less resistant and
weather faster
(break easily)
-weakens the
minerals in the rock
so that it breaks
easier
Dominant type of weathering graph
• Weathering, Erosion, Deposition Quiz 1
• 1) What are the two types of weathering?
• 2) What are the types of physical weathering?
• 3) Describe the location where frost wedging
occurs. I do NOT want a location.
• 4) What type of weathering is present below?
• 5) What type of weathering is present below?
• 6) During which type of weathering is the
composition of the rock unchanged?
• 7) During which type of weathering is the
composition of the rock changed?
• 8) In what type of climate is physical
weathering most common (dominant)?
• 9) In what type of climate is chemical
weathering most common?
• 1) What are the two types of weathering?
Physical and Chemical
• 2) What are the types of physical weathering?
Frost wedging
Root action
Abrasion
exfoliation
• 3) Describe the location where frost wedging
occurs. I do NOT want a location.
The location must be cold enough for water
to freeze but warm enough for the ice to
melt
• 4) What type of weathering is present below?
Exfoliation
I guess
physical
weathering
• 5) What type of weathering is present below?
Root action
• 6) During which type of weathering is the
composition of the rock unchanged?
Physical weathering
• 7) During which type of weathering is the
composition of the rock changed?
Chemical weathering
• 8) In what type of climate is physical
weathering most common (dominant)?
Cold/moist climates
• 9) In what type of climate is chemical
weathering most common?
Warm/ moist climates
Example of weathering and erosion
over time…
Appalachian Mountains
Currently
• highest peak of the Appalachians of 6,684 feet
(Mount Mitchel),
• the Rockies highest peak is 14,440 feet
(Mount Elbert)
Some debate on how high they used
to be…
• 29,029
Soil
• The result of weathering and biological
activity over long periods of time
I
• Parent rock breaks down into smaller pieces
(sediment)
II
• Organisms help break up the rocks as they go
through the broken rock particles. Organic
material is added to the rock particles when
they die.
III
• The top layer (horizon A) is usually rich with
organic matter. More growth of plants on the
surface further weakens the rocks and adds
organic material
IV
• The soil continues to form and minerals leach
into the lower levels. Soil continues to thicken
and develop
• Dark brown to black soil with high organic
content
• Tan to orange soil with high clay content,
some rock fragments
• Light gray to black soil, coarse rock fragments
Residual Soil
• Soil is the same substance as the underlying
bedrock
• Soil formed and stayed in the same place
Transported Soil
• Soil is made up of completely different
material than the underlying bedrock
• Soil was moved or transported.
Erosion
• The transportation of weathered rock
materials
Agents of Erosion
•
•
•
•
•
Streams (running water)
Glaciers (moving ice)
Wave action
Wind
Mass movements (gravity)
Deposition
• The dropping out of weathered rock materials
Factors that affect deposition
• Velocity- as the transporting medium slows
down, sediments begin to settle out
Factors that affect deposition
• Shape: rounder particles settle faster than
flatter particles
Factors that affect deposition
• Size: larger particles settle faster than smaller
particles
Factors that affect deposition
• Density- most dense particles settle faster
than less dense particles
Sorting of Sediments
• Sorted: larger, more dense, rounder particles
settle out first.
Sorting of Sediments
• Unsorted sediments: sediments are dropped
out in no order
Sorted or unsorted?
Sorted or unsorted?
Horizontal Sorting
• Occurs when a stream enters a large body of
water
• Velocity of stream slows down
• Large particles settle out first
http://hmxearthscience.com/Warehouse/geology/surface_processes/animations/horso
rting.swf
Vertical Sorting
• Sorting of sediments from bottom to top
• Largest, roundest, most dense particles settle
out first and are on the bottom
Graded Bedding
• Series of depositional events that occurs at
different times
• You can count the events by counting the beds
Graded bedding
Horizontal or graded?
Horizontal or graded?
Horizontal or graded?
Gravity
• All agents of erosion are driven by gravity.
• Examples of erosion by gravity alone including
landslides dropping off cliffs and mass
movement down steep slopes
Running water
• Most erosive agent
• Gravity causes water to flow downhill
• Sediments are weathered by abrasion and
become smaller, rounder and smoother
Running Water Cont.
• The faster the water moves, the larger the
particles it can transport
• As the water slows down, the larger, rounder,
more dense particles settle out first
Running Water
Ways in which sediment is carried:
• Solution: sediments are dissolved
• Suspension: sediments remain mixed in with
water
• Flotation: materials float on water
• Bedload: sediments bounce on the bottom
Ways in which sediment is carried
Streams
• Any body of water with a current
– Brooks, creeks, tributary, river
Velocity of a stream is influenced by…
• 1. Gradient: the steeper the slope, the faster
the water flows
• 2. Volume: The greater the volume of water,
the faster it flows
– Discharge: volume of water
Velocity of a stream is influenced by…
• 3. Channel shape: water moves quickest
through a straight smooth stream
– Meander- a curve in a stream.
• Water moves the fastest on the outside (erosion)
• Water moves slowest on the inside (deposition)
Velocity of a stream is influenced by…
• 4. Large sediment: if a stream has a lot of large
rocks, they will slow down the flow of water
Stream Profiles
Life of a Stream
• Youth:
– High energy
– Fast moving
– Steep gradient
Life of a stream
• Mature:
– Gentler gradient
– Slower moving water
– Valley becomes wider than the river channel
– Flood plains develop
Life of a stream
• Old Age:
– Land is almost flat
– May form oxbow lakes
Deltas
• As rivers enter a larger body of water they
slow down
• When streams slow down, _____________
happens.
• When deposition exceeds the amount of
sediment moved by waves and tides, deltas
form
Drainage Basin
• Area where water from precipitation drains
downhill into a body of water.
Watershed
• Area where water flows from
• Surface water that feeds a river
Tributary
• A creek or stream that flows into a larger body
of water
Ocean Waves
• Wave action rounds sediments as a result of
abrasion
• Shores are protected by sand dunes and
barrier islands
• Creates beaches: formed from weathering and
erosion of continental and oceanic rocks
• Forms sandbars: a ridge of sand, formed along
a shore by the action of waves and currents
– The protect barrier islands from erosion
• Barrier island: a long narrow island, running
parallel to the main land, made of sand.
– Built up by the actions of waves, currents and
wind that distribute the sand
– Protect the coast from erosion
• Waves approaching the shoreline: surf and
tides move sand parallel to the shore within
the zone of breaking waves.
Glaciers
• Large, very slow moving ice
• Form in high latitudes and high elevations
• Gravity causes glaciers to flow down a valley
or spread out over a continent
Glaciers cont.
• Push, drag and carry sediments
• Can carry any size sediments, including
boulders
• Depositon is unsorted
• Features include striations (scratches) on the
rock and parallel groves in the bedrock
Valley Glacier Features
• Form U shaped valleys
• Glacial Till: unsorted sediment deposited by a
glacier
Things associated with Glaciers
•
•
•
•
Boulders
Striations
U shaped valleys
Unsorted sediment
Finger Lakes
• Formed by glaciers
• When ice retreated deposits left behind
dammed the stream valleys
• Melt water filled the valleys
• Direction of lakes show glacier movement
through the former stream valleys
Great Lakes
•
•
•
•
•
Formed at the end of the ice age
Approximately 10,000 years ago
Glaciers carved out the bedrock
Glacial melt waters filled the basins
Lakes contain approximately 20% of the
worlds fresh surface water
Wind Erosion
•
•
•
•
Most common in arid (dry) climates
Common in deserts and beaches
Weathering by abrasion
Surface features include dunes and sand
blasted rock
Wind direction by using dunes
Landscape Regions
• Forms from the interaction of crustal
movement, type of bedrock, and climate
• A-Mountain
• B-Ridges
• C-Plateau
• D-Plain
Geologic Factors that influence
landscape
• 1) crustal movement
• 2) Type of bedrock
• 3) Climate
Drainage Patterns
• Determined by the topography of the surface
and the underlying bedrock
Dendritic
•
•
•
•
Most common stream pattern
Tributaries seem to flow in the same direction
Looks like branches on a tree
Usually on undisturbed, horizontal rock layers
Radial
• Occurs when the stream flows away from a
high point
• Looks like spokes on a wheel
• Develops over a smooth dome or volcanic
cone
annular
• Occurs on an eroded dome
• Appears to be a circular pattern with small
tributaries going into each circle
rectangular
• Occurs where drainage flows along folds and
faults
• Looks like parallel lines with tributaries going
into each path