Download Weathering Erosion and Deposition

Weathering
and Erosion
CHAPTER 1
Weathering, Erosion, and
Deposition
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Weathering:
Weathering is the breakdown of rocks. There are two types of weathering ! Mechanical/
Physical and Chemical.
Mechanical/Physical Weathering ! this is the physical breaking apart of the rock into
smaller pieces.
Chemical Weathering ! this is the process of breaking rocks down atom by atom through
chemical changes.
Types of Mechanical Weathering:
Frost wedging
When water gets into cracks of rocks, freezes and expands making the crack larger.
Thermal Expansion and Contraction
Crystals in rocks will expand and contract as they are heated and cooled, as this
process happens it can cause for the rock to begin to fracture/break. The process is
slow. Desert regions with large temperature differences experience mechanical
weathering of rock through expansion and contraction due to large temperature
variances.
Crystal Growth
Common when salt water environments seep into rock fractures and the water then
evaporates allowing for crystals to grow and then expand the fracture as they grow.
Exfoliation
When sheets of rock ‘peel off’. It is caused when surface rock weathers and falls off
thus releasing pressure on underlying rock allowing that rock to expand and ‘peel
off’.
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Types of Chemical Weathering:
Dissolution/Carbonation
When mineral grains are torn apart and ions are carried away in solution. Caves are
a result of dissolution.
Cave formation: rainwater contains dissolved CO2 (carbon dioxide). The CO2 produces carbonic acid (a weak acid). The rainwater will become more acidic from organic acids created from plant decomposition as it filters down through soil. If the
bedrock or underlying rock is limestone (a carbonate rock ! which means it will
dissolve in acid) the acidic water will ‘eat’ away and dissolve atom by atom of material giving rise to open spaces/caverns/caves in the rock. The process takes a long
time. Rapid/quick in cold moist areas.
Plant Action
Tree roots grow into cracks of rocks breaking the rock apart.
Abrasion
When rocks rub against other rocks as they fall or move leaving marks on the rock.
Oxidation
When minerals react to the air. Most know this type as ‘rust’.
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Hydrolysis (hydro ! water; lysis ! reaction)
Involves direct reaction with water molecules.
Controlled by moist climates since water is needed.
Affects most silicate minerals – especially feldspars which are the most common in
earth’s crust.
Factors that Affect the Rate of Weathering:
• Surface Area ! more surface area the greater the weathering rate
• Mineral Composition ! some minerals are more resistant than other. For example:
Quartz is resistant to chemical and physical weathering.
• Climatic Conditions ! Cold and/or dry climates favor mechanical weathering; Warm
and wet climates favor chemical weathering. Frost action works best where temperatures fluctuate.
• Pollution ! sulfuric and nitric acid (from pollution) mix with rain creating acid rain
which enhances chemical weathering.
Erosion: the movement/transportation of weathered materials.
Four Agents of Erosion:
• Gravity
• Water
• Wind
• Glaciers
Click the link below to see what types of climates produce the different types of mechanical
weathering and chemical weathering:
Gravity:
Pulls weathered particles downhill and causes Mass Movement
http://www.as.uky.edu/sites/default/files/elearning/module07swf.swf
Types of Mass Movement:
1. Creep
Very low velocity event
Caused by heating/cooling, freezing/thawing, wetting/drying
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2. Slump
High velocity event
Material breaks off
Rotational
Creates scarps
Click the link below to learn about Mass Movements: Make sure to read and go through all
buttons!
http://www.as.uky.edu/sites/default/files/elearning/module11swf.swf
3. Landslides
High velocity event
Material is loose
Material is dry
Results in Talus (big pieces of fallen rock)
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Water:
Most common type of erosion (water is everywhere)
Causes abrasion, rounded pebbles, forms rivers
4. Mudslides ! landslide with water
Stages of River Development:
1. Youthful
Has a rapid flow
Steep slopes
Narrow V-shape Valley
Can carry gravel and boulders
5. Avalanche ! landslide of snow
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2. Mature
Steady flow
Gentler slope and flattened land surfaces
Sand-sized particles
Features that Form From a River Flowing Down a Mountain Along a Floodplain, then
into a Large Body of Water:
1. Alluvial Fan ! sediments deposited at the base of a mountain
2. Floodplain !the area to where water will flow during a flood. They extend for miles on
either side of the river.
3. Delta !sediment deposited in a fan shape when it hits a larger body of water. Refer to
above picture for profile view.
3. Old Age
Slow flowing
Almost no slope
Silt
Carrying Capacity of Streams and Rivers:
The diagram below shows which size particles drop out (settle/deposit), in order, as a
stream’s velocity slows down or empties into a larger body of water such as a lake or ocean.
Oxbows and River Turns:
The diagram below illustrates where deposition (D) and erosion (E) will take place as the
water flows in the river. The movement of water is from left to right. Eventually the meanders (bends in the river) will pinch off and create an Oxbow Lake. The velocity is faster at
the outside of the meander (bend) and slower at the inside of the meander.
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Sandblasting/Abrasion ! when particles of sand carried by wind rub against the surface
of other materials scouring them away.
Glaciers:
Glaciers are rivers of slowly flowing ice. The glaciers will break up rock and transport it to
new locations. Create a U-shaped valley. Leaves striations (linear scratches on the surface
below the glacier).
Two Types of Glaciers:
Alpine: individual glaciers found on mountains (example: The Alps)
Continental: thick ice sheets that cover large areas of land (example: Antarctica)
Wind:
Occurs mainly in dry climates.
When sand is blown around it can ‘pit’ other rocks (mechanical weathering).
Types of Wind Erosion:
Saltation ! particles bounce which loosens particles (also occur in rivers as water moves
particles in the river flow)
Alpine Glacier:
Deflation ! the blowing of loose sediments that leave the surface
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Continental Glacier: showing features created after the glaciers retreats (gets smaller)
Soil: is a mixture of minerals, water, gases and humus. Humus is decaying or decayed animal and plant material. Soil develops as weathering of bedrock occurs. There are two ways
soil form. The first is residual soil, this soil has bedrock as its parent material (where it
comes from). The second type is transported soil, which is formed from parent material that
has been eroded (transported) by winds, glaciers, or rivers and then left/deposited.
A layer of soil is called a horizon. Horizons are categorized by the type of material in them.
Below is a Soil Profile of the different layers.
:
Click the link below to run glacier simulations to learn how they work:
http://phet.colorado.edu/en/simulation/glaciers
There are three main horizons in a soil profile. They are:
Horizon A ! topsoil (hums), sometimes Horizon A is broken into an additional layer
called Horizon O ! organic layer.
Horizon B ! subsoil (minerals leached from layer A, and
Horizon C ! partially weathered bedrock (usually the zone of saturation).
The bottom most and oldest layer is the parent material (layer R) from which the soil horizons and soil profile formed.
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Karst Topography: landforms made from the dissolving of limestone by carbonic acid in
groundwater. Limestone is a sedimentary rock that commonly has certain features associated with it due to the dissolving of it from carbonic acid. The following is a list of features
with a diagram below representing these features:
• Caverns ! caves (1)
• Sinkholes ! form when the roof of a cave collapses (2)
• Stalactites ! when water with dissolved minerals drips down and solidifies before falling all the way to ground. Looks like an icicle (3)
• Stalagmites ! when the dissolved calcite that drips down from the ceiling of the cave
falls to the floor of the cave and hardens and then begins to build a mound upwards. (4)
• Columns ! when a stalactite and stalagmite join together after 10,000’s of years forming creating one connecting piece from the ceiling to the floor. (5)
• Disappearing Streams ! when stream go into a sinkhole and continue to flow underground eventually reappearing above ground downstream (6)
• Underground Stream ! created from the disappearing river (7)
• Limestone ! sedimentary rock, has the brick pattern (8)
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Deposition: when eroded (transported) materials are dropped (deposited) in a new location.
Factors Affecting Rate of Deposition:
1. Size: larger particles settle out first when running water or wind slow down
2. Shape: the rounder the particle the faster it will settle.
3. Density: the higher density particle will settle faster than a lower density particle.
Rapid Sorting: When sediments are deposited fast.
Gradual sorting: When moving water begins to slow down, particles are deposited.
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Erosion and Deposition by a Glacier:
A glacier is a naturally occurring mass of ice and snow that forms overtime as snow falls,
builds up, and doesn’t melt. As snow falls onto the previous fallen snow it adds weight
turning the lower layers of snow into ice by compressing it. Glaciers move due to gravity.
How Glaciers Move:
Moves faster at the center near the top due to less friction
Moves slower at the bottom and sides due to friction with the bottom and sides of the land
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Erosion Landscapes from a Glacier:
• U-shaped valley
• Hanging Valley
• Cirques
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• Arete!
• Horn
• Polished Rock (from constant rubbing/friction of glacier)
• Striated Rock (has linear scratches in the rock form the glacier going over it)
• Abrasion (wearing, scraping, or rubbing away of rock surfaces by friction)
• Plucking (processes that cause rocks to become loose, picked up, and carried away by
glaciers)! !
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Over time rocks transported by water will become smaller and rounded.
Click the link to observe how sediments are deposited when a river or stream enters into a
larger body of water. Pay attention to the particle sizes.
http://www.classzone.com/books/earth_science/terc/content/visualizations/es0604/es0
604page01.cfm?chapter_no=visualization
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U-Shaped Valleys and Hanging Valleys:
A glacier will leave behind sediments that are unsorted (glacial till). These deposits are usually found at the front of the glacier 9Terminal Moraine). Deposits left at the side of the glacier are called lateral moraines.
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