Unit 2: Surface Processes and the Hydrosphere Lesson 6: Processes and Features of Erosion ( Heath...
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Transcript of Unit 2: Surface Processes and the Hydrosphere Lesson 6: Processes and Features of Erosion ( Heath...
![Page 1: Unit 2: Surface Processes and the Hydrosphere Lesson 6: Processes and Features of Erosion ( Heath Earth Science – Pg. 190-202)](https://reader036.fdocuments.in/reader036/viewer/2022062801/56649e405503460f94b31aac/html5/thumbnails/1.jpg)
Unit 2: Surface Processes and the Hydrosphere
Lesson 6: Processes and Features of Erosion(Heath Earth Science – Pg. 190-202)
![Page 2: Unit 2: Surface Processes and the Hydrosphere Lesson 6: Processes and Features of Erosion ( Heath Earth Science – Pg. 190-202)](https://reader036.fdocuments.in/reader036/viewer/2022062801/56649e405503460f94b31aac/html5/thumbnails/2.jpg)
Today’s Objectives Relate the processes associated with
weathering and erosion to the resulting features, including: identify the processes (e.g., abrasion,
dissolution) by which glaciers, running water, wind, and wave action erode rock and sediment
differentiate between erosional and depositional features formed by glaciers, running water, wind, and wave action
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Types of Erosion Erosion can be carried out in many different
ways Today we will look at 4 different processes of
erosion: 1) Glacial Erosion 2) Running Water Erosion 3) Wind Erosion 4) Wave Erosion
In addition to looking at these processes, we will also identify some features created by erosion, as well as features formed by deposition
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Erosional vs. Depositional Erosion:
The incorporation and transportation of material by a mobile agent, such as water, wind, or ice
Deposition: The process by which
materials are added to a landform after being transported by a mobile agent
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Glaciers – Chapter 11 A glacier is a thick mass of ice originating on land
from the compaction of snow that shows evidence of flow
Two main kinds of glacier: Valley glacier (alpine glacier)
Occur in all parts of the world where mountains stretch above the snow line
2000-100,000 meters long, 100-1000 meters thick Continental glacier (ice sheet or ice cap)
Occur in polar areas where the snow line is close to sea level Up to 12.5 million km2, up to 5 km thick!
Glacier Simulation
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Advancing vs. Receding Glaciers Accumulation zone: Area of glacier where
accumulation > melting Ablation zone: Area of glacier where melting >
accumulation Firn (snow) line: line where melting = accumulation When the amount of snow falling in the accumulation
zone is larger than the amount of snow melting in the ablation zone, the glacier will advance
When the opposite is true, the glacier will recede Advancing glaciers will create erosional features Receding glaciers will create depositional features
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Glacial Erosion - Abrasion Glaciers erode the
bedrock largely by using pieces of rock as cutting tools
These pieces are dragged over the bedrock by the forward movement of the glacier, in a process called abrasion
The scratches left behind on the rocks are called striations
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Glacial Erosion - Plucking Another process of glacial erosion is plucking Plucking occurs when melt-water beneath the
glacier penetrates cracks in the bedrock, then freezes to the rock (video)
As the glacier moves forward, the rock is pulled from the ground
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Glacial Erosional FeaturesYou should be able to name and recognize the following erosional features, and how they are formed:arete, cirque, horn, hanging valley, U-shaped valley, roches moutonnees, fjord, tarn
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Glacial Erosional Features
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Glacial Deposition Once a glacier begins to recede, the material
from beneath, within, or on top of the glacier will be left behind
This material will form many features called depositional features
You should be able to name and recognize the following depositional features, and how they are formed: Till, moraine, outwash plain, drumlins,
eskers, kames, kettles, and erratics
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Glacial Depositional Features
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Glacial Depositional Landforms
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Homework Complete the homework package that you are
given! Due: Next class
Next day: We will continue discussing erosion and erosional/depositional landforms
Soon: Unit Test!
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Running Water Erosion – Chapter 10 Another agent of erosion is running water Running water transports sediment in
three ways: Solution Suspension Bed load
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Running Water Erosion Solution:
Material that has dissolved from the bedrock are carried in solution
Minerals such as calcium and magnesium are often carried in solution
Suspension: When a river looks muddy, it is
carrying material in suspension Suspended material includes clay, silt,
and fine sand Are kept from sinking because of
turbulence Faster moving water can keep more
material in suspension
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Running Water Erosion Bed load:
Sand, pebbles, and boulders that are too heavy to be transported in suspension may be moved along the stream bed
Very common during floods Boulders and pebbles roll or slide along the
riverbed Sand grains jump and bounce along the bottom Sediment moved along the stream bed is called the
bed load
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Running Water - Abrasion Much like in glaciers, weathering and
erosion by running water also involves abrasion:
Sand, pebbles, and even boulders carried as load in the water will grind and hammer away at its bed
Over time, this abrasion causes rock to be worn down and rounded: this rock is known as river rock
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Erosional Features – V-shaped Valleys Running water wears away and erodes the
surface, of mountains they flow down creating river valleys
River valleys are typically V-shaped: High speed water easily scours away the
streambed Upper valley walls are widened by weathering
and erosion
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River Valley Drainage Patterns Topography influences the shape of the
rivers drainage system
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Erosional Features - Potholes Streams running over irregular beds develop
small circular currents called whirlpools As whirlpools develop, sand, pebbles, and small
boulders abrade the streambed, grinding out deep oval or circular holes called potholes
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Depositional Features – Oxbow Lakes Mature river valleys develop wider floors Rivers are easily deflected from side to side,
forming meanders As a meander gets larger and larger, the
curve can become a loop and break through its bank This is called a cutoff
Result is an abandoned meander, or oxbow lake
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Depositional Features – Oxbow Lakes
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Depositional Features - Levees In times of heavy rain, rivers may overflow
their banks and cover part of the valley floor This part of the valley floor is called the flood
plain As water flows over the river bank, it slows
down and releases some of its sediment load Largest, heaviest sediment is released first Finer sediment released last
This larger sediment forms a “wall” or levee on each river bank, a natural form of flood protection
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Depositional Features - Levees
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Depositional Features - Deltas When a river meets the sea, or a lake, the
velocity of the water slows down dramatically As it slows, the fine sediment in the
suspended load will be deposited at the mouth of the river, forming a delta
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Depositional Features – Alluvial Fans Similar to a delta, but occur in dry regions
where a steep mountain stream meets flat, dry land at the bottom of the mountain
Again, water velocity slows down greatly, sediment load is dropped forming a fan-shaped deposit, called an alluvial fan
Different from a delta in that: 1) formed on land, not in water 2) sediment is coarse sand and gravel instead of
fine sediment 3) surface is sloping, not flat
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Depositional Features – Alluvial Fans
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Homework You should be able to identify and explain the
following erosional/depositional features formed by running water: delta, alluvial fan, oxbow lake, pothole, levee, v-shaped valley
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Wind Erosion – Chapter 12 Another agent of
erosion is wind Just like running
water and ice, abrasion is a process of wind based weathering and erosion
High winds pick up sand particles, which grind away at rock features the wind blows into
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Erosional Features - Ventifacts Boulders and rocks that have been shaped
by sand blasting winds, are called ventifacts Have one or more sides that have been
worn away by sand blasting
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Wind Erosion Another effect of wind erosion is deflation Deflation describes the removal of loose
rock particles by wind Usually sand, silt and clay will be blown away first,
leaving behind pebbles and boulders Material carried away by wind and deposited
elsewhere is called loess Such a surface is known as desert
pavement The heavy surface material of desert
pavement protects the material beneath from further deflation
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Erosional Features – Desert pavement
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Erosional Features - Blowouts In some areas where larger materials are not
present, blowouts are common A blowout is a hollow resulting from the
removal of huge amounts of soil due to deflation
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Depositional Features - Dunes Hills of sand deposited by wind are called dunes,
or sand dunes Dunes form when deposited sand piles up against
shrubs, boulders, or other obstructions Found wherever there are strong winds and
enough loose sand If wind blows steadily from one direction:
Dunes have long, gentle slope on windward side Short, steep slope on the leeward side
Dunes occur in many different shapes, dependent on the amount of sand available, strength and steadiness of winds, and amount of vegetation present
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Depositional Features – Dunes
Pg. 213-214
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Wind Depositional Features - Crossbedding Over time, winds can change direction, reversing direction of the
dunes As older dunes get buried, pressure builds turning them into stone This process creates another feature, called crossbedding
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Homework You should be able to identify and explain the
following erosional/depositional features formed by wind: dunes, cross-bedding, blowouts, desert pavement, ventifacts
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Wave Erosion – Chapter 12 One last agent of erosion is wave action Waves repeatedly pounding against the
coast, along with abrasion, can create numerous erosional and depositional landforms
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Anatomy of a Wave Wave height is the difference between its
high point (crest), and its low point (trough) Wavelength is the distance from one crest to
the next The period of a wave is the amount of time it
takes one wavelength to pass a given point Almost all waves are generated by wind
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Erosional Processes – Longshore drift As waves strike the
coast at an angle, sediment is picked up at an angle, then dropped as the water follows gravity back to the ocean
This causes sediment to migrate down the coast, a process called longshore drift
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Erosional Features – Sea Stacks and Sea Arches
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Erosional Features – River rocks, Undercutting
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Wave Depositional Features
Homework:You should be able to recognize and explain the following erosional and depositional features created by wave action:Sea arch, sea stack, tombolo, spit, beach, sandbar