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Transcript of Earth Science
Earth Science Pd. 7-8
There are five types of mechanical weathering
An Example of Plant Action
An Example of Oxidation
An Example of a Retaining Wall
Two types of weathering
There are two major types of weathering. One is physical and the other is chemical. The physical weathering is also called mechanical weathering, and different types of mechanical weathering include frost action, plant action, abrasion, and pressure unloading. Different types of chemical weathering are oxidation, Acid rain, and lichens. Water can also dissolve limestone. These types of weathering all affect rocks and the landscape in a different way
An example of mechanical erosion: a waterfall
Transporting Systems of Erosion
The several components involved in transporting systems
a driving force
the sediments being moved
an agent of erosion
The driving force of erosion tends to be gravity. Rocks and sediments have gravitational potential energy (rocks at high elevations) some of which changes into kinetic energy when gravity pulls them downward. This process is never-ending because heat energy from Earth's interior raises landmasses.
Energy from the sun also plays a role in erosion.The sun's energy does many things such as drive the water cycle, producing precipitation that results in running water and glaciers. Insulation "fuels" wind patterns that create ocean currents and waves.
The factors affecting the rate of weathering
The rate of weathering can be determined by the exposure of rocks to the atmosphere, the size of the particles, the mineral composition of the rock, and the climate. If a rock is closer to the surface of the earth, the rock will usually erode faster. If the rocks are very small, they will erode faster because they have a bigger surface area than a solid rock with the same volume. If the weather in a certain place is very warm and wet, there is more chemical weathering. If it is cold and moist, frost action is very common.
Erosion is the process by which the Earth gets weathered down. The weathering of rock produces particles that as sediments, are transported through the process of erosion. Sediments found in different areas other than their source are evidence for erosion. These sediments are found in places such as muddy streams, on beaches, along riverbanks, in rock fields near glaciers, and in soils.
Weathering, Erosion, and Deposition
The Difference Between Weathering and Erosion
Weathering is when rocks are decomposed by forces that do not carry the particles to different locations. Erosion is caused by forces that could carry the particles far away to different places. Waves, for example, erode rock and carry the sediments out to sea to the sea floor or a beach depending on particle size. Plants, on the other hand, cause rocks to weather by cracking them with their roots.
How Waterfalls erode:
Waterfalls have a layer of hard rock that is not eroded as quickly as the soft rock right below where the water falls. The soft rock erodes away as the hard rock does not. This makes the waterfall taller. The more it erodes, the taller the waterfall gets.
Gravity is the driving force behind erosion. Gravity leaves unsorted sediments at the base of cliffs. It also leaves angular sediments.
Gravity causes sediments to move downslope by running water, glaciers, and underwater currents. Gravity also pulls rocks and sediments downhill in mass
movements. These can be referred to as landslides.
Running Water Erosion
Running water is sometimes considered the most dominant agent of erosion. This type of erosion often begins with the splashing of raindrops, which displace silt and clay. During storms, sheets of water can flow over the land and cause running water erosion. These sheets of water can become confined to a channel of a temporary stream valley called a rill.
Factors causing deposition
Deposition happens when erosional forces slow down or stop. An example that can be used is a piece of paper blowing away in the wind. It will keep blowing around until the wind stops or slows down. Then the piece of paper is then deposited, or it lands on the ground. There are two factors affecting the rate of deposition, one is the velocity of the erosional and the other is the characteristic of the sediment.
Soils are formed when rock particles and an organic matter mix together. Living plants help make soil by dropping leaves on rocks. The leaves decay and leave acid to weather the rock. The roots of a plant can also crack rock. This forms the rock particles.The decayed leaves then become humus, a source of plant nutrients that can be added to the soil. The soil can then be transported to different places by wind, and water.
Most of the time, as either the slope or the discharge increases, the velocity increases. A wide, flat stream channel has a larger surface in contact with moving water and therefore more friction is generated to slow the stream down. a semicircular stream channel has less friction and greater stream velocity.
The First Type: Frost Action
Frost action is also known as ice wedging and is caused by water getting into a crack in a rock and freezing. Because the special property of water allows it's frozen state to have a larger volume but the same mass, the crack expands. When the ice thaws, the amount of water goes down ,but more water fills into the now larger crack and freezes, making the crack larger. This repeats until the rock cracks completely.
The Second Type: Plant Action
Plant action is what happens when plants grow on rocks. The roots of a plant anchor onto a rock, extend into a crack in the rock, and grows. When the plant grows, the roots grow thicker and cracks the rock even more. The plant keeps growing until the rock splits in half. This is seen on sidewalks where weeds are growing in the cracks. Ivy growing on an old building is also a good example. The ivy digs into the cracks in the cement and climbs up the building.
The third and fourth type of mechanical weathering go together. Abrasion happens first when a glacier carries rocks and pebbles near the ground. The rocks and pebbles scrape the top layer of a rock off as the glacier grows in size and travels down a mountain. Then, pressure unloading occurs. Pressure unloading is when rocks under another layer of rock are exposed and crack because of the sudden decrease in pressure.
The Third and Fourth Type:
Abrasion and Pressure Unloading
Animal action is caused by many things, including ants, rabbits, and moles. When ants build their anthill, dirt and small pebbles are transported outside to form the hill. When rabbits make rabbit holes, the rabbit excavates some dirt and larger pebbles. Moles are sometimes very annoying, but they also excavate dirt and pebbles to be weathered or eroded.
The Fifth Type: Animal Action
if you can find this, say aye
There are four types of chemical weathering
Oxidation is seen on old bicycles and scooters. Iron gets rusty because of oxidation. Some rocks have iron in them ,and they form reddish brown streaks when the iron reacts with the atmosphere and gets rusty.
The First Type: Oxidation
The Second Type: Water
The third way is acid rain. Acid rain can be formed when volcanoes erupt and release nitrogen combined with a random amount of oxygen and can be made with pollution. The acid rain is acidic and can dissolve rocks when it falls. It also hurts wildlife. The last way is when the growth of lichens makes acids and they help to break down rocks.
The Third Type:
The Fourth Type:
The second way is when carbon dioxide combines with water to dissolve things in acid. The water can infiltrate into small cracks that were far away from where the acid was formed. When the acid weathers limestone, the acid reacts with the calcite and the calcite dissolves. This forms limestone caves with stalagmites and stalactites.
Side cutting by streams
Things that cause mass movement
Water can dissolve many minerals, including halite. Rock salt contains halite, and it could be weathered away when it comes in contact with water. Water can also speed up chemical reactions to weather faster.
Life Cycle Of A Stream
Old Age Stream
Lateral Erosion (side to side)
Flows slowly through a broad, flat floodplain that it has carved
Factors For Determining Average Stream Velocity
Gradient-slope of stream
Discharge- volume of water in the stream
Stream channel shape- the shape of the bed of rock or loose materials that confine the stream
V-Shaped Valley- An extended depression in the Earth that is bound by hills or mountains, and is occupied by a river or stream
Cut Bank- Outside of a water channel, also known as a river cliff
Oxbow Lakes- A U-shaped body of water formed when a wide meander is cut off, creating a free body
Levees- Prevent overflow of river
Meander- River flowing over gently sloping ground that begins to curve back and forth across the landscape
Delta- Area where a river enters a larger body of water
Sand bar- A raised area of sand with a top that is near the surface in a body of water
Floodplain- Low, flat, periodically floodd lands adjacent to bodies of water
Factors Affecting Deposition
Size- The smaller particles settle slower
Shape- Determines the amount of resistance the particles will undergo
Density- influences the rates at which sediments settle
Velocity- Determines when sediments will be deposited
Wind erosion occurs when wind transports fine dust particles around. Sediment that has been eroded by wind is smaller, frosted (polished stones) and pitted (has holes).
Sandblasting- The action of forcibly propelling a stream of abrasive material against a surface under high pressure to smooth a rough surface.
Factors That Affect Wind Erosion
Wind Velocity and Tubulence
Loess- Deposits of wind-blown silt and clay deposited layer on layer
Dunes- Formed of a particle to heavy for wind to carry
Cross Bedding- When sand is deposited upwind on the side of a dune. As each layer falls down the slip face, cross beds are formed
Deflation- The process of smaller materials being selectively transported by wind.
Arches- Tectonic stress forms fractures in rock which become further defined from weathering. Wind and gravity then cause the arch form
Desertification- Occurs as a result of climatic changes
Desert Pavement- The rockier surface left behind after deflation
The roots of the plant are elevating the sidewalk
Mass Movement is when a large amount of rock falls or slides of the top of a hill (avalanches and rock slides).
Mass movement, sometimes called direct gravity erosion, involves two forces, the constant downward pull of gravity, and friction. Friction attempts to keep objects in place. Loose materials, such as rocks, slide downward when the force of gravity becomes stronger than the forces holding them in place.
Mass amounts of water and earthquakes can trigger mass movement. They are the most common and have disastrous consequences.
Four Main Factors That Effect Mass Movement
Angle of slope- The angle of the slope increases or decreases the amount pressure the slope "feels"
Slope Material- What the slope is made out of
Water- A lot of water loosens the bonds between mineral grains
Vegetation- The vegetation helps hold topsoil together
Rate of Deposition
Characteristics of Sediments and Rate of Deposition
Velocity of an Erosional System and Rate of Deposition
Sorting of Sediments and Deposition
Unsorted Glacial and Mass Movement Deposits
Agents of Deposition
Classification Of Slope Material
Deposition by Glaciers
Deposition by Streams
Deposition on Coastlines by Waves
Deposition by Mass Movement
Unconsolidated rock- Loose materials that are not bound together. These are extremely prone to mass movement
Crystalline Rock- Rocks such as gneiss and granite are very stable and rarely give in to mass movement
Dip Slope- When the layers of a sedimentary rock tilt downward, allowing it to slide down a hill
Fractures- When a rock fractures, than bonds are loosened and it becomes more susceptible to mass movement
Plant Roots- Help keep unsolidated soil together and can split rock
Rivers sort sediments and deposit it when a river enters a body of water. They form a delta and the sediment get's deposited and sorted. The smaller sediments are deposited closer to the body of water, while the larger pieces of sediments are deposited closer to the river.
Glaciers deposit sediment in moraines that are unsorted and not layered. Glaciers also gouge out U-shaped valleys in mountains. Mass movement causes unsorted , not layered, angular sediments in a talus slope. The angle of repose is about 30 degrees.
Types of Mass Movement Events
Fall-The object under mass movement falls from a great height with nothing but the friction in the air to slow it
Slides- When the object slides down the surrounding rock and is slowed by friction
Flows- When rocks such as clay or sand become liquid-like as if exposed to water. This is known as quicksand
Types Of Glacier
Alpine- associated with mountain ranges, flows in confined areas
Cirque- Glaciers that form from bowl-shaped depressions near a mountaintop
Valley- Large alpine glaciers that flow down mountain valleys
Piedmont- When an alpine glacier flows out of a valley and into an unconfined plain at the foot of a mountain range
Tidewater- Where an alpine glacier descends and terminates into an ocean body
Ice Cap- Domed unconfined glacial mass that flows outward in all directions
Ice Sheet- A very large and unconfined ice mass that flows in all directions
The factors that determine the speed of glacier movement
There are three properties that affect the rate of deposition:
The size of the particle affects the rate of deposition. The bigger the particle, the faster it will be deposited on the river bed. If a particle's shape is more hydrodynamic, the particle will travel faster and settle after the particles that are not very streamlined are deposited. The density of a particle also affects the rate of deposition. The more dense a particle is, the faster it will be deposited on the earth.
Deposition by Wind
Deposition by wind is caused when the wind slows down so it can no longer carry any particles in suspension. Depositional features include:
Sediments deposited by wind are angular, pitted, and frosted.
When glaciers deposit things, they generally deposit them in moraines, piles of sediment that signal the furthest the glacier has extended. Depositional features include:
The sediments that glaciers deposit are unsorted and not layered.
Mass movement happens when a large amount of rock falls or slides off the top of a hill. Mass Movement forms a talus slope and the bottom of a cliff. The angle of repose is the angle of the sediments at the base of the cliff. The angle of repose is usually around 30 degrees.
Thickness of ice- More thickness means more stress on ice
Temperature of ice- Warmer ice undergoes more internal deformation
Steepness of glacial slope- Helps basal sliding
Surges- Meltwater accumulates at the base of a glacier helping it surge forward
Waves are formed when storms overseas blow winds. The winds cause the waves to slosh around and form. The sediments at the bottom of the ocean floor are moved around by the waves. Beaches are formed when sediments are deposited by waves.
Streams deposit sediments that are sorted. All the sediments that streams and rivers deposit are rounded by the friction of the water flowing by them. Rivers form deltas when they enter other bodies of water. Deltas form when the water slows down. The decrease in the velocity of the stream makes the larger particles settle first, while the smallest particles settle last.
This indicates that the wind blows from the right
Notice how the top is higher than the bottom
Till- consists of unsorted deposits of glacial sediment
Erratic- glacial sediment that have been transported far from their point of origin
Outwash Plain-deposited clay and silt suspended from the streams
Loess- winds blowing picks up silt from drying outwash plains and deposits them
Striations-grooves cut into the bedrock surface as rock fragments are carried along the base of the glacier
Cirque-bowl shaped depression formed on a mountainside where the head of the glacier developed
Arete- Sharp ridge separating glaciated valleys
Col-a small gap in Arete
Horn- steep peak created by erosion of cirque glaciers
Tarn-small lake that partially fills a cirque
U Shaped Valley-glaciers erode across the valley creating a U shape
Hanging Valley- smaller valley glaciers that flowed into the main valley glacier
Always cold (Greenland, Antarctica)
Directly deposited by ice
Outwash plains deposited by meltwater
Broad, domed shaped
Carries sediments in front of glacier, on top of glacier, along the glacier suspended in the ice
The faster an erosional system is traveling, the more sediment it can carry in suspension. If an erosional system has a low velocity, there will be more deposition. One example is when rivers enter deltas. The water slows down as it enters a body of water and all the sediment that was carried by the river is deposited.
Running water confined to a channel = Stream
A smaller stream that flows into a larger stream = Tributary
Dissolved materials are carried in solution
Solid sediments are usually carries by rolling, sliding, or bouncing along the stream bottom, which causes stream abrasion (spheroidal weathering)
Streams carve V-Shaped valleys (results from downcutting, runoff, and mass movement)
The area drained around any one stream = Watershed (vary in size)
Water does not always move at the same velocity throughout the stream. The region of maximum velocity changes when the stream changes direction. Maximum velocity is at the center of a stream when it is straight, but when it curves, maximum velocity is on the outside of the curve. Maximum velocity is also greatest just below the surface and the least at the channel bottom. The faster the stream, the larger the sediments particles it can carry.