landforms content

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Landforms ContentLandforms Content

Competency Goal 2: The learner will make observations and conduct investigations to build an understanding of landforms.

Alex Richardson

Elementary Science Coach

[email protected]

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Objective 2.01Objective 2.01 Identify and analyze forces that Identify and analyze forces that cause change in landforms over time including cause change in landforms over time including water, wind, and gravitywater, wind, and gravity

• The Earth’s surface changes over a period of time.

• Slow processes of weathering and erosion are caused by water, wind, glaciers, and the force of gravity.

• Exposed surface areas of rocks are subject to increased weathering as rocks break apart.

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Objective 2.01 Objective 2.01 cont’dcont’d

• Weathering and erosion are slow processes that wear away rocks and carry away sediment.

• Weathering is the process that breaks down rock and other materials at Earth’s surface.

• Erosion is the movement of rock particles by wind, water, ice, or gravity.

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Types of WeatheringTypes of Weathering

• Mechanical (physical change): rock is physically broken into smaller pieces and have the same composition as the rock they came from

• Chemical (chemical change): rock changes from chemical reactions which produce rock particles that have different substances

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Forces of Mechanical Forces of Mechanical WeatheringWeathering

Heating and Cooling

Freezing and Thawing

Plant Growth

Abrasion

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Heating and CoolingHeating and Cooling

• The outside of a rock can be heated more rapidly than the inside by the sun or a forest fire.

• This heating may cause the outside of the rock to flake off.

• Rain may help the cooling process by suddenly cooling heated rock causing it to crack.

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Freezing and ThawingFreezing and Thawing

• Water seeps into cracks in rocks and freezes when the temperature drops.

• Water expands when it freezes.

• The most important force of mechanical weathering is freezing and thawing in cool climates.

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Freezing and Thawing cont’dFreezing and Thawing cont’d

• Wedges of ice and rocks that widen and deepen cracks is a process called ice wedging.

• When ice melts, the water seeps deeper into the cracks.

• Repeated freezing and thawing slowly expands cracks until pieces of rock break off.

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Plant GrowthPlant Growth

• Roots of trees and other plants enter cracks in rocks.

• Cracks in rocks are forced farther apart as the roots grow.

• Over time, the roots of small plants can pry apart cracked rocks.

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AbrasionAbrasion

• Wind driven sand helps shape rocks.

• Wind, water, or ice can carry sand and other rock particles to aid in weathering.

• Exposed rock surfaces face weathering slowly over spans of time as abrasive materials pound against it.

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Forces of Chemical Forces of Chemical WeatheringWeathering

Water

Oxygen

Carbon Dioxide

Living Organisms

Acid Rain

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Water

is most important agent of chemical

weathering

weathers rock bydissolving; mixes

uniformly to make asolution

will dissolve many rocks over time

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Oxygen

Iron combines withoxygen in the

presence of waterin a process called

oxidation.

The product of oxidation is rust. Rock

that contains ironalso oxidizes, or rusts.

Rust makes rock softand crumbly and gives it a red or brown color.

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CarbonDioxide

is a gas found in the air that dissolves in

rainwater and in waterthat sinks through air

pockets in the soil

The result is a weak acid called carbonic

acid.

Carbonic acid easily weathers marble and

limestone.

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LivingOrganisms

Plant roots produce weak acids.

The acids slowly dissolve rock around

the roots.

Lichens, plantlike organisms that grow

on roots, also produce weak acids

that chemicallyweather rock.

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Acid Rain

Burning coal, oil, andgas can pollute the

air with sulfur, carbon,and nitrogen compounds.

The compounds reactchemically with the water vapor in the

clouds forming acids.

Acids mix with raindrops and fall as

acid rain which causesvery rapid chemical

weathering.

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Objective 2.02Objective 2.02 Investigate and discuss the role of Investigate and discuss the role of the water cycle and how movement of water over the water cycle and how movement of water over

and through the landscape helps shape landforms.and through the landscape helps shape landforms.

• Water is constantly recycled through the environment in the water cycle.

• The water circulates up, down and around and among the ocean, atmosphere and land as a continuous process.

• The sun is the primary energy source that powers the water cycle.

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Role of Water CycleRole of Water Cycle

• The water cycle is one of Earth’s cycles that sustains life.

• The water cycle is a vital component in the shaping of the land.

• The cycling of water is composed of several different phases that include evaporation, condensation, precipitation, and run-off.

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Components of the Water Components of the Water CycleCycle

• Water storage in oceans• Water storage in ice and snow• Snowmelt runoff to streams• Water in the atmosphere• Evaporation• Sublimation• Springs• Evapotranspiration

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Components of the Water Cycle Components of the Water Cycle (cont’d)(cont’d)

• Infiltration• Surface runoff• Freshwater storage• Ground-water storage• Ground-water discharge• Condensation• Precipitation• Stream flow

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Location of Earth’s WaterLocation of Earth’s Water

• Water covers about 75% of Earth’s crust.

• Most saltwater, 97.2 %, is in the oceans.

• Less than 3% of Earth’s water is freshwater.

Frozen icecaps and glaciers 2.15%

Groundwater 0.62%

Surface water 0.03%

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Movement of WaterMovement of Water

• The amount of water cycling through the water cycle is one factor shaping landforms.

• A falling raindrop starts the process of erosion and creating landforms.

• The force of a falling raindrop can loosen or pick up soil particles.

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Movement of Water (cont’d)Movement of Water (cont’d)

• Soil particles are carried as water moves over the land.

• The moving water is called runoff.

• Runoff is the remaining water that moves over and through the Earth’s surface.

• Movement of water is one of the main forces that causes erosion.

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How People Use the

Land

Shape of the Land

Type ofSoil

Vegetation

Amount ofRain in an

Area

Five Main Factors of

Runoff

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Objective 2.03 Objective 2.03 Discuss and consider the wearing away Discuss and consider the wearing away and movement of rock and soil erosion and its and movement of rock and soil erosion and its importance in forming: canyons, valleys, meanders, importance in forming: canyons, valleys, meanders, and tributaries.and tributaries.

• Moving water can weather and erode rocks and soils.

• The breaking down of Earth’s surface creates some landforms through processes of weathering or erosion.

• Various landforms such as canyons, valleys, meanders, and tributaries were primarily created by the constant flow and wearing action of a river or stream.

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Landform FormationsLandform Formations

• Canyons are formed by weathering action from the force of water. As the force of water shapes the land, areas are exposed to weathering and erosion.

• Valleys can be formed as a result of river erosion. The river is often fast-flowing and generally follows a straight, narrow course. Steep slopes along the river erode rapidly creating a deep v-shaped valley.

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Landform Formations (cont’d)Landform Formations (cont’d)

• Valley glaciers form when snow and ice build up high in a mountain valley.

• The sides of mountains keep these glaciers from spreading out in all directions.

• Valley glaciers usually move down valleys that have already been cut by rivers and have a u-shape.

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• Meanders develop where water flows through easily eroded rock or sediment. A meander is a looplike bend in the course of the river.

• Meanders are common along gently sloping flood plains of a river as it widens from side to side. Meanders erode the outer bank and deposit sediment on the inner bank of a bend. Over time the meander becomes more and more curved.

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• A tributary is a stream that flows into a larger stream. Large tributaries can also flow into large streams or rivers.

• A river begins at its headwaters, or head which is usually a mountainous region.

• A river ends at its mouth. A delta often forms at a river’s mouth, but not always.

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Objective 2.04 Objective 2.04 Describe the deposition of eroded material Describe the deposition of eroded material and its importance in establishing landforms including and its importance in establishing landforms including deltas and floodplains.deltas and floodplains.

• Deposition from runoff, rivers, groundwater erosion, glaciers, waves, and wind creates some landforms.

• Some landforms are formed from erosive forces of water and wind.

• New landforms are shaped by transported sediment that is deposited during the course of its movement.

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Deposition by RiversDeposition by Rivers

• Sediments are carried with water as it moves. When moving water slows down, it drops or deposits some of the sediment.

• As water slows, fine particles fall to the river’s bed. Larger stones quit rolling and sliding.

• Alluvial fans are created when a stream suddenly becomes wider and shallower. The water slows down and sediments are deposited in an alluvial fan. This deposit is shaped like a fan.

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Deposition by Rivers (cont’d)Deposition by Rivers (cont’d)

• A delta is formed when sediment is deposited where a river flows into an ocean or lake. The sediment in the water drops to the bottom and builds a landform.

• A flood plain forms when a river’s power of erosion widens its valley rather than deepening it. The river spreads out and erodes the land depositing sediment as new soil.

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GroundwaterDeposition

The action of carbonicacid on limestone canresult in deposition.

Inside limestone caves,deposits called stalactites and

stalagmites form fromlimestone water dripscontaining carbonicacid and calcium.

As the water evaporates, a deposit of calcite forms from the roof of the cavecalled stalactite and from the floor called

stalagmite.

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GlacialDeposition

When a glacier melts,it deposits the

sediment it eroded from the land creating

various landforms.

The mixture of sediments that a glacier

deposits directly on the surface is called till.Till is made up of manydifferent particle sizes.

Clay, silt, sand, gravel,and boulders can be

found in till. Till deposited at the edgesof a glacier forms a

ridge called a Moraine.

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WaveDeposition

Waves shape the coast through erosion aswell as deposition.

Deposition occurs whenwaves slow down and

the water drops its sediment.

As waves reach the shore, they drop

sediment forming a beach. The sediment dropped on beaches

is usually sand.

Most sand comes from rivers that carry erodedrock particles into theocean. Some beaches

are made of smallfragments of coral

and sea shells.

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Wind Deposition

Wind erosion anddeposition may form sand dunes and loess

deposits.

Over time, thesand shifts with the

wind from one side ofthe dune to the other side. Sand dunes are

usually made of coarser sediments.

Finer wind-depositedsediment is called loess. Loess helps

form fertile soil. Areaswith thick loess

deposits are valuablefarmlands.

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Objective 2.05Objective 2.05 Discuss how the flow of water and the Discuss how the flow of water and the slope of the land affect erosion.slope of the land affect erosion.

• When gravity pulls water down a slope, water’s potential energy changes to kinetic energy, and it does work.

• Water running down hill is a dominate erosion process; the steeper the slope the more material will be eroded.

• Some landforms are made by the slope of the land and the amount of running water.

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Flow of WaterFlow of Water

• The power of a river to cause erosion and carry sediment depends on several factors.

• A fast-flowing river carries more and larger particles of sediment.

• Larger particles of sediment are deposited first when a river slows down.

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Flow of Water (cont’d)Flow of Water (cont’d)

• Most sediment washes or falls into streams or is eroded from streambeds by abrasion.

• The slope of an area and the amount of water delivered to an area contributes to the erosion of the land.

• A typical river transports most sediment in suspension, a lesser amount in solution, and the least amount along its bed.

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Slope of the LandSlope of the Land

• If the slope increases, then the water’s speed also increases.

• The slope of an area and the amount of water delivered to an area contributes to the rate of erosion.

• An increased slope and water flow result in an increased rate of erosion.

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Objective 2.06 Identify and use models, maps, and aerial Objective 2.06 Identify and use models, maps, and aerial photographs as ways of representing landforms.photographs as ways of representing landforms.

• Maps are abstractions of realities and can represent large or small areas.

• Maps and models are ways of representing information about your neighborhood, city, state, county, and waterways.

• Floor plans can be considered a map of your home.

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Topographic MapsTopographic Maps

• Topographic maps show surface features of an area.

• Topographic maps use a variety of symbols to portray the land as if you were looking down on it from above.

• Topographic maps provide data necessary for the planning of bridges, highways, and other large construction projects.

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Topographic Maps (cont’d)Topographic Maps (cont’d)

• Topographic maps provide highly accurate information on the elevation, relief, and slope of the ground surface.

• Topographic maps are usually large scale maps. The larger the scale of a map, the smaller the area covered.

• Large scale maps show a close-up view of part of the Earth’s surface.

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Topographic Maps (cont’d)Topographic Maps (cont’d)

• Most nations have a government agency that is responsible for making topographic maps.

• In the United States, that agency is the U.S. Geological Survey, or USGS.

• Many USGS maps are at a scale of 1:24,000, or 1 in.=2,000 ft.

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Models Models

• A model is a representation of how something works.

• Models are useful to study objects or systems.

• Models can construct meaning through visual representation.

• Some models can be physical or generated on a computer.

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Aerial PhotographsAerial Photographs

• Aerial photographs are taken from airplanes to make highly accurate maps, thus given the name aerial photographs.

• Aerial photographs aid scientists in understanding Earth.

• Pictures are taken from satellites to display the Earth’s land surface-plants, soil, water, sand, rock, snow and ice.

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Objective 2.07Objective 2.07 Discuss and analyze how humans influence erosion Discuss and analyze how humans influence erosion and deposition in local communities, including school grounds, as a and deposition in local communities, including school grounds, as a result of: clearing land, planting, vegetation, and building dams.result of: clearing land, planting, vegetation, and building dams.

• Land use impacts erosion and deposition of soils.

• Humans can have a positive influence and negative affect on the land.

• The geography or topography can be affected by humans.

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Human InfluencesHuman Influences

• Erosion carries away soil particles.

• Deposition is the process of depositing transported or eroded materials.

• Vegetation helps to decrease the rate of erosion.

• Dams assist in the containment of water to prevent flooding and erosion.

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