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Landforms and Weathering

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Title: Landforms and Weathering


1
Landforms and Weathering
  • Grade 5
  • Goal 2
  • EOG Tested

2
Major Unit Goal/Learning Outcomes
  • Students should be able to
  • Describe how forces change landforms over time
  • Rate the effects of weathering forces
  • Understand how water movement shapes landforms
  • Describe the characteristics of landforms
  • Discuss how water flow effects erosion
  • Identify landforms using maps and aerial
    photographs
  • Understand the influence of humans on erosion and
    deposition

3
Objective 2.01
  • Identify and analyze forces that cause change in
    landforms over time including
  • Water and Ice
  • Wind
  • Gravity

4
Objective 2.02
  • Investigate and discuss the role of the water
    cycle and how movement of water over and through
    the landscape helps shape land forms.

5
Objective 2.03
  • Discuss and consider the wearing away and
    movement of rock and soil in erosion and its
    importance in forming
  • Canyons
  • Valleys
  • Meanders
  • Tributaries

6
Objective 2.04
  • Describe the deposition of eroded material and
    its importance in establishing landforms
    including
  • Deltas
  • Flood Plains

7
Objective 2.05
  • Discuss how the flow of water and the slope of
    the land affect erosion.

8
Objective 2.06
  • Identify and use models, maps and aerial
    photographs as ways of representing landforms.

9
Objective 2.07
  • Discuss and analyze how humans influence erosion
    and deposition in local communities, including
    school grounds, as a result of
  • Clearing land
  • Planting vegetation
  • Building dams

10
What are Landforms?
  • Landforms are the natural features of the earth.
  • Mountains, plateaus, plains and hills are all
    examples of landforms.

11
Changes Over TimeWeathering
  • Landforms constantly develop and change as the
    forces of weathering and erosion change rocks and
    break them down. Weathering is the force that
    causes rocks to fragment, crumble, crack and
    break down either chemically or physically.

12
Weathering of Rocks
  • Rocks weather in different ways and at different
    rates depending on the mineral composition and
    location of the rock. The rocks break down into
    small rock fragments as they are weathered.
    These fragments are broken down further into
    particles that comprise soil along with organic
    material.

13
Ice Wedging
  • When water is frozen it expands, so when water
    seeps into cracks in rocks then freezes, the
    expanded ice can cause the rock to split and
    crack. This process is known as ice wedging and
    it can reduce a rock to rubble over time.

14
Soil/Plant Wedging
  • Soil can also collect inside of the cracks of
    rocks. Plants can grow in this soil and
    eventually the roots grow large enough to cause
    pressure on the rocks, causing the crack to
    expand. The rock can split apart from this
    expansion.

15
Chemical Weathering
  • Minerals found in the rocks can change to other
    minerals due to the reaction with water or air.
    Reactions such as rusting or acid formation can
    also cause the rock to break down into smaller
    fragments.

16
Changes Over TimeErosion
  • Erosion carries away the rock debris caused by
    weathering. The eroded rocks and sediments are
    deposited by forces such as volcanoes, wind,
    water, ice and waves to various depositional
    environments on Earths surface.

17
Water Erosion
  • A variety of landforms are carved by water.
    Moving water erodes rocks and transports the
    small pieces of rock.
  • Groundwater or underground water can dissolve
    limestone causing caverns or sinkholes.
  • Ocean waves shape our coastline. The waves also
    transport sand and rocks causing extensive
    erosion.

18
Wind Erosion
  • Wind moving at high speeds can transport a large
    amount of dust and sand.
  • Erosion of this type shapes deserts by carrying
    the sand and by sandblasting rock. If soil
    doesnt contain plants to hold its place, it can
    be exposed to vast amounts of erosion.
  • Loss of soil can cause loss of farmland.

19
1930 Dust Bowl
  • During the Dust Bowl in the 1930s, over
    cultivation of the farmland removed the native
    grasses that held the soil in place.
  • Drought and wind stripped the land of its fertile
    soil.

20
Glaciers
  • Glaciers also help to shape landforms. These
    huge sheets of ice move slowly over the land in
    the polar regions of the Earth and in high
    mountains where vast amounts of snow build up and
    turn to ice.
  • The mass of ice moves slowly, only a few inches
    per day. This movement is caused by layers of
    ice moving each other or by the layers of ice
    sliding on a thin layer of water that begins to
    melt at the bottom of the glaciers.

21
Glaciers (continued)
  • As the glaciers moves, it pull out pieces of the
    bedrock which become embedded into the bottom of
    the glacier.
  • As the glacier moves over the land, these pieces
    of embedded rock grind down on and under the
    glacier, shaping a variety of landforms.
  • When glaciers retreat, possible landforms that
    are created include canyons, huge boulders, rock
    piles, hills, valleys and lakes.

http//www.youtube.com/watch?vqbQjukRmLSg
22
Forces that Build
  • Plate tectonics is a major force that builds
    large masses of land.
  • Faults, volcanoes and mountains are formed as
    rocks are moved across the surface of the Earth
    and shape mountains.

Watch this 3 minute video. Click on the link
below
http//www.youtube.com/watch?vnfziy_860GU
23
Deposition
  • There are smaller building forces that can occur
    by transporting weathering agents such as water,
    wind and ice.
  • These are the same forces that erode the land.
  • These weathering agents can carry sediment and
    deposit it somewhere else through a process
    called deposition.
  • Deposition of sediment can form beaches, deltas,
    sand dunes and change
  • the shape of rivers and
  • coastlines.

24
People and the Land
  • People have a direct affect on weathering,
    erosion and deposition.
  • People can speed up erosion by clearing the land
    for farming, housing developments, building
    roads, deforestation and strip mining.
  • People change the course of rivers by channeling
    them and building dams across them
  • The shapes of mountains are changed by building
    roads and highways.
  • Coastlines are changing by building roads and
    houses that may alter the natural changes of the
    coastline.

25
Examples of LandformsValleys
  • Valleys are depressions on the surface of the
    Earth that are borders by hills or mountains.
  • The naturally formed troughs are made by water
    and/or ice (glacier) erosion.
  • As rivers and streams flow through valleys, they
    carry sediments and other materials of land.
  • Fertile soil is found at the bottom or floor of
    the valley. The valley floor slopes downstream.

26
V-Shaped Valleys
Valleys formed by rivers have more v-shape.
27
U-Shaped Valleys
U-shaped valleys are formed by glaciers.
28
Plateaus
  • Plateaus are formed in different ways
  • Some are formed as a result of lava flows
    covering a large area and building up the
    surface.
  • They can also formed by the forces of upward
    folding, followed by the erosion of surrounding
    land. These forces leave large areas of fairly
    level highlands that are separated from land by
    steep slopes.
  • Plateaus can be surrounded by mountains or can be
    higher than the land around them.

29
Mountains
  • Mountains are created by huge forces in the Earth
    over a long period of time.
  • They are formed by the movements of the Earths
    plates (plate tectonics).
  • The forces of heat and pressure underneath the
    Earths crust cause movements in the Earths
    plates.
  • These movements are what most scientists believe
    form most of the mountains.

30
Plate Tectonics
  • The lithosphere of the Earth is divided into
    sections called plates.
  • Through plate tectonics these plates move and
    collide, separate, and slide past each other.
  • When some plates collide, one moves under the
    other and causes the eruption of volcanoes.
  • Other plates compress causing folding and
    wrinkling of the crust. (Appalachian Mts.)

31
Plains
  • Plains are wide stretches of land that do not
    have significant changes in elevation.
  • Some plains (Great Plains) are found inland while
    others found along the coast.
  • Plains contain fertile soil so these areas are
    often well populated.
  • Roads, towns and cities are also easily built in
    these areas.
  • Coastal Plains are stretches of lowland along the
    seacoast that slope towards the ocean.

32
Fall Line
  • Along the NC coast, the coastal plain is
    flooded by the ocean and the edge of
    the North American continent is actually
    submerged beneath the ocean. In some areas the
    plains is part of an elevated ocean floor.
  • Sediments and other solid materials are carried
    by rivers and waves where they are deposited
    along the coastline extending the coastline
    seaward.
  • The sharp upward slope of land along the plains
    inward is called the fall line.

33
Lakes
  • Lakes are bodies of water that are different from
    marine environments.
  • They are small, fairly closed systems, and have
    less pronounced tides.
  • When sediment flows into lakes, the coarser sand
    and gravel are deposited in the shallow areas of
    the lakes, especially during the summer.
  • The finer silt and clay are deposited in the
    deeper areas of the lakes, especially during the
    winter.

34
Varves
  • Alternating thin layers of light-colored and dark
    colored finer grained sediment are called varves,
    this is one type of deposit and forms in all
    types of lakes (glacier and nonglacial).
  • While most sediment deposits in lakes come from
    rivers, some deposits are from wind, ice-rafting
    and volcanic rock erosion.

35
Volcanoes
  • Volcanoes create different types of rocks because
    of the various mineral compositions that compose
    magma.
  • Depending on the amount of gas found in the magma
    and the thickness of magma, the volatility of
    volcanic eruptions and the landforms that are
    made differ.

36
Lava
  • Lava in mountain building environments is the
    most thickness and has higher gas content.
  • The eruptions from these volcanoes are more
    explosive and form an extrusive, solid volcanic
    material called tephra.
  • Rich fertile soil is formed from ash and is used
    for growing crops.
  • In the USA most volcanoes are found in Hawaii,
    Washington and Oregon.

37
Volcanic landforms
  • As a results of volcanic activity, there are
    three different types of landforms that are
    created.
  • 1. Lava Plains and Lava Plateaus are volcanic
    landforms that are created when a large volume
    of fluid lava flows over a wide surface area.
  • The result is topography with extremely
  • flat surfaces that aggrades with each
  • successive lava flow.

38
Volcanic composite cones
  • Composite cones are very distinctive in
    appearance.
  • They have layers of interbedded, blocky tephra
    that is composed mainly of ash and cinder.
  • The peaks can rise several thousands of meters
    with narrow circular bases.
  • Mount Rainer in Washington is an example of a
    composite volcano.

39
3. Calderas
  • These are created by volcanoes that have erupted
    then have later collapsed inward.
  • Composite cone volcanoes are much more likely to
    form calderas due to the tephra sheets that they
    contain.
  • Crater Lake in Oregon and Yellowstone Plateau in
    Wyoming are calderas.

40
Grand Canyon
  • Not all landforms are created by deposition.
  • The Grand Canyon is a landform that was created
    by the erosive forces of water and wind that cuts
    and etched the land over millions of years.
  • The Colorado River cut deep gorges into less
    resistant rock and created the canyon while the
    more resistant, less weathered rock remained.

41
Other Types of LandformsAlluvial Deposits
  • Alluvial deposits are rock debris and sediments
    such as silt and clay that are carried down by
    mountain streams or rivers to the valley floor.
  • Alluvium is soil or sediments deposited by a
    river or other running water.
  • Alluvium is typically made up of a variety of
    materials fine particles of silt or clay, larger
    particles of sand and gravel.

42
River Flows
  • A river constantly picks up and drops sediment
    throughout its length.
  • Where the river flows quickly, more particles are
    picked up than dropped.
  • Where the river flows slowly, more particles are
    dropped than picked up
  • Areas where more particles are dropped are
    called alluvial or flood plains, and the dropped
    particles are called alluvium.

43
Alluvium Fans
  • Alluvium often contains valuable ores such as
    gold and platinum as well as a wide variety of
    gemstones.
  • Such concentrations of valuable ores are termed a
    placer deposit.
  • Stream flows that occurs in humid climates are
    distributed into fan shaped landforms called
    alluvial fans.

44
Alluvial Soils
  • Alluvial soils are finely layered and deep.
  • The alluvial sands found close to river banks and
    on natural levees are sandier, but can be more
    clayey or peaty when close to swampy areas.
  • Some alluvial deposits have rich top soil and are
    very fertile allowing for the area to be a
    crop-growing region.

45
Colluvial Deposits
  • Colluvial deposits are materials that are moved
    down slope by gravity and/or erosion and collect
    at the base of mountains or foothills with little
    or no sorting. (Soils from colluvial deposition
    are deep and hard, clay soils are more common).

46
Eolian Desert
  • Eolian desert deposits are found in arid regions
    around the world.
  • Dry air masses create wind systems that transport
    then deposit sediment.
  • Silt particles, called loess, are carried by the
    wind and collect around the fringes of the
    deserts.
  • Large areas of the desert environment that have
    more than 125 square kilometers of eoloan sands
    are called sand seas or ergs.

47
Eolian Desert
  • Smaller areas are called dune fields
  • Variable wind directions and wind force transport
    and deposit sand creating different types of
    dunes.
  • Some dunes are shaped by the wind into ridges,
    strings, domes, stars, or half-moon shaped dunes.
  • Desert consist mainly of wind-deposited sand that
    originated from sandstone that has eroded over
    time.

48
Glacial Deposits
  • Glacial deposits can move huge amounts pf soil
    and bedrock.
  • Over 10,000 years ago glaciers extended into
    lower latitudes and elevations than in the
    present.
  • The climate became warmer and these glaciers
    began to melt and wear away the bedrock below the
    glaciers.

49
Rate of Glacier Melts
  • Different rates of ice melt caused the eroded
    sediment to fall out of the retreating glaciers.
  • This glacier till formed deposits called moraines
    and drumlins.
  • The melt-waters flowing in around the margins of
    the glacier accumulated deposits known as outwash
    plains and depressions (kettles), small mound
    shaped accumulation of sand or gravel called
    kames, and eskers (narrow ridges of sediment).

50
Loess Deposits
  • Loess deposits are commonly located in or near
    glacial regions but can also be found in the
    desert regions of the world.
  • These deposits are composed mainly of silt
    grains, with less significant amounts of clay and
    sand.
  • Mineral quartz is dominant in loess with
    feldspar, carbonates and clay minerals in smaller
    amounts.
  • Depending on the type of region where the loess
    is found, there will be varying types of
    minerals, rocks and sediments.

51
Glacial Outwash
  • Outwash is transported to floodplains by rivers
    that drained form glacier melt-water.
  • These outwashes are composed of sand, silt and
    clay.
  • This debris becomes airborne by strong winds
    because there is very little vegetation to hold
    the sediment down.
  • These loess can be suspended several kilometers
    high and travel hundreds of kilometers in
    distance.

52
Marine Deposits
  • Marine deposits mainly rework and distribute
    carbonate materials forming ooids on the marine
    shelf.
  • Moderate water circulation on the marine shelf
    brings nutrients from deep water to shallow water
    that aids in organic growth of ooids that
    eventually become cemented together.

53
Waves
  • Waves move the fine carbonate mud and coarser
    sediment to form sand and gravel covered tidal
    flats, beaches, dunes, marshes, lagoons and
    swamps.
  • The waves can also move these sediments towards
    the sea forming spits, tidal deltas as well as
    bar and barrier islands.
  • The pounding waves against the shore also
    contribute to rock particles and sediment on the
    coastal shelf.

54
Reefs
  • Reefs can be characterized as either thick masses
    of living carbonate rock or structures produced
    by sediment-binding, live organisms.
  • Other marine depositional environments include
  • Deltas estuaries
  • Beaches lagoons
  • Barrier bars tidal flats

55
Other Deposits
  • Estuarine deposits consist of cross bedded sands
    and mud, or a mixture of both sand and mud.
  • Lagoonal deposits include evaporites, fine
    grained sediments and black shale.
  • Delta deposits and tidal flat deposits contain
    primarily mud in the upper zone, mud and sand in
    the middle zone and sand in the lower zone.
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