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.