Framing an Appropriate Research Question 6b9b26d93da94caf993c038d9efcdedb.pdf
Chapter03 for CD.ppt
1. Introduction to Geography
People, Places, and Environment, 6e
Carl Dahlman
William H. Renwick
Chapter 3: Landforms: The
Dynamic Earth
Holly Barcus
Morehead State University
And Joe Naumann
UMSL
2. 2
Geologic Time – in 24 hours
• Humans
have
been
around
for ½ of
one
minute
on this
scale.
3. 3
Geomorphology
• Study of landforms and processes that
create them
• Lithosphere
–Rocks and soil
–Surface landforms
• Plains, hills, plateaus, & mountains
• valleys, depressions
4. 4
Landform Processes
• Endogenic (endogenous)
– Internal forces beneath or at Earth’s surface
• Mountain building (diastrophism)
• Earthquakes
• Volcanism
• Exogenic (exogenous)
– External forces
• Weathering – physical (mechanical) & chemical
• Erosion by moving water, air, or ice
7. 7
Plate Tectonics
• Fixed Earth Theory
– Continents and oceans fixed in place
• Pangaea Hypothesis
– Supercontinent
– Alfred Wegener, 1900s
• 1960s = Plate Tectonics Theory
9. 9
Process of Continental Drift
• Appears to be generated by heat-sustained
convection cells in the interior (particularly the
asthenosphere which is not solid)
• Movement occurs where plate boundaries abut
– Divergence – spreading along mid-ocean ridges which lie above
and upwelling in the cell
– Convergence (subduction) – colliding plates over the downward
portion of a convection cell
– Ring of Fire – largely an area of subduction
10. 10
Earth’s Crust & Layers
• Mantle
– Rock beneath
crust
• Tectonic plates
– Earth’s rigid
crust
• Plate movement
– Earthquakes
– Volcanoes
– Mountain
building
13. 13
Plate Boundaries: click pictures
• Divergent
– Plates spreading apart
• Seafloor spreading
• Rift Valleys in Africa
• Convergent
– Plates push together
• Dense plates dive below
• Volcanic eruptions
• Transform
– Grinding of plates past each
other
• San Andreas Fault, CA
17. 17
Convergent Boundary
• Continental plate meets continental plate and
massive uplift occurs – click picture to see a
video that reviews this type of plate boundary
as well as the others.
18. 18
Earthquakes
• Focus
– Place of actual
movement
• Epicenter
– Surface directly
above focus
• Seismograph
– Recording device for
seismic waves
– Richter Scale, 1935
• Seismic waves
– Recordable vibrations
• Click on the diagram
above to see the video
19. 19
Extent of Seismic Wave Transmission
• Due to
differences in
the nature of
the bedrock in
those areas
• New Madrid
amplifies
more than
San Andreas
20. 20
Richter Scale
• An increase in one whole number signifies an
earthquake 10 times greater power and a
decrease in one number signifies an earthquake
of 1/10th the power
• An increase in two whole numbers signifies an
earthquake of 100 times greater power, etc.
• Compared to a 5.6 quake, one of 6.6 is 10
times more powerful and one of 7.6 is 100 times
more powerful and one of 8.6 is 1000 times
more powerful.
21. 21
Earthquakes
When Where RS Casualties
2/29/1960 Morocco 8.8 12,000
5/21/1960 Southern Chile 9.5 5,700
6/28/1976 Tangshan, China 8.0 750,000
3/31/1983 Papayah, Colombia 5.7 200,000
5/31/1970 Peru 7.7 66,794
6/20/1990 Caspian Sea (Iran) 7.6 50,000
12/7/1988 Armenia 6.9 28,854
24. 24
Volcanoes: Most frequent along
subduction zones.
• Magma
– Molten rock below the Earth’s surface
• Lava
– Molten rock reaching Earth’s surface
• Volcano
– Surface vent for lava
27. Volcano Type: Strato-volcano
• Composite cone volcanoes (strato-volcanoes)
– Krakatau in Indonesia, largest
– Ash, pyroclasts, sulfurous gas
– Explosive
– High relief
28.
29. 29
Life Cycle of a Hot Spot Island
Stages of development: (1) formation over hot spot (2)
moved past the hotspot & inactive (3) being eroded by
the action of the sea.
30. 30
Volcanoes & casualties
When Where Casualties
3/5/1815 Mt. Tambora, E. Indies 162,000
1/11/1683 Mt. Etna, Sicily 60,000
8/26/1883 Krakatau 37,000
5/8/1902
8/30/1902
Mt. Pele, Martinique 29,000
2,000
11/13/1985 Northern Columbia 25,000
3/25/1669 Mt. Etna, Sicily 20,000
1792 Mt. Unzen, Japan 15,000
31. 31
Rock Formation
• Igneous
– Cooled molten crustal material
– Basalt, granite
• Sedimentary
– High pressure
– Sandstone, shale, limestone
• Metamorphic
– Compacted by heat, pressure
– Marble from limestone
– Slate from shale
39. 39
Types of Faults – seismic activity
• Normal fault
• Reverse fault
• Left slip fault
• Right slip fault
40. 40
Earthquakes and Volcanoes can
Trigger Tsunamis
• Click on the picture on
the left to see the video
on tsunamis,
particularly December
26, 2004.
41. 41
Rocks & Landforms
• 3 influences
– Crust movement = Landform creation
(endogenic)
– Rock movement
• Reactions to crustal stresses
• Weak (greatly affected by weathering & erosion)
• Strong (less affected by weathering & erosion)
– Mineral composition of rocks affects soils
• Also affects the degree to which it can be
weathered and the type of weathering to which it is
most susceptible.
42. 42
Exogenic Forces
• Weathering
• Erosion – reaction to the force of gravity
overcoming inertia
– Mass wasting
– Moving water
– Moving air
– Moving ice (glaciers)
• Deposition – the flip side of erosion
43. 43
Weathering
• Process of breaking rock into pieces
• First step in formation of soil
– Chemical weathering,
• Process of breaking down rock by:
– Exposure to air and water
– Acids released by decaying vegetation
– Oxidation
– Leaching
– Decomposition of calcium carbonate
– Mechanical weathering
• Process of rocks breaking down by physical force
44. 44
Weathering and Climate
• The combinations of temperature and
precipitation affect the speed and extent of
weathering.
45. 45
Mechanical Weathering: Ice
• Ice contracts as the temperature drops to a point around
4ºF – below that temperature, it begins to expand
• This is the same process that prepares streets for
potholes in the winter.
46. 46
Freezing & Thawing at Work
• frost shattered granite bedrock in Manitoba, Canada –
similar occurrences in Siberia.
47. 47
Mechanical Weathering: Exfoliation
• Some rock seems to
have layers that peel off,
hence the name
• The surface of the rock
expands and contracts
more readily and to a
greater degree than the
interior. This weakens
bonds and the surface
breaks off.
48. 48
Movement of Weathered Material
• Mass movement (Mass wasting)
– Slow gradual movement occurring near the surface,
soil creep
– Dramatic movements such as rock slides, landslides
and mudflows
• Surface erosion
– Caused mostly by rainfall
– Runoff (overland flow)
49. 49
Agents of Erosion and Deposition
• Running Water
– Stream Landscapes
• in Humid Areas
• in Arid Areas
• Groundwater
• Glaciers
• Waves and Currents
• Wind
• Gravity
We live on a water
world where water is
a very active force
70%
50. 50
Humans Are the #1 Earth Movers
1000
1000
4300
14000
24000
30000
45000
0 10000 20000 30000 40000 50000
Tons of earth moved per year
Winds
Ocean Waves
Glaciers
continental mountain building
rivers
oceanic mountain building
Humans
Process
Who Moved the Earth
Series1 1000 1000 4300 14000 24000 30000 45000
Winds
Ocean
Waves
Glaciers
continental
mountain
rivers
oceanic
mountain
Humans
Source:
Discover
Magazine,
October
2004
53. 53
Stream Drainage
• 2 sources
– Ground water
– Overland flow
• Drainage basin
• Discharge
– Volume of water
carried per unit time
• Sediment transport
– Movement of material
– l Deposition
54.
55. 55
Side-cutting by streams
• As the grade
becomes less steep
(as one approaches
the mouth of the
stream), side-cutting
action becomes
more active than
down-cutting and the
valley widens and
the stream
meanders.
56. 56
Running Water: Erosion and
Deposition
• Weathering
breaks rock down
into smaller
pieces which can
then be carried
away by moving
water with
sufficient speed
and volume.
57. 57
Erosion and stream (valley) formation
• Where the slope is steep, the down-cutting action is greatest
• Where the slope is slight, the side-cutting action is greatest.
58. 58
Stages of Stream Development
• Youthful – V-shaped – relatively straight course
• Mature – U-shaped – moderate meandering & possible
braiding
• Old Age – wide floodplain – meandering stream and ox-bow
lakes
60. 60
Stream Action in Arid Areas – less
rounded and more angular landforms
Moving water is the
major erosional and
depositional force
even in desert areas!
61. 61
Stream Gradation
• Exogenic forces operate to reduce all earth land
features to sea level. Click the picture below to see the
video
64. 64
KARST TOPOGRAPHY
This involves the combination of
chemical weathering and moving
water to create a very unique kind
of topography found where there
are deep layers of limestone.
69. 69
Erosion from Human Activity
• Faster than that which occurs geologically
– Accelerates natural processes
• Sharply increase amount of sediment in streams
– Increasing the possibility of and extent of flooding.
• Major contributors include:
– Deforestation – clear-cutting in particular
– Agricultural development
– Urban development – particularly choosing land not well
suited for development, i.e., floodplains
72. 72
Using Water Table Water
• The Water table reflects the surface somewhat
• Water drawn from the water table is the major
source for life in some areas.
73. 73
Soil and ground water
• More porous soil (right) allows more water to percolate down into
the soil & move slowly move toward streams, raising them
gradually
• Less porous soil (left) allows more water to run off and raise
stream levels more quickly
74. 74
Vegetative cover encourages water
absorption by soil
• Vegetation temporarily
holds & water releases
it slowly so it can be
more easily absorbed
by the soil.
• Where vegetation is
absent, water may fall
faster then bare earth
can absorb it and run
downhill to streams
causing floods
75. 75
Groundwater Use
• When the rate of withdrawing groundwater exceeds
the rate of recharging, the water table drops. Wet
years with flooding = high water table & drought
years – low water table
Recharging
Withdrawing
76. 76
Artesian systems
• Aquiclude (impermeable rock layer) above and beneath the
aquifer holds or “traps” the water under pressure.
• Often used to irrigate crops in arid areas.
When water is
withdrawn at a rate
greater than the
recharge rate, the
aquifer is gradually
emptied – it will take
nature much longer
to recharge it than
humans to drain it.
77. 77
Flooding can cause big changes
• THEY CALL IT A FLOOPLAIN BECAUSE FLOODING IS A
NATURAL OCCURANCE – IT IS THE “RELEASE VALVE” OF
THE DRAINAGE BASIN
1993 N. Mississippi Basin Flashflood in northern Arizona
78. 78
FLOODPLAINS
• Floodplains are
not appropriate
places for
intensive,
expensive
developments.
Appropriate uses of
floodplains include
farming, wildlife
preserves, parks,
recreation areas for
camping boating, etc.
79. 79
Ice, Wind & Waves
• Glaciers – currently not very active
• Wind causes erosion wherever soil is
bare
– Deserts
– Farmlands
– Coastal areas
• Coastal areas
– Active areas of erosion
– Pounding waves and surf
– Land lost or gained
80. 80
MOVING ICE: GLACIAL
ACTION
Glaciers are melting back more than they are
advancing today. When glaciers advance, erosion is
the major action; however, when they melt back,
deposition is the major action.
81. 81
Alpine Glaciers
• Rivers of ice flowing from colder to warmer
regions
• Act like conveyor belts picking up sediment
and dropping it in depositional areas
– Moraines
• Terminal moraines
• Lateral moraines
• Medial moraines
82. 82
Two Primary Categories
• Alpine or valley glaciers – in the last 100 years,
these have been greatly reduced in number and
size due to melting back.
• Continental glaciers – those that cover large
expanses of land – Antarctica and Greenland are
the last two remaining areas of this type. There is
evidence that both are thinning and shrinking.
83. 83
Glacier Terms:
• Fjord (fiord): As tidewater glaciers retreat, the steep-sided
valleys fill in with sea water.
• Calving: Tidewater glacier sheds icebergs off its face into
the sea -- sections as large as huge buildings.
• Moraines:The accumulation of eroded rock that a glacier
picks up and drops as it recedes. This can be seen at the
face of a glacier (end moraine), the side of a glacier (lateral
moraine) or at the glacier's farthest point of advance
(terminal moraine). Underwater moraine shoals can
decrease the depth of a fjord from hundreds of feet to less
than ten feet over very little distance.
• Terminus:The front or termination of a glacier. The
beginning of a glacier is called its head.
94. 94
Glacier Facts #1
• Presently, 10% of land area is covered with glaciers.
• Glaciers store about 75% of the world's freshwater.
• Glacierized areas cover over 15,000,000 square
kilometers.
• Antarctic ice is over 4,200 meters thick in some areas.
• In the United States, glaciers cover over 75,000 square
kilometers, with most of the glaciers located in Alaska.
• During the last Ice Age, glaciers covered 32% of the total
land area.
• If all land ice melted, sea level would rise approximately 70
meters worldwide.
• Glacier ice crystals can grow to be as large as baseballs.
95. 95
Glacier Facts #2
• The land underneath parts of the West Antarctic Ice Sheet
may be up to 2.5 kilometers below sea level, due to the
weight of the ice.
• North America's longest glacier is the Bering Glacier in
Alaska, measuring 204 kilometers long.
• The Malaspina Glacier in Alaska is the world's largest
piedmont glacier, covering over 8,000 square kilometers
and measuring over 193 kilometers across at its widest
point.
• Glacial ice often appears blue because ice absorbs all
other colors and reflects blue.
• Kutiah Glacier in Pakistan holds the record for the fastest
glacial surge. In 1953, it raced more than 12 km in three
months, averaging 112 meters per day
96. 96
Glacier Facts #3
• In Washington state alone, glaciers provide 470
billion gallons of water each summer.
• Antarctic ice shelves may calve icebergs that are
over 80 kilometers long.
• Almost 90% of an iceberg is below water--only
about 10% shows above water.
• The Antarctic ice sheet has been in existence for at
least 40 million years.
• From the 17th century to the late 19th century, the
world experienced a "Little Ice Age," when
temperatures were consistently cool enough for
significant glacier advances.
97.
98. 98
Impact of Past Glaciations
• Soils
– Advance and retreat of glaciers leave behind
highly fertile soil
• Water supply
– Retreating glaciers left sand and gravel
deposits yielding large supplies of ground water
• Transportation routes
– Water transport is heavily influenced by glacial
melt water channels left behind by receding
glaciers
• Check Ohio & Missouri River courses!
99. 99
WIND ACTION
Wind is most active in arid
regions, but never as
important as water in
altering the earth surface
and creating landforms
100. 100
Effects of Wind on Landforms
• Significant shaper of landforms in dry
regions and regions not well covered by
vegetation
• Carries great quantity of fine grained
sediment such as sand and loess
101. 101
Wind Speed
• As the wind speed
increases, larger particles
can be carried by the
wind (erosion)
• As the wind speed
decreases, larger
particles begin to settle to
the surface first
(deposition)
102. 102
Arid Landscapes
• Erosion and
deposition by wind
helped create this
landscape, BUT
moving water was
the more active
shaping force here.
103. 103
Land shaping water in the desert
• Water
carved
this
canyon
and wind
and mass
wasting
assisted.
104. 104
Coastal Erosion
• Waves
– Form of energy traveling horizontally along the
boundary between water and air
• Longshore currents
– Currents traveling parallel to the shore, caused by
repeated breaking of waves. Capable of carrying
enormous amounts of sediment
• Sea-level change
– Continuing to rise as seawater volume increases from
glacial melting
– Causes increased erosion as waves break closer to
shore
105. 105
Oceans, Waves, & Gradation
• Wave
action
erodes and
builds the
coastal
margins of
islands and
continents
106.
107.
108.
109. 109
Dynamic Waves and Currents
• The shoreline is constantly changing – click on the
picture below to see the video
110. 110
Rates of Landform Change
• Horizontal movement
• Vertical movement
• Human activity
111.
112. 112
Landform Regions
• Plains
• Hills and Low
Tablelands
• High
Tablelands
• Mountains
• Widely Spaced
Mountains
• Basins or
Depressions
113. 113
Major Landform Types
Plains: level to gently rolling land at a low elevation
Plateaus: level to gently rolling land at a higher elevation and
often with a sharp drop-off or scarp (escarpment) on at least
one side.
Hills: rounded landforms with little level land and at moderate
elevations (1,000 to 5,000 ft.)
Mountains: steeply sloped landforms with narrow ridges and
practically no level land – found at high elevations usually
above 5000 feet.
Major Landforms in
Profile Escarpment
