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
Geologic Time – in 24 hours
• Humans
have
been
around
for ½ of
one
minute
on this
scale.
2
Geomorphology
• Study of landforms and processes that
create them
• Lithosphere
– Rocks and soil
– Surface landforms
• Plains, hills, plateaus, & mountains
• valleys, depressions
3
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
4
Endogenous (endogenic) –
Exogenous (exogenic)
• Forces
from Inside
the earth
• Forces
from
outside the
earth
5
Endogenic Forces
• Plate Tectonics
• Volcanism
• Seismic action
6
Plate Tectonics
• Fixed Earth Theory
– Continents and oceans fixed in place
• Pangaea Hypothesis
– Supercontinent
– Alfred Wegener, 1900s
• 1960s = Plate Tectonics Theory
7
Understanding Geological Activity
Spanning Geologic Time
• Continental Drift
– Alfred Wegener, etc.
– International Geophysical Year research
8
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
9
Earth’s Crust & Layers
• Mantle
– Rock beneath
crust
• Tectonic plates
– Earth’s rigid
crust
• Plate movement
– Earthquakes
– Volcanoes
– Mountain
building
10
Convectional Cell Movement
11
Types of Crustal Forces
• Tensional
– dragging
action
• Compressional –
pulling
action
• Sheer –
oblique
action
12
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
13
14
Convergent Boundary: click the
diagram below to see the video
• Oceanic plate meets oceanic plate, and
an island arc develops.
15
Convergent Boundary
• Oceanic plate
meets
continental
plate and a
volcanic
mountain chain
forms on the
continental plate
16
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.
17
Earthquakes
• Focus
– Place of actual
movement
• Epicenter
– Surface directly
above focus
• Seismograph
– Recording device for
seismic waves
– Richter Scale, 1935
• Seismic waves
• Click on the diagram
– Recordable vibrations
above to see the video
18
Extent of Seismic Wave Transmission
• Due to
differences in
the nature of
the bedrock in
those areas
• New Madrid
amplifies
more than
San Andreas
19
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.
20
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
21
Earthquake Damage
• Rebound theory -- left
• Alaska ’64 - above
• Some soils may liquefy
22
Earthquake zones
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
24
Volcanoes
• Click on the volcano to see a video
25
Volcano Type: Shield Volcano
• Runny lava – low
relief
• Basalt rock
• Mauna Loa,
Hawaii
26
• Sedate
Volcano Type: Strato-volcano
• Composite cone volcanoes (strato-volcanoes)
–
–
–
–
Krakatau in Indonesia, largest
Ash, pyroclasts, sulfurous gas
Explosive
High relief
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.
29
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
30
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
31
Igneous
Rock
Formation
• Igneous rock is
cooled, hardened
magma or lava
32
Formation of Sedimentary Rock
• Click on the picture to see the video
33
Metamorphic Rock Formation
• Metamorphic
rock has been
structurally
changed – both
igneous and
sedimentary
rock may
become
metamorphic
rock.
34
Minerals - Ores
• Natural substances that comprise rocks
• Types
– Sima
• Denser rocks = silicon, magnesium, iron minerals
– Sial
• Less dense
• Silicon and aluminum
• Distribution
– Crustal movement
– Continental shields
• Mining districts – where concentrations in ore are above
average.
35
Shields are the anchors of continents, being
composed of the oldest rock formations.
These often contain good mineral deposits.
Faults
• Fractures in Earth’s crust from stress
• Types
– Normal
• Divergent plate boundary
• Stretching
– Reverse
• Convergent plate boundary
• Compressed rock
• Appalachian Mountains, Wasatch Range, Himalayas
– Thrust
• Horizontal movement
37
Normal & Reverse Faults
Normal Fault
Reverse Fault
Types of Faults – seismic activity
• Normal fault
• Reverse fault
• Left slip fault
• Right slip fault
39
Earthquakes and Volcanoes can
Trigger Tsunamis
• Click on the picture on
the left to see the video
on tsunamis,
particularly December
26, 2004.
40
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.
41
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
42
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
43
Weathering and Climate
• The combinations of temperature and
precipitation affect the speed and extent of
weathering.
44
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
45
potholes in the winter.
Freezing & Thawing at Work
• frost shattered granite bedrock in Manitoba, Canada –
46
similar occurrences in Siberia.
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.
47
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)
48
Agents of Erosion and Deposition
• Running Water
– Stream Landscapes
• in Humid Areas
• in Arid Areas
•
•
•
•
•
Groundwater
70%
Glaciers
Waves and Currents
Wind
We live on a water
world where water is
Gravity
a very active force
49
Humans Are the #1 Earth Movers
Who Moved the Earth
45000
Humans
30000
Process
oceanic mountain building
24000
rivers
14000
continental mountain building
4300
Glaciers
Source:
Discover
Magazine,
October
2004
Ocean Waves 1000
Winds 1000
0
10000
20000
30000
40000
50000
Tons of earth moved per year
Series1
Winds
Ocean
Waves
Glaciers
continental
mountain
rivers
oceanic
mountain
Humans
1000
1000
4300
14000
24000
30000
45000
50
Remember the damaged houses in
Black Jack, Missouri in the 1970s?
Curved trunks are evidence of
soil creep.
52
Soil Creep at Missouri Bottoms
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
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
56
meanders.
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
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
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-bow59
lakes
Stream Action in Humid Areas
Cycle of Landmass
Denudation
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
Stream Gradation
• Exogenic forces operate to reduce all earth land
features to sea level. Click the picture below to see the
video
62
Waterfalls
• Click on the picture below to see the video
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.
65
Karst Topography Development
• St. Louis, MO, is located in a karst area.
66
Diagram of Karst Features
• When large caverns collapse, large depressions are
formed
67
Karst Features
Springs
68
Illinois Sink holed (plugged)
69
70
71
United Kingdom Karst
72
Karst Regions
73
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
74
Human-enhanced erosion by water
75
Homes in danger
76
Sea surges undercut hotel
77
Movement of Water in Soil
• This is a major part of the hydrologic cycle.
78
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.
79
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
80
stream levels more quickly
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
81
Groundwater Use
Recharging
Withdrawing
• When the rate of withdrawing groundwater exceeds
the rate of recharging, the water table drops. Wet
years with flooding = high water table & drought 82
years – low water table
Artesian systems
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.
• Aquiclude (impermeable rock layer) above and beneath the
aquifer holds or “traps” the water under pressure.
83
• Often used to irrigate crops in arid areas.
Flooding can cause big changes
1993 N. Mississippi Basin
• THEY CALL IT A FLOOPLAIN BECAUSE FLOODING IS A
NATURAL OCCURANCE – IT IS THE “RELEASE VALVE” OF
THE DRAINAGE BASIN
84
Flashflood in northern Arizona
85
FLOODPLAINS
Appropriate uses of
floodplains include
farming, wildlife
preserves, parks,
recreation areas for
camping boating, etc.
• Floodplains are
not appropriate
places for
intensive,
expensive
developments.
86
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
87
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.
88
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
89
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.
90
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.
91
Glaciers
• Click on the picture to see the video
92
Valley Glaciers (Alpine) Merging
93
Mountains before glaciation
Before
94
Mountains after glaciation
Horn
Pater noster lakes
Bridal veil fall
After
95
Glacial Valleys & Fjords
• Fiords form when rising sea levels fill the bottom of
coastal glacial valleys after melt back occurs.
96
Coastal Glaciers
• Icebergs
present
a hazard
to
shipping
lanes
Calving
Small fiord
Icebergs
97
Some Glacial Landforms
98
Eskers, Kettles, & Kames
99
Glacial till plain with disrupted
drainage
100
Drumlins
& Kames
101
Kame
102
Drumlins
103
Continental Glaciation
104
4 Advances in North America
105
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.
106
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 107
months, averaging 112 meters per day
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
108
significant glacier advances.
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!
110
WIND ACTION
Wind is most active in arid
regions, but never as
important as water in
altering the earth surface
and creating landforms
111
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
112
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)
113
Arid
Landscapes
• Erosion and
deposition by wind
helped create this
landscape, BUT
moving water was
the more active
shaping force here.
114
Land shaping water in the desert
• Water
carved
this
canyon
and wind
and mass
wasting
assisted.
115
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
116
Oceans, Waves, & Gradation
• Wave
action
erodes and
builds the
coastal
margins of
islands and
continents
117
Dynamic Waves and Currents
• The shoreline is constantly changing – click on the
picture below to see the video
121
Rates of Landform Change
• Horizontal movement
• Vertical movement
• Human activity
122
Landform Regions
• Plains
• Hills and Low
Tablelands
• High
Tablelands
• Mountains
• Widely Spaced
Mountains
• Basins or
Depressions
124
Major Landform Types
Major Landforms in
Profile Escarpment
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 125
above 5000 feet.
Environmental Hazards
• Environmental processes
– Natural
– Tornadoes, landslides, earthquakes
– Human vulnerability
– Rebuilding after natural disaster
– Seawalls
– Levees
126
The Rock Cycle
• Much of
the earth,
and all
living
things, is
composed
of recycled
materials.
127
End of Chapter 3