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Chapter 16
Earth’s Surface
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•Principle
of Earth’s
uniformity
Interpreting
surface
(James Hutton)
• “The present is the key to the past.”
• Rocks are changed today by the same
processes that changed them in the past
• Replaced catastrophic models of previous
thinkers
• Catastrophic events contribute
nonetheless
• Volcanoes, earthquakes, meteorite
impacts, …
Diastrophism
• Any process of deformation that
changes the Earth’s surface
• Produces structures such as plateaus,
mountains and folds in the crust
• Related to volcanism (the movement
of magma) and earthquakes
• Basic working theory is plate tectonics
Stress
and deformation
Possible
material
responses to stress
1. No change
2. Elastic change with
recovery
3. Plastic change with
no recovery
4. Breaking from the
pressure
Stress
and deformation Cont.
Rock variables
1.
2.
3.
4.
Nature of the rock
Temperature of the rock
Speed of stress application
Confining pressure
Interplay between these variables
produces observed rock structures
• Sedimentary rocks
• Originate from flat
sediment deposits
• Layers usually
horizontal
• Folds
• Bends in layered
bedrock
• Result of stress
produced plastic strain
• Widespread horizontal
stress can produce
domes and basins
Folding
Domes
Basins
Faulting
Fault
Produced by relative
movement on
opposite sides of a
crack
Footwall: mass of
rock below the fault
Hanging wall: mass of
rock above the fault
Fault plane: surface
between the footwall
and hanging wall
Faulting Cont.
Shows how the hanging wall
has moved relative to the
footwall.
Hanging wall is on the left
Footwall to the right
Three Classes of Faults
• 1. Normal fault
• Hanging wall has moved
down relative to the
footwall
• Related features
• Graben
• Block surrounded by
normal faults drops
down
• Horst
• Block surrounded by
normal faults is
uplifted
Other Faults
• 2. Reverse fault
• Hanging wall moved upward
relative to footwall
• Result of horizontal
compressive stress
• 3. Thrust fault
• Reverse fault with a low-angle
fault plane
• Faults provide information on
the stresses producing the
formation
Earthquakes
• Quaking, shaking, vibrating or
upheaval of the ground
• Result from sudden release of energy
from stress on rocks
• Vibrations are seismic waves
• Most occur along fault planes when
one side is displaced with respect to
the other
Causes
of earthquakes
• Elastic
rebound
theory
• Two plates press
tightly together
• Friction restricts
motion
Causes of
earthquakes Cont.
Stress builds until
friction or rock
rupture strength is
overcome
Stressed rock snaps
suddenly into new
position
• Focus
• Actual origin
of seismic
waves
Locating
and
measuring
• Epicenter
earthquakes
• Location on Earth’s surface directly above the focus
Locating and measuring
•earthquakes
Seismometer
• Instrument used to detect and
measure earthquakes
• Detects three kinds of waves
1.P-wave (longitudinal)
2.S-wave (transverse)
3.Surface wave (up and down)
Seismic
data
P-waves travel faster
than S-waves
Difference in arrival
times correlates to
distance from
earthquake
Triangulation used to
pinpoint epicenter and
focus
Earthquake
Magnitude
• Effects: structural
damage to buildings,
fires, landslides, displacement of land
surfaces, tsunami (tidal wave)
• Richter scale
• Based on swings in seismograph
recordings
• Logarithmic scale
• Number increases with magnitude of
the quake
• 3(not felt); 9(largest)
Anchorage, March 1964 (9.2)
Northridge, January 1994 (6.7)
Oakland, October 1989 (6.9)
Tsunomi
• Very large ocean waves
• Generated by strong disturbance in ocean
floor
• Earthquake, landslide, volcanic explosion
• Speeds of up to 725 km/h (459 mi/h)
• Wave height can be over 8 m (25 ft)
• Very long wavelength of up to 200 km (120
mi)
Indian Ocean Tsunami
Before
and
After
Before and After
•WARNING:
GRAPHIC PICTURE
After Tsunami
•
Origin
of mountains
•
Elevated parts of Earth’s crust rising abruptly above the surrounding
Mountains
•
•
surface
Created by folding and faulting of crust
Three basic origins
1.
2.
3.
Folding
Faulting
Volcanic activity
Folded and faulted mountains
• Domed mountains
• Broad arching fold
• Overlying sedimentary rocks
weather away, leaving more
resistant granite peaks
Folded and faulted mountains Cont.
Fault block
mountains
Rise sharply
along steeply
inclined fault
planes
Weathering
erodes sharp
edges
Volcanic mountains
Volcano
• A hill or mountain
formed by the
extrusions of lava or
rock fragments from
magma below
• Structure: vent, crater,
lava flow
Mt. St. Helens
May 18, 1980
Eruption!
Ash Clouds
Before and After
Before and After
Spirit Lake Before
Spirit Lake After
Spirit Lake – 2006
Mt Adams from
Mt. St Helens
showing tree
damage
Edge of Blast
Growing Lava Dome
Growing Lava Dome
Hot Spots
• Thermal blooms
• Maybe up to 2000 miles deep
• Plate moves over hot spot
• Islands develop over time---depends how long in
one area
Volcanic Hot Spots
Shield Volcano
Processes That Tear Down
 Slow changes
resulting in the
breakup, crumbling
and other destruction
of solid rock
 Includes physical,
chemical and
biological processes
 Contributes to
1. The rock cycle
2. Formation of soils
3. Movement of rock
materials over
Earth’s surface
Mechanical weathering
 Erosion:
The process of
physically removing
weathered
materials
 The physical breakup
of rocks without
chemical change
 Disintegration
processes
 Wedging
 By frost
 By trees
Chemical weathering
Decomposition of
minerals by
chemical reactions
1. Oxidation
• Reactions with
oxygen
• Produces red iron
oxides
Chemical weathering Cont.
2. Carbonation
• Reactions with carbonic acid (carbon
dioxide dissolved in water)
• Easily dissolves limestone
3. Hydration
• Reactions with water
• Includes dissolving in water and combining
with water
Erosion
• Mass movement
• Erosion caused directly
by gravity
• Creep
• The slow movement
of soil down a steep
slope
• Landslide
• Any slow to rapid
downhill movement
of materials
Running water
•
•
Streambed transport:
1. Dissolved materials
2. Suspended
materials
3. Rolling, bouncing
and sliding along
stream bed
Streambed evolves
over time
Streams
 Youth
Landmass recently uplifted
Steep gradient, V-shaped valley w/o floodplain
Boulders, rapids and waterfalls
 Maturity
Stream gradient smoothed and lowered
Meanders over floodplain
 Old age
Very low gradient
Broad, gently sloping valleys
Sluggish flow; more floods
Stream
development
Cont.
Three
stages
in the
aging and
development of a
stream
(A) Youth
(B) maturity
(C) old age
Deltas
• Deposits of
sediment at the
mouth of a river or
stream
• Stream flow
dissipates into an
ocean or lake
• Erosive and
sediment-carrying
abilities lost
Glaciers
• Masses of ice on
land that move
under their own
weight
• Form from snow
accumulated
over a number of
years
Glaciers
Cont.
• Alpine glaciers
• Form at high elevations
• Flow through valleys
• Also “valley glaciers”
• Continental glaciers
• Cover large area of a continent
• Today in Greenland and Antarctica
Tracy Arm, Alaska
Glacier
erosion
Glaciers:
Three
mechanisms:
1. Bulldozing
• Forms deposits called moraines
2. Abrasion
• Produces powdery, silt-sized rock flour
3. Plucking
• Glacier water freezes into surrounding
rock and pulls it along
Wind
 Considerably less
efficient than water or
ice
 Two major processes
1. Abrasion
 Natural
sandblasting
 Produces ventifacts
 Shape can depend
on prevailing winds
2. Deflation
 Loose material
picked up and
carried away by
the wind
Wind Cont.
•Wind-blown deposits
•Dunes: low mound or
ridge of sand or other
sediment
•Loess: fine dust
deposited over a large
area
Death Valley
Indiana Dunes
Great Sand Dunes
Loess Hills
Scenic
Byway
Loess Hills