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Natural Science II – ERTH 1040
The Earth’s Surface
J. D. Price
Keep in mind the major (and fundamental)
sources of energy available to the surface of
the Earth.
•Heat transfer from the interior – which
discussed in the previous lectures
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•Heat transfer from the Sun
Radiation transfer from the surface of this
star.
There is only one other periodic source of
energy external to the Earth: meteorite impacts
Heat redistribution from the Earth’s interior
means:
Volcanic eruptions
Crustal uplift
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These build mountains (and lowlands)
This leads to potentials in gravity (potential
energy that may change into kinetic energy).
Simply: stuff will move downhill
As we’ll see, the distribution of solar across the Earth’s
surface (recall direct sunlight falls only between the
tropics) drives the evaporation and precipitation of
water.
1. Water vapor from low
places is elevated to
high places
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2. Liquid water moves
downhill*
3. Carries with it other
materials
*Most movement is underground
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Changes in deposition
produces layers of
sediments.
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Sequential layering –
newer sediments
deposited on older.
Erosion exposes the layers
and permits easy direct
observations
Original horizontality
Q: where are the oldest rocks
in a sequence of layered
sediments?
•Flat lying sediments are found forming in large
packages today - gulf coast basin.
•Smaller packages can be found in lakes, on river
floodplains, adjacent to mountains.
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•The result of gravitationally driven erosion, transport,
and deposition.
•But what causes the gravity to be a force of
deposition?
Deviatoric
Stress
Compression
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Extension
Shear
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Strain
Q: What’s the difference
between stress and strain?
Brittle - faulting
Extensional (Normal)
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Compressional (Reverse)
Parallel to stress (Strike slip
or transform)
An example from Big
Bend N.P. Boquillas
Cañon, view to Mexico
from Texas across Rio
Grande
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Compressional or
extensional?
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Graben
Horst
Fault block mountains
Figure 20.17
20-405
Inclined Strata
An example from Twin
Mountains, near Canyon
City, CO
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Rotated half grabens
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Series of N-S fault blocks
make up the mountains of the
Basin & Range.
Siccar Point, Scotland
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Devonian
Silurian
Angular unconformity
Inclined strata below (Arbuckle Group, Cambro-Ordovician) is eroded
and covered by stream channel strata (Collings Ranch Conglomerate,
Pennsylvanian). Represents ocean deposition, compression, extension,
and stream deposition. Arbuckle Mountains, OK.
Ductile – folding
All compressional
Anticline
Syncline
Q: Why no extensional folding?
What does extension do to ductile
materials?
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Thrust fault – low angle reverse
Anticline and fault – brittle deformation
is localized to the fault, ductile
elsewhere.
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Arbuckle Mountains, OK
Arbuckle Mountains, OK
Rattlesnake Mountain, WY
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Glastonbury Anticline, CT
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Ouachita Mountains, Oklahoma
The Adirondacks are a prime
example of doming. Note now
orange (Ordovician) and light blue
(Cambrian) colors wrap around
the pink, dark blue, and stippled
areas (1.2Ga rocks).
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Dome
Figure 20.16
20-404
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Asymmetric folding
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Asymmetric folding
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Earthquake
The ground motion associated with energy release
during brittle deformation.
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Breaking transfers energy through surrounding
material by moving it (seismic waves)
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elastic rebound theory
Figure 20.12
20-401
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Fault-related
earthquake
Q: What is the difference
between the epicenter and
the focus?
locating earthquakes
Q: How do the two different
types of waves differ from each
other?
Figure 20.14
20-403
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Q: What is the difference in ground
motion between a magnitude 5
quake and a magnitude 6 quake?
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Richter TNT for Seismic
Magnitude
Energy Yield
Example
(approximate)
-1.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
6 ounces
30 pounds
320 pounds
1 ton
4.6 tons
29 tons
73 tons
1,000 tons
5,100 tons
32,000 tons
80,000 tons
1 million tons
5 million tons
32 million tons
Breaking a rock on a lab table
Large Blast at a Construction Site
7.5
8.0
8.5
9.0
10.0
12.0
160 million tons
1 billion tons
5 billion tons
32 billion tons
1 trillion tons
160 trillion tons
Large Quarry or Mine Blast
Small Nuclear Weapon
Average Tornado (total energy)
Little Skull Mtn., NV Quake, 1992
Double Spring Flat, NV Quake, 1994
Northridge, CA Quake, 1994
Hyogo-Ken Nanbu, Japan Quake, 1995;
Largest Thermonuclear Weapon
Landers, CA Quake, 1992
San Francisco, CA Quake, 1906
Anchorage, AK Quake, 1964
Chilean Quake, 1960
(San-Andreas type fault circling Earth)
(Fault Earth in half through center,
OR Earth's daily receipt of solar energy)
Trinitrotoluene (TNT)
Amounts of TNT are used as units of energy, based
on a specific combustion energy of TNT of
4.184 MJ/kg
= 1 calorie per milligram
= 1.9 MJ per pound
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But…it’s not just the energy but the rate at which it’s
delivered (power).
The Earth receives 6.08 E 17 MJ of energy from the sun but over
a day (6.08 E 17 MJ / 8.6 E 4 s) 7.037 E 12 MW
And…it’s also the area on which its applied
Earth = 4!re2 = 5.10 E 8 km2 ) The Earth receives 1.38 E 4
MW/km2 of sunlight
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NBC miniseries “10.5”
20 million viewers tuned in to
watch a story based on a westcoast destroying earthquake
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Earthquake magnitudes are a
function of the length and
depth of the fault
A 10.5 could only occur on a
fault that encircles the globe
more than once.
Good new for bad science - a
sequel has been filmed.
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In absence of a
seismometer, the
intensity of an
earthquake may be
approximated using
the modified Mercalli
Scale
Likewise, you can
compare the type of
damage done
knowing the Richter
Scale.
The 1964 Good Friday Earthquake Valdez, Alaska - largest historical quake
in the U.S.
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house
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The earthquake
produced a
landslide and a
tsunami
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Locomotive engine
Local land surfaces were
noticeably uplifted
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The tsunami was the second
to hit the pacific in 4 years
Volcanoes
Where partial melts of the Earth’s Interior
reach the surface.
•Partial melts – magmas (mostly liquid with
some solid)
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•These are hotter than surroundings – lose
heat and solidify
•These originate at depth – depressurize as
they ascend
Q: What determines the nature of a volcanic
eruption? How do these factors influence the
morphology of a volcanic structure?
The shape given to volcanic edifices is due to its
eruptive style. It’s eruptive style is due to magma:
Composition – including dissolved gasses
Low Si – more fluid
High volatiles – more explosive
Supply rate – material from the Earth’s interior
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Fast – frequent eruptions from same vent
Slow – vents solidify, more explosive
The nature of an eruption is a function of the
pressure of the magma.
Kilauea, Hawaii
March, 1996
Q: What are some common volatile
components in a magma?
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shield volcano
Hawaii: Hot asthenospheric mantle, below
provides hot material that intrudes
lithosphere and melts below oceanic crust.
Generally low Si
Low volatile
High rate
Mauna Kea, Hawaii
Cinder Cones
Shield
Q: What tectonic feature produces
volcanism in Hawaii?
Pu’u Hulu
Mauna Loa, Hawaii
Pahoehoe
Q: What are the names given to
these two types of lava?
Kalapana Gardens
Kilauea, Hawaii
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Fissure
Cinder Cone
Low Si
High volatile
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high rate
Mauna Kea, HI
Mauna Loa
Summit Cone, Mauna Kea
Pu’u O’o cone
Q: What does this lava
lake signify in terms of
volatiles?
Composite volcano
Mixed but generally
Composite volcanoes build up
over time from localized vents.
Higher Si
High volatile
Low rate
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Mount Saint Helens: pre 1980
Mount Saint Helens is an example of
a composite stratocone - the locus of
volcanism for hundreds of thousands
of years
Q: What tectonic feature produces
volcanism in the Cascades?
In 1980, the mountain began
to erupt small plumes of ash
from an area near the
summit.
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The first eruption in the
conterminous US since that
of Mount Lassen (northern
California) in 1914.
Mount Saint Helens:
March, 1980
The north side of the
mountain swelled during
April and early May. It
failed and slid away on May
18 releasing the gasses and
magma in a cataclysmic
explosion.
Mount Saint Helens:
May 18, 1980 0832
The release of heat melted
the glaciers. Gas propelled
ash into the upper
troposphere.
Mount Saint Helens:
May 18, 1980
Wyerhouser Logging Trucks
Mount Saint Helens
Meltwater, fallen trees, and
ash choked the streams,
destroying adjacent lands.
Q: Is partially melted rock the only
product of an eruption?
The eruption removed the top
1,800 feet of the mountain.
View from the north
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Several smaller eruptions
continued through 1980.
This included two that sent
ash southward over the city
of Portland, OR.
Portland, OR
View from South Rim, June 1991
Q: What is a
volcanic dome?
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Dome on Soufriere Hills Volcano
Montserrat
Soufriere Hills Volcano
Montserrat
Soufriere Hills Volcano
Montserrat
Q: How might volcanoes contribute
to continental growth?
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Caldera
Moderate – high Si
High volatile
Low rate
Crater Lake, Oregon
Q: How do volcanoes
impact climate?
Earth’s surface is dynamic
Advantages: transfer of abundant energy
Rivers (from mountains) to Hydrothermal
Life utilizes the energy in these systems - not
just in an electrical generation sense!
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Disadvantages: transfer of abundant energy
Volcanoes, earthquakes, and floods
Produce enough energy to displace matter and
wreck habitats
Q: Which is the most efficient energy transfer
mechanism?
•Asteroid or comet collision
•Loss of magnetic field
•Large earthquake
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•Catastrophic eruption
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