Geology 1001-section 4
Dr. Dutrow
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OCEANS
(incomplete versions of overheads)
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Covers 71 % of the Earth's surface (with saltwater)
in five major oceans: Atlantic, Pacific, Indian,
Arctic, and Antarctic
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Exploration of the seafloor began with the HMS Challenger
(1872)
- they discovered the rich topography of seafloor:
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high mountain ranges
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hilly topography
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flat plains
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deep trenches
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submarine volcanos
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mid-ocean ridge
- Most progress being made in the last 30 years due
to new instrumentation and deep sea submersibles
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These features and observations were key to development
of the theory of PLATE TECTONICS (not observations on continents)
EDGE OF THE SEA
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Coastlines - interplay of erosion in conjunction
with waves, currents, and tides as well as tectonics
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Coasts - broad region where land meets sea
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shoreline - boundary where water body intersects
dry land
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Waves - key to shoreline dynamics
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have a
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appear away from shore and eventually
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develop due to
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- causes water to
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-
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- velocity = speed at which
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e.g. 30 - 90
km/hr
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-length = distance between
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- height = distance from
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e.g. ocean
waves - 2 - 5 meters
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wave heights are a function of:
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Swells - low, broad, regular rounded ridges
that develop first.
PATTERN OF WATER MOTION
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water particles move in a
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- rises and falls as
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- short distance from
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movement decreases in magnitude until a depth of
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=
(Note: wavelength - distance between adjacent
crests or troughs, measured crest to crest or trough to trough)
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Shallow water wave interactions
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the orbital motion become restricted and more elliptic
when
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this orbital flattening makes the water
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friction causes decrease in
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results in high and steeper asymmetric wave
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surf - water in wave moves
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Beach - wave interactions
- Swash (uprush of water) and backwash
(back flow of water) can carry
- results in
- Change in wave motion as
first arrival loses
, deeper water moves
- if swells approach at an angle, the initial waves
i.e. the water shallows more quickly and refracts
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Refraction is less intense
i.e. where wave energy is
water returns to sea perpendicular to
- Longshore drift - occurs when the swash
and backwash
- Longshore current - shallow water current
- Rip current - "undertoe"; strong current
!!! swimmers hazard!!! to escape, swim parallel
to shore
TIDES
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Related to the position and phases of the
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Due to gravitational interactions
1. Earth - Moon:
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have strong gravitational attraction that is greater on
- High Tide - ocean facing
- Low Tide - occur simultaneously
on opposite
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as the Earth rotates, the tides
The Earth-Moon cycle is 24 hours and 50 minutes
2. Earth - Sun:
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has large mass and gravity to overcome
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produces tides ca.
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Sun tides are not
The Earth-Sun cycle is every 24 hours (length of
solar day)
3. The nonsynchronous cycles and the slower
lunar cycle means that
- Rising tide elevated water
, advancing
=
tide
- Falling tide lower water
=
tide
Distance between local low and high tide =
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There can be large variations in the magnitude of tides
due to
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0.5m in Hawaii; 20 m in Bay of Fundy
Tidal flats - muddy/sandy coastal between
exposed at
4. Spring Tides - when Moon, Earth and
Sun a
- highest tides occur every
5. Neap Tides - lowest tides occur when
moon and sun are
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Tidal flats - muddy/sandy coastal
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NOTE: combination of high tide and hurricane landfall
can be disastrous
SHORELINES
Most significant factor is
Where Energy is concentrated,
occurs
Where Energy is dissipated,
occurs
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BEACHES - large sandy areas; dynamic environment
- Beach budget consists of several
- Coastal Erosion - typical of tectonically uplifted
rocky coasts
erosion claims large areas of
produces landforms: wave cut
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produces stacks - isolated
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terraces - wave cut
- Coastal Deposition - tectonically
longshore
currents transport sediment
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produces spits -
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barrier islands -
e.g. Grand Isle, LA
!!! Beware of longshore currents and building on the beach!!!
Human induced Coastal Deposition
Man made structures disrupt
Breakwaters - walls to intercept
result
in
Groins - Shore-protection strutures perpendicular
to
Jetties - extend stream channels
CHANGES IN SEA LEVEL
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At low sea level, there is
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At high sea level, there is
estuary formation- coastal body of water connected
to ocean and supplied with fresh water from rivers.
STOP HERE!!!!
ANATOMY of an OCEAN FLOOR
Oceans are bounded by
1. Continental Shelf - shallow, submerged
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average ca. 65 km with angles of 0.07'
-exception is tectonically
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small hills and ridges and depressions cut by
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Shelves have been mapped with precision which allows development
of
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passive margin - continental borderland
far from
- consist of flat-lying
- e.g. such as Atlantic, opened 180 Ma, broken and
rifted at margin by upwelling of magma
2. active margins - margins associated with
e.g. in tectonically deformed shelves, Pacific,
typically a coincidence of
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economically valuable for fishing, oil reserves
2. Continental Slope - regions of steep slope
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slope decreases at depths of 2000-3000m to the:
3. Continental rise - sediment apron at base of
slope
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hundreds of km wide grading into the:
4. Abyssal Plain - wide flat plain that covers
large areas of
5. Seamounts - submerged mountain with
e.g. Bermuda - extends to surface, capped
with
6. Mid-Ocean Ridge
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in center of ocean floor, ridges with
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hot magma produces hydrothermal waters
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- U-shaped
- broader and shallower
7. isolated volcanic islands develop throughout the ocean
floor e.g. Hawaii
TURBIDITY CURRENTS
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mixtures of water and sediment that moves downhill along
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provides best mechanism to explain
DEEP-SEA SEDIMENTATION
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Pelagic sediments - terrigenous fine grained particles
rich in
- accumulate at
- may react with sea water to form
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Foraminiferal oozes - sandy and silty sediments composed
of
- Carbonate compensation depth: depth at which
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Silica ooze - produced by sedimentation of