Download 2017Geological Oceanography

Geological Oceanography
The study the geology of the ocean.
(underwater landforms, map making,
and plate tectonics)
Mapping the oceans
– Greek Contributions
● Pytheas (314 B.C.) Could determine how far
North or South one was from the North Star by
measuring the angle between the horizon and the
North Star.
● Eratosthenes (264-194 B.C.) is credited
with two contributions:
● 1. He calculated the Earth’s circumference (only
off by 100 miles!)
● 2. He invented the first latitude/longitude
system.
NOAA Ocean Service Education
Latitude/Longitude System
● The purpose of the latitude and longitude mapping system
is to identify specific locations on the Earth’s surface.
● Latitude Lines
● Also called parallels
● Run east-west
● 0º parallel is also called the equator
● Longitude Lines
● Also called meridians
● Run north-south
● Prime Meridian is located on the longitude
of the Royal Naval Observatory in
Greenwich, England. 00 longitude
● Further Accuracy
● Degrees are subdivided into 60 minutes,
minutes are subdivided into 60 seconds.
• Modern scientists measure in decimals of
degrees
Mapping the Oceans – Ocean Depth
• Cartography – the
science of making
maps
– Dry land forms are
mapped using
topography.
– Underwater landforms
are mapped using
bathymetry.
“Real World”
Contour Map
What is
the
contour
interval?
Mapping the Oceans – Who does it?
Mapping the Oceans – Who does it?
Private Oceanic Institutions
● 1912 - Scripps Institute was founded in La
Jolla, CA
● 1930 - Woods Hole Institute was founded on
Cape Cod of Massachusetts
● Our local marine lab is Grice Marine
Laboratory Located at Ft. Johnson on James
island. Operated by the College of
Charleston.
Mapping Oceans - Technology
● SONAR, which stands for Sound Navigation and
Ranging ,bounces sound waves off the ocean
floor in order to study depth and shape of the
seafloor
● Satellites in space help relay information and
track location with GPS, make maps of the
ocean floor, detect algal blooms, monitor global
climate, track ocean temperatures, and
currents
Sonar Technologies have evolved to more accurately
survey the ocean floor
http://www.earthguide.ucsd.edu/earthguide/diagrams/sonar/s
onar.html
Satellite GPS is accurate within 1 or 2 meters
whereas previous methods were accurate
within about a mile.
Satellite imagery
Ocean salinity
Seafloor mapping
Dive Suits
• Hard Hat Diving - 1840s Air from
surface hose, heavy, walk on sea
floor
• Scuba - 1943 “Self Contained
Underwater Breathing
Apparatus”, lightweight, swim like
a fish
•
Excess gas is absorbed by your blood as
you dive to deeper pressures. Divers
must come to the surface slowly in
order to avoid decompression sickness
(The rapid expansion of the gasses in the
bloodstream).
Mapping the Oceans Technology
Submersibles:
• Bathyscaphe - attached to a float, can only
go up and down. Have bulky ballast tanks
– Ex. Trieste was 1st ship to bottom of
Marianas Trench
• HOV - Human Occupied Vehicle, manned
submersible, excellent maneuverability.
– Ex. Alvin discovered Hydrothermal
Vents
• ROV - Remotely Operated Vehicle, can
stay below the water longer and collect
more data. Tethered to a ship.
– Ex. Hercules ROV
Famous Subs
Alvin - Discovered
Titanic and Hydrothermal
Vents
Johnson Sea Link
MIR-1 and MIR-2 - Featured in
Titanic
AUV - Autonomous Underwater Vehicles
• AUVs are untethered robotic devices that are
controlled and piloted by an onboard computer.
• Some are propelled by motor and some are
propelled by utilizing different densities of water in
the water column (Glider style).
• AUVs are untethered. They operate completely
independently. Transmit data to satellites.
• Drifter style AUVs drift in the ocean collecting data.
Some can move vertically to collect data at
different depths. Can operate for 1-2 years.
Deep-Ocean Basins
• The seafloor is a blanket
of sediment covering the
rock of the Earth’s crust
• Consists of oceanic
ridge systems and
abyssal plains
• The abyssal plains are
scattered with islands,
hills, trenches, active
and extinct volcanoes
Geologic features
on continents
and the seafloor
are created by
tectonic activity
at the boundaries
between tectonic
plates.
Characteristics
of the crust
affect the
influence of
tectonic
forces.
Oceanic vs. Continental Crust
 Oceanic Crust
 Denser, thinner and younger than
continental crust
 Oceanic crust lies lower on the
mantle because of increased density.
 Continental Crust
 Lighter, thicker and older than
oceanic crust
 Continental crust rises higher above
mantle because of lesser density.
Continental Margins
• These are the areas of the edges of the
continental crust that are under water
– 2 subdivisions: Continental Shelf and Slope
Continental Shelf
• Shallow extension of the continent
– Can be narrow, quickly becoming steep
– Or can be broad, gently sloping downward
• They look much like the continent from which they
extend: hills and depressions
• The sediment on the shelf is eroded dirt and debris
from the dry land above it
– Sediment is rich in minerals, oil and gas
Continental Slope
• The transition between the shelf and the
deep-ocean floor
– The shelf break marks the transition
– Very steep
• Continental rise is past the slope
– It is oceanic crust covered with sediment from
the land
Submarine Canyons
• These canyons cut into the continental shelf and
slope, ending in a deep-sea fan
• Sometimes they extend from the mouth of a river
that drains sediment and fast flowing water out to
sea
– Created by erosion
like canyons on land
• Sometimes they are
created by earthquakes
that cause an “avalanche”
of sediments
Continental Drift
Sir Francis Bacon (1600s)and Leonardo
DaVinci(1500s)
Noticed that the continents seemed to fit together
like a puzzle
Alfred Wegener backed up idea with
evidence:
Coal deposits and other geological formations
across oceans matched
Fossils of a land reptile across oceans also matched
Fossilized tropical plants in Antarctica
Modern Theory of Plate Tectonics:
• Crust is broken up into lithospheric plates that move
on top of the mantle.
• The plates move because of convection currents in
the mantle.
Plate Tectonics Map by USGS
Evidence for plate tectonics found on
the sea floor.
–1. Orderly pattern of oceanic ridges and
volcanoes suggesting the Earth’s crust is
divided into sections.
–2. Sediment samples – the layers were thin
or absent at the oceanic ridges, and thicker
away from the oceanic ridges. This suggests
newer crust at the ridges.
Pacific Ring of Fire
• Zone along the edge of the Pacific Ocean that
has many volcanoes and earthquakes.
• This horseshoe-shaped belt stretches about
25,000 miles.
Evidence for plate tectonics
– 3. Radiometric dating was used to determine the
age of rocks. Scientists have found seafloor rock to
be significantly younger than rock in the center of
the continents.
– 4. Magnetometer data -This instrument measures
the polar orientation of magnetism of minerals. A
symmetrical pattern exists in the magnetic
alignment in seafloor rock. This pattern radiates
outward from the point of seafloor spreading.
Age of Oceanic Rocks:
Red = Newest Blue = Oldest
3 Types of Tectonic Plate Boundaries
• At a spreading or divergent boundary, two
plates are moving apart. As this happens, the
crust pulls apart and forms valleys. Magma
flows up through the rift valleys creating new
crust and widening the seafloor.
• At a colliding or convergent boundary, two
plates push together.
– Movements along these destroy or recycle crust.
• At a transform boundary or fault, two plates
slide past each other.
Divergent Boundary
Mid-ocean ridges
and rift valleys
mark divergent
boundaries.
Cause seafloor
spreading
Volcanoes
along oceanic
ridges
Only one
island: Iceland
Formed by divergent boundaries:
Oceanic Ridges
• A chain of mountains formed during seafloor
spreading.
– Composed of “new” basaltic rock with no
sediment
– If they extend above the water, they are called
islands
•
Formed by divergent boundaries:
Seamounts and Guyots
• Seamounts are volcanoes that are below
ocean surface
• Guyots are flat-topped seamounts
that once went above the ocean
surface
– flattened by waves and erosion
Formed by divergent boundaries:
http://www.divediscover.whoi.edu/vents/video.html
Convergent boundaries
• Oceanic-Oceanic
• Causes underwater
volcanoes and island
formation.
• ContinentalContinental
• collide and “push
together” forming
mountain chains
–Example:
Himalayas
Convergent boundaries
• Continental-Oceanic
• The oceanic plate is
subducted underneath
the continental plate
• As plate moves down
into mantle it melts
• Increased magma is
forced up through
surface forming land
volcanoes
– Example: Mount St.
Helens
Formed by convergent boundaries:
Trenches and Island Arcs
• Trenches are deep pits in the ocean where the
converging plate is subducted
– Recall the cold ocean crust is sinking into the
upper mantle of the continental plate
– V-shaped due to spherical shape of Earth
• Parallel to the side of the trench, the molten
rock from the subducted plate is coming back
up through volcanoes called an island arc.
– Example is Caribbean islands
Mountain ranges formed by
convergent boundaries
Snack Tectonics
• Transform boundaries: rub 2
dry graham crackers side by
side
Snack tectonics
Divergent Boundaries: Push fruit roll-ups apart
• Oceanic-Oceanic: Mid-Atlantic Ridge
• Continental-Continental: Great Rift Valley, Africa
Divergent
Boundaries
Snack Tectonics
• Continental-Oceanic convergent: Colliding
Graham cracker and fruit roll up
– Andes Mountains, Mt. St Helens, Caribbean
Islands
Snack Tectonics
• Continental-Continental Convergent: Push 2
wet graham crackers together.
– Alps, Himalayas, Rockies
Plate Boundaries Poster
• Use the descriptions in table 3.1 pg 75 to draw all the types of plate
boundaries.
• Divergent Boundaries
– Ocean-Ocean
– Continent-Continent
• Convergent Boundaries



Ocean-Ocean
Continent-Continent
Ocean-Continent
• Transform Boundaries
• Illustrations must be colorful, fill the entire poster, show direction of
plate movement, label type of boundary, and describe events
observed there.
Distance from North America (Km)
5,700
4,600
4,800
5,000
5,200
5,400
5,600
5,800
6000
0
150
300
450
600
750
900
1,050
1,200
1,350
Atlantic Ocean Depth (m)
0
39o N