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Oceanography 1
Exam 1
44
Geology
Undergraduate 1
02/03/2016

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Cards

Term
Eratosthenes
Definition

On June 21 (= summer solstice), midday sun directly over city of Syene (Aswan)

On June 21: Angle of sun at midday in Alexandria was 7.2o If the world was flat than there should be no difference in the angle. (500 miles)(360o /7.2o ) = x = 25,000 miles

Term
Pytheas
Definition

worked out simple method for determining la)tude: • determine the angle between the horizon and the North Star (Polaris) 

Term
Latitude & longitude
Definition

Lat across, long up and down. Grid system used to precisely describe locations on the Earth’s surface. Based on angular relationships to Earth’s center. Expressed in degrees (o); each degree is divided into 60 minutes (‘), each minute into 60 seconds (“)  

Term
Latitude
Definition

• “parallels” = grid lines that are parallel to the Equator

 • 0o at Equator, 90o at poles • 0o -90o N = N. Hem.

• 0o -90o S = S. Hem.

Everywhere on Earth’s surface: 1o lat. = 60 nautical miles, 1’ lat. = 1 nautical mile.

Term
Longitude
Definition

• “meridians” = grid lines that intersect at poles

• 0o = “PrimeMeridian” (Greenwich, England)

• 180o = halfway around Earth

• 0o-180o to west of Greenwich = W. Hem.

• 0o-180o to east of Greenwich = E. Hem.

Term
sextant and chronometer
Definition

sextant is a tool to measure the angle of the sun to the horizon to get lat and chronometer compares your time to Greenwich time. (The difference between your time and GMT) X (15o Longitude per hour) = Your Longitude. If you are ahead of GMT you are in the Eastern Hemisphere (E is for Earlier).

Term
celestial navigation
Definition

determine latitude by measuring the angle of the north star from the horizon. Use southern cross in the southern hemisphere.

Term
Soundings
Definition
Weighted lines lowered from ships. Time consuming, relatively few, questionable accuracy
Term
echo sounding (2D)
Definition

Sound source & receiver (hydrophone) on hull of ship. High frequency sound waves travel through the water, reflect off the seafloor, and are recorded by the hydrophone. Provide continuous 2-dimensional depth profiles along a ship’s track. d = (v)(t/2)

Term
multi-beam or side-scan sonar (3D)
Definition

Like an echo sounder, but it images a 60 km swath of seafloor š Overlapping swaths = complete coverage (3-D)

Term
Matthew Maury
Definition

First attempt at a bathymetric map by Matthew Fontaine Maury based on soundings. Showed vast relatively shoal area in Mid-Atlantic. 

Term
Techniques to see the structure of the sub-seafloor
Definition

Lower frequency energy source (stronger sound source with fewer sound waves per second). Deeper penetration into sedimentary layers and ocean crust

Term
seismic reflection profiles
Definition

Sound source and hydrophone towed by ship. 2-D, continuous profile. Lower frequency energy source (stronger sound source with fewer sound waves per second). Deeper penetration into sedimentary layers and ocean crust

Term
satellite altimetry
Definition

Precise altimeters (using microwaves) can map the relief of the ocean surface with centimeter-scale resolution š Bathymetric highs and lows on the seafloor, and differences in rock density, cause measureable gravitational distortion of the ocean surface

Term
bathymetric map
Definition

depict the topography, or relief of the seafloor; isobaths connect points of equal depth, like the contours lines on topographic maps

Term
Crust
Definition

Oceaninc and Continenetal

Term
Mantle
Definition

Oceaninc crust, and lava part.

Term
Moho
Definition

Thin region between the mantle and crust.

Term
Lithosphere
Definition

all crust portions

Term
Asthenosphere
Definition

the upper mantle part that is lava right under oceanic crust.

Term
Oceanic Crust
Definition

less thick than continental and denser cause primarily basalt. Subducted at trenches during collision.

Term
Continental Crust
Definition

thicker and less dense than oceanic cause primarily granite. Preferentially preserved during collision.

Term
Calculation of crust density
Definition

Density=mass/volume.

Term
Isostasy
Definition

the state of gravitational equilibrium between Earth's crust and mantle such that the crust "floats" at an elevation that depends on its thickness and density of underlying roots of the low density of the mountain.

Term
continental shelf
Definition

offshore extension of the continent relatively shallow; 

Term
continental slope
Definition

underlain by thinned continental crust dissected by numerous submarine canyons

Term
continental rise
Definition

- thick accumulation of terrigenous sediments at base of the slope (= deep-sea fans)

Term
abyssal plains
Definition

deep, extensive, virtually flat plains

Term
volcanoes
Definition

islands, atolls, guyots, seamounts, abyssal hills

Term
atolls
Definition

fringed by coral reefs that continue to grow up as it subsides Makes steeps sided pillar.

Term
guyots
Definition

– flat topped volcanic peak. Once at surface, but wave-cut then subsiding

Term
trenches
Definition

deep, long, narrow, steep-sided troughs seismically active associated with volcanism landward of the trench

Term
spreading centers
Definition

convection of rising hotter lava in mantle drives upward creating cracks that drive coninents outward from it on both sides. 

Term
Passive margins
Definition

edge of shelf that is pushing against another due to being side furthest from spreading center.

Term
active margins
Definition

edge of shelf that is not getting pushed against another due to being the side closest to the spreading center.

Term
“Ring of Fire”
Definition

- the perimeter around the pacific plate that is exerting force almost all the way around resulting in a circle of volcanoes and earthquakes.

Term
ocean-ocean collision
Definition

results in island arcs

Term
ocean-continent collision
Definition

results in volcanic mountain range near the edge of a continent

Term
continent-continent collision
Definition

results in high mountain range since thick buoyant continental lithosphere cannot be subducted.

Term
Divergent
Definition

where upwelling Asthenosphere results in melting and new ocean crust (basalt) is formed; the Mid-Atlantic Ridge is a slow spreading center, whereas the East Pacific Rise is a fast spreading center. Spreading centers are characterized by shallow earthquakes. Ocean ridges.

Term
Transform faults
Definition

occur at off-sets of oceanic ridges (spreading centers); they represent strike-slip plate boundaries and are characterized by shallow earthquakes.

Term
magmatic arcs
Definition

(= volcanoes in the ocean or on land) forms landward of the trench on the overriding plate.

Term
“hot spots”
Definition

are volcanoes formed by stationary mantle plumes from deep in the mantle, unrelated to convection in the Asthenosphere (i.e., they are not related to plate tectonic processes such as subduction or seafloor spreading); hot spots produce linear island chains (e.g., Hawaiian Island-Emperor Seamount Chain) .

Term
Spreading rates
Definition

The profile of the ridge is related to the size of the magma chambers and the rate of seafloor spreading

Fast Spreading Rates - large magma chambers - poorly-defined central rift valley - broad oceanic ridge due to high heat flow - e.g., East Pacific Rise

Slow Spreading Rates - small, discontinuous magma chambers - well-defined central rift valley - relatively narrow and steep oceanic ridge - e.g., Mid-Atlantic Ridge

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