Studied by 6 people
bathymetry
measurement of ocean depths and the charting of shape, or topography of ocean floor. determining bathymetry involves measuring vertical distance from ocean surface down to mountains, valleys, plains on sea floor.
how are most ocean floor features generated
plate tectonic processes, and different sea floor features exist in different oceanographic locations
underwater features
deep trough, ancient volcanoes, submarine canyons, great mountain chains.
what are the three major ocean provinces
continental margins, deep ocean basins, mid ocean ridge
how do we measure bathymetry
soundings, posidonius made first sounding in 85 BC. line with heavy weight 2km long. used for 2000 years.
fathom
standardized unit of measure. 1.8 m, 6 feet
HMS challenger
made first systematic measurements in 1872. Deep ocean floor has relief, variations in sea floor depth.
echo sounders
sends a signal (ping) into the ocean. bounces off any object that is a diff density than seawater. like a radar on land.
when was the mid atlantic ridge discovered
in 1925 by a german ship named meteor.
pdr
precision depth recorder. made in 1950,s focused high frequency sound beam to measure depths to a resolution of 1 m. produced first reliable sea floor maps.
how wide are sea floor echo sounder strips
60 km, 37 miles wide
side scan sonar
can be towed behind ship to provide detailed bathymetric strip map. detailed image of seabed.
satellite mapping
measures sea floor features based on gravitational bulges in sea surface. dips (trenches) have lower gravitational attraction. bulges and seamounts have higher gravitational attraction.
seismic reflection profiles
provide information about structures beneath sea floor. strong, low frequency sounds produced by explosions or air guns. detail ocean structure beneath sea floor.
passive continental margins
not close to any plate boundary, no major tectonic activity (earthquakes, volcanoes, mountains)
active continental margins
associated with convergent or transform plate boundaries. lots of tectonic activity. transform active margin, san andreas fault.
convergent active margin
oceanic continent convergent plate boundaries. active continental volcanoes. narrow shelf, offshore trench, W. S. America (Nazca plate subducted beneath S. A. Plate
Transform Continental margin
less common, transform plate boundaries, linear islands, banks, deep basins close to shore. Coastal california along san andreas fault.
continental shelf
flat zone from shore to shelf break (where increase in slope angle stops). featureless bc of marine sediment. average slope of 1/10 of a degree. topography =coastal region of continent. underlying rock is granitic continental crust.
continental shelf features
type of continental margin determines shelf features. passive margins have wider shelves, CA’s transform active margin has a continental borderland (high degree of relief, islands, shallow)
continental slope
where deep ocean basins begin. topography similar to land mountain ranges. slope>continental shelf. averages 4 degrees, varies 1-25. marked by submarine canyons
submarine canyons
narrow, deep, v shaped. steep to overhanging walls. extend to base of continental slope. 3500 m below sea level. carved by turbidity currents.
turbidity currents
underwater avalanches mixed with rocks and other debris. dislodged sediment mixes with water as it moves down slope under influence of gravity to produce a turbidity current. flow of dense fluid is erosive and cuts a gully in the slope.
continental rise
transition btwn. continental crust and oceanic crust. marked by turbidite deposits from currents. graded bedding in turbidite deposits coarser at bottom. deposits generate deep sea fans.
abyssal plains
base of continental rise to deep ocean basins. some of deepest flattest parts of earth. (without bottom is what it translates to). average btwn. 4500-6000 m. suspension settling of very fine particles.
Atlantic ocean abyssal plain
most are in the atlantic ocean. deep ocean trenches in Pacific ocean prevents sediment from moving past continental slope.
abyssal plain volcanic peaks
poke through sediment cover. below sea level there is seamounts, tablemounts, guyots. abyssal hills or seaknolls are less than 1km above sea floor.
ocean trenches
deep linear scars in ocean floor caused by collision of two plates along the convergent plate margin.
volcanic arc
chain of volcanoes, hundreds to thousands of miles long. forms above a subduction zone
island arcc
curved chain of volcanic islands at tectonic plate margine, with deep ocean trench on convex side.
continental arc
volcanic arc at a topographic high region along a continental margin
pacific ring of fire
occurs along margins of pacific ocean. where majority of world’s active volcanoes and earthquakes occur.
mid ocean ridge features
longest mountain chain, covers 23%. Global mid ocean ridge is continuous fractured submarine mountain range that extends through the middle of all ocean basins for some 75,000 km.
how above the surrounding sea floor is the mid ocean ridge
1.5 miles
what does the mid ocean ridge originate from
completely volcanic in origin. lava of basaltic composition. along the crest is a central down dropped rift valley created by sea floor spreading processes. small shallow quakes. lots of fresh lava flow.
pillow lava
“pillow basalt” shapes formed when hot basaltic lava cools quickly. smooth rounded lobes of rock resembling stacked pillows.
ridge vs rise
ridge is mountainous with steep irregular slopes and oceanic rises where slopes are gentler. differences in overall shape between ridges and rises are due to spreading rate differences. oceanic ridges have slower spreading rates than oceanic rises.
hydrothermal vents
sea floor hot springs, foster unusual deep ocean ecosystems able to survive without sunlight
warm water vents
temps below 30 degrees C
white smokers
temps from 30-350 degrees C. emit white water because of light colored substances like BaS
black smokers
temps above 350 degrees C. black colored metal sulfides, FeS, NiS, CuS, ZnS
transform faults
along mid ocean ridge to counteract spreading zones. causes: to accommodate spreading of a linear ridge on spherical earth. different segments spread apart at different rates. seismically active zone
fracture zones
along pacific ocean mid ocean rise. seismically inactive, occur beyond offset fragments of rise. are ancient, inactive fault scars embedded within a plate.
where are transform faults found
between ridge axis and denote a plate boundary
where are fracture zones found
outside of the ridge axis and have a vertical scar with the younger portion at a higher elevation than the older portion of the same plate. transform faults are plate boundaries, fracture zones are intraplate.
what are the three types of oceanic islands
those associated with volcanic activity along mid ocean ridge
associated with hot spots (hawaiian islands)
island arcs associated with convergent plate boundaries.
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