Transcript File
Bathymetry
of the
Ocean Floor
The ocean floor is mapped by SONAR.
(Sound navigation and ranging)
Depth = (time x 1500 m/sec)/2 (round trip)
At 25 degrees Celsius
Relationship above and below the water
Ocean Floor Topography
Major features: continental shelf, trenches, abyssal
plains, mid-ocean ridges.
After 1920’s, these features could be mapped in detail
by sonar (bouncing sound waves off the ocean floor).
Continental Shelf
Area of shallow water along passive continental margin (not an
active plate boundary).
Continental Margin – consists of continental crust (think shallow end of pool)
Shelf drops off abruptly at outer edge.
Much of shelf was above sea level during past glacial periods.
Continental Rise
gentle slope at the base of the continental slope caused
by:
- turbidity currents - deposition of sediment by
underwater landslides and other processes that
carry mud, sand & silt down the slope
- occurs at the base of the slopes & gently slope
seaward to the deep sea floor
Submarine Canyons
Submarine Canyons - ripple marks observed on the
floor of submerged canyons and sediments fanning out
at the end suggest they were formed by moving
sediments and water
- as flow reaches bottom, it slows down, fans out
and the sediment settles out
Submarine canyons cut through the shelves and slopes,
look like river valleys on land.
Trenches
Occur along active margins (present-day plate
boundaries) where subduction is taking place
deepest part of the ocean floor, typically 3 - 4 km
deeper than surrounding seafloor
most occur in the Pacific, mostly western Pacific, but most of
the Pacific is surrounded by trenches
deepest spot in the oceans is the Challenger Deep in the
Marianas Trench, 11,035 m
trenches are associated with active volcanoes and earthquakes
most are near chains of volcanic islands
Deep Ocean Basin - Abyssal
Plane
Flat areas making up much of the ocean
floor apart from trenches and mid-ocean
ridges
Deep Ocean Basin - seaward of the
continental margin
In most places, seafloor is a flat plain - Abyssal Plain
covered by sediment deposits of turbidity currents
covering an irregular seafloor plain interrupted by:
seamounts - individual mountains made of volcanic material.
Rise steeply, sometimes above the surface to form islands.
guyots - (flat topped seamounts found most often in the Pacific)
table mounts, - many have ancient coral reefs on top indicating that
they were once at the surface
- flat tops due to wind & rain erosion
- subsided due to their own weight & crustal movement
Mid-Ocean Ridges
Largest topographic features on
earth.
Broad ridges (where plates pull
apart from one another) with a
deep rift valley down the center.
Rift Valley-forms between the
ridges of mountains.
Location where basaltic lava
flows erupt.
Age of the ocean floor
Detailed studies in 1950’s showed that
there are bands of similar aged rocks
parallel to mid-ocean ridges.
Bands get older with greater distance from
the ridges.
Basins
Abyssal plains
Seamount
Guyot
Trenches
Mid Ocean ridges
Rift Valley