Chapter 3: Marine Provinces Flashcards
What three main provinces can the ocean floor be divided into?
- Continental Margins
- Deep-ocean Basins
- Mid-ocean Ridges
Shallow water areas close to continents
Continental Margins
Deep water areas further from land
Deep-ocean Basins
Shallower areas near the middle of an ocean
Mid-ocean Ridges
The measurement of ocean depths and the charting of the shape, or topography of the ocean floor.
Bathymetry
The letting out of line before the heavy weight on the end of the line touches the bottom.
Sounding
The standard unit of ocean depth; equal go 1.8 meters (6 feet)
Fathom
What did the first systematic bathymetric measurements indicate?
The measurements indicated that the deep ocean floor was not flat but had significant relief (variations in elevation), just as dry land does.
Sends a sound signal (called a ping) from the ship downward into the ocean, where it produces echoes when it bounces off any density difference.
Echo Sounder
How is the echo sounder useful?
The time it takes for the echoes to return is used to determine the depth and as a result, the corresponding shape of the ocean floor.
Developed in the 1950s; uses a high frequency sound beam to measure depths to a resolution of about 1 meter (3.3 feet)
Precision Depth Recorder (PDR)
Use multiple frequencies of sound simultaneously and side-scan sonar (an acronym for sound navigation and ranging).
Multibeam Echo Sounders
The first multibeam echo sounder; made it possible for a survey ship to map the features of the ocean floor. Uses sound emitters directed away from both sides of a survey ship, with receivers permanently mounted on the ship’s hull.
Seabeam
Why are multibeam surveys useful?
They provide incredibly detailed imagery of the seabed.
Tall volcanoes on the sea floor
Seamounts
Strong low-frequency sounds produced by explosions or air guns penetrate beneath the sea floor and reflect off the boundaries between different rock or sediment layers, producing what?
Seismic Reflection Profiles
Continental Margins can be classified into what two groups?
Passive Margins or Active Margins
Embedded within the interior of lithospheric plates and are therefore not in close proximity to any plate boundary.
Passive Margins
Associated with lithospheric plate boundaries and are marked by a high degree of tectonic activity.
Active Margins
What two types of Active Margins exist?
- Convergent Active Margins
2. Transform Active Margins
Associated with oceanic-continental convergent plate boundaries. From the land to the ocean, features include an on-shore arc-shaped row of active volcanoes, then a narrow shelf, a steep slope, and an offshore trench that delineates the plate boundary.
Convergent Active Margins
Less common and are associated with transform plate boundaries. At these locations, there are usually offshore faults that parallel the main transform plate boundary fault and create linear islands, banks (shallowly submerged areas), and deep basins close to shore.
Transform Active Margins
Defined as a generally flat zone extending from the shore beneath the ocean surface to a point at which a marked increase in slope angle occurs, called the shelf break.
Continental Shelf
A marked increase in slope angle on a continental shelf.
Shelf Break
For Transform Active Margins such as along California, the presence of offshore faults produces a continental shelf that is not flat. Rather, it is marked by a high degree of relief (islands, shallow banks, and deep basins) called a what?
Continental Borderland
Lies beyond the shelf break, and is where the deep ocean basins begin.
Continental Slope