1. Measuring bathymetry Ocean depths and topography of ocean floor
Measurement of depths from sea surface to underwater features : bathymetry as measurement of elevation on land : topography

2. Bathymetric techniques
Echo sounding/Sonar
Reflection of sound signals
Side-scan sonar
Towed behind research vessel (ship)
Ex. GLORIA
Sound waves are influenced by differences in density; ie. seawater and seafloor – sediment and rock; speed of sound depends on density of material; refraction v. reflection (less energetic)

3. Bathymetric techniques
Fig Seismic Profiling
Distance to the object is equal to the velocity in the material times one-half the time required for the sound signal to travel from the surface to the object and back to the receiver. Echo sounder can be used to determine distance to objects on ocean floor; thickness of rock or sediment requires small explosions.

4. Bathymetric techniques, cont…
Data gap in center
Fig. 3.2

5. Bathymetric techniques, cont…
Satellite Measurements
Ocean floor features cause sea surface to rise

6. Marine provinces Continental margins Deep-ocean basins Mid-ocean ridge
3 major provinces
Continental margins
Shallow-water areas close to shore
Deep-ocean basins
Deep-water areas farther from land
Mid-ocean ridge
Submarine mountain range

7. Continental margins Passive or active Passive (Atlantic-type)
Not close to any plate boundary
No major tectonic activity
Ex: coast of United States
east

8. Continental margins, cont…
Active (Pacific-type)
Associated with convergent or transform plate boundaries
Much tectonic activity
Convergent active margin
Oceanic-continental convergence
Ex: South America
western

9. Continental margins, cont…
Transform active margin
Associated with transform plate boundaries
Ex: Coastal California along the fault
San Andreas

10. Continental margins
Fig. 3.6

11. Continental shelf Extends from shoreline to shelf break
Shallow, gently sloping

12. Continental slope
Submarine canyons cut into slope by turbidity currents
Mixture of seawater and sediments
Move under influence of gravity

13. Continental rise
Transition between continental crust and oceanic crust

14. Deep ocean basin features
Depths greater than 4000 m
Abyssal plains
Volcanic peaks
Ocean trenches
Oceanic ridges and rises

15. Abyssal plains
Very flat depositional surfaces from base of continental rise

16. Volcanic peaks
Poke through sediment cover
Below sea level:
Seamounts

17. Ocean trenches Associated with subduction zones Deepest parts of ocean
Ex. Mariana Trench

18. Mid-ocean ridge and rises
Longest mountain chains
Basaltic lava
Divergent plate boundary

19. Volcanic features of mid-ocean ridge
Hydrothermal vents
Heated subsurface seawater migrates through cracks in ocean crust