1. Continental Margins & Deep Ocean Basins
Seafloor Features:
Continental Margins
&
Deep Ocean Basins

2. Shape of the Ocean Floor
The ocean is not shaped like a bath tub (ex. Shallow edges, deep center)
continental margin- Submerged edge of the continent
ocean basin- Sea floor

3. Continental Margins
Diverging plates have passive margins that have little (volcanic/seismic) activity
Converging plates have active margins with high (volcanic/seismic) activity

4. Continental Shelf- Shallow submerged edge of continent
220 miles out from shore with an avg. depth of 250 ft (gentle incline)
Shelf was exposed 18,000 years ago during ice age, and during late Cretacous sea level was 1,000 ft higher and flooded 35% of the land
Many natural
resources are
found here

5. B. Continental Slopes-
The transition between the shelf and ocean floor
4 degree slope or descends 144 ft/mile (greatest- 25 degree slope)
Depth of 12,000 ft
Bottom of the slope is the true edge of the continent

6. C. Continental Rise-
The base of the continental slope that is covered by accumulating sediment
Sediments can be carried there by turbidity currents rushing down the slope like an avalanche

7. D. Submarine Canyons-
V-shaped indentations incised into the continental shelf and slope, often terminating on the deep sea floor in a fan of sediment
Turbidity currents cause sediments to fall into the canyons
Can be as large as the Grande Canyon
Navy submarines can hide within these

8. Deep Ocean Basins
The seafloor is blanketed by sediments overlying basaltic rocks
Deep ocean basins account for ½ of the Earth’s surface
The deep ocean floor consists of ocean ridges, plains, trenches, and masses of sediment

9. A. Ocean Ridges-
A mountain chain of young basaltic rocks at an active spreading center (they cover the earth like the seams of a baseball)
When they project out of the seaislands
Rift valleys form as new ocean emerges between lithospheric plates (young rock at the center, oldest at edges) and ridges become steeper

10. 1. Hydrothermal Vents on Ridges
Hot springs that have upwellings of mineral laden water at temperatures of 660 F
Water descends in cracks on the ridge, comes in contact with super heated hot rocks
The superheated water dissolves minerals & gases escape upward through vent by convection
Plays a major role in ocean chemistry

11. B. Abyssal Plains & Hills
Abyssal means “without bottom”
25% of the earth’s surface
is covered by abyssal plains
and hills
Abyssal plains-are flat, cold featureless expanses of sediment between cont. margin & ridges at 12,000-18,000 ft
Abyssal hills-small hills of sediment covering extinct volcanoes (> 650 ft tall)

12. C. Trenches Arc shaped depression where ocean plates subduct
Most active geologic feature on earth (earthquakes/ tsunamis)
Marianas Trench is 36,163 ft (7 miles) below sea level, 20% deeper than Mt. Everest is tall, & 44 miles wide by 1,600 miles long

13. D. Island Arcs
Curving chains of volcanic islands and seamounts that parallel trenches
trenches and island arcs formed by subducting plates
Descending plates melt as they subduct, magma rises and lava forms a chain of islands behind the trench

14. E. Seamounts
Circular or elliptical projections about .6 of a mile high with a steep slope (25 degree)
Usually numbering in any given area and thought to be submerged inactive volcanoes formed at spreading centers
Movement of plates away from spreading center moves seamounts out and down

15. F. Guyots Seamounts with flat peak due to wave erosion
guyots also form near spreading centers and are transported out and down as the plates move