Seafloor Features:

1
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 Earths
  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 earths 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 (gt 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 10-100 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