Download Seafloor Features:

Seafloor Features:
Continental Margins
&
Deep Ocean Basins
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
Continental Margins
• Diverging plates have passive
margins that have little
(volcanic/seismic) activity
• Converging plates have active
margins with high
(volcanic/seismic) activity
A. 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
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
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
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
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
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
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
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 12,00018,000 ft
• Abyssal hills-small hills of
sediment covering extinct
volcanoes (> 650 ft tall)
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
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
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
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