TOPOGRAPHY
OF THE
SEAFLOOR
NOTES
CONTINENTAL MARGIN
Area of the continent (land) that is
underwater.
 Area that has been flooded and covered
with water over many years.
 This is made up of continental crust
(mainly granite).
 The east coast’s original shoreline used to
be 70 miles further out to sea.

FEATURES FOUND ON
CONTINENTAL MARGIN:
Continental Shelf
 Continental Slope
 Continental Rise
 Submarine Canyon

CONTINENTAL SHELF
Gently sloping part of the continent that
is underwater.
 Used by nations as a legal boundary.
 The east coast’s shelf is a lot larger than
the west coast’s
shorter shelf.

CONTINENTAL SLOPE

The steep sloping edge of the continent
that extends from the edge of the shelf
to the ocean floor.
CONTINENTAL RISE
A mound of sediments that separates the
continental slope from the ocean bottom.
 The sediments found here is terrigenous
(found from land), but the floor here is
made of basalt (ocean floor).

SUBMARINE CANYON




Canyon carved out of the continental shelf.
Typically runs perpendicular to the shoreline.
Carved out by water (typically rivers).
Remember the continental shelf used to be
“land.”
OCEAN BASIN
The part of the ocean that is oceanic
crust.
 Made primarily of basalt.

FEATURES FOUND ON
CONTINENTAL MARGIN:
Abyssal Plain
 Mid-Ocean Ridges
 Rift Valley
 Seamounts
 Guyots
 Atoll
 Trenches

ABYSSAL PLAIN

Very flat area of the ocean floor at the
edge of the continental rise.
MID-OCEAN RIDGES
Long, underwater mountain chains.
 These are associated with spreading
centers (divergent plate boundaries).
 New seafloor is being formed here.

RIFT VALLEY
A deep valley which runs down the center
of a mid-ocean ridge.
 Magma oozes out of these valleys which
harden into new seafloor.

SEAMOUNTS





Underwater mountains, usually volcanic.
The biggest mountain on earth is Mauna Loa (Hawaii).
Seamounts build-up over time underwater (usually over a hot spot)
and eventually break the surface of the water.
Seamounts above water turn into islands.
When they move away from the hot spot, the seamount will start to
“deflate” and go back underwater.
ATOLLS
After the seamount becomes an island,
coral reefs typically form around the
island.
 The point in which the island subsides
back underwater, and the coral reef is still
in tact, it becomes an atoll.

GUYOTS



Flat-topped seamounts, formed from being above sea level
at one time.
When seamounts are above water, they experience a lot of
weathering and get worn-down and flatten out over time.
Guyots are the “deflated” seamounts that have subsided
back underwater (the coral reef is no longer present).
TRENCHES




A long, narrow, deep depression of the sea floor
with steep sides.
These are the deepest places on Earth.
NOT associated with mid-ocean ridges.
Typically formed from earthquakes and tectonic
activity.