TOPOGRAPHYOF THE

SEAFLOORNOTES

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.