Transcript The Seafloor

The Seafloor
The Continental Shelf
• The shallowest part of the continental
margin is the continental shelf.
• They are the biologically richest parts
of the ocean with the most life and the
best fishing.
• The shelf is a part of the continent that
presently happens to be under water
• During times of low sea level in the past, in fact, most of the continental shelves
were exposed. At these times, rivers and glaciers flowed across the shelves and
eroded deep canyons. When the sea level rose, these canyons were submerged and
gave rise to much larger submarine canyons.
Shelf Break
•
The shelf extends outward at a gentle slope that in most places is too gradual to see with the naked eye. The
shelf will vary in width. The continental shelf ends at the shelf break; usually occurs at depths of 400-600 feet
but can be as deep as 1,300 feet
The Continental Slope
• It is the closest thing to the exact edge of the continent. It begins at the shelf break and descends
downward to the deep sea floor.
The Continental Rise
• Sediment moving down a submarine canyon accumulates at
the canyon’s base in a deposit called a deep-sea fan, similar to
a river delta. Adjacent deep-sea fans may merge to form the
rise. It consists of a thick layer of sediment piled up on the sea
floor.
Active and Passive Margins
• The nature of the continental
margin depends to a large extent
on the plate tectonic processes
occurring.
• Active margin- areas of intense
geological activity. (earthquakes,
volcanoes & trenches)
• Passive Margins- typically have
flat coastal plains, wide shelves,
and relatively gradual continental
slopes. (no tectonic processes to
remove it)
• Usually have a thick continental
rise. For example ;Gulf of Mexico
Deep Ocean Basins
• The sea floor is almost
flat and is called the
abyssal plain. It is not
perfectly flat and rises
toward the mid-ocean
ridge.
Abyssal Plain
• The abyssal plain is dotted with submarine volcanoes called
seamounts and volcanic islands. Distinctive flat-topped
seamounts are called guyots (common in parts of the Pacific)
• At trenches, where the plate descends into the mantle, the sea
floor slopes steeply downward. Trenches are the deepest parts
of the world ocean.
•Seamounts
•Guyots
•Trenches
The Mid Ocean Ridge
• The mid ocean ridge itself is
an environment that is
unique in the ocean. This is
a zone where plates are
pulling apart leaving a gap or
depression known as the rift
valley.