Download Unit 5: Ocean Floor Structure and Plate Tectonics

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Ocean Floor Structure and Plate Tectonics
Sea Floor Features:
Earth's rocky surface is divided into two types:
1. oceanic crust
 thin
 dense crust
 6 km-10 km thick.
 It is made of basaltic type rock
2. continental crust
 thick
 light (lower density than the oceanic crust)
 crust about 50 km thick.
 floats higher on the mantle than the oceanic crust. This forms the basins that hold our oceans
 It is made mostly of granitic rock.
The diagram below illustrates the basic set up of the ocean floor.
Continental Shelves –
 the area beside a continent
 goes from the low-water line to the edge of the continent under
water,
 Maximum depth is about 200 m,
 They are often areas of rich in sea life
 They are important economic zone of the nearby countries.
Continental Slope –
 the drop off at the edge of the continental slope
 Both the continental shelf and slope are considered structurally part
of the continents, even though they are below the sea surface.
Continental Rise –
 The gentler slope at the bottom of the slope
 It is made of sand and sediments that comes from the land and the
continental self.
 Kind of like a rubble pile.
Abyssal Plain –
 The relatively flat bottom of the ocean
 They are the deepest parts of the ocean, except for the trenches.
 The average depth is about 4000m (4 km) from the surface to the abyssal plain.
Mid-ocean ridges –
 continuous mountain chains on the sea floor.
 They occur where two oceanic plates are moving apart
(diverging)
 Magma bubbles up between the 2 plates forming new land.
Abyssal Hills –
 Small, cone shaped formations on the ocean floor
 Shorter than 1000 m
Seamounts –
 underwater mountains that are at least 1000 m (1 km) tall.
 They are usually cone-shaped.
 They are volcanoes mountains that rise from the ocean floor
(abyssal plain).
Volcanic Island –
 A seamount that extends above the surface of the water.
Guyots –
 a seamount with a flat top created
by wave action when the
seamount was at sea level
When one plate dives beneath another (subduction) …
Trenches –
 trenches are long, narrow, and deep
depressions of the sea-floor
 they have steep sides that form at subduction
zones.
 Subduction is when one tectonic plate dives
beneath another.


The deepest trench on Earth is found in the Pacific
Ocean. It is called the Marianas Trench. The deepest
part of the Marianas Trench is 11 km deep.
Island arcs –
 volcanic island chains that form on the other side of a
subducted plate.
 This happens when to ocean plates crash into each other.
Canyons –
 are deep cuts into the continental shelf and slope,
 the largest canyon in The North Atlantic is called The
Gully
 The Gully is just off the coast of Nova Scotia.
 The Gully is home to lots of different forms of life.
 The Gully is now a protected area so that endangered
animals have a chance to recover.