Download A. Continental Slope Transition from the Cont. Shelf to the ocean

A. Continental Slope
 Transition from the Cont. Shelf to the ocean
floor.
 “Active” plate boundaries = steep cont. slope
 “Passive” plate boundaries = slope is not as
steep
 Has submarine canyons that are carved out in
by turbidity currents.
B. Seamounts
 Seamounts are oceanic islands that do not
reach the surface.
 Often occur in chains & have an active
volcanic island at one end caused by a
“hot spot”. Ex – Hawaii
 Quite different in structure & composition
from mid-ocean ridges.
C. Abyssal Plain
 Flat floors of the ocean.
 Average depth is about 4-6 km.
 Covered by a layer of sediment, mostly <1 km
thick.
 The flattest areas on the planet.
D. The Mid-Ocean Ridge System
 The largest tectonic feature on the earth.
 More than 1500 km wide, 64,000 km
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(40,000 miles) long.
Rises 2-3 km (up to 2 mi) high above the
abyssal plain.
Has a central rift valley.
Composed of basalt rocks.
Faulted with strike-slip faults.
Shallow earthquakes occur along central rift.
E. Island Arcs
 A curving series of volcanic islands created
through the collision of oceanic plates.
Subduction at these plate boundaries makes
island arcs.
 Parallel deep-sea trenches.
 Oceanic islands are nearly all basaltic volcanoes.
F. Continental Shelf
 An underwater extension of the coastal
plain.
 Varies in width from almost zero up to the
1,500-km-wide (930-mi) Siberian shelf in the Arctic
Ocean. Average width is 78 km (48 mi).
 The Atlantic shelf is much wider because it is
a passive margin, while the Pacific is very narrow
because it is an active margin.
G. Deep Sea Trenches
 Deep-Sea Trenches parallel volcanic arcs.
 They are the deepest parts of the oceans, up
to 11 km (7 miles) below sea level.
 They are the sites of the subduction of
oceanic crust.