Download Ocean Basins

Chapter 4
Continental Margins and Basins
Continental Margins
• These are the areas of the edges of the
continents that are under water
– Passive margins face edges of diverging plates and
have little earthquake/volcanic activity. Ex: East
Coast of USA
– Active margins face edges of converging plates
and have lots of activity. Ex: West Coast of USA
• 2 subdivisions: Continental Shelf and Slope
Continental Shelf
• Shallow extension of the continent
– Can be narrow, quickly becoming steep
– Or can be broad, gently sloping downward
• They look much like the continent from which they
extend: hills and depressions
• The sediment on the shelf is eroded dirt and debris
from the dry land above it
– Sediment is rich in minerals, oil and gas
Continental Slope
• The transition between the shelf and the
deep-ocean floor
– The shelf break marks the transition
– Very steep
• Continental rise is past the slope
– It is oceanic crust covered with sediment from
the land
Activity
• Draw, label, and color figure 4.8 on pg 93
•Draw, label, and color figure 4.10 on pg 94
Submarine Canyons
• These canyons cut into the continental shelf and
slope, ending in a deep-sea fan
• Sometimes they extend from the mouth of a river
that drains sediment and fast flowing water out to
sea
– Created by erosion
like canyons on land
• Sometimes they are
created by earthquakes
that cause an “avalanche”
of sediments
Deep-Ocean Basins
• The seafloor is a blanket
of sediment covering the
basalt rock
• Consists of oceanic ridge
systems and plains
• The plains are scattered
with islands, hills,
trenches, active and
extinct volcanoes, and
seafloor spreading
Oceanic Ridges
• A chain of mountains formed during seafloor
spreading
– Composed of “new” basaltic rock with no
sediment
– If they extend above the water, they are called
islands
•
Seamounts and Guyots
• Seamounts are volcanoes that are below
ocean surface
– From hot spots or spreading
centers
– Found alone or in groups
• Guyots are flat-topped seamounts that once
went above the ocean surface
– flattened by waves and erosion
Distance from North America (Km)
5,700
4,600
4,800
5,000
5,200
5,400
5,600
5,800
6000
0
150
300
450
600
750
900
1,050
1,200
1,350
Atlantic Ocean Depth (m)
0
39o N
Trenches and Island Arcs
• Trenches are deep pits in the ocean where the
converging plate is subducted
– Recall the cold ocean crust is sinking into the
upper mantle of the continental plate
– V-shaped due to spherical shape of Earth
• Parallel to the side of the trench, the molten
rock from the subducted plate is coming back
up through volcanoes called an island arc.
– Example is Caribbean islands
Mapping the Oceans
• Cartography – the
science of making
maps
– Dry land forms are
mapped using
topography.
– Underwater landforms
are maps using
bathymetry.
Alvin explored
the Titanic (HOV)
The Trieste explored the
Mariana’s Trench in
1960 (HOV)
Hercules ROV
SONAR
• Sound Navigation and Ranging provided a
rapid method of looking through water to
identify features in the water beneath a vessel
and on the sea floor.