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
Atla
ntic
Oce
an D
epth
(m)
Distance from North America (Km)
0
4,6004,8005,0005,2005,4005,6005,8006000
015
030
045
060
075
090
01,
050
1,20
01,
350
5,70
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
• Cartography – the science of making maps– Dry land forms are
mapped using topography.
– Underwater landforms are maps using bathymetry.
Mapping the Oceans
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.
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