chapter 4 continental margins and basins. continental margins these are the areas of the edges of...
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Chapter 4
Continental Margins and Basins
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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
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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
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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
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Activity
• Draw, label, and color figure 4.8 on pg 93
•Draw, label, and color figure 4.10 on pg 94
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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
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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
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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
•
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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
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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
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39o N
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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
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• Cartography – the science of making maps– Dry land forms are
mapped using topography.
– Underwater landforms are maps using bathymetry.
Mapping the Oceans
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Alvin explored the Titanic (HOV)
The Trieste explored the Mariana’s Trench in 1960 (HOV)
Hercules ROV
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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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