Transcript Outer Core - Wikispaces

Oceanography
Unit 2
Earth’s Layers
Four distinct layers
 Inner Core (1,228 km radius)
– Hottest
– High density solid nickel and iron

Outer Core (2,260 km thick)
– Hot
– Molten nickel and iron

Mantle (2,890 km thick)
– Less dense than inner and outer cores
– Molten silicates

Crust (8-12 km thick)
– solid
Crust
Mantle
Outer Core
Inner Core
Page 55
Earth’s crust “floats”

Lithosphere – strong, rigid behavior
– Consists of crust and the upper mantle material
fused together

Asthenosphere – weak, ductile behavior
– Low velocity plastic layer (molten magma)
Earth’s Crust

Oceanic Crust (Basalt)
– Lots of silica and iron
– More dense than continental crust
• Always subducts under continental
– Not much more than 7 km thick generally

Continental Crust (Granitic)
– Lots of silica and aluminum
– A few km (edge of continents) to over 32
km (middle of continents)
12 Major Plates
Mountain Mover, Earth Shaker
Oceanic Ridges/Rises
Divergent oceanic plate boundary
 Undersea mountain ranges
 Rift Valley – where volcanism occurs
and new crust is created

– Mid-Atlantic Ridge – 2.2 inches/year
– East Pacific Rise – 12.6 inches/year
video
Deep Sea Trenches
Subduction Zones – Plate Convergence
 May be twice as deep (almost 12,000 m)
as the regular deep-sea floor (up to
6,000 m)
 Excess crust subducted and melted
 Earthquake activity

Hydrothermal
Vents
Seafloor outlet for
high-temperature
water and
associated mineral
deposits (a hot
spring)
 High interest area
of study

video
Brine Shrimp Life Cycle
Ocean Soundings
Our ability to accurately map the features of the
sea floor has been acquired only recently and
continues to improve with advancing
technology.
Early soundings included:
 Rocks tied to ropes
 Cannonballs and piano wire
Now:
 Echo soundings
– consistent speed of sound in seawater and
accurate time measurements
Continental Margin

Consists of shelf, shelf break, slope, and
rise
Passive vs. Active

Passive continental margins:
–
–
–
–

found around the rim of the Atlantic Ocean
are not plate boundaries
have little or no seismic or volcanic activity
form when a continent rifts apart creating a new
ocean basin between the fragments.
Active continental margins:
–
–
–
–
are found around the rim of the Pacific Ocean
are plate boundaries
are typically seismically and/or volcanically active
tend to be relatively narrow
Continental Margin
Continental Shelf
 very flat edges of the continental crust
covered by marine waters
– Narrow shelves associated with steep slopes
– Wider shelves associated with relatively flat
continental regions
Seafloor Features
Submarine Canyons
 Deep v-shape
 Cut across continental margins
 Some can be traced from river systems
Abyssal Plain
 Flat ocean basin floor
 Extends seaward from continental slope
and rise
Seafloor Features
Abyssal hills
 Less than 1000 m high
Seamounts
 Greater than 1000 m high
Guyots
 Flat-topped seamounts
Islands
 Seamounts that rise above the sea
surface
Coral Reefs
Often built on islands and seamounts
Fringing Reef
 Attached directly to the shore of an island
or continent
Barrier Reef
 Parallels land but is some distance
offshore with water between
Atoll
 Ring-shaped coral reef that encloses a
lagoon
