creation, aging and recycling of the ocean floor how is the ocean floor made? why does the ocean...
TRANSCRIPT
Creation, Aging and Recycling of the Ocean
Floor
Creation, Aging and Recycling of the Ocean
FloorHow is the ocean floor made?
Why does the ocean floor get deeper with age?
How are volcanic arcs made and why are they so dangerous?
How is the ocean floor made?Why does the ocean floor get deeper with
age?How are volcanic arcs made and why are
they so dangerous?
Formation of Ocean Formation of Ocean LithosphereLithosphere
Formation of Ocean Lithosphere
Mid-ocean ridges-- global circuit of plate divergence-- youngest ocean floor-- shallowest ocean floorArchitecture of oceanic plates-- seismic profiling-- ocean drilling-- fossil slivers of ocean floor
Seismic Profiling (sound energy)
Seismic Profiling (sound energy)
Ocean DrillingOcean Drilling
International program(20 nations; began 1968)
2-month cruisesDeepest hole: 2 km
But, new vessel will drillto >6km!
International program(20 nations; began 1968)
2-month cruisesDeepest hole: 2 km
But, new vessel will drillto >6km!
Fast vs. Slow SpreadingFast vs. Slow Spreading
Fast Spreading Ridge(10-20 cm/yr)
Slow Spreading Ridge(1-5 cm/yr)
Mid-Ocean Ridges
Uniform process of mantle melting, lava freezing- magma chambers- effects of spreading rate- segmentation
Ocean Crust LayeringOcean Crust Layering
Su
perf
ast
Sp
rea
d C
rust
Mis
sio
n to
Hol
e 1
256
DS
upe
rfa
st S
pre
ad
Cru
st M
issi
on
to H
ole
12
56D
Su
perf
ast
Sp
rea
d C
rust
Mis
sio
n to
Hol
e 1
256
DS
upe
rfa
st S
pre
ad
Cru
st M
issi
on
to H
ole
12
56D
Mineralized Volcanic Breccia
(1027-1029 mbsf)o
o
10 cm
Sea floor deepens with distance from the spreading ridges -- why?Sea floor deepens with distance from the spreading ridges -- why?
Plate Aging involves heat loss through Conductive Cooling
Relation: Depth increases with the square root of age
A New View on Plate CoolingAdam & Vidal, Science, April 2, 2010
And, heat loss through Hydrothermal Circulation
Hydrothermal CirculationHydrothermal Circulation
Hydrothermal Circulation
• Natural consequence of porous, hot rock and seawater• Chemical exchange• Fluid venting -- black smokers• Chemosynthetic ecosystems• Crack sealing and sedimentation
Hydrothermal Vent SitesHydrothermal Vent Sites
Hydrothermal Vents VideoHydrothermal Vents Video
The ocean floor ages and accumulates sediments
The ocean floor ages and accumulates sediments
Plate Aging and Recycling
Slab sinking -- denser than asthenosphere
Plate Subduction and MeltingPlate Subduction and Melting
Pacific NWPacific NW
Mt St HelensMt St Helens
Water, from slab, promotes mantle melting and leads to explosive danger of arc volcanoes
Krakatoa (1883)Tambora (1815)
Toba (71,000 B.C.)
-3000 times as big as Mt St Helens-- Sulfuric acid and dust blocked sunlight, reducing temperatures 5°C for several years
- May have reduced human population to <5000!
Mt HoodMt Hood
Broken TopBroken Top
Three SistersThree Sisters
Crater Lake (Mt. Mazama)Crater Lake (Mt. Mazama)
Volcanic ash (tephra)Volcanic ash (tephra)
