creation, aging and recycling of the ocean floor how is the ocean floor made? why does the ocean...

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

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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)