Creation, Aging and Recycling of the Ocean Floor 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? 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 Lithosphere

Mid-ocean ridges -- global circuit of plate divergence -- youngest ocean floor -- shallowest ocean floor Architecture of oceanic plates -- seismic profiling -- ocean drilling -- fossil slivers of ocean floor

Seismic Profiling (sound energy)

Ocean Drilling FInternational program (20 nations; began 1968) F2-month cruises FDeepest hole: 2 km But, new vessel will drill to >6km! FInternational program (20 nations; began 1968) F2-month cruises FDeepest hole: 2 km But, new vessel will drill to >6km!

Fast 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 Layering

Superfast Spread Crust Mission to Hole 1256D

Mineralized Volcanic Breccia ( mbsf) o o 10 cm

Signs of the Apocalypse for April, 2006 Apocalypse Rating: (5 out of 7) Drilling Our Way to Satan Meddlesome scientists claimed to be pursuing knowledge rather than the chthonian layer of the Unlord when they drilled nearly one and a half kilometers beneath the ocean floor. What they found down there was a "fossilized magma chamber" instead of the Beast they were secretly seeking. I'm not sure how a rock can become fossilized, but what I am sure of is that drilling deeper than oil is dangerous. I would have told people not to even drill as deep as oil if at all possible, but I wasn't around when they first started doing that. Whether or not deep oil wells have unleashed Satan on our world is open to debate by the wisest scholars of the Weekly World News, but this deep drilling for no good reason has got to stop. We can't just rove around all willy-nilly and drop a drill miles underground wherever we please. Even if the devil is deeper than our drills could ever reach there's got to be something bad down there like Morloks or CHUDs or something. Having those cats out and about is not going to slow down our careening rollercoaster ride towards the Final Battle…….. Superfast Spread Crust Mission to Hole 1256D

Thanks to Captains, Crews, and Happy Science Parties of ODP Leg 206 and IODP Expeditions 309 & th December, 2005, Hole 1256D, Gabbro!

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 Cooling Adam & Vidal, Science, April 2, 2010

And, heat loss through Hydrothermal 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 Sites

Hydrothermal Vents Video

The ocean floor ages and accumulates sediments

Plate Aging and Recycling Slab sinking -- denser than asthenosphere

Plate Subduction and Melting

Plate Subduction FVolcanic Arcs FElement recycling FDistillation of the mantle FGrowth of continents FVolcanic Arcs FElement recycling FDistillation of the mantle FGrowth of continents

Pacific NW

Mt 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.) 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 Hood

Broken Top

Three Sisters

Crater Lake (Mt. Mazama)

Volcanic ash (tephra)