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) Continental Crust (Granitic) 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