The Ocean Floor

The Ocean Floor The World Ocean Imaging the Ocean Floor Continental Margins The Deep-Ocean Floor Oceanic Ridges

GEOL 131: The Ocean Floor The World Ocean

The World Ocean Earth’s surface is 71% ocean GEOL 131: The Ocean Floor The World Ocean Earth’s surface is 71% ocean Majority is in Southern Hemisphere Northern Hemisphere Southern Hemisphere

GEOL 131: The Ocean Floor: The World Ocean

Oceans vs. Continents Continents Oceans GEOL 131: The Ocean Floor: The World Ocean Oceans vs. Continents Continents Average elev.: about 2800 feet above sea level Highest point: about 30,000 feet a.s.l. Oceans Average depth: about 12,200 feet Deepest point: about 36,000 feet

Imaging the Ocean Floor GEOL 131: The Ocean Floor Imaging the Ocean Floor

Ocean Floor Mapping HMS Challenger British 1872-1876 GEOL 131: The Ocean Floor: Imaging the Ocean Floor Ocean Floor Mapping HMS Challenger British 1872-1876 All oceans except Arctic Used weighted ropes to find ocean depths

Ocean Floor Mapping HMS Challenger’s route British 1872-1876 GEOL 131: The Ocean Floor: Imaging the Ocean Floor Ocean Floor Mapping HMS Challenger’s route British 1872-1876 All oceans except Arctic Used weighted ropes to find ocean depths

Ocean Floor Mapping Sonar Single beam Multibeam GEOL 131: The Ocean Floor: Imaging the Ocean Floor Ocean Floor Mapping Sonar Single beam Multibeam

Ocean Floor Mapping Sonar Travel time of ping / 2 = depth GEOL 131: The Ocean Floor: Imaging the Ocean Floor Ocean Floor Mapping Sonar Travel time of ping / 2 = depth

Seismic Reflection Profiles GEOL 131: The Ocean Floor: Imaging the Ocean Floor Seismic Reflection Profiles Seismic waves penetrate mud, bounce off rock

Seismic Reflection Profiles GEOL 131: The Ocean Floor: Imaging the Ocean Floor Seismic Reflection Profiles

Ocean Floor Provinces Revealed by ocean floor imaging techniques GEOL 131: The Ocean Floor: Imaging the Ocean Floor Ocean Floor Provinces Revealed by ocean floor imaging techniques Continental margins Passive and active Deep-ocean floor Oceanic ridges

GEOL 131: The Ocean Floor: Imaging the Ocean Floor Ocean Floor Provinces

GEOL 131: The Ocean Floor Continental Margins

Continental Margin Types GEOL 131: The Ocean Floor: Continental Margins Continental Margin Types Passive Little geologic activity Gentle slope Flatter coastlines Active Frequent geologic activity Steeper slope More rugged coastlines

GEOL 131: The Ocean Floor: Continental Margins Passive Margins

GEOL 131: The Ocean Floor: Continental Margins Passive Margins

Passive Margin Formation GEOL 131: The Ocean Floor: Continental Margins Passive Margin Formation Crustal stretching & thinning Initial, narrow ocean basin forms Mature basin with passive margins

Passive Margins: Submarine Canyons GEOL 131: The Ocean Floor: Continental Margins Passive Margins: Submarine Canyons Undersea “landslides” move down continental slopes and cut into shelves to form submarine canyons.

Passive Margins: The Hudson submarine canyon GEOL 131: The Ocean Floor: Continental Margins Passive Margins: The Hudson submarine canyon Modern Hudson River mouth Hudson River mouth during last ice age

Active Margins (aka subduction zones) GEOL 131: The Ocean Floor: Continental Margins Active Margins (aka subduction zones)

Active Margins (aka subduction zones) GEOL 131: The Ocean Floor: Continental Margins Active Margins (aka subduction zones)

Trenches Deepest places in the oceans Subduction-related GEOL 131: The Ocean Floor: Continental Margins Trenches Florida Deepest places in the oceans Subduction-related Sediment traps Puerto Rico Trench

GEOL 131: The Ocean Floor The Deep-Ocean Basin

Key Deep-Ocean Basin Features GEOL 131: The Ocean Floor: The Deep-Ocean Basin Key Deep-Ocean Basin Features Abyssal plains Seamounts

Abyssal Plains Very flat Deep sediment GEOL 131: The Ocean Floor: The Deep-Ocean Basin Abyssal Plains Very flat Deep sediment

Abyssal Plains GEOL 131: The Ocean Floor: The Deep-Ocean Basin Abyssal plains are dark blue

Form islands if peaks are above sea level GEOL 131: The Ocean Floor: The Deep-Ocean Basin Seamounts Undersea volcanoes Form islands if peaks are above sea level Most are not

GEOL 131: The Ocean Floor Oceanic Ridges

Elevated, linear features GEOL 131: The Ocean Floor: Oceanic Ridges Oceanic Ridges Elevated, linear features

Also called “spreading centers” or “divergent plate boundaries” GEOL 131: The Ocean Floor: Oceanic Ridges Oceanic Ridges Also called “spreading centers” or “divergent plate boundaries” Two crustal plates are spreading apart New crust formed at center of ridge

Diagram of an oceanic ridge GEOL 131: The Ocean Floor: Oceanic Ridges Diagram of an oceanic ridge Central rift valley w/ volcanoes Plate motion Plate motion Fault blocks Rising molten rock from mantle

Oceanic ridge formation GEOL 131: The Ocean Floor: Oceanic Ridges Oceanic ridge formation

Earth’s Largest Topographic Feature GEOL 131: The Ocean Floor: Oceanic Ridges Earth’s Largest Topographic Feature Over 70,000 km long

Seafloor Sediments

Three type of ocean sediments Biogenous Formed in the ocean by organisms Terrigenous Washed or blown in from continents Hydrogenous Formed in the ocean by precipitation from seawater

Biogenous Calcareous ooze Plankton shells made of calcium carbonate

Biogenous Siliceous ooze Plankton shells made of silica (silicon + oxygen)

Terrigenous Anything derived from continental rocks Gravel, sand, silt, clay Delivered to oceans mainly by rivers and wind Dust plume blowing out of Sahara Desert about 1,000 miles in Atlantic Ocean.

Hydrogenous Chemical solids precipitated from seawater Sulfide metals around hydrothermal vents Manganese nodules in deep ocean Plume of sulfide metal particles spewing from hydrothermal vent on the ocean floor. Potato-size manganese nodules in south Pacific, depth 3 miles

Distribution of seafloor sediments

GEOL 131: The Ocean Floor End of Chapter