Chapter 20Chapter 20Ocean BasinsOcean Basins

Section 2Section 2

Features on the Ocean FloorFeatures on the Ocean Floor

Notes 20-2Notes 20-2

Ocean FloorOcean Floor

Continental MarginsContinental Margins Shallower parts of the ocean floorShallower parts of the ocean floor Made of continental crust and thick sediment Made of continental crust and thick sediment

layerlayer Deep Ocean BasinDeep Ocean Basin

Made of oceanic crust and thin sediment layerMade of oceanic crust and thin sediment layer

Monterey Bay, San Francisco, CAMonterey Bay, San Francisco, CA

Continental MarginsContinental Margins

Often the boundary between continent and Often the boundary between continent and ocean floor is found offshore beneath ocean floor is found offshore beneath ocean and thick sedimentsocean and thick sediments

Continental ShelfContinental Shelf:: Slopes gentlySlopes gently Covered by shallow water – only about 60 mCovered by shallow water – only about 60 m Part of continental marginPart of continental margin Average = 70 km wideAverage = 70 km wide

• Widest is from Siberia to Alaska in the Arctic Widest is from Siberia to Alaska in the Arctic OceanOcean

Continental MarginsContinental Margins

United States:United States: East coast = 170 km on averageEast coast = 170 km on average West coast = about 40 km on averageWest coast = about 40 km on average

Affected by ocean levelsAffected by ocean levels Lower sea level = more erosion and Lower sea level = more erosion and

weatheringweathering Higher sea level = places for deposits of Higher sea level = places for deposits of

sedimentssediments

Continental MarginsContinental Margins

Continental SlopeContinental Slope:: Steep side to the continental shelfSteep side to the continental shelf Boundary between continental crust and Boundary between continental crust and

oceanic crust is at the base of the slopeoceanic crust is at the base of the slope Submarine canyonsSubmarine canyons::

• Deep valleys cut into the continental shelf and Deep valleys cut into the continental shelf and slopeslope

• Can be associated with river mouths or turbidity Can be associated with river mouths or turbidity currentscurrents

• Turbidity CurrentsTurbidity Currents: dense currents that carry large : dense currents that carry large amounts of sediments down the slopeamounts of sediments down the slope

Turbidity CurrentsTurbidity Currents

Form when landslides of material run Form when landslides of material run down a slopedown a slope

Can be caused by earthquakes or by Can be caused by earthquakes or by excessive sediment loadsexcessive sediment loads

When the sediments come to a stop, at When the sediments come to a stop, at the bottom of the slope, will cause a the bottom of the slope, will cause a continental risecontinental rise

Deep Ocean BasinDeep Ocean Basin In the deep ocean, there are mountains, In the deep ocean, there are mountains,

plains, trenches and volcanoes.plains, trenches and volcanoes. Mountains are higher and plains flatter in the Mountains are higher and plains flatter in the

oceanocean Trenches: Trenches:

Deepest land features on the earthDeepest land features on the earth Long, narrowLong, narrow Mariana Trench is deepest place in the worldMariana Trench is deepest place in the world

• Over 11,000 m deep (11 km)Over 11,000 m deep (11 km)• Found near the island GuamFound near the island Guam• Most are found along the Pacific Ring of FireMost are found along the Pacific Ring of Fire

Mariana TrenchMariana Trench

Deep Ocean BasinDeep Ocean Basin

Abyssal Plain:Abyssal Plain: Extremely flat area – flattest on the earthExtremely flat area – flattest on the earth Usually over 4 km below the ocean surfaceUsually over 4 km below the ocean surface Cover over half the ocean basinCover over half the ocean basin Sediments fall to the abyssal plain from the Sediments fall to the abyssal plain from the

continental marginscontinental margins• Atlantic Ocean has thick sedimentsAtlantic Ocean has thick sediments• Pacific Ocean doesn’tPacific Ocean doesn’t• Trenches catch most of the sediments and hold Trenches catch most of the sediments and hold

themthem

Deep Ocean BasinDeep Ocean Basin

Mid-Ocean Ridges:Mid-Ocean Ridges: Continuous series of mountain ranges that Continuous series of mountain ranges that

run along the floors of all the oceansrun along the floors of all the oceans Most are under the waterMost are under the water

• Iceland is one exceptionIceland is one exception Form when plates move away from each Form when plates move away from each

otherother• Causes a rift in the middle of the mountain rangeCauses a rift in the middle of the mountain range• Different parts break at different ratesDifferent parts break at different rates• Creates fracture zones – series of faultsCreates fracture zones – series of faults

Deep Ocean BasinDeep Ocean Basin

Seamounts:Seamounts: Submerged volcanic mountainsSubmerged volcanic mountains At least 1,000 m highAt least 1,000 m high

• Anything less is called an abyssal hillAnything less is called an abyssal hill Generally associated with hotspotsGenerally associated with hotspots

• Hawaii and Canary IslandsHawaii and Canary Islands Erosion occurs and seamounts sinkErosion occurs and seamounts sink Flat-topped, submerged seamounts – guyots Flat-topped, submerged seamounts – guyots

(GEE-oze) or tablemounts(GEE-oze) or tablemounts

Hawaiian Chain Seamounts

Emperor Chain Seamounts

Hawaiian Seamounts/Hot SpotsHawaiian Seamounts/Hot Spots

LinksLinks

SeamountsSeamounts http://www.coast-nopp.org/visualization_moduhttp://www.coast-nopp.org/visualization_modu

les/physical_chemical/basin_coastal_morpholles/physical_chemical/basin_coastal_morphology/principal_features/deep_ocean/seamountogy/principal_features/deep_ocean/seamounts/seamounts.htmls/seamounts.html

General InfoGeneral Info http://oceanexplorer.noaa.gov/http://oceanexplorer.noaa.gov/ http://http://www.noaa.govwww.noaa.gov//

HomeworkHomework

Sec. Rev.Sec. Rev.

p. 398p. 398

1-31-3