Ch. 23 The Ocean Floor Studying the ocean floor - PowerPoint Presentation

1. Ch. 23The Ocean Floor

2. Studying the ocean floorSubmersibles, satellites, and other technology allow scientists to study the structure and composition of the ocean floor.

3. a system that uses transmitted and reflected sound waves to measure distances to the ocean floor; SONAR.measure how long it takes for signal to be emitted and come backmulti-beam echo sounding measures area twice as wide as shipuse info to make seafloor mapsintensity of sound beams determine seafloor compositionrock & gravel reflect more strongly than mud1. Echo sounding

4. Echo sounding

5. Core sampling: hollow cylinder removes long cores of material from seafloorlayers are preserved1-1500m of sediment are gatheredcan analyze past climate, life, and ocean events2. Sediment Sampling

6. greater range & speed for mappingdoesn’t reach floor, bounces off surfaceOcean surface varies based on what’s belowhigher over mountains, lower over trenchesdetermines differences down to cm’smakes high-resolution seafloor image3. Satellite observations

7. Pacific and Western Atlantic OceansHIGH RESOLU-TIONSEAFLOOR IMAGE

8. In order to understand the continental margin, we must first understand the crust of the Earth.The continental margin is part of the crust.The CONTINENTAL MARGIN

9. the Earth has 4 main physical layers:LAYERS OF THE earthDepth from Surface (km)Temperature (K)State of MatterComposition*Crust0-65<1000, increases w/ depthSolidRock we live onSi, O, Al*Mantle66-28901500-3200 increases Solid w/ liquid propertiesFe, Si, MgOuter Core2891-51503700-5500 increasesLiquidFe & NiInner Core5151-6371approx. 6000solidFe & Ni

10. LAYERS OF THE earth

11. Continental Crustlighter, less dense rockMakes up all continents, but not necessarily all islandsOceanic Crustdarker, dense rockany ocean floor or ocean basintwo types of crust

12. all of the crust is divided into ‘pieces’ or plates(Called lithospheric plates or tectonic plates)the plates move around on the semi-solid mantlewhere the plates meet or connect are called plate boundariesat plate boundaries, the crust can be moving side by side, apart, or togetherdifferent topographic features are created, depending on the type of boundarytopography: the shape of the landTHE MOVING CRUST

13. World plate boundaries

14. The underwater portion of the continental crust.There are two types of continental margins.The CONTINENTAL MARGIN

15. continental margins that occur along plate boundaries plates are moving side by side or together when one plate sinks under another, a trench is formed when plates move past each other, a fault is formed continental rise is small or nonexistent rocky, short beach w/ cliffsrugged, coastal mountains on landEX: West coasts of North America and South America1. Active CONTINENTAL margins

16. continental margins that don’t occur along plate boundaries broad continental shelf long, sandy beach no trenches, mountains, or faultsEX: East coast of North America2. Passive continental margins

17. continental shelf: part of the continent that extends from the shoreline to the continental slopeflat, lengths vary depending on locationcontinental slope: begins at the shelf edge where depth decreases rapidly to the rise.20km long; descends 3.6kmsediment builds up temporarily, then fallscontinental rise: descends gradually from the slope to the ocean floorconsidered part of ocean basin very long & gradualParts of the continental margin

18. an undersea gully that cuts across the continental shelf and slope rivers erode the continental shelf and deposit sediment on continental slope gravity and powerful turbidity currents carry sediment down to the continental riseVery powerful agents of erosion coarse particles settle first, then fine such as claySubmarine canyon

19. Abyssal Plain – flattest of all Earth’s surfaces, composed of sediment from continentsOccur in all oceansMore in Atlantic Ocean where there are fewer trenchesAbyssal hills – small hills, occur in groups next to oceanic ridge systemsOcean Basin

20. Deep-sea trenches – long, narrow, steep-sided troughs that run parallel to continental margins or to volcanic island chains called island arcsExist at subduction zonesCommon sites of earthquakes and volcanic activityDeep-sea trenches

21. A marginal trench forms if one plate is oceanic and the other is continental. If the oceanic plate descends below the continental, a line of volcanoes stands on the overriding continental plate, forming mountain chainsIf both plates are oceanic, an arc of volcanic islands forms on the overriding plateUsually in western PacificDeep-sea trenches

22. Deep-sea trenches

23. Deep ocean vent – geyser that erupts underwater, mixing hot and cold water and bringing up minerals from beneath the surfaceMid-ocean ridges- are undersea mountain ranges, form at divergent plate boundaries where 2 plates are moving apart and magma is risingVents and ridges

24. Seamounts are cone-shaped mountain peaks that rise high above the ocean floorOccur in all oceans, but more abundant in Pacific OceanVolcanic in origin (ex. Hawaiian islands)Guyots are flat-topped seamountsWaves removed their tops when they rose above sea levelSea mounts & guyots

25. Corals are tiny sea animals that live in shallow, warm waters. Reefs form when new corals grow on top of the dead ones.A coral atoll is a ring-shaped coral island. It forms when a coral reef develops around a volcanic island. The mountain sinks below the water, leaving a circular reef with a lagoon where the mountain was.Coral &coral Atolls

26. Sediment reaches the ocean floor in several ways: turbidity currents, fall from above, settle from glaciers, remains of microscopic shellsTerrigenous sediments – come from continental rocks an minerals broken down from weathering an erosionwash into rivers and out to seamay come from glaciers breaking and dropping into seaOcean Floor Sediments

27. Biogenous sediments come from living sources; they are oozes made mostly of shells and skeletons from tiny marine animalsCalcareous ooze=calcium carbonateMost common from shells and skeletonsDissolve as they sink below 4500 metersSiliceous ooze=silicon dioxideMore common around Equator and AntarticaOcean Floor Sediments

28. Hydrogenous sediments form when chemical reactions cause minerals to crystallized from seawater.Manganese nodules are most common – has manganese, iron oxide, nickel, cobalt, copper…They form on the sea floor from sediment that falls on them and mixes with the sea water, a few mm every million yearsImportant to humans but hard to getOcean Floor Sediments

29. By studying the layers of sediment in the ocean, scientists can determine:the extent of former polar ice sheetsthe history of water temperatures on sea floorthe pasts behaviors of prevailing windspattern of changes in Earth’s climateThe sediments, unique organisms, magnetic records, industrial resources on the ocean floor represent a past look at Earth’s hydrosphere, biosphere, and geosphere.Importance of sediments

30. Ocean floor