Oceans & divergent boundariesQuestions to contemplateFeatures of the OceansProfile of the Atlantic Ocean seafloorPowerPoint PresentationOcean features are a result of tectonicsPassive versus Active continental marginsPassive and Active marginsSlide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Deep trenchesSlide 35Slide 36Slide 373. Volcanic peaksSlide 39Slide 40Slide 41Slide 42Lecture 21Seamounts and guyots often related to Hot SpotsSlide 45Hawaiian Hot spotSlide 47Slide 484. Oceanic PlateausSlide 50Oceanic Plateaus as Triggers for Continental Break-upSlide 52Slide 53Slide 54Slide 55Slide 565. Mid Ocean ridgesSlide 58Slide 59Slide 60Slide 61Slide 62Slide 63Slide 64Slide 65Slide 66Slide 67Slide 68Slide 69Slide 70Slide 71Slide 72Slide 73Slide 74Slide 75Slide 76Slide 77Slide 78Corals host organisms that need lightSlide 80Carbonate Compensation Depth – High pressure in deep sea causes CaCO3 to dissolveRe-capOceans & divergent Oceans & divergent boundariesboundariesLecture 20Lecture 20Questions to contemplate•What are the parts and processes of an active margin? A passive margin?•Please describe the various parts of the oceans from continental shelf to abyssal plains•How does oceanic crust form?•How is oceanic crust dynamic?Features of the OceansContinental shelfContinental slopeContinental riseAbyssal plainsMid ocean ridgesTrenchesRidgesSeamountsGuyotsAtollsReefsProfile of the Atlantic Ocean seafloorOcean features are a result of tectonicsPassive versus Active continental marginsPassive and Active margins•Passive margins – Trailing edge of the continent; no present tectonic boundary–Ex. US East coast–Barrier Islands–Estuaries–Gently dipping continental slopePassive and Active margins•Active margins–Presently active tectonic boundary–Ex. US West Coast–Steeply dipping continental shelf–Sharp wave-cut features•Sea arches, sea stack, sea cliffs–More erosion than passive marginsThe three primary features of the ocean floor along a passive continental margin are: 1. Continental shelf 2. Continental slope 3. Continental riseA. Passive Continental MarginsThe continental shelf is a gently sloping submerged surface extending from the shoreline toward the deep-ocean basinContinental ShelfThe shelf is composed of continental crust (up to many kilometers thick), and is actually a flooded extension of the continentsContinental Shelf is the Continent MarginAt the seaward edge, the average continental shelf is only 130 meters (425 feet) deepAlthough, continental shelves only represent 7.5% of the total ocean floor area, they have significant economic value (oil, natural gas, fishing grounds, sand, gravel)Continental ShelfWhat are these?What are these?Like valleys on dry land, submarine canyons or valleys cut into the continental shelfSubmarine CanyonsAlong a passive coast, the continental slope gradually merges into the continental riseThe slope of the continental rise averages about 0.3 degrees and it can extend for hundreds of kilometers out into the deep-ocean basinContinental slope & Continental riseTurbidity currents are underwater mass wasting deposits composed of mud, sand and waterThey create submarine deep sea fans of debris at the foot of the continental slope and out onto the continental riseTurbidity CurrentsTurbidity CurrentsTurbidity currents can flow for great distances beyond the continental slopeAbyssal Plains – deep, sediment covered areas adjacent to Continental rises of Passive Margin coastsIn many active margins, continental slope descends abruptly into a deep-ocean trenchEx) western South AmericaThe deep trench can be as little as 50 kilometers (30 miles) offshoreB. Active Continental MarginsTrenches are where active subduction occursSediments washed down from the continents and sediments scraped off of the subducting plate can accumulate by the trench in a chaotic mixture called an accretionary wedgeActive Continental MarginsBetween the continental margins and the mid-oceanic ridges lies the deep-ocean basinsThese basins cover almost 30% of the Earth’s surface, an area comparable to the percentage of dry, continental landDeep-Ocean BasinsWe know more about the Moon and Mars than we do about the deep-ocean basinsDeep-Ocean BasinsWe do know that this region contains:1. Deep-ocean trenches: Extremely deep, linear canyons 2. Abyssal plains: Remarkably flat areas 3. Seamounts and guyots: Tall underwater volcanic peaks 4. Oceanic plateaus: Large flood basalt provinces 5. Mid ocean Ridges: Long spreading centers where ocean crust is madeDeep-Ocean BasinsDeep-ocean trenches typically extend 3 to 4 km (2 to 2.5 mi) below the level of the surrounding oceanic floor They are the deepest surface features on EarthFive trenches in the Pacific Ocean exceed 10,000 meters (33,000 feet) in depthAnother four trenches exceed 8,000 meters (26,000 feet) in depth1. Deep-Ocean TrenchesDeep trenchesTrench Ocean Average DepthMarianas Pacific 10,911 metersTonga Pacific 10,882Kuril Pacific 10,542Philippines Pacific 10,540Kermadec Pacific 10,047Bonin Pacific 9,780 Japan Pacific 9,000Puerto Rico Atlantic 8,605 Peru-Chile Pacific 8,065 Deep-Ocean TrenchesThe flatness of these plains is the result of the accumulation of a blanket of sediments, up to 5 kilometers thick, which overlies the basaltic rocks of the oceanic crust 2. Abyssal PlainsThis seismic profile shows how the sediments almost completely cover the otherwise rugged ocean floor3. Volcanic peaks•Volcanic Islands–Rise above water surface•Seamounts–Submerged volcanic peaks•Guyots–Flat topped seamounts (cut by wave erosion)Dotting the ocean floor are submarine volcanoes called seamountsThey can rise above the ocean floor from hundreds of meters to even a couple thousand metersThey are found in all oceans, but by far the greatest number occur in the Pacific OceanSeamounts and GuyotsThere are more than a million seamounts in the oceans (only a couple thousand are plotted on the map below)Seamounts and GuyotsThey tend to form in long linear chains, each volcano being created as the tectonic plate moves over a hot spot (like the Hawaiian chain) Or away from a Mid Ocean RidgeSeamounts and GuyotsLecture 21•Ocean basins and divergent zones, continued.Seamounts and guyots often related to Hot SpotsHawaiian Hot spotHot spots around the