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The sea floor. seafloor water covers 70% of Earth’s surface.

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Presentation on theme: "The sea floor. seafloor water covers 70% of Earth’s surface."— Presentation transcript:

1 the sea floor

2 seafloor water covers 70% of Earth’s surface

3 seafloor deep seafloor largely unknown prior to 1950’s seafloor map from Dana (1894)

4 seafloor oceans originated mostly from volcanic de-gassing of water vapor from Earth’s interior additional small amount may have come from late comet impacts after the Earth reached close to its current mass

5 studying the seafloor direct methods rock dredges sea floor drilling submersibles indirect methods sonar seismic reflection profiling

6 rock dredges direct methods

7 sediment corer direct methods

8 sea floor sediment core direct methods

9 JOIDES Resolution (1990’s-being overhauled) DSDP (Deep Sea Drilling Project); ODP (Ocean Drilling Project) …IODP (Integrated Ocean Drilling Project)…

10 Chikyu Japanese drill ship

11 submersibles manned or unmanned direct methods

12 sonar (sound navigation and ranging) sound sent from ship, bounced off sea floor, and recorded at ship indirect methods distance to seafloor is calculated from speed of sound in water multiplied by time to get return signal divided by two (wave goes down and up)

13 known for a long time that sound travels through water 1822 attempt to determine speed of sound in water indirect methods

14 seismic reflection indirect methods penetration of sediments by sound waves hydrophones record signals echo sounding, swath bathymetry, sidescan

15 sea floor profile indirect methods

16 South Pacific sea floor indirect methods

17 sea floor was critical in development of plate tectonics yellow lines are plate boundaries seafloor, continents, and plate boundaries

18 general profile through ocean features of the seafloor from left to right shelf, slope, abyssal plain, mid-oceanic ridge seamounts, trench, slope shelf passive continental margin (no plate boundary) active continental margin (plate boundary) mid-oceanic ridge (plate boundary)

19 slope angle is only 4-5° continental shelf and slope topographic profile has 25x vertical exaggeration (vertical and horizontal scales are not the same) broad, shallow shelf (100-200 m water depth) steeper slope dives to abyssal plain

20 passive margin NO plate boundary at edge of continent shelf and slope continental rise (less steep than slope) abyssal plain (smooth, deep seafloor)

21 submarine canyons and abyssal fans start on shelf and end at base of slope allow for transport of sediment from shelf to sea floor

22 sand falls offshore Baja, California

23 submarine canyons and abyssal fans (California) “turbidity currents” flow down canyons and deposit on fans


25 offshore southern California


27 landslide triggered by earthquake submarine canyons cable breaks in different locations at different times as landslide arrives

28 continental rises and abyssal plains continental rise: gently sloping wedge of sediment of sediment at base of slope abyssal plain: flattest region on Earth; form where turbidity currents bury features sediments deposited by turbidity currents and contour currents move along elevation contours

29 active margin plate boundary at edge of continent shelf and slope oceanic trench (deepest features in ocean) volcanoes (on-land) Wadati-Benioff zone --dipping zone of earthquakes that begin at trench and extend landward (red stars)

30 active margins (trenches-plates converge)

31 mid-ocean ridge (plate boundary-plates diverge)

32 NORTH AMERICAAFRICA sea floor spreading (divergence) axial valley from: 80,000 km long; 1,500-2,500 km wide mid-ocean ridge elevations of 2,000-3,000 m above sea floor rift valley ~1,000 m deep at crest of ridge

33 basalt flows and volcanism mid-ocean ridge high heat flow and small, shallow earthquakes hot springs supporting biological communities

34 black smoker (first ever seen) 1979


36 life at oceanic ridge tube worms giant clams spider crab

37 explore using submersibles ALVIN was first one; 3 passenger

38 both from: exposed on-land in Iceland mid-ocean ridge

39 transform faults mid-ocean ridge fracture zones continuation of transform fault beyond ridge --no eq’s-- offset of mid-ocean ridge between adjacent ridges --earthquakes occur along them (red stars)--

40 transform fault--fracture zone animation green are ridge segments; red is transform fault

41 from:

42 other sea floor features seamount conical mountain that rises > 1,000 m above sea floor; basaltic volcanoes; chains of seamounts occur (aseismic ridges) (Emperor seamounts) guyot flat-topped seamount; erosion from waves; reefs common around them

43 seamount chains and ages of seamounts in one (hot spot track -- more later) Emperor seamounts

44 pelagic: accumulate by settling through water column …clays from wind; skeletons of microsopic organisms… sea floor spreading leads to greater thickness of pelagic sediments away from ridge crest (no sediment at mid-ocean ridge) sea floor sediments terrigenous: derived from land and brought to sea floor …sands/silts that make up continental rise…

45 composition of the oceanic crust seismic surveys suggest ~ 7 km thick with 3 layers 1) marine sediments (sampled) 2) pillow basalts (sampled) 3) gabbros (not sampled) (intrusive equivalent to basalt)

46 pillow basalts

47 resources of the ocean offshore drilling

48 mining the ocean floor? manganese nodules

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