Today’s Tunes ❥ Fathoms Below / Under the Sea ❥ From soundtrack of Disney’s The Little Mermaid Continental shelf Submarine canyons (cut into the c. slope) Abyssal plain Continental rise Continental slope Seafloor Features: Continental Margins Abyssal plain Seamounts Abyssal Hills (linear hills) Seafloor spreading center (e.g., East Pacific RISE or Mid-Atlantic RIDGE) Deep Ocean Seafloor Features: Deep Ocean ❥ Plate Tectonic Boundaries Ridges or Rises Trenches Transform Faults, Fracture Zones The Shifting Crust Continental Drift ❥ Alfred Wegener -1912 – large “supercontinent” (Pangea) existed and then split into pieces – fossil & glacial deposit evidence ❥ Wegener not able to provide MECHANISM for his theory ❥ Major mechanism later found in the OCEANS Seafloor Spreading & Plate Tectonics ❥ Harry Hess - 1960s – new ocean basins form from volcanism – ocean floor forms IN BETWEEN pieces that have split – SEAFLOOR SPREADING Seafloor Spreading & Plate Tectonics ❥ Theoretical breakthrough – PLATE TECTONICS – surface of earth composed of “plates” (LITHOSPHERE) that move on a “conveyor belt” (ASTHENOSPHERE) [...]... crust is thin and dense – dives “CRUNCH” - collision of continental plates – India into Tibet and China – continental crust is thick and light Sliding By j Transform faults – plates neither created nor destroyed j j Transform faults are active Fracture zones are inactive extensions of transforms – “fossil transforms” Young & Old j j j j j j Oldest seafloor - 200 million years Oldest land - billions of... spreading, is the earth expanding? Why is seafloor so young relative to continents? SUBDUCTION “law of conservation of ocean floor” Convergent j Convergent - subduction – trenches – Tonga Trench, Cascadia Subduction Zone Divergent Plate Boundaries j Divergent - seafloor spreading – mid-ocean ridges or rises – Mid-Atlantic RIDGE, East Pacific RISE Translational j Translational - strike-slip faulting – transform... floor data to solidify ideas and convince scientific community! The oceans rule! One Mechanism j j j seafloor-spreading lithosphere asthenosphere Another Mechanism j j j subduction world’s most explosive volcanos are formed over subduction zones Oregon’s Cascades Mtns over Cascadia Subduction Zone – Juan de Fuca plate under N American plate “Munch and Crunch” j j “MUNCH” - subduction of oceanic plate... field a mystery currents in liquid core one hypothesis SF Spreading Proof - 2 j j j j j Earth’s magnetic field flips back & forth magma freezes magnetic minerals minerals lines themselves up w/ prevailing field of earth anomaly in field is the key - normal (positive) or reversed (negative) Vine and Matthews noted this in the ‘60s and flagged this as PROOF for seafloor spreading Grocery bar code Calibrated... Divergent - seafloor spreading – mid-ocean ridges or rises – Mid-Atlantic RIDGE, East Pacific RISE Translational j Translational - strike-slip faulting – transform faults (active) - San Andreas Fault – fracture zones (inactive) - Mendocino FZ Plate Boundaries j j j j j j How do we know where these boundaries are? bathymetry earthquakes deepest earthquakes at CONVERGENT boundaries (subduction zones/trenches) . plate “Munch and Crunch” ❥ “MUNCH” - subduction of oceanic plate under continent or ocean – oceanic crust is thin and dense – dives ❥ “CRUNCH” - collision of continental plates – India into Tibet and. took ocean floor data to solidify ideas and convince scientific community! ❥ The oceans rule!