L5 | SEAFLOOR SPREADING

• SEAFLOOR SPREADING

  • called this recycling process as seafloor spreading, wherein the mid-oceanic ridges are formed, spread sideways to form seafloor, and disappear into the ocean trenches.
• SEAFLOOR SPREADING

  • The process on how the convection currents in the interior of the Earth made the seafloor spreading was explained by HARRY HESS, an American geophysicist in 1960.
  • also mentioned that these currents ensure that the materials formed in the lithosphere are recycled into the mantle.
• • oldest seafloor is relatively younger (about 170 million years old) than the oldest rocks (about 3 billion years old) of land. 
  •  the nearer the ocean floor to the ridge, the younger it is compared to ones farther from the ridge.
• OCEAN BASIN

  • regions that are below sea level. 
  • About 70% of these areas hold the planet's water. 
  • can be identified as active or inactive. 
  • If active, there are a lot of new structures being created and shaped, or they can be inactive, where their surface is slow to change and does little more than collect sediment.
• EXAMPLES OF OCEAN BASIN:

  • PACIFIC OCEAN
  • ATLANTIC OCEAN
  • INDIAN OCEAN
  • ARCTIC OCEAN
• BATHYMETRY

  • measurements of ocean depths and the charting of the shape or topography of the ocean floor.
• BATHYMETRY

  1. SOUNDING LINE
  2. ECHO SOUNDING
  3. SATELLITE ALTIMETRY
• SOUNDING LINE

  • weighted rope lowered overboard until it touched the ocean bottom
  • old method 
  • time-consuming & inaccurate.
• ECHO SOUNDING

  • a type of SONAR that measures depth by emitting a burst of high-frequency sound and listening for the echo from the seafloor.
  • Sound is emitted from the source on the ship and the returning echo is detected by a receiver on the ship. 
  • Deeper water means a longer time for the echo to return to the receiver.
• SATELLITE ALTIMETRY

  • profiles the shape of the sea surface by measuring the travel time of a radar pulse from the satellite to the ocean surface and back to the satellite receiver. 
  • The shape of the sea surface approximates the shape of the seafloor.
• OCEAN BASIN

  • COMPOSITION: gabbro and basalt (dark-colored igneous rocks)
  • GABBRO
  • forms deeper in the crust
  • BASALT
  • forms from magma on the ocean floor
• SUBMARINE CANYONS

  • Submarine valleys or underwater canyons found near continental shelves
• ISLAND ARC

  • Curved chain of volcanic islands found near subduction zones
• MID - OCEANIC RIDGE

  • The underwater mountain range that forms where tectonic plates are pulling apart.
  • has a central rift valley and rugged topography on its flanks.
  • submarine mountain chain that winds for more than 65,000 km around the globe. 
• OCEAN TRENCHES

  • Long, narrow depressions, deepest parts of the ocean
• ABYSSAL HILL

  • Small hills on the deep ocean floor
  • elongate hills, typically 50-300m high, common on the slopes of the mid-oceanic ridge.
• ABYSSAL PLAIN

  • extremely flat sediment covered stretches of the ocean floor, interrupted by occasional volcanoes, most extinct, called seamounts.
• VOLCANIC ISLANDS

  • those that rise above the ocean surface
• GUYOT

  • Flat-topped volcanic mountains due to erosion
• CONTINENTAL FEATURES:

  • continental rise
  • continental shelf
  • continental slope
• CONTINENTAL RISE

  • Gently sloping area at the base of the continental slope
  • A large, underwater depression in the Earth's crust.
• CONTINENTAL SHELF

  • Shallow, gently sloping part of the continent
• CONTINENTAL SLOPE

  • broad, gently sloping area of the seabed next to a continent.
• CONTINENTAL FEATURES:

  A) Continental Shelf

  B) Continental Slope

  C) Continental Rise

  
• CONTINENTAL MARGIN

  • submerged outer edge of the continent 
  • continental crust transitions into oceanic crust.
• 2 TYPES OF CONTINENTAL MARGIN:

  • PASSIVE OR ATLANTIC TYPE
  • ACTIVE OR PACIFIC TYPE
• PASSIVE OR ATLANTIC TYPE

  • wide, gently sloping continental shelf (50-200m depth), a steeper continental slope (3000-4000m depth), and a flatter continental rise. 
  • also known as aseismic or passive margins because they have relatively little earthquake
• ACTIVE OR PACIFIC TYPE

  • narrow shelf and slope that descends into a trench or trough. 
  • Also known as seismic or active margins because they are seismically very active.
• STRUCTURES OF OCEAN BASIN

  1. Mid oceanic ridges
  2. Abyssal plain
  3. Abyssal Hills
  4. seamounts
  5. guyot
  6. continental rise
  7. continental shelf
  8. continental slope
  9. continental margin
  10. volcanic islands
• TYPES OF PLATE BOUNDARIES

  1. DIVERGENT BOUNDARY
  2. CONVERGENT BOUNDARY
  3. TRANSFORM BOUNDARY
• DIVERGENT BOUNDARY

  1. oceanic - oceanic
  2. continental - continental
• OCEANIC-OCEANIC (DIVERGENT)

  • Plates moving away from each other
  • Forms elevated ridge with rift valley at the center; submarine volcanism and shallow earthquakes
  • Mid-Atlantic ridge
  • East pacific rise 
• CONTINENTAL-CONTINENTAL (DIVERGENT)

  • Plates moving away from each other
  • Broad elevated region with major rift valley, abundant volcanism and shallow earthquakes
  • East African Rift valley
  • Red Sea
• CONVERGENT BOUNDARY

  1. OCEANIC - CONTINENTAL
  2. CONTINENTAL - CONTINENTAL
  3. OCEANIC - OCEANIC
• OCEANIC-CONTINENTAL (CONVERGENT)

  • Plates moving toward each other
  • Dense oceanic plate slips beneath less dense continental plate
  • trench forms on the subducting plate side and extensive volcanism on the overriding continental plate; 
  • earthquake foci becoming deeper in the direction of subduction
  • Western South America
• OCEANIC-OCEANIC(CONVERGENT)

  • Plates moving toward each other
  • Older, cooler, denser plate slips beneath less dense plate; 
  • trench forms on subducting plate side and island arc on overriding plate
  • band of earthquakes becoming deeper in the direction of subduction
  • Aleutians
  • Marianas
• CONTINENTAL-CONTINENTAL (CONVERGENT)

  • Plates moving toward each other
  • Neither mass is subducted; 
  • Plate edges are compressed, folded, and uplifted resulting in the formation of major mountain range
  • Himalayas
  • Alps
• TRANSFORM BOUNDARY

  • Plate sliding past each other
  • Lithosphere is neither created nor destroyed
  • most offset oceanic ridge systems while some cut through continental crust
  • characterized by shallow earthquakes
  • Mid-ocean ridge
  • San Andreas Fault
• GEOLOGIC FEATURE:

  1. FAULTLINE
  2. TRENCHES
  3. VOLCANOES
  4. MOUNTAIN RANGES
  5. RIDGE
  6. RIFT VALLEY
• 1. FAULTLINE

  • A transform boundary connects two diverging boundaries, creating a fault line. 
  • represents an area of shear, where two plates are moving horizontally against one another.