seafloor spreading

• • Mid-oceanic ridges are openings in the seafloor where molten materials from the Earth’s interior come from.


  When the molten materials rise, they slowly spread sideways. This motion makes the seafloor above it to be pulled apart, creating a break or an opening called mid-oceanic ridge, where the molten materials go out. 
• • New oceanic crust is formed at mid-oceanic ridges.


  New oceanic crust is formed from the outpouring of the molten materials, and as the process continues, oceanic ridges or underwater mountain ranges are built
• • Oceanic ridges are underwater mountain ranges that form through the accumulation of molten materials that go out of mid-oceanic ridges.

  . Oceanic ridges are composed of volcanic rocks.
• • Seafloor spreads as new molten materials come out from the Earth’s interior pushing the ocean floor as they flow out.
  • As the seafloor spreads, structure of the ocean basins evolves depending on the plate boundary that they lie on.
• In 1960, the American geophysicist, Harry Hess, explained how the convection currents in the Earth’s interior make the seafloor spread.
• Convection currents carry heat from the molten materials in the mantle and core towards the lithosphere. These currents ensure that the materials formed in the lithosphere are “recycled” back into the mantle.
• In this “recycling” process, which was later named as seafloor spreading, the molten materials flow out to form mid-oceanic ridges, spread sideways to form seafloor, and disappear into the ocean trenches.
• As the molten materials continuously flow out from the ridges, the seafloor also keeps on spreading forming a central valley, or a rift valley, at the summit of the oceanic ridges.
• Trenches are depressions on the ocean floor.
• . The molten materials push the seafloor away from the ridges and towards the trenches
• . When the molten materials are brought near the trenches, they start to cool, become denser and sink back down into the Earth where it is heated and melted again. The spreading of the seafloor continues as a “recycling” process. As new seafloor is created, it continues the process until it disappears back into the deep ocean trenches.
• As new oceanic crust is formed at the oceanic ridge, it pushes away the older materials. This means that the nearer the ocean floor to the oceanic ridge, the younger it is compared to the ones farther from the ridge.
• Oceanic ridges are formed at divergent boundaries, where plates move away from each other;
• while trenches are formed at subduction zones where plates collide with each other or at convergent boundaries.