What actually happens when the seafloor spreads? It can lead to a series of destructive natural happenings, from rising sea levels to earthquakes and more. Seafloor spreading was discovered circa World War I , when the Navy started using echo-sounding devices to measure the ocean's depth, according to USGS.
The Navy sent sound signals from the ship to the ocean's floor, and back, and while it helped them gauge how deep the water was, it also helped them recognize that the ocean floor was rugged with mountains that sometimes reach a full mile high, despite previous assumptions that the ocean floor was flat, according to a Bill Nye video. The ocean floor's ruggedness, they found, is caused by seafloor spreading , a geological process National Geographic defines as when "tectonic plates — large slabs of Earth's lithosphere — split apart from each other.
Heat then rises from the lower mantle and core to the less dense surface crust, eventually causing it to crack, and hot magma to bubble up and fill the fractures. After the war, scientists pieced together the ocean depths to produce bathymetric maps, which reveal the features of the ocean floor as if the water were taken away. Even scientist were amazed that the seafloor was not completely flat Figure below. The major features of the ocean basins and their colors on the map in Figure above include:.
When they first observed these bathymetric maps, scientists wondered what had formed these features. Sometimes — no one really knows why — the magnetic poles switch positions. North becomes south and south becomes north. During WWII, magnetometers attached to ships to search for submarines located an astonishing feature: the normal and reversed magnetic polarity of seafloor basalts creates a pattern.
Magnetic polarity is normal at the ridge crest but reversed in symmetrical patterns away from the ridge center. This normal and reversed pattern continues across the seafloor. What Forms in Divergent Boundaries? Three Types of Stress on the Earth's Crust. Landforms of Plate Boundaries. Types of Geography Features at a Plate Boundary. Facts About the African Plate. How Does an Earthquake Form a Tsunami? The Definition of Tectonic Activity. Natural Disasters Caused by Plate Tectonics.
The oceanic crust is composed of rocks that move away from the ridge as new crust is being formed. The formation of the new crust is due to the rising of the molten material magma from the mantle by convection current. When the molten magma reaches the oceanic crust, it cools and pushes away the existing rocks from the ridge equally in both directions. A younger oceanic crust is then formed, causing the spread of the ocean floor.
The new rock is dense but not as dense as the old rock that moves away from the ridge. As the rock moves, further, it becomes colder and denser until it reaches an ocean trench or continues spreading. It is believed that the successive movement of the rocks from the ridge progressively increases the ocean depth and have greater depths in the ocean trenches. Seafloor spreading leads to the renewal of the ocean floor in every million years, a period of time for building a mid-ocean ridge, moving away across the ocean and subduction into a trench.
The highly dense oceanic crust that is formed after a progressive spreading is destined to two possible occurrences. It can either be subducted into the ocean deep trench or continue to spread across the ocean until it reaches a coast. Subduction is the slanting and downward movement of the edge of a crustal plate into the mantle beneath another plate.
It occurs when an incredibly dense ocean crust meets a deep ocean trench. On the other hand, if the ocean crusts continuous to move along the ocean and not found a trench, no subduction will occur. It will continue to spread until a coast is found and literally pushing it away towards its direction.
Two possible things could happen in the subduction of ocean crust.
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