An increased rate of seafloor spreading generally causes sea level to rise. This is due primarily to the expansion of the oceanic ridges and the displacement of water.
Here's a breakdown of how this process works:
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Increased Ridge Volume: When seafloor spreading accelerates, more magma is forced upwards at mid-ocean ridges. This leads to the creation of a larger, more voluminous ridge system. Think of it like blowing more air into a balloon – the balloon gets bigger.
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Water Displacement: The expanded ridge system displaces ocean water. Since the ocean basins have a finite volume, this displacement results in a rise in global sea level. Imagine placing a large rock in a bathtub; the water level rises.
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Thermal Expansion of Lithosphere: Faster spreading rates mean that newly formed oceanic lithosphere (the rigid outer layer of the Earth) is hotter. Hotter lithosphere is less dense and occupies more volume compared to older, cooler lithosphere. This also contributes to water displacement.
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Distance Traveled Before Cooling: At faster spreading rates, the new, hot lithosphere moves a greater distance away from the ridge before it cools and contracts. This means a larger area of the seafloor is characterized by relatively elevated, hotter lithosphere.
In simpler terms, imagine a conveyor belt constantly adding hot material (the lithosphere) to the ocean floor. When the belt speeds up (faster spreading), the overall volume of the material being added increases and displaces more water.
In summary, a faster rate of seafloor spreading leads to a larger and hotter ridge system, which displaces ocean water and causes sea level to rise.
