Get Sea-floor Spreading; A Computer Animation And Paper Model

Match Magma comes out of the rift valley. Magma cools to rock and hardens. Rock is pushed away as new rock is formed at MOR. Oceanic crust and continental crust meet at the trench. Oceanic crust bends down under the continental crust. Gravity pulls rock towards mantle. Rock melts to mantle.

Seafloor spreading is the process of magma welling up in the rift as the old crust pulls itself in opposite directions. Cold seawater cools the magma, creating a new crust. The upward movement and eventual cooling of this magma has created high ridges on the ocean floor over millions of years.

Seafloor spreading occurs at divergent plate boundaries. As tectonic plates slowly move away from each other, heat from the mantle's convection currents makes the crust more plastic and less dense. The less-dense material rises, often forming a mountain or elevated area of the seafloor. Eventually, the crust cracks.

In the general case, seafloor spreading starts as a rift in a continental land mass, similar to the Red Sea-East Africa Rift System today. The process starts by heating at the base of the continental crust which causes it to become more plastic and less dense.

The continents bordering the Atlantic Ocean, for example, are believed to be moving away from the Mid-Atlantic Ridge at a rate of 1–2 cm (0.4–0.8 inch) per year, thus increasing the breadth of the ocean basin by twice that amount.

Support for Hess's theory of seafloor spreading included evidence from molten material, magnetic stripes, and drilling samples.

The Evidence Comes Together The seafloor has a large mountain range running through it. Deep trenches are found far from the ridges. ... The magnetic polarity of the seafloor changes. The center of the ridge is of normal polarity. ... The youngest seafloor is at the ridge. The oldest is farthest from the ridge.