With the aid of a labelled diagram, explain what happens at divergent plate boundaries. Divergent plate boundaries (boundaries of construction) • At divergent plate boundaries, plates move apart. These plates are often called boundaries of construction. (1 SRP) • The process which drives the plates apart is called sea-floor spreading. (1 SRP) • Over millions of years sea-floor spreading leads to formation of new oceans. (1 SRP) • Sea-floor spreading was proposed by Harry H Hess in 1960. (1 SRP) • As the plates, driven by convection currents in the mantle, move apart, cracks form on the ocean floor. These cracks are filled by magma from the mantle. (1SRP) • This lava (magma, on reaching the earth’s surface, is called lava) spreads across the ocean floor, forcing the plates apart, forming oceanic crust. (1 SRP) • Hess noticed that the age of the sea floor is youngest where new rock is formed along the mid-ocean ridges. (1 SRP) • The plates carrying Eurasia and North America separated over 100 million years ago along the Mid-Atlantic Ridge moving no faster than 2.5cm per year. (1 SRP) • The Mid-Atlantic Ridge lies beneath the Atlantic Ocean and extends from the North Pole to the South Pole. It reaches a height of 2,500m to 3,000m above the ocean sea floor. (1 SRP) • The Mid-Atlantic Ridge comes to the surface forming islands, e.g. Iceland the Azores. (1 SRP) • Divergence is occurring on the east side of Africa forming the East African rift valley. Cracks on the sea floor are being filled by magma which is causing East Africa to split from the rest of the continent, forming the Red Sea. (1 SRP) • Black Smokers sometimes occur at mid-ocean ridges. They are chimney-like vents on the floor of the ocean which emit hot water. Often they contain dissolved minerals and bacteria which support marine organisms. (1 SRP) Sea-floor spreading: • There are three proofs for sea-floor spreading 1. The existence of mid-ocean ridges such as the Mid-Atlantic Ridge. (1 SRP) 2. The age of the sea floor is youngest where new rock is formed along the mid-ocean ridges. (1 SRP) 3. Deposits of glacial material and fossils similar in type and age are found where continents where once attached. (1 SRP)
Knowt
Note
Studied by 1 person
