Rifts
Rifts are linear zones caused
by tectonic
plates and the Earth's crust and lithosphere are spreading or splitting apart. Rifts are usually accompanied by orogeny , volcanoes and earthquakes.When rifts remain above sea level they form a rift valley, which can be filled with water forming a rift lake.
Rift valleys are also called grabens, which means “ditch” in German.
Rift valleys are different from river valleys and glacial valleys because they are created by tectonic activity and not by the process of erosion.
Rift valleys are created by plate tectonics which are huge rocky slabs made up of the Earth's crust and upper mantle. They are always in motion—shifting against each other, falling beneath one another (which is a process called subduction) and crashing against one another.
Tectonic plates also tear apart from each other; this is called divergent plate. When the Earth’s plates move apart, the Earth’s crust separates, or rifts.
Rift valleys can lead to the creation of entirely new continents, or deepen valleys in existing ones.
Most rift valleys have been found underwater, along with large ridges that run all through the ocean.
These mid-ocean ridges are formed as tectonic plates move away from one another. The plate’s separate, molten rock from the Earth’s interior well up and harden and touches the sea, forming new oceanic crust at the bottom of the rift valley.
This takes place along the northern crest of the Mid-Atlantic Ridge, where the North American plate and the Eurasian plate are splitting apart. The Mid-Atlantic Ridge rifts at an average of 2.5 centimetres (1 inch) per year. Over millions of years, the Mid-Atlantic Ridge has formed rift valleys as wide as 15 kilometers (9 miles).
In the Pacific Ocean, the East Pacific Rise created rift valleys where the Pacific plate is separating from the North American plate, Riviera plate, Cocos plate, Nazca plate, and Antarctic plate. (The Pacific plate is the largest on Earth.) Like most underwater rift valleys, the East Pacific Rise is dotted with hydrothermal vents. The activity below the underwater rift valley creates these vents, which spew super-heated water and sometimes-toxic vent fluids into the ocean.
There are only two rift valleys on Earth within continental crust, the Baikal Rift Valley and the East African Rift.
Tectonic movement splits continental crust in the same way it does with mid-ocean ridges. As the sides of a rift valley move farther apart, the floor sinks lower.