What is a rift and how is it formed?

The rift zonesor simply rift, are areas of the earth's crust in which they appear fissures and faults as a result of the divergence of two tectonic plates. They are zones of frequent magmatic and seismic activity and the appearance of volcanic fissures and tectonic pits is typical in them. They are located in the so-called constructive limits, which are the limits between two tectonic plates that separate and where new crust is formed from the magma that rises from the mantle. For example, oceanic ridges or continental rifts.

Rifts begin to form with a linear stretching of the upper lithosphere. This divergence produces a series of initially unconnected faults that leave separate basins. As the rift evolves, some faults grow and may join with others to form large valleys and depressions.

The Earth's crust is becoming thinner and the transition zone between the crust and the mantle (Mohorovičić discontinuity or Moho) gets closer and closer to the surface. Finally, the forces of tension and the push of the magma from the mantle break the crust producing a large number of fissures and cracks through which magma comes out. The magmatism of these zones represents approximately 80% of all the magmatic activity of the earth's surface.

Rifts can go through several phases alternately over millions of years. For example, the North Sea rift shows evidence of several isolated phases in time that occurred over a period of more than 100 million years, from the Permian, when a large united continental mass still existed, to the early of the Cretaceous, when the continents as we know them today were much more defined.

Rift at mid-ocean ridges

Mid-ocean ridges are the clearest examples of a mature rift zone. For example, the mid-atlantic ridge It is the rift zone where the Eurasian tectonic plate and the North American plate separate and which is located in the center of the Atlantic Ocean. The magma comes out of the fissures and solidifies to form new ocean floor. The rate of magma outflow and plate separation determines how much magma accumulates in height. In the most active areas, called hot spotsthe accumulation of magma forms mountains that can rise above sea level and form islands, such as Iceland or Hawaii.

The continuous outflow of magma at these hot spots creates characteristic structures, such as shield volcanoes. These volcanoes are large and gently sloping as they have been formed over many years by successive layers of fluid basaltic magma. Some of the most prominent examples are the Mauna Loa volcano in Hawaii or the Skjaldbreidur volcano in Iceland (its shape gave rise to the name shield volcano).

continental rifts

Rift zones can also appear on land in areas where new tectonic separation is being created. These zones are called continental rifts and the best example is the Great Rift Valley, in East Africa. The divergent forces along this new separation zone cause the land to sink, forming a great valley, called rift valleys, deeper and deeper between two mountain ranges. Along this zone there are hot spots and volcanic fissures through which magma flows from the mantle. Over time, the valley will drop below sea level and ocean water will begin to enter and a new ocean will begin to form.

Failed rift zones

Failed rift zones are known as those rift zones that are not located between two separating plates. They originate in rift zones between three tectonic plates, two of them end up forming a new separating ocean floor and the third ends up forming the structure known in geology as aulacogena continental rift valley.

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