The formation of a rift valley by tensional forces typically involves two stages:
- Rift Initiation: During this stage, tensional forces within the Earth’s crust start to pull it apart. As the crust stretches, a linear depression or graben begins to form. The initial stretching is often caused by the divergence of tectonic plates or the upwelling of mantle material. As the tension increases, the lithosphere (the rigid outer layer of the Earth) weakens and fractures along a central fault line.
- Rift Development: In this stage, the rift valley continues to widen and deepen. As the crust separates along the central fault line, blocks of the Earth’s crust move away from each other. This movement causes the valley floor to sink while the surrounding blocks (horsts) are uplifted. The process is often accompanied by volcanic activity, as the upwelling of molten material fills the void created by the separating crust. Over time, the rift valley can extend for hundreds or thousands of kilometers, creating a distinct topographic feature with steep sides and a flat valley floor.
It’s important to note that the formation of a rift valley is a complex and dynamic process that occurs over millions of years. The two stages described above provide a simplified overview of the general sequence of events involved in rift valley formation.
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