How does a rift valley form when Earth’s crust is pulled apart?

A rift valley forms when the Earth’s crust undergoes extension, causing it to stretch and fracture. As large crustal blocks or lithospheric plates diverge, the brittle crust breaks along normal faults, allowing a central segment of the crust to drop downward into the resulting gap.1234

This process creates a tectonic depression known as a graben, which is characterized by a relatively flat floor and steep, mountainous sides. In some instances, such as the East African Rift System, this rifting is associated with the upwelling of hot material from the asthenosphere, which pushes the lithosphere upward and causes it to bulge and stretch before the valley floor subsides.5132

While the floor drops, the adjacent blocks may remain at their original height or rise, creating the dramatic elevation differences seen in rift landscapes. This geological activity is often accompanied by volcanism and can eventually lead to the formation of new ocean basins as the plates continue to separate.31452