Question

rift valley how it forms, which type of plate movement

Answer 1

A rift valley is a long, narrow lowland formed when the Earth’s crust is pulled apart. It forms at a divergent plate boundary — i.e., where tectonic plates move away from each other under tensional (extensional) forces.

How it forms (brief sequence)
- Upwelling mantle/heat causes the lithosphere to dome and weaken.
- The crust stretches and thins; tensional stress produces normal faults.
- Blocks of crust drop down between bounding normal faults, creating a down-dropped block (a graben) flanked by higher blocks (horsts) — the rift valley.
- Magma commonly rises through the thinned crust, producing volcanism and basaltic eruptions; continued spreading can produce a new ocean basin (mid-ocean ridge) if rifting continues.
- If rifting stops, a “failed rift” (aulacogen) may remain as a valley or basin.

Key features
- Caused by divergent (pull-apart) plate movement.
- Characterized by normal faulting, steep sides, volcanism, earthquakes, and often linear lakes or basins.
- Can occur within continents (continental rift: East African Rift, Baikal Rift) or underwater as mid-ocean ridges (Mid-Atlantic Ridge).

In short: rift valleys form by extension (divergent movement) of the crust, producing normal faults and down-dropped blocks, often with associated volcanism.