Here's why:

* Vast Shallow Depression: Rift valleys are large, elongated depressions in the Earth's surface.

* Crust Drawn Down by Convection Currents: Rift valleys form when the Earth's tectonic plates pull apart (diverge). This separation is caused by convection currents in the mantle, which pull the crust downward.

Let me know if you'd like more details about rift valleys!