Final answer:
Rift valleys are formed at divergent plate boundaries where lithospheric plates move away from each other, leading to geological features such as shallow earthquakes and volcanism.
Step-by-step explanation:
The type of tectonic activity that forms rift valleys is associated with divergent plate boundaries. At divergent boundaries, the Earth's lithospheric plates move away from each other, and this movement can create a rift valley. For example, the Mid-Atlantic Ridge is a well-known divergent boundary located at the bottom of the Atlantic Ocean, where the Eurasian and North American plates are moving apart. Similarly, the African Rift Valley is an example of a rift forming on land, as the African continent is splitting.
Rift valleys are characterized by the presence of shallow earthquakes and some volcanism due to the upwelling of magma that fills the space left by the separating plates. In contrast, convergent plate boundaries are where plates move toward each other and may create mountains or volcanic chains due to subduction. Transform plate boundaries occur where plates slide past each other, mainly causing shallow earthquakes without volcanism.
The type of tectonic activity that forms rift valleys is divergent plate boundary. In divergent boundaries, the lithospheric plates are moving away from each other. As the plates separate, fractures in the Earth's crust widen, creating a rift valley. The valley walls slowly move at a rate of only a few millimeters a year.