When two plates move away from each other, it produces parallel faults, which are zones of fractures. The rocks between the faults collapse, forming a rift valley. As the plates move, the decrease in overlying pressure causes parts fo the underlying mantle to melt, forming magma. Magma rises through the weaker areas in the crust to the surface, forming volcanoes. Earthquakes occur as stress and tension is released when plates move.
For example, the Nubian and Somalian plates move away from each other, forming the Great Rift Valley. There are also many volcanoes nearby, such as Mount Kenya and Mount Kilimanjaro.