CONTINENTAL BREAKUP
Dynamic aspects of continental breakup: Why do continents break ?
If, passive rifting is not applicable to the East African rift system what is the alternative?
Gravitational force is a volume force that acts within the plate. It results from lateral variation in densities. Active rifting is a dynamic mode of rifting where extension and thinning result from action of the grativational force. The East African Rift system is underlain by hotter upwelling mantle as shown by the P-wave velocity anomaly (see below). This hot and therefore less dense mantle produces extensional stresses within the African plate. At the surface of the East African rift, volcanoes testify for decompression melting in the mantle. "Active rifting" comes from the fact that mantle upwelling is active during this dynamic mode of extension.