440 TECTONICS/Rift Valleys Figure Satellite remote sensing image of the northern Kenyan Ethiopian section of the East African Rift showing a string of separate lakes Image taken by the TERRA satellite using the MODIS instrument (moderate resolution imaging spectroradi ometer) and enhanced with SRTM30 shaded relief Figure Cross rift structures seen clearly in this satellite image of the East African Rift This is a shaded relief map pro duced from SRTM30 data with colour added to indicate land elevations why many early hominid remains have been located in rift sediments Of particular importance in this regard are the deposits in the East African Rift, which have been excavated and studied by many palaeoanthropologists, including successive members of the Kenyan Leakey family The development of the new topographical features of a rift will disrupt pre-existing continental drainage patterns and result in a very different landscape Before rifting the topography is often subdued, with a very small number of large and ancient rivers draining towards the continental margin The impact of rifting on the rivers will depend on their orientation If the new rift parallels existing rivers, it can capture most or all of them, but if it cuts across the general trend of the drainage, streams can be beheaded, diverted, or even reversed Domed sections of rifts are particularly effective at diverting rivers The effect is similar to that of piling up soil into a heap so that water falling onto it is shed in all directions, giving rise to a radial pattern of channels Active faults form steps in the landscape, which can also affect rivers Where there is more than one parallel fault, rivers can be caught between the two steps and flow parallel to the rift axis for many hundreds of miles Margin uplift and tilting of fault blocks both tend to divert rivers away from rift basins Drainage that has been affected in this way is often captured by continental river systems; for example, the Nile was augmented by the waters of rivers that were diverted away from the Red Sea and Gulf of Aden rifts In some rifts cross-rift structures form topographical barriers that pond up drainage systems to form lakes Good examples of this aspect of rifts are Lakes Baikal and Magadi in the Baikal and East African Rifts, respectively (Figure 5) In some rifts