Theory question 204
Rivers and River LandformsWrite explanatory notes on the formation of any two of the following: (a) Waterfalls (b) Deltas (c) Inselbergs
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(a) Waterfalls: form where a band of hard rock lies across a river over softer rock; the soft rock downstream is eroded faster, leaving a steep step; plunge pool formed by hydraulic action and abrasion at the foot; undercutting makes the lip collapse so the fall retreats upstream (gorge); also at fault scarps, plateau edges, hanging valleys (e.g. Kainji area, Victoria Falls).
(b) Deltas: where a river enters a sea or lake its speed falls and it deposits its load; deposition faster than waves and currents can remove it; sheltered coast, gentle offshore slope and large load favour them; the river splits into distributaries through the deposits; types arcuate (Niger, Nile), bird's foot (Mississippi), estuarine.
(c) Inselbergs: isolated steep-sided hills rising abruptly from a plain in tropical/semi-arid areas; made of resistant rock (often granite); surrounding weaker rock removed by deep chemical weathering and erosion, leaving the hard core standing; examples Idanre, Olumo Rock, Zuma Rock.
For each feature, name the process and say why that place is affected.