Cascade of water in a river or stream. It occurs when a river flows over a bed of rock that resists erosion; weaker rocks downstream are worn away, creating a steep, vertical drop and a plunge pool into which the water falls. Over time, continuing erosion causes the waterfall to retreat upstream forming a deep valley, or
gorge. Good examples of waterfalls include Victoria Falls (Zimbabwe/Zambia), Niagara Falls (USA/Canada), and Angel Falls (Venezuela).
© RM 2009. Helicon Publishing is division of RM.