Rivers often begin high up on mountains, and they run downhill to the sea. The water in rivers comes from rain, lakes, springs, and melting ice and snow.
Most of the time, a river starts out as a tiny trickle called a rill. As it flows downhill it joins other rills, gets larger and becomes a stream. Streams then join to make a river. A river may also have other rivers flowing into it, and so it gets bigger and bigger.
As they flow downhill, rivers always find the easiest route. For example if a river meets a hill, it simply flows around it. That is why rivers don’t usually run straight.
Rain-water can wear away limestone, making holes and caves underground. If a river flows in such an area it may pour down a hole in the rock and flow through the caves underground.
Most waterfalls form when a river flows over a layer of hard rock and then over another layer of softer rock. As it flows the river wears away the softer rock faster than the hard rock, making a step. With time, the step gets deeper and the river plunges over it, creating a waterfall.
The world’s longest river is the Nile. The Nile flows through East Africa into the Mediterranean Sea. The world’s largest river is the Amazon in South America.
© 2005 Al Bawaba (www.albawaba.com)
