Streams flow down the slopes of a volcano at right, forming a radial pattern . If you flew over the volcano in an airplane, the streams might resemble a bicycle tire or an octopus. Rivers in Action Many rivers begin as melting snow high in scenic mountains, often leaping to life as rocky rapids or cascading waterfalls. As they enter lowlands, rivers begin to run more slowly, growing in size as they re fed by other rivers and streams. They generally become a little less clear as their load of silt grows.
Rivers never flow in a perfectly straight line.
Rather, they follow the path of least resistance, funneling down a tiny valley or flowing around a giant boulder. Some rivers meander like drunken snakes. Meandering loops may eventually be cut off, forming isolated lakes called oxbows . Rivers may split into several separate channels , forming a braided river . Eventually, a river or stream reaches its mouth , the location where it enters the sea.