A waterfall is formed where water flows over a cliff or very steep drop in the river's bed.

There are two types of waterfall:

1. Cataracts are found where there are many rapids in a large river. A large volume of water flows down these rapids.

2. Cascade waterfalls have a small volume of water. A series of falls may form one waterfall.

Formation of waterfalls

Different rates of erosion

Waterfalls are usually found in the upper course of a river in the hills or mountains. The Dunn's River Falls in Jamaica is the only known waterfall which forms the mouth of a river. Waterfalls form when there is a hard layer of rock covering a soft layer of rock.

Water flows over hard rock. When it reaches the soft rock, the water starts to erode or wear away the soft rock. Over thousands of years, the soft rock is eroded and the river begins to cut down vertically into the rock. This makes a cliff over which the water can topple. Over time, the cliff becomes steeper and deeper and a waterfall is formed. At the bottom of the waterfall a plunge pool is created. Some of the water splashes onto the cliff and makes a large, hollow plunge pool by a process called undercutting.

Watch an animation on how waterfalls are formed.

Glaciers

Some waterfalls are made by glaciers. During the last Ice Age (about 10 000 years ago), the pressure of the ice in glaciers cut deep valleys into the mountains. Smaller valleys have been left hanging above the larger valleys. Waterfalls are found where the smaller valleys join the larger valleys. The river flowing through the valleys has to fall many metres to join the main river below. Examples of this type of waterfall are the Multnomah Falls in Oregon and the Yosemite Falls in California.

Yosemite Falls

Facts

The tallest waterfall in the world is the Angel Falls. It is 979 metres high.

The highest waterfall in Africa is the Tugela Falls at 947 metres. It is found in South Africa.

Europe's highest waterfall, Utigard in Norway, is 800 metres high.

The Yosemite waterfall (739 metres) is the highest waterfall in the USA.

The Niagara Falls are visited by thousands of tourists each year.

Tourism and waterfalls

Every year, thousands of people visit waterfalls. The most famous waterfalls are the Victoria Falls on the Zambezi river in Africa, the Iguassu Falls on the Parana River in South America and the Niagara Falls on the border of Canada and the USA. The Niagara Falls are the easiest waterfalls for people to reach. People visit waterfalls to stand and stare at the spectacular sight of an endless amount of water crashing down.

Waterfalls and power

Waterfalls are a natural source of power. Sometimes hydro-electric power stations are built by massive waterfalls. The water is forced to fall down long pipes to the power station below. The force of the water spins wheels  which turn the turbines or engines. These turbines generate electricity known as hydro-electric power. A hydro-electric power station has been built by the Niagara Falls to make electricity for the surrounding area.