Effects

• A waterfall forms when a river or stream flows over a cliff that is composed of very hard rock that does not readily erode from the effects of the water. In most circumstances, water is able to erode the rock that it passes over when it comes to a cliff, causing the riverbed to be lowered and sometimes forming a canyon upstream. In a waterfall, the hard rock that resists erosion will many times have a layer of softer rock beneath it that the cannot stand up to the power of the water cascading near it. This rock will eat away and depressions called rock houses can form behind the falling water. Sometimes the softer rock will become so weakened that the hard rock above it will fall down due to its own weight and boulders and rocks will wind up at the base of the waterfall.
  
  

Features

• A plunge pool is a term for an area carved out by the falling water at the base of a waterfall. Plunge pools can be quite deep, as the erosion and abrasion from rocks and boulders falling and colliding with each other, along with the agitation of the volume of water hitting it from the waterfall above, create a force significant enough to erode the base of the waterfalls.
  
  

Size

• Victoria Falls, on the border of Zimbabwe and Zambia in Africa, is regarded as being one of the world's widest waterfalls. It has the highest volume of water cascading over its cliff face--an estimated 19 million cubic feet per minute in the rainy season. Victoria Falls is on the Zambezi River and is more than a mile wide at 5,604 feet. The water falls from a height of 262 feet at the western end and from as much as 360 feet at its eastern end. Niagara Falls is North America's largest falls by sheer volume. Located 17 miles north-northwest of Buffalo, New York, Niagara Falls is on the Niagara River. It is separated into two parts as it goes over the cliff face, with the Horseshoe Falls being about 2,600 feet wide and dropping over 170 feet and the American Falls over 1,000 feet wide and 100 feet high in some spots.
  
  

Geography

• One of North America's tallest waterfalls is Yosemite Falls in California's Sierra Nevada Mountains. It is fed by snow melt in the spring when it is at its most spectacular, as the Yosemite Creek plunges a total distance of over 2,400 feet down a gray rock cliff. Olo'upena Falls, on the Hawaiian island of Molokai, is almost 3,000 feet high and is surrounded by mountains on both sides; it is one of three tall Hawaiian waterfalls, the other two being Pu'uka'oku Falls and Waihilau Falls. Colonial Creek Falls in Washington is over 2,500 feet tall--slightly taller than the cascading Johannesburg falls in the same state.
  
  

Types

• Waterfalls as classified into various types by the way the water actually does fall. For example, a tiered waterfall will see its water come down a series of rocky tiers before reaching the bottom. A block waterfall is wide at the top, such as Niagara Falls. A plunge waterfall has water that falls vertically and does not touch the surface of the rock as it descends. A fan waterfall has water that spreads out in a horizontal direction as it maintains contact with the rock while falling.