Rivers and Waterfalls

In nature, an essential phenomenon of the planetary cycle of moisture between land, sea and air cannot be missed. The sun causes the water in the oceans and the seas to evaporate, making it form into clouds. This water falls to the earth as it cools down and then collects in valleys and flows back into the seas. The whole process gets recycled again. The flow of rivers plays a major role in the shaping of our natural world. In the case of glaciers, the eroded material is usually carried downstream in the form of very fine particles of rock, much of which is deposited in the seas. The rivers in the world are responsible for taking almost eight thousand million tonnes of material from the land each year and dumping them into the seas. When flooding takes place, rivers deposit their accumulated load on both sides of their courses, building up alluvial plains. For example, Nile’s annual flooding for centuries has brought fresh soil to the narrow and fertile lands of Egypt until the Aswan High Dam was constructed in the nineteen sixties, curbing the flow of the river. Now, the silt gets deposited behind the dam where the giant reservoir, Lake Nasser, gets filled. The Nile is the longest of all rivers and runs at 4,187 miles. The Amazon in South America is the widest and the second longest river at 4,007 miles. Amazon has almost one thousand five hundred tributaries and it drains the biggest area among all rivers. The hardness of the terrain that a river flows through, determines the shape of the valley it is able to carve. If the rock is hard, the steeper will be the sides of the river. This produces the waterfall phenomenon. Waterfalls occur when a layer of hard rock over which the river flows is followed by softer rock. The river will then form a slope that produces rapids or cascades and when the drop becomes vertical; you have a waterfall. In some cases, the falls tend to eat their way back upstream. For example, Niagara Falls between the United States of America and Canada are retreating at the rate of almost three feet every year. In about three thousand years, they are supposed to have cut back by about four miles. The highest falls in the world are the Angel Falls on Mount Auyan Tepui in South East Venezuela. They have a drop of 2,648 feet. They are named after an American pilot, James Angel, who explored that area by aircraft when he was looking for gold in 1935.