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Waterfalls. Birth & Death |
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Waterfalls are amongst the most beautiful natural wonders on earth and are exceptionally pleasing to the eye. The setting is always spectacular with often large quantities of water cascading and free-falling a great distance downwards into a pool of bubbling whitewater frenzy below. Rainbows are often experienced close by to waterfalls as their mist creates the colors of the spectrum when sunlight makes contact. How waterfalls are formed is no mystery. They're created whenever streams or rivers flow over the edges of steep landforms. Countless tiny waterfalls fueled by melting snow cascade down mountains around the world. (Maybe you've heard of a mountain range in the Pacific Northwest known as the Cascades.) Some of the largest waterfalls are created when rivers flow over the edges of plateaus-high flatlands. The highest waterfall in the world, Venezuela's Angel Falls, crashes down from a tepui, one of many spectacular isolated plateaus that are scattered through the rainforests of northern South America. 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 that forms the mouth of a river. Waterfalls form when there is a hard layer of rock covering a soft layer of rock.
As the river flows along, it passes over different kinds of rocks underneath it. Some of these rocks are hard and do not erode easily, while other rocks are soft and erode very easily. 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. Occasionally a waterfall will appear as a result of earthquake activity where valleys become deeper, increasing river flows. Some rivers develop waterfalls after earthquakes change the valleys beneath them. So, a waterfall on a once peaceful river might mark an earthquake fault.
There are two types of waterfall:
Waterfalls don't last forever. The ground beneath is constantly being pounded by the water flowing over it. In many cases, the water eats directly through the rock it flows over, gradually eroding a shallower course as waterfalls turn into rapids and rapids gradually become calmer. If the bedrock a river flows over is especially hard, the waterfall undercuts it when it hits the ground, forming a basin sometimes called a plunge pool. It is here that weaker rocks are eroded, affecting the rocks above. Eventually, the rocks above come tumbling down, creating a new waterfall slightly upstream from the former waterfall. Over many years, a waterfall can migrate many miles upstream. The famous Niagara Falls has migrated about seven miles from its original location since it was created at the end of the Ice Age, a mere 10,000 years ago. If you want to see it, you'd better hurry, as it may disappear in about 25,000 years! www.geobop.com
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Some
of the most spectacular waterfalls were created by "hanging valleys"
carved by glaciers. Imagine a V-shaped river valley taken over
by an enormous glacier that grinds the rock beneath into a broad,
deep U-shaped valley. After the glacier melts, the tributaries
that once entered the main river directly now flow into a steep-walled
valley that sends them tumbling down towards the river far below.
Such waterfalls are common in the Alps, Norway, and in glaciated
mountains in western North America. Examples of this type of waterfall
are the Multnomah Falls in Oregon and the Yosemite Falls in California.
One of the highest waterfalls in the world - California's 2,425-foot
Yosemite Falls - tumbles out of a hanging valley.