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Waterfall Wonders


Waterfall Wonders
Big waterfalls are among the most spectacular geological features on Earth. The thundering waters of Niagara Falls can fill an Olympic-sized pool every second. Visitors are drenched with spray and deafened by volumes reaching 100 decibels, equivalent to a rock concert.

Waterfall Wonders

A waterfall is simply a river or stream flowing down a cliff or rock steps. They commonly form when rivers flow downhill from hard to softer bedrock. The weak rock erodes faster, steepening the slope until a waterfall forms. The Iguazú Falls on the Argentina-Brazil border, for example, tumble over three layers of old resistant lava onto soft sedimentary rocks.
Any process that increases the gradient can generate waterfalls. A 1999 earthquake in Taiwan thrust up rock slabs along a fault in the Earth’s crust, creating sharp drops along several rivers in the area. A series of new waterfalls appeared in minutes, some up to seven metres (23 feet) high – taller than a double-decker bus.
Many waterfalls were created by rivers of ice during past ice ages. These glaciers deepened big valleys, such as Milford Sound in New Zealand. The ice melted and shallow tributaries were left ‘hanging’ high above the main valley. Today the Bowen River joins Milford Sound at a waterfall 162 metres (531 feet) high, almost as tall as the Gherkin skyscraper in London.
Waterfalls vary enormously in their appearance. Some are frail ribbons of liquid while others are roaring torrents. All waterfalls are classed as cascades or cataracts. Cascades flow down irregular steps in the bedrock, while cataracts are more powerful and accompanied by river rapids.
Gigantic waterfalls seem ageless, but they last only a few thousands of years – a blink in geological time. Debris carried by the Iguazú River is slowly eroding the soft sediments at the base of the falls, causing the lava above to fracture and collapse. Erosion has caused the falls to retreat 28 kilometres (17 miles) upstream, leaving a gorge behind.
The erosional forces that birth waterfalls eventually destroy them. In around 50,000 years, there will be no Niagara Falls to visit. The Niagara River will have cut 32 kilometres (20 miles) back to its source at Lake Erie in North America and disappeared. The sheer force and power of waterfalls makes them impossible to ignore. Daredevils across the centuries have used them for stunts.