Niagara Falls
We all know it; we are all impressed with its beauty. But do we all know how it was actually formed?
Towards the end of the last Ice Age, something like 12,000 years ago, retreating glaciers gouged out what would become the Great Lakes and caused the formation of the Niagara River, which runs between Lake Erie and Lake Ontario. The course of the river has changed a number of times since its formation, settling into the present one about 5,000 years ago. This flows over the Niagara Escarpment and, because the river is split into channels by Goat Island, the water forms three waterfalls, the Horseshoe, or Canadian, Falls, the American Falls and the smaller Bridal Veil Falls. Immediately below the falls themselves, the river turns at an abrupt right angle, forming the Whirlpool, and continues through the Whirlpool rapids. Both the falls and the rapids are the largest such features in North America and, although the falls themselves are not particularly high, at about 170ft (52m), they are very wide. The largest, the Horseshoe Falls, are about 2,600ft (790m) wide and get their name from their shape, where the rock of the escarpment has eroded to form a semicircular drop.
The name is an adaptation of the original Native American name of Onguiaahra, which means ‘Thunder of Water’ and refers, of course, to the huge noise of such a large volume of water crashing over the falls. The water itself is famously blue-green in colour, a feature remarked upon by Charles Dickens when he visited in 1842, and is caused by its high mineral content, gained from the eroding properties of its turbulence. This erosion was causing the falls to retreat by about 4ft (1.2m) a year until, at the start of the 20th century, water began to be diverted away from the falls to power hydroelectric generating plants. The amount of water diverted has increased over the years, particularly at night, and this, together with preventative engineering measures, has reduced the erosion considerably.
The edges of the falls have been strengthened and weirs built to redirect the most destructive currents. In 1969 the Niagara River was directed away from the American Falls for several months, by an earth dam constructed across the mouth of the channel leading to it, while faults in the rock were stabilised. The faults had previously led to a huge rock fall from the face of the falls, forming a large pile of scree (a mass of small loose stones that form or cover a slope on a mountain) that can be seen at the base of the falls today. Luna Island, the small piece of ground separating the American Falls from the Bridal Veil Falls, has been off-limits to the public for years because it is thought to be unstable as a result of cracking in the rock and it could collapse at any time.
~ JM
Image Credit: Labelled for reuse: http://bit.ly/1Hsqg9A Accessed on 26/06/16
More info: Niagara Parks. Facts & Figures: http://bit.ly/R0g1WJ Tesmer, I. H., & Bastedo, J. C. (1981). Colossal Cataract: The Geologic History of Niagara Falls. SUNY Press. Grabau, A. W. (1901). Guide to the geology and paleontology of Niagara Falls and vicinity (Vol. 7, No. 1). University of the State of New York. Philbrick, S. S. (1970). Horizontal configuration and the rate of erosion of Niagara Falls. Geological Society of America Bulletin, 81(12), 3723-3732.