Saturday, January 14, 2012

learn something about Niagara Falls

Postcard from Canada: Niagara Falls


Where is the Niagara Falls?

Collectively they are called "Niagara Falls".

Categorized by these three names:
American Falls (between Prospect Point and Luna Island) far left.
Bridal Veil Falls (between Luna Island and Goat Island) mid left,
Canadian Falls (between Goat Island and Table Rock) right.

Canadian "Horseshoe" Falls
Horseshoe Falls is the most powerful waterfall (vertical height along with flow rate).

The features that became Niagara Falls were created by the Wisconsin glaciation about 10.000 years ago. The same forces also created the North American Great Lakes and the Niagara River. All were dug by a continental ice sheet that drove through the are, deepening some river channels to form lakes, and damming others with debris. Scientists argue that there is an old valley, burried by glacial drift, at the approximate location of the present Welland Canal.

When the ice melted, the upper Great Lakes emptied into the Niagara river, which followed the rearranged topography across the Niagara Escarpment. In time, the river cut a gorge through the north facing cliff or cuesta. Because of the interactions of three major rock formations, the rocky bed didnt erode evenly. The top rock formation was composed of erosion-resistant limestone and Lockport dolostone. That hard layer of stone eroded more slowly than the underlying materials. The aeroal photo on the right cflearly shows the hard caprock, the Lockport Formation (Middle Silurian), which underlies the rapids above the falls, and approximately the upper third of the high gorge wall.

Immediately below the hard-rock formation, comprising about two thirds of the cliff, lay the weaker,softer,sloping Rochester formation (Lower Silurian). This formation was composed mainly of shale, though it has some thin limestone layers. It also contains ancient fossils. In time, the river eroded the soft layer that supported the hard layers, undercutting the hard caprockwhich gave way in great chunks. This process repeated countless times, eventually carving out the falls.

Submerged in the river in the lower valley, hidden from view, is the Queenston formation (upper ordovician), which is composed of shales and fine sandstone. all three formation were laid down in an ancient sea, their differences of character deriving from changing conditions within that sea.

Niagara Falls is not listed as UNESCO World Heritage - despite attracting more than 17million visitors annually. The Niagara Escarpment, however, is a UNESCO biosphere reserve - partly because it straddles the border of two countries (Canada has nominated it but the US hasnt).

You can learn more about Canada here :)

Have a nice day!

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