Niagara Falls History - Geology of the Canadian Shild and Glaciers

Niagara Escarpment along the Niagara River The Niagara Escarpment is the reason the Falls of Niagara was born. Today's 1,609 kilometer (1000 mile) long Niagara Escarpment begins in Watertown New York, USA and continues north to Lake Huron and then westerly along the Manitoulin Island in Ontario, Canada, and then bends through Wisconsin and Illinios. The section between Hamilton, Ontario and Watertown, New York the escarpment ranges from 183 meters (600 feet) above sea level to 189 meters (620 feet) above sea level.

The Niagara Escarpment was created long before Ice Age glaciers. The land that is now Southern Ontario was the bottom of an ancient tropical salt water sea, as evidenced by ancient fossils in the area's rocks dating back to 430 - 415 million years ago. The area emerged from the sea in the Paleozoic Era about 245 million years ago. It was much later, approximately 65 million years ago (between the Cretaceous and the Tertiary periods), scientists believe a giant asteroid collided with the Earth near Mexico's Yucatan Peninsula, leading to the extinction of the dinosaurs.

There were three distinct Ice Ages Over the past 65,000 years, with a huge glacier stretching south from Hudson Bay, known as "the Wisconsin Glacier". During those times, the Niagara Escarpment was covered with a sheet of ice 2 - 3 kilometers thick. The last Ice Age lasted approximately 8,000 years before retreating 12,000 years ago. As the Glacier retreated, the water levels slowly lowered forming four lakes:

As the glacier retreated, the land pushed up ("isostatic rebound," without the weight of solid ice upon it) cutting off these outlets with the exception of the Niagara River. At that time, the glacier still blocked the St Lawrence, so water over the Niagara drained to the ocean via the Mohawk and Hudson River Valley. Later, as the land in this area rose, the route to the ocean shifted east to the Champlain Valley, dropping the water level in Lake Iroquois dropped 15 meters (50 feet).

Exposed tree roots in the eroded Niagara Gorge When the Wisconsin Glacier had retreated north of the St. Lawrence Valley, allowing water to drain east, Lake Iroquois's water level dropped close to sea level. Over the past ten thousand years, the land around Lake Ontario continued its post glacial rebound uplift, bring its elevation to current levels. During the past 100 years alone, continued glacial rebound at the eastern end of Lake Ontario has lifted the water level at the western end of the lake by 0.3 meters (1 foot).

Twelve thousand years ago, the Niagara River became the main water outlet for much larger Lake Erie to flow over the escarpment into a larger Lake Iroquois (Lake Ontario). At that time, the lake plain of Lake Iroquois (Lake Ontario) was within 11 meters (35 feet) of today's level of the Niagara Escarpment at Queenston, Ontario. The height of the initial Niagara Falls was only 11 meters (35 feet) at Queenston falling right into Lake Iroquois below. Over time, the water chewed through the glacial material and the limestone rock of the Niagara Escarpment to form today's Niagara Gorge.

Eleven thousand (11,000) years ago, the land rose enough that the entire flow of the Upper Great Lakes flowed into the Lake Erie basin through the Niagara River. The Niagara River today drains an area of 254,708 square miles (409,901.5 square kilometers) including the Upper Great Lakes.

Four thousand - five hundred (4,500) years ago, the crest line of the Falls was located north of the current Whirlpool Bridge. Two thousand (2,000) years ago, the crest line of the Falls was located north of the current Rainbow Bridge. Niagara Falls has eroded 11.4 kilometers (7.1 miles) during the last 12,300 years The mean rate of erosion was 3.5 meters (5 feet) per year. Since 1942 the rate has been much slower (about a1 foot per decade), attributed to water going through the hydro power generators instead of over the Falls.

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