The power of Niagara falls

The thundering roar at the base of Niagara Falls is awesome indeed. On an average summer day, about 40 million gallons of water spill over the half-mile–wide Canadian portion of the cataract each minute.

After falling over a cliff taller than a 16-story building, water pummels the rocks below, incessantly eroding the base of the cliff and triggering rockfalls.

Before the 20th century, when engineers weakened the Niagara River by diverting some of its flow to produce hydroelectric power, the falls marched upstream an average of more than a meter per year.

Niagara Falls is one of the last links in an impressive chain: Water flows from Lake Superior and Lake Michigan to Lake Huron, onward to Lake Erie, then down the Niagara River and over the falls to Lake Ontario and thence to the sea. Today the falls seem unstoppable, but scientists have learned that there was a time after the most recent ice age when Niagara Falls was a mere trickle and the Great Lakes were a little less great.

Niagara falls

During the ice age, which began about 100,000 years ago, a kilometers-thick ice sheet smothered the region. And Niagara Falls — or the ice-covered cliff that would become the falls —was located several kilometers downstream of its current site.

Sometime around 13,000 years ago, the ice retreated northward, leaving meltwater to accumulate in gouges that were left behind.

With the first flush of meltwater, lake levels rose and the falls raged. Studies show that as ice retreated and climate dried, however, the falls slowed to a trickle for several millennia, starting about 10,000 years ago.

Scientists once thought that the falls slowed because the overflow from Lake Erie was rerouted to a different spillway when the landscape tilted and shifted as it was relieved of its icy burden.

But now they are learning that some of the rivers connecting one lake to another simply disappeared during a long dry spell that started about 12,500 years ago.