Formation of Niagara Falls

Although the Falls at Niagara are about 12,000 years old, the story of their formation can be traced back hundreds of millions of years into the past.

Five hundred million years ago the Earth was very different from the way it is today. Its climate was mostly tropical, and the land masses that would one day become North America and Eurasia were still in the process of separating from one another.

Most of the western and central portions of what was to become North America (including the Niagara region) lay underneath shallow tropical seas and brackish ponds. The eastern park of this future continent was dominated by the Taconic Mountains, a range that was taller than the still unformed Rockies would ever be.

The Taconics no longer exist in our world. Five hundred million years of erosion have reduced them to the Appalachian, Allegheny, and Catskill mountains that we know today. The silt and minerals that were worn away from the Taconics, however, provided the materials that formed the Niagara region and (much later) the Niagara Falls.

Water runoff from the Taconics carried sediment down to the west, where it settled to the bottom of tropical seas and ponds. Later deposits built up on top of earlier ones, compressing them into layers of rock. Over time, different mineral solutions washed down to the sea bottoms, resulting in the formation of different types of rock layers.

The lowest layers deposited in the Niagara region were the “red beds”– the soft, iron-bearing Queenston shales. These were laid down under very shallow, brackish water.

The next several layers to be formed in Niagara were sandstones and shales (mostly soft), interspersed with harder layers of limestone.

The last layers of rock to be deposited were composed of a hard magnesium-bearing limestone known as Lockport dolomite (also called dolostone). The dolomite layers were formed under a true tropical sea (sea level was higher than when the red beds were formed), and now contain many marine fossils. The outer edge of the dolomite deposits formed a huge semicircle that has now become the edge of the Niagara Escarpment- a 600 mile ridge that sweeps west and north from Rochester, NY into Canada.

By about two hundred million years ago, the rock strata of the Niagara region were more or less in the form they hold today. No great changes occurred in the ocean beds of Niagara from then until fairly “recent” times.

Then about twenty million years ago, the Earth’s climate began to change. The planet grew gradually cooler and the polar ice caps began slowly to expand. As more and more water was frozen into the ice caps, the sea levels began to drop.

Two million years ago, the Niagara region began to see the effects of the climate change. The ocean beds were uncovered by the retreating sea, and the growing northern glaciers crept southward into what was to become the Great Lake region.

Four major glaciations occurred during the next two million years. The greatest advance of the glaciers took place during the last half-million years. It was during this glaciation that the ice masses gouged out he Great Lakes basins.

The last glaciers melted away from the Niagara area about 12,000 years ago. Huge torrents of water, released into the upper Great lakes by the melting ice, channeled along what became the Niagara River and poured over the edge of the Niagara Escarpment (the dolomite cliff) at what is now Lewiston, New York. This was the beginning of the Niagara Falls.

The water of the newly-formed falls began very slowly to cut into the cliff over which it poured. The highest underground layer of rock, the layer at the top of the cliff, was (and is ) the Lockport dolomite – a very hard, erosion-resistant material. The underlying layers of rock (those that support the dolomite), however, were mostly soft.

Water from the river above the falls seeped down through cracks in the dolomite layer and into the layers of softer rock below. The pressure of the water caused the soft under-layers to be pushed out form the face of the cliff behind the falls. These soft layers sheared off, thus removing the dolomite’s supports.

With nothing left underneath to hold up the top edge of the cliff, the dolomite layer collapsed under its own weight and fell to the base of the cliff at the bottom of the falls. The water pouring over the falls pounded down on to the rubble and wore it slowly away.

The soft under-layers of the cliff continued to shear away behind the falls. The dolomite at the brink of the falls continued to collapse as its support was removed, and the falls began to move slowly upstream.

Today, 12,000 years later, the falls have moved more than seven miles (eleven kilometers) upstream from their original location. In the process of moving they carved out the Niagara Gorge – a seven-mile canyon.

About 6,000 years ago, when the falls were roughly halfway to their present location, they reached a sharp bend in the river. At the outer edge of the bend was the end of an older river gorge, a gorge that had been filled in with rubble the last glacier. The falls wore their way around the bend, scoured out the end of the filled in gorge, and produced the Whirlpool Basin (the site of the present-day Niagara Whirlpool).

The Falls then continued to move slowly upstream – a process that goes on today.

The present rate of erosion of the Falls has been slowed by the diversion of water upstream for the generation of electricity. The shape of today’s Niagara Falls is now maintained by the regulation of water flow over specific portions of the cliff, but these human-caused effects will not be permanent. The Falls of Niagara are constantly changing, providing a living example of the geologic processes that formed them.