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Here at Niagara Falls, half a million gallons of water per second cascade down to 180 feet into the gorge below. About 10,000-15,000 years ago, receding Pleistocene glaciers released water from Lake Erie which first began spilling over the Niagara escarpment close to 10 miles downstream of where it is now.
In it's descent from Lake Erie
to Lake Ontario, the 33 mile long Niagara River flows over the
Erie Plain bound by the Onondaga escarpment which is capped by Limestone of the Devonian Period. Further north the river flows
over the Tonawanda Plain which once was the site of a tremendous
glacial lake. In the Tonawanda Plain, Niagara River encounters
Niagara falls as a Dramatic step in the elevation, where the water carves it's way
South.
At the rate of a few feet per year Niagara Falls eroded the underlying Lockport Dolomite, Rochester Shale, and Medina Group Sandstones of the Silurian period, and plunge below an unconformity between Ordovician shale and Silurian Carbonate deposits that tell a tale of advancing and retreating seas throughout much of the Paleozoic Era.
American Falls
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At the American Falls, demonstrated by the presence of large boulders at the base of the cliff, the water's rapid pour eats away the softer underlying rock (Rochester Shale, Medina Sandstone). When enough is eaten away, sections of the top collapse as sufficient erosion recedes to joints in the caprock (Lockport Dolomite). The total 180 foot height may be impeded to fall to as low as 80 feet do to the collection of boulders below. Bridal Veil Falls is separated at the far end of American Falls by Luna Island. Note the people for scale.
Goat Island
Niagara Falls is currently working on
creating the gorge around Goat Island which is bound by the American Falls on the American side, and
the Horseshoe Falls on the Canadian side.
Horseshoe Falls
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90%
of the water spilling over Niagara Falls spills over here and thus
produces a faster erosion rate. Eventually enough
will be eroded on this side of Goat Island so as to make one waterfall,
letting the American Falls go dry as the southward cutting spill eats it's
way around the Island. Horseshoe Falls is named for the shape of the
precipice that the water cascades over, and it is a direct result of the
erosion being faster towards the center, where the water's speed is
fastest. On summer weekend nights, the Falls are lit up in an array of
colors.
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Niagara
Gorge
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In the process of erosion along the Niagara River a great gorge was left in its wake. Each of these photos taken progressively at greater distances from the falls characterizes where the location of the waterfalls had spilled. All the layers of rock can be seen.
