Why is Niagara Falls an example of a nickpoint? Without human intervention, what do you think will eventually take place at Niagara Falls?

Niagara Falls, an awe-inspiring natural wonder, is also a classic example of the dynamic nature of waterfalls, particularly in how they evolve due to erosional processes. At the heart of these processes is the interplay between different rock types. The upper layers of Niagara Falls are composed of hard, resistant dolomite rock, which overlays softer, more easily eroded shale and limestone.

Over time, the relentless force of water cascading over the falls preferentially erodes the softer rock underneath. This erosion creates an undercut, eventually leading to chunks of the overlying dolomite breaking off. This process, known as 'undercutting', causes the falls to slowly retreat upstream.

Without human measures to slow the erosion, like the ones currently in place, the falls would continue to recede. Eventually, this would expose a river bed that may not be conducive to maintaining a waterfall, but more likely a series of rapids, altering the landscape dramatically. Understanding the erosional mechanisms behind waterfalls like Niagara is vital for both preserving such natural phenomena and managing the landscapes they shape.

Waterfalls are formed through a combination of geological activity and the erosive power of flowing water. Initially, there must be a sudden change in riverbed elevation, typically due to the presence of different rock types, with varying resistance to erosion. In the case of Niagara Falls, the hard dolomite rock is much more resistant compared to the underlying softer shales and limestones.

When a river encounters such variations, it can cut through the softer rock faster, causing a drop in the riverbed and the characteristic plunge of a waterfall. The process can start with small disturbances in the river's course, such as a landslide or a rock fall, which then continue to expand due to erosion and the force of the falling water.

Waterfall formation is not a static event; it is a dynamic phenomenon that gradually evolves over time. The cycle of erosion, undercutting, and collapse will repeatedly occur, leading to the further retreat of waterfalls. This gradual but persistent change is a testament to the natural forces that continuously shape our environment.

River gradient, or the slope of a river's channel, plays a key role in the speed and energy of flowing water. When the gradient is steep, the water flows more rapidly and has greater potential to erode the riverbed and banks. Nickpoints, like waterfalls, are prime examples of abrupt changes in gradient.

These points of change can occur naturally due to shifts in the underlying geology or through events such as earthquakes. A change in gradient results in a change in the river’s energy, with steeper gradients generally resulting in more vigorous erosion and vice versa. Over time, the erosional force at a nickpoint will work to smooth out the gradient, reducing the difference in elevation and, consequently, the waterfall's height and power.

In essence, rivers are inclined to seek the path of least resistance and energy expenditure, sculpting the landscape as they move sediment and rock. This process eventually leads to a river profile that is energetically efficient and stable, but only over a vast timescale.