A stream flowing along on its way may encounter a broken gradient that drops gradually or abruptly—if gradually, the stream flows faster and creates rapids; if abruptly, the stream changes its flow drastically, falling over the edge of the break and becoming a waterfall. The spot at which this sudden change in stream elevation occurs is called a nickpoint, sometimes spelled knickpoint. Over time, the force of falling water gradually erodes a nickpoint, causing it to retreat. The nickpoint of the Horseshoe Falls at Niagara Falls is retreating at a rate of about 4.3 feet a year. This is “knickpoint retreat on a grand scale” and further evidence that the surface of the Earth is volatile, surging and shifting, changing in many ways constantly, all the time, even at this moment.

Pattiann Rogers