Nickpoints are breaks in the stream gradient where either waterfalls or steep rapids form. This happens in areas where bedrock consists of layers with different resistances to erosion, as shown below. At waterfalls, tumbling water excavates softer rock at the base, eventually leading to a continual series of small collapses by the more resistant surface rock. In this way, the nickpoint moves slowly upstream. Perhaps the most famous nickpoint is Niagara Falls, which is moving upstream at about 1.2 meters (4 feet) per year.