A waterfall is a steep drop from a river or other body of water over a rocky ledge into a pool below. Cascades are another name for waterfalls. The erosion of the earth, or the process of the earth being worn away, plays a significant role in the formation of waterfalls. Cascades themselves likewise add to disintegration. When streams move from soft rock to hard rock, they frequently form waterfalls. This occurs both laterally (as a stream traverses the surface of the earth) and vertically (as a waterfall's stream drops). In the two cases, the delicate stone dissolves, leaving a hard edge over which the stream falls. The fictitious line along which parallel rivers plunge as they move from highlands to lowlands is called a fall line.

 Geologists and hydrologists use the number of waterfalls in a region to determine the fall line and underlying rock structure of the region. Sediment is carried by a stream's movement. Pebbles, boulders, or even microscopic silt are examples of the sediment. Soft rock stream beds like sandstone or limestone can be eroded by sediment. At some point, the channel of the stream cuts so deeply into the stream bed that only a harder rock, like granite, is left. These granite formations form cliffs and ledges, which in turn create waterfalls. As a stream approaches a waterfall, its velocity increases, causing more erosion. Rocks can become extremely flat and smooth as a result of the water's movement at the waterfall's peak. The plunge pool at the base is being eroded by the raging water and sediment that fall over the waterfall. Strong whirlpools that erode the plunge pool's rock may also be created by the water's crashing flow.

 The resulting erosion can be quite dramatic at the base of a waterfall, causing the waterfall to "recede." A "rock shelter" is a hollow, cave-like structure created by erosion in the area behind the waterfall. The outcropping, a rocky ledge, may eventually fall, sending boulders into the stream bed and plunge pool below. As a result, the waterfall "recedes" several meters downstream. The boulders on the previous outcropping are being reduced by the waterfall erosion process once more. One of the processes that can create waterfalls is erosion. Over a fault or crack in the Earth's surface, a waterfall might form. Waterfalls can also be caused by an earthquake, landslide, glacier, volcano, or other calamity that disturbs stream beds. Grouping Cascades There is definitely not a standard method for ordering cascades.