Do you believe that the pebbles on the river bank are formed by the impact and friction of running water?
Most explanations for the formation of the cobblestones are that smaller stones, after a long period of slow erosion by water and rolling against each other, eventually formed the cobblestones of 'Today. In fact, many questions are unclear. Without careful observation it is impossible to give a correct description of the formation of the cobblestones.
First of all, don't imagine that the stone always rolls continuously. In fact, this is not the case at all. When a cornerstone falls into a river, the front surface of the stone will first be washed away by running water and quicksand, and with a certain degree of polishing, the front surface of the stone will form a vortex in the water during flow. Rotation process, in this way the sand under the front end of the stone will be removedlittle by little and carried away, causing the front end of the stone to form a concave, and the front end of the stone will slowly sink into the water. the concave, which will slowly cause the back part of the stone to sink. As the ground tilts upward, the space formed by the sloping rear end will cause the flow of water to turn in the opposite direction and carry away the sand at the rear end, creating the concave. concave rear end. In this way, a sand nest will be formed under the whole stone and the stone will be sunk into this sand nest of flowing water.
In this way, a stone in a river spends most of its time half-buried in the sand of the river bed and remains stable. A stone half buried in sand, because it only exposes part of the top most of the time the top is always impacted and rubbed which can easily flatten it. Furthermore, the force of impact friction being fluid mechanics, the quatre corners are the easiest to handle. Under the force, the stone becomes a certain ellipse.
When this effect occurs for a certain period of time, during periodic and large floods, the stone which has been crushed into a semi-elliptical surface is carried away by the rapids and moves with the water, in certain conditions, the stone will eventually fall to the bottom of the water. When falling to the bottom of the water, the surface has reached a certain degree of smoothness due to previous impact and friction. smaller than the surface area that has not been rubbed, so during the falling process, the stone is most likely to fall to the bottom of the river first, causing the stone to fundamentally overturn. The previously crushed surface faces the river bottom and is. buried in the sand. And without being rubbed. The side that has not been ground before faces upwards, and is impacted and rubbed, gradually forming a flat and smooth surface. LWhen this situation was repeated alternately, the stones of the river bed formed the shape of today's flat pebbles.
During the process of the stone being uplifted and turned over by the flood, if it falls across the river, it will also be turned and smoothed due to the unequal force of the water at both ends, which ensures that the rollers are always oblong for reasons other than spherical shape.
It is a long process for the stones to form paving stones. The sand in the flowing water plays a decisive role. In rivers without sand or in the upper reaches of streams with little sand, there are practically no pebbles, but just a little gravel or large stones, but some sand can also be formed by collision and friction, so river sand is more common in the middle and lower reaches of rivers, and it is not surprising that pebbles are oftennt accompanied in the middle and lower course. sections of rivers.