Theory of Stream Placer Geology

The theory of placer geology highly relies on the rate of the stream erosion and how it is transported and because of this it is vital to understand the language and words that are used because they are often times found in literature that has to do with mining. One of the most important contributions to erosion has to do with the amount of water the stream carries. Consequently bigger streams, or smaller ones that are in a flood stage, are the most active when it comes to erosion, transporting and depositing. Speed has to do with the speed the water travels at and this is controlled by the stream gradient which means the angle that the streams flows in comparison to the level surface of the crust of the earth. If the angle is steeper, the speed is increased and there is more potential for erosion. The effects of the stream erosion assist in controlling deposition of a lot of the idiosyncrasies of different streams that prospectors are faced up to when prospecting. Some of these can be seen above the surface of the stream and other can be located below the surface. Scientifically all streams and valleys are formed or try to be formed in a V shape, however this does not usually take place in nature. The bedrock underneath stops the downward erosion and the stream underneath starts to broaden, which causes at bedrock a moderately flat bottom. The discharge, speed and nature of the load as well as the resistance of the bedrock will determine the ending shape of the bottom of a stream. Even though most of the streams that are prospected today are relatively stable in their formation, the erosion of bedrock continues on occurring. Rapids and waterfalls are two very ordinary effects of erosion that prospectors are familiar with. Rapids happen when there is a very quick drop in the gradient or a quick narrowing of the width of the stream. When there is a vertical drop or very close to being vertical for several feet, the effect is what we know as a waterfall.

Potholes become formed when the stream water twirls in a circular movement. This load is then suspended and works similar to a grinding wheel and forms a basin or pothole in the stream bed. When two streams flow close by one another and through soils that have different types of resistance to erosion, it is common to for them to come together and for one to get sidetracked into the other. This is what is more commonly known as stream piracy. When it is said that streams become more mature it simply refers to the fact that the speed or velocity is almost balanced with the load (not in the case of flood stage though). During this time of the history of the stream it is known as a graded stream. This kind of stream consists of most of the modern time streams. Nonetheless even though this type of stream only cuts down a teensy bit, it is still able to erode the sides.There are also many occasions in which a stream will wonder from side to side in S patterns, which are called meanders. Every once in awhile during flood season, the water will cut across the S and will cut off a curved area into an oxbow lake. A stream that comes together and then separates is known as a braided stream.