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Water2 Essay, Research Paper

WATER: IT MOVES THE WORLD Water does move the world, but not always in a noticeable or dramatic way. Erosion is a key element in making the world possible to live in. Erosion forms the valleys, literally dissolves solid rock, moves 3 ton boulders, and builds bridges. Water is the most abundant and therefore most powerful resource on the planet. Although water creates landmarks the size of the Grand Canyon, man cannot see the process, only the result. RAIN EROSION According to Rain Erosion: graphics.lcs.mit.edu, rain erosion is a result of kinetic energy developed by water as it flows over the surface of the material. Material particles are detached from the mass and transported to another location. Although one raindrop has little effect on the earth, the accumulated effect of rainfall over long periods of time can accomplish large amounts of erosion. Erosion begins when rainfall hits materials traveling at a high velocity and forces the materials to crumble into small particles. This continues until the rain creates small grooves. Continuing rain causes these grooves to overflow with a combination of water and particles. This is called run-off. Continuous run-off breaks up the surface into smaller and smaller particles. Accumulating run-off on the surfaces moves down the slopes. This causes sheet erosion. This down slope run-off detaches these particles and moves them with the water. These moving particles strike against other particles on the surface which sets them into motion: this process is called abrasion. The velocity and turbulence of the run-off affect the degree of the sheet erosion; also some materials are less abrasive than others which also affects the degree of sheet erosion. Matter can be transported in three different ways: heavier particles will roll along the surface–these are called rolling matter. Smaller particles will bounce along at a faster rate than rolling matter—-these are called bouncing matter. The smallest particles are completely suspended by the water and travel the fastest—–these are called suspended matter. The particles comes to rest when resistance forces are greater than the velocity of the run-off. RIVER EROSION There are three types of river erosion: chemical erosion; hydraulic erosion, and abrasion. Chemical erosion occurs when chemicals in the water react with minerals in the surface materials and cause them to dissolve and break apart; the dissolution can cause chemical compounds to form such as salts. The salts are carried in the form of ions. Rock gypsum, for example, contains the compound Calcium Sulfate. When this is dissolved in water it creates calcium ions and sulfate ions without several other salt compounds. It does not effect the taste of the water. Hydraulic erosion is based completely on the force of the moving water. A rapidly moving stream can widen cracks and break off large chunks of fractured rock. According to Lakes and Streams by Laurence Pringle, . . .in 1923 a stream at flood stage in the Wassatech Mountains of the northwestern United States wrenched loose boulders weighing up to 90 tons and carried them over a mile downstream. Abrasion is the third and most powerful form of river erosion. VALLEYS A young valley is usually a gully or ravine on a mountainside. It will usually zigzag and have steep sides. The bottom is usually rock with potholes and boulders. The brooks have many waterfalls, rapids and pools. Downstream from a young valley there is usually an older, or mature valley. Mature valley?s streams are longer, straighter and wider, due to years of erosion. They have a smooth bottom liminating rapids and pools. Down sloping in the valley has reduced the steepness of the slopes, therefore slowing down the flow of the stream and slowing also the process of erosion—so the bigger a valley gets, the longer it takes to get any bigger. Mature valleys are much wider than they are deep. The stream now runs in a narrow channel on the valley floor. Years of erosion have transformed boulders and cobble into sand and gravel . Old valleys are extremely wide compared to their depth. The stream flows slowly through a winding channel on the valley floor. The stream is now so slow that erosion is scarce. The stream work consists mainly of transportation and deposition. An extremely old valley can be miles wide and only a few yards deep. The walls can still be as steep as they were in the young valley stage. If you were traveling through a valley you can sometimes see young, mature, and old valleys in order, in only a few miles. A valley can only go as deep as sea level or base level which is the lowest point at which erosion can occur. Geologists have coined the term, Local Base Level which is the lowest land in the region being considered. While valleys may be formed by erosion, there are a variety of other natural occurrences which can interfere with this process: a valley damin occurs when a landslide dams up the stream. This will create a lake until the water finds a way to escape. This can also occur by a lava flow. If seismic activity occurs, causing a portion of the valley to sink, much or all of the river?s power could be lost. A plate in the valley?s floor could be raised, shifting the stream into another valley. Uplift can also change the gradient of the stream, causing it to be stronger; this is called rejuvenation. In a wide valley, rejuvenation can cause the stream to cut a narrow gorge (or young valley) in the old valley floor. If a coast sinks, sea water can travel into the coastal valleys. This can cause sea water to travel far inland and create bays and estuaries. When a stream is flowing rapidly in a narrow valley, it can create interesting sculptures. One type of sculpture is called an alcove. This is a cave made in the valley?s side by the stream, at a turn in the stream. When rounding the turn, water digs hard into the outside channel and makes a wide cave—the

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