Hydrosphere Flashcards
V- shaped valley
V-shaped valleys are mainly found in the upper course of the river. In this area the water flows naturally downhill and erodes downwards. Boulders, stones and rock particles are scraped along the channel bed, creating steep valley sides using the processes of hydraulic action, corrasion and corrosion. Hydraulic action is when the power of the water forces air into the gaps in the banks and weakens them so they eventually collapse. Corrasion is wearing away the riverbed and banks by the load hitting against them. Corrosion is when the water dissolves minerals from the rocks and washes them away. Overtime, as the river cuts down, steep sides are attacked by weathering called freeze-thaw. This breaks up and loosens the soil and rock. Gradually the loosed materials move down the valley sides creating the v-shape. The river then transports the materials away and the river channel becomes wider and deeper creating a v-shaped valley.
Waterfalls
waterfalls are found where there is a layer of hard rock on top of a softer rock. The softer rock is eroded more quickly. This is called differential erosion. the water is powerful and erodes the softer rock by hydraulic action. This is the force of the water hitting the rock. The softer rock is worn away and the hard rock is undercut, leaving an overhang of hard rock. At the base, a plunge pool is formed. The overhanging rock is left unsupported and falls into the plunge pool. Rock fragments swirling around deepen the plunge pool by abrasion. Hydraulic action also deepens the plunge pool. This process is repeated over a long period of time and the waterfall repeats upstream forming a steep-sided gorge.
Meanders
eanders are common in the middle and lower courses of a river. They are formed as a result of the processes of erosion and deposition. Due to lateral erosion, the river widens and spreads across the valley floor. Pools develop where the flow is deepest, and riffles develop in the shallow flow. The fastest current is found on the outside of the bend because the depth of the water is deeper, so there is less friction resulting in higher speeds. The outside bend of the river is eroded to form a river cliff. The processes happening at this point are corrosion, where the load of the rivers wears away the banks, and hydraulic action, where water gets into small cracks forcing pieces to break off the riverbed and banks. the material is removed by helicoidal flow. The slowest current is on the inside of the bend as it has more contact with the riverbed. This causes the river to deposit some of the load it carries and forms a river beach or slip-off slope. Continuous erosion of the outer bank and deposition on the inner bank form a meander in the river.
Oxbow lakes
erosion of the outside of the meander means that the neck of land becomes narrower and narrower over time. During periods of flood or high discharge, the river breaks through the neck, creating a straighter, easier channel for the river to flow through. This creates an oxbow lake. Deposition over time causes the lake to be sealed off from the main channel of the river. Over time the water can dry out but since this is the rivers floodplain, at times of high rainfall, water might once again fill up the oxbow lake.
