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Water Erosion Chapter 9 Section 2 Runoff and Erosion • Moving water is the major agent of the erosion that has shaped Earth’s land Power source Condensation Precipitation Evaporation Runoff Groundwater Runoff Water Cycle Runoff and Erosion • Runoff is water that moves over Earth’s surface • Five factors that influence amount of runoff – Amount of rain – Vegetation – Type of soil – Shape of the land – How people use the land • Generally, more runoff means more erosion Runoff and Erosion • As water runoff travels it forms grooves in the soil rills – tiny grooves gullies – formed after a rain as rills flow together streams – formed as gullies flow together. They rarely dry up Runoff and Erosion River – a large stream Tributary – a stream or river that feeds into a larger stream or river Runoff and Erosion • Drainage basins or watersheds are areas from where rivers and tributaries collect their water Erosion by Rivers • V-shaped valleys – caused by fast flowing rivers that carve steep slopes along the sides Erosion by Rivers • Waterfalls – where water flows over hard rock that erodes slowly, then flows over softer rock that erodes quickly Erosion by Rivers • Rapids – areas of rough water where a river tumbles over hard rock. Erosion by Rivers • Flood Plain – where a river slows down, spreads out and erodes the land forming a wide river valley Characteristics -Steep sides -Mountainous or hilly regions -Rapidly flowing water -White water rapids and water falls -Curving stream -Gradual slope -Erodes sides -Less swiftly moving -Meanders -Flood plains -Very slow -Broad flat flood plain -Oxbow lakes Erosion by Rivers • Meanders – bends in the river as it erodes softer rock on its bank • Oxbow Lakes – a meander that has been cut off from the main river Video Deposits by Rivers • Alluvial fans – when a river comes off a mountain and widens, it slows down and deposits sediment as new soil Deposits by Rivers • Deltas – When a river flows into a body of water, slows down and drops its sediment. Groundwater Erosion • Groundwater – water that soaks into the ground. It fills in the spaces and cracks of soil and rock. - can cause erosion through chemical weathering Groundwater Erosion • Caves – water that mixes with CO2 forms a weak acid that can break down buried limestone and produce hollows • Sinkholes – caused when caves fall in Groundwater Erosion • Carbonic acid and calcite can be deposited on cave roofs and floors to form stalactites, stalagmites, and columns. stalactite stalagmite column Groundwater Erosion • Karst Topography – an area where there are a lot of sinkholes due to the underground erosion of limestone.
