Presentation on theme: "Erosion and Deposition"— Presentation transcript:
1 Erosion and Deposition Water Sculpting the Earth’s Surface
2 WaterWater covers over 70 percent of the surface of the planet..
3 Hydrologic CycleA continuous renewal of the Earth’s supply of fresh waterSources:The Ocean – Largest sourceAll other bodies of water
4 Processes of the Water Cycle The water cycle operates through a series ofprocesses. These processes are:Evaporation – from ocean, lakes, riversCondensation – water vapor cools and forms cloudsPrecipitation – falls to the Earth’s surface as rain, snow, etc.
5 After falling to the ground… 1 of 3 process can occur: 1. Infiltration - absorbed into the ground 2. Runoff – moves across the Earth’s surface into lakes, rivers, oceans 3. Transpiration – absorbed by plants and then released back into the atmosphere
6 The Water CycleWater’s movement between the atmosphere, earth and biosphere makes up the water cycle.
7 Stream flowInfluenced by gravity. The time that it takes water to flow from the land to the sea depends on the water’s velocity.
8 Where rivers run straight, their velocity is fastest at midstream Where rivers run straight, their velocity is fastest at midstream. In bends, water runs fastest along the outer banks.
12 Stream flowThe ability of a stream to erode and transport sediment depends on velocityThree factors that determine velocity of a streamGradientChannel CharacteristicsDischarge
13 Gradient - The steepness of a stream channel. - The steeper the gradient, the more energy the water has therefore more erosion will take placeMississippi River
14 Channel Characteristics A stream channel is the course the water follows. As the water flows, it encounters friction from the stream’s sides and bottom. Large smooth streams flow the most. Small rough streams flow the least.
15 DischargeDischarge is the amount of water passing a point in a given time. Discharge is usually measured in meters3/second.
16 Factors affecting discharge 1. Precipitation: As additional water reaches the stream due to precipitation, discharge increases.2. Stream Channel Width: The wider the stream channel, the more water it discharges3. Stream Contour: The smoother the stream channel, the more the discharge.
17 The world’s largest river, the Amazon, has a discharge rate of 212,000 meters3/second.
18 Changes Between Upstream and Downstream While gradient decreases between the head waters and the tail waters of a river, discharge increases. This is because all along its course, rivers are fed by tributaries.MississippiRiverBasin
19 Base LevelAt Base level (or sea level) rivers enter wide, flat valleys. Here rivers and streams begin to bend back and forth and form meanders.Thames River,England
21 Erosion Streams and rivers eroded their channels by : 1. abrasion 2. grinding3. dissolving soluble materials.
22 Sediment Transport Streams transport sediment in three ways: In solutionIn suspensionRolling material along the bottom.
23 In solutionMaterial carried in solution by a river is called its dissolved load.
24 In suspensionMaterial in suspension is called its suspended load. The majority of sediments carried by a river is its suspended load.
25 Rolling material along the bottom. These materials are called the bed load.
26 Competence versus Capacity A streams competence measures the largest particle it can carry. Competence increases with velocity.Capacity is the maximum load that a stream can carry. Capacity is directly related to its discharge.
27 DepositionDeposition occurs when stream flow drops below a critical velocity thus allowing a particle to settle out.AlluvialIron deposits in aSteam inNew Zealand
28 DepositionDuring deposition, like-sized particles tend to fall out. This causes deposits to be constructed of similar-sized particles. This process is called sorting. These deposits are called alluvium.Alluvial depositsfollowing theeruption of Mt.St. Helen
29 Depositional Environments When a river enters the relatively still waters of a lake or ocean, its velocity decreases and forms deltas, or broad, fan-shaped alluvial deposits.Niger Riverdelta
30 Depositional Environments When streams overflow their banks, they create mounds of sediment parallel to the stream called natural levees.
31 Stream Valleys Narrow Valleys V-shaped valleys with rapids and waterfallsThe primary work of the stream is downcutting toward base level
32 Stream Valleys - continued Wide ValleysFlat valley floors or floodplains, streams with meandersDowncutting becomes less and as a result the stream’s energy is directed against the sides widening the valley
33 Floods and Flood Control Most floods are caused by rapid snowmelts in the Spring and heavy rains over a large region..UpperMississippiRiver ValleyFlood-1993
34 Measures to Control Flooding Artificial LeveesLimiting DevelopmentFlood-control Dams