Presentation on theme: "Erosion The transport of earth materials from one place to another."— Presentation transcript:
1Erosion The transport of earth materials from one place to another. AGENTSRunning water (MOST ACTIVE AGENT)Moving air (Wind)GlaciersFORCE driving all agents = GRAVITY
2Erosion by water Streams carry sediments four (4) ways: Floatation – Light materials on surface.Suspension – materials between top and bottom, sometimes causing streams to look muddySolution – Materials that dissolve in water (soluble materials) can’t be seen.Traction – Bed load materials along bottom of stream.
3Sediment size & Stream velocity All sediments are moving slower than the stream due to gravity and friction.Size of sediments that can be eroded depend on the velocity of the stream (See pg 6 ESRT).As velocity decreases larger sediments are deposited.As velocity increases lager sediments are eroded.Become familiar with chart on page 6 ESRT and page 261 in text.
4DEPOSITION Factors that affect RATE of DEPOSITION: Particle size – The larger particles settle fastest.Particle shape – The roundest ones settle fastest.Particle density – The more dense sediments settle fastest.Stream velocity – As already discussed
5Sorting of Sediments GLACIAL DEPOSITS ARE UNSORTED. All mixed up!!! Since some sediments settle faster or slower than others they tend to get separated (sorted) by size, shape & density.SORTING only happens with WIND or WATERGLACIAL DEPOSITS ARE UNSORTED. All mixed up!!!
6Two types of sorting Vertical sorting or Graded bedding Associated with still water.Larger sediments on bottom smaller on top.Horizontal SortingAssociated with moving water that is slowing down.Larger sediments near the mouth smaller sediments farter down stream.
7Mission of a RiverRunning water (Most active agent of weathering & erosion.The job of a river is to lower the land!!!Steep slopes = high velocityHigh velocity = lots of erosionErosion decreases slopeDecreased slopes = lower velocityLower velocity = more deposition usually further down hill.
8Erosion vs. Deposition along Meanders! Outside of MeanderFaster water (high velocity)Deeper channel due to more erosion*SEE PICTUREInside of MeandersSlower water (lower velocity)Shallower channel due to more depositionSand and Gravel bars
10Dynamic equilibrium UPLIFT vs. EROSION If the forces of UPLIFT are more active than EROSION that part of the crust will appear to grow higher.If the amount of EROSION is greater than the amount of UPLIFT that part of the crust will be lowered.
11Stages of stream development Rivers take hundreds or thousands of years to wear down the land. Rivers go through stages of development as they do their work.YouthfulMatureOld age
12Youthful Early stage of stream development. Low volume of water (Discharge).Very steep slopes (Gradient).Lots of kinetic energy used to “down cut” a narrow “V” shape (lots of erosion).Straight path (Stream channel) for water. Water attempts to blast through obstacles rather than go around.
13Mature Middle stage of stream development. Tributaries and groundwater add to stream volume.Slope (gradient) become less steepLess kinetic energy (erosion & deposition)Meanders Develop Stream channel begins to bend as water goes around obstacles.
14Old age Late stage of stream development Stream volume is greatest Kinetic energy is least. Very gentle slopes. Lots of silt and clay transported.Meanders shift side to side across the “wide valley” floor. Oxbow Lakes form as river changes course.Flood often depositing silt on valley floor