River Erosion and Deposition Flashcards
What is the movement of sediment from one location to another called?
Erosion (Weathering is the actual breaking of existing rock into sediment)
What is the placement of sediment called?
Deposition
In the upper course of a river, what is the shape of the channel?
The channel is narrow, straight, with more erosion of the bed than the sides.
In the upper course of a river, why is the water moving quickly?
The upper course of a river has a steeper slope than the middle and lower courses.
In the middle course of a river, how does the channel change?
The channel widens, and meanders form.
What is a meander?
A curve in the river channel that forms when faster water erodes one bank, while slower water deposits sediment on the opposite bank.
What is a levee?
A natural or artificial build up of the banks of a river channel.
How do natural levees form?
During a flood, sediment-rich water will deposit larger pieces near the banks of the river.
How does a floodplain form?
During a flood, sediment-rich water will carry finer particles until the water speed slows enough to deposit them.
Why are many cities and towns built near rivers?
Rivers provide fertile soil for agriculture. They can be a source of freshwater. They can be used to transport goods.
Why should artificial levees be built away from the banks of the river?
The sedimentation process from periodic flooding replenishes soil. The river channel is not constricted, which decreases pressure on the levees.
What is a floodway?
A channel or area adjacent to a river where floodwaters are diverted to prevent damage to buildings and people.
How can dams be used to control floods?
Dams are built upstream to control the amount of water in the channel near a populated area.
What is a tributary?
A smaller stream that flows into a larger stream.
How does a alluvial fan form?
When the slope of the land abruptly changes from the upper course to the middle course, larger pieces of sediment are deposited at the base of mountains.
What is a delta?
A triangular-shaped deposit of sediment that forms where a river enters a larger and slower body of water.
In what order is sediment usually deposited in a delta?
The largest sediment will be near the mouth of the river: gravel, sand, silt, and clay.
How does draining wetlands affect an area’s ability to deal with flooding?
Draining wetlands compacts sediments, which can lower the elevation and create areas for flood waters to fill. Draining wetlands can also increase erosion during flooding.
What is a tidal surge?
A wall of water that comes on to the shore during a hurricane?
What are two problems associated with building near coasts that are prone to hurricanes?
Increase number of people and buildings that can sustain damage. Removal of seagrass and other vegetation that can buffer the coasts from tidal surges.
What are distributary channels?
A series of small streams that flow out from the main river and transport sediment to form a delta.
What is the mouth of the river?
The location where the river enters a larger body of water.
What are the headwaters of a river?
The location where precipitation or other water source forms a channel that will become a river.
Why might more water be located in the middle course of a river than in the upper course?
Tributary channels converge to add water to the river.
Why might deltas have different shapes?
The shape depends on the amount and size of sediment entering the body of water, the speed of the river as it enters the body of water, and the amount of erosion.
How might humans affect the shape of a delta?
Structures such as dams and levees can control the amount of sediment and speed of the river water. Removing vegetation can increase the amount of erosion that occurs. Building on the delta can compact the sediments.
What sized particles form the sedimentary rock conglomerate?
Larger sediment such as gravel or pebbles.
What sized particles form the sedimentary rock shale?
Mostly clay and some silt-sized particles
Peat is partially decayed plant matter. Over geologic time, which sedimentary rock can it form?
Coal
The remains of microscopic marine organisms can form which sedimentary rock?
Limestone
