Physical Geog- Hydrology

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Deposition

When a river loses energy, it will drop or deposit some of the material it is carrying.

  • Deposition may take place when a river enters an area ofshallow wateror when thevolume of water decreases- for example, after a flood or during times of drought.
  • Deposition is common towards theend of a river's journey, at the mouth.
  • Deposition at the mouth of a river can formdeltas- for example, theMississippi Delta.

Examples of depostion are levees and floodplains. 

Levee- when a river is about to flood, the water is at the top of the river and the fastest part of the river is the middle. This means the middle has more energey, therefore can carry more sediment. When the river is absolutely full, the top layer of water and sediment cascades over the side causing the sediment to be deposited causing a levee.

Floodplain- before a river floods, the floodplain is bumpy. After the river floods, the sediment is deposite onto the floodplain, evening it out. Also, any water that is left over will eventually evaporate and will also leave sediment behind.

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Limestone solution

CO2 H2O --> H2CO3 (carbonic acid)

  1. Limestone is made of calcium carbonate. When carbon dioxide is dissolved in rainwater, it makes a weak acid called carbonic acid.
  2. When carbonic acid comes into contact with limestone and passes through joints and bedding planes, it reacts with the rock to form calcium bicarbonate.
  3. The calcium bicarbonate is soluble and is carried away in solution, gradually weathering the limestone.
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Freeze-Thaw Weathering

  1. Water - eg from rainfall or melting snow and ice - becomes trapped in a crack or joint in the rock.
  2. If the air temperature drops below freezing, the water will freeze and expand putting pressure on the rock.
  3. The ice will melt when the temperature rises above freezing.
  4. If this process happens repeatedly, the rock will weaken and eventually shatter into angular fragments.
  5. The fragments may then be deposited as scree at the foot of a slope.
  6. It is most effective where the temperature fluctuates around 0°C.
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