Geocentric Science

Running water plays a huge role in shaping the Earth’s surface and is considered a powerful agent of erosion.

Streams and rivers slowly change the surrounding landscape by weathering and eroding the underlying bedrock. Running water also has the power to quickly modify the Earth’s surface (especially during flooding events).

Common stream features include: meanders, oxbow lakes, meander scars, point bars, cut banks, floodplains, natural levees, deltas, and alluvial fans. Additionally, the velocity of the river or stream plays an important role in determining the shape of the river and the features that surround the river.

1. What is a meander? How does it form?

   Answer: Meanders are the “s” shaped patterns (the curved looping pattern) that a river or stream makes as it travels from high elevation to lower elevation. Over many years, the river or stream carves its way into the less resistant rock by weathering and eroding the bedrock and creating the stream or river channel.

2. What is an oxbow lake?

   Answer: Over time, as a result of weathering an erosion on the outer edges of the meander, the meanders will eventually come together. The stream will form a new shorter channel (and will not flow around the meander, thus leaving behind an abandoned meander). The water will flow through the steeper and straighter path. Eventually, the old meander (abandoned meander) will become separated from the stream, leaving behind a lake (an oxbow lake).

3. What is a meander scar?

   Answer: Since water is no longer flowing into the oxbow lake, it eventually dries up. This old, dried-up lake is known as a meander scar.

4. What is a point bar and cut bank?

   Answer: There are two important features of a meander; the inner and outer sides. The water velocity is slower on the inner side of a meander. Therefore, deposition dominates (sediments are put down or settle out of the water column). Point bars are also known as beaches. However, the water is has a greater velocity on the outer side of the meander, and therefore, erosion dominates (water is moving quickly and can pick up and transport more sediment).

   

5. What is a floodplain?

   Answer: During a flood, a stream or river transports more sediment and water. The stream or river spills water and sediment on either sides of the channel. This process decreases the water velocity, and allows deposition to take place. This process forms a floodplain.

6. What are natural levees?

   Answer: During a flood, sediment will spill over the stream or river’s channel to create a floodplain. However, most of the larger sediment will collect closest to the stream (along the banks) to form a natural levee (a build-up of coarser sediment on along the channel).

7. What are deltas and alluvial fans?

   Answer: As a fast flowing stream or river flows into a slower moving body of water (such as a lake, sea or ocean), deposition occurs (due to the decrease in water velocity). This occurs at the mouth of a stream and results in a fan shaped pile of sediment known as a delta. Alluvial fans form when a stream or river flows down a steep mountain valley and reaches flat open land and deposition occurs. The picture below shows an alluvial fan.

8. What controls stream velocity?

   Answer:

   A. The amount of water a stream or river is carrying

   B. The size of the channel

   C. The gradient (steeper land = faster velocity)

   D. The amount of water, the size of the channel, and the gradient will affect the types of stream features that are observed.