Getting swept up in the Confluence! EarthCache

"In times of high water this is an area of dynamic change."

"In geography, a confluence is the meeting of two or more bodies of water. Also known as a conflux, it refers either to the point where a tributary joins a larger river, called the main stem, or where two streams meet to become the source of a river of a new name, such as the confluence of the Monongahela and Allegheny rivers in Pittsburgh, Pennsylvania creating the Ohio River."

In this lesson we will be learning the following:

• How confluences can change the environment by the power of water.  
• How erosion really changed the landscape at Ground Zero.  
• Different types of erosion in this particular area, and how it carves into the land.

Changes from source to mouth

A river flows from an upland source, in this case of GZ the dam. Here the velocity of water is faster than downstream because the river's gradient is steep. Near a river's source the valley has a narrow floor and steep sides (v- shaped) (This is evident in the photograph above). 

The middle course of the river has a wider floor and the sides of the valley are more gently sloping and you can discover this further down. The velocity is slower than the upper stage. However, the channel is wider as the amount of water flowing in it increases as other streams and rivers join it. 

The lower course of the river is very gentle sloping, almost flat. The channel is usually at its widest and deepest here because the amount of water flowing within the river is at its greatest.

It is important to understand that with the work of gravity and the weight of water one can determine the force.  There are equations to understand flow rate and power and you can learn that more in another Earth Cache on this trail.  Right now for this EC, I really want you to understand these two things.  Water always flows from a higher source, and that water carries a lot of mass (but no strength as water will flow on the path of least resistance), thus causing erosion in epic proportions especially in flooding.  So lets learn about four basic types of erosion.

Erosion: the process by which the surface of the earth is worn away by the action of water, glaciers, winds, waves, etc.​

Rivers erode in four ways: 

• Abrasion or corrosion - This is when large pieces of bedload material wear away the river banks and bed.
• Attrition - This is when the bed load itself is eroded when sediment particles knock against the bed or each other and break, becoming more rounded and smaller.
• Hydraulic Action - This is when the force of water erodes softer rock. 
• Solution or corrosion - This is when acidic water erodes rock.

 "Because water has mass or weight (8.33 pounds per gallon), that when it is in motion it can move with great force as in the current of a river or as waves in the ocean. Such forces shape the land on the earth’s surface."

Did you know?

The Baer-Babinet law (or sometimes, the law of Baer) is a concept in geology which states that the process of formation of rivers is influenced by the rotation of the earth. According to the hypothesis, because of the rotation of the earth, erosion occurs mostly on the right banks of rivers in the Northern Hemisphere, and in the Southern Hemisphere on the left banks. In 1926, Albert Einstein wrote a paper explaining the causes of the phenomenon in 1926.

Now that we learned a little bit about erosion, take a moment to study ground zero, as well as the placard for GZ.  With the information above, and information at GZ you should be able to answer the following questions.  You have 24 hours to send me an email (found in my geocaching profile) with the correct answers.  Failure to do so will result in the removal of your "Found it log".   Please add the GC code and title in the subject line.  If you are sending answers for multiple people in your group, please add all the names in your email to ensure they don't have their log deleted :)  Photos with you or your group in the GZ area would be greatly appreciated.

Requirements: (please do not put your answers in the log)

1 According to the Ground Zero Placard, what two creeks join to make one creek?

2 What Process of erosion is going on at the confluence?

3 Explain what has happened to the bottom of the creek.

4 Define Hydraulic action in your own words.

5 Is the water from the creeks after the confluence faster?

6 In your own words how has the erosion changed the environment after the confluence?

If you would like to learn more, please visit the following sources that I used to create this Earth Cache!

Baer-Babinet law

Erosion Definition 

River Geography 

Confluence 

Arkansas Geological Survey