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Mississippi River Delta as an example (Phase III) (image #STS51C-143-027)

Now we can extend the inquiry of the Mississippi River Delta further. Let's focus on the question "What happens when a river flows into the ocean?" In fact, that question becomes more and more interesting, the deeper you look into it.

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Before we think about the generalized question, let's look at the specific local question: "What happens when the Mississippi River reaches the Gulf of Mexico, as shown in this image taken in January 1985?" First you have to go to the larger context and make sure your students understand some basic information about the Mississippi River. Have them look at a map of the US, and follow the river from the headwaters in Minnesota to the New Orleans delta. Make sure they notice how other rivers feed into it, and how it grows as it moves south.

Now have them look at the image, and trace the pathway of the river. It bends just south of New Orleans and then continues relatively straight into the delta region. Does it all flow out of one point (such as area A)? Or does it flow out in many places? Have them look more closely at area B, where the river branches, then sub-branches and sub-sub-branches. What is going on here?

Now let's look at the issue of the dirt in the water. Ask your students why they think the river is brown (they probably expect it to be blue). They will probably guess or figure out that the river is brown because of the silt, or dirt, it picks up and carries as it flows. Some dirt settles in along the banks and floor of the river, but much gets carried all the way to the delta. This makes the river into a very powerful force in the erosion and deposition of the Earth's surface. Have your students look at how brown the whole area of the delta is. Do they think dirt is being deposited in the delta? In fact, that's how the delta formed, by the constant deposition of soil from the river.

Teacher's Guide                    Page9.17