1 The Case Of The Disappearing Shoreline

Humans change the earth's climate in many ways. One change is the increase of carbon dioxide in the atmosphere. As we burn more fossil fuels, we release more and more carbon dioxide into the atmosphere. Most scientists think that, over time, this will change the earth's atmosphere. Some say it will make the earth become warmer; others think it will make the earth become cooler. In either case, small temperature changes can have large effects on the earth's geography. For example, if the average annual temperature increases, more ice and snow at the poles will melt. This would cause a rise in ocean levels all around the world. Some coastal cities might be flooded.

In this activity, imagine that larger amounts of carbon dioxide will cause a warming trend in the atmosphere. You will study the effects such a change might have on the Virginia shoreline.

Procedure

1. Assume that each 0.1 °C rise in the earth's a. 0.1 degree C annual temperature, will cause the sea level to b. 0.2 degree C rise by 1.0 m. Diagram A shows a cross-section c. 0.4 degree C of Norfolk. On the diagram, show what will d. 0.7 degree C happen for each of the temperature changes at e. 1.0 degree C the right. Use a different color for each temperature rise.

2. Suppose Diagram B shows part of the southeastern shoreline. The elevation of a number of points is given. Draw what you think the new shoreline would look like if the annual average temperature rose by each of the amounts given in step 1. For each temperature rise, use a different color.

Analysis

1. List problems that might occur along the southeastern coast if the earth's annual temperature rose by 0.2 degrees C.

2. Suppose the prediction we used above is wrong and increasing amounts of carbon dioxide cause the earth's annual temperature to go down. This would cause the polar ice caps to grow. How would that change your shorelines on Diagrams A and B?

3. What advantages and disadvantages are there if the earth's average temperature increases by 0.4°C? Answer this (a) for people living near the shore and (b) for people living 200 km inland.

2 Beaches, Sand, and Currents

The United States coast from New Jersey to Florida has many sandy beaches. But these -beaches are not all alike. Where wave action against the beach is heavy, the sand grains are large. The beach itself slopes sharply into the sea. Less exposed beaches tend to have wide, shallow shores with gentle slopes.

The most common mineral in sandy beaches is quartz, which comes from inland on the continent. Rock fragments are eroded away by rivers and carried down to the ocean. When these pieces of rock reach the ocean, they are pounded into tiny grains by the movement of waves against the shore. Other sources of materials for sand are rock outcroppings along the shore and the shells of marine animals. Along the coast of North Carolina, for example, as much as 10% of the beach materials are ground-up shells. Farther south the sands are made from weathered rocks carried by rivers from the Appalachian Mountains. Still farther south the eastern beaches of Florida can be almost pure quartz or quartz mixed with shell and coral.

Some of the most beautiful and valued beaches in this region are on barrier islands. These are islands of sand built up by the ocean and parallel to the mainland. Barrier islands are formed along gently sloping sandy coasts where the water remains shallow far from the shore. Their name comes from the fact that these stretches of sand are between the ocean and the mainland. Figure C shows barrier islands, the lagoon behind, their inlets, and a river that empties into the lagoon.

Once formed, barrier islands are far from permanent. Giant winter storms with their huge waves can form new inlets or close older ones. During these storms, large amounts of sand can be dug from one place and deposited elsewhere along the beach. Even during the calmer weather of summer, the ever-present surf is constantly reshaping the islands. Breaking waves carry sand with them as they run back into the sea. Longshore currents pick up this sand and move it down the coast. Since the longshore currents in this area usually move southward, they are slowly carrying the barrier islands in that direction. Where there is an arm of land into the ocean or an inlet, sand is deposited on the north side and eroded away on the south side. This constant migration of sand can cause entire sections of beach to disappear or the mouths of inlets to move as much as 25 meters a year.

Because barrier islands are such splendid areas, many people want to live and work on them. To do so, they try to change the island to fit their needs. Figure D shows how the people who live in Fishville plan to change Blue Inlet. They want to stop the migration of the inlet by putting in jetties, or walls, along the inlet. Should this plan be carried out? Look at the diagrams and the information, then answer the questions below.

1. How does the Blue River contribute to the formation of barrier islands?

2. Why do you think people at Fishville are concerned about the movement of Blue Inlet?

3. If you were the State Park Director how would you react to the plan? Why?

4. If you were in charge of the Coast Guard Station how would you react to the plan? Why?