BARRIER ISLANDS
   AND  THEIR
  FORMATION
 Created by
    Nancy Vest
    Caroline Leggett
   Jennifer Williams











Goal:  To enable students to acquire scientific knowledge by applying concepts, throries, principles and laws from life/environmental, physical and earth science.
Enable students to gain a better understanding and appreciation of the earth and how the changing earth can affect the lives of humans.
 

OBJECTIVES
1.  Use a diagram to explain the statement "Barrier islands are constantly changing"
Theme 2.1:  The development of models provides a conceptual bridge between the concrete and the abstract.
2.  List one effect of the sand sharing system
Theme 2.5:  The interactions within and among systems may result in changes in the properties, position, movement, form, or function of systems.
3.  Explain how one barrier island has changed throughout years due to the sand sharing system
Theme 2.6: In any natural process the form may change but nothing is lost.

ENGAGE:  In the winter of 1999, on the island of Hatteras Island, North Carolina, a major construction was underway.  The magnificent Cape Hatteras Lighthouse, built in 1870, is being moved from its original location to a new one.  When built, it was approximately 1,500 feet from the shoreline.  Over time, the ocean inched its way closer so that in 1999, it lay only 160 feet from the Atlantic.  This extraneous process will take approximately 1 year transport and reconstruct this historical structure.



EXPLORE:
Why would it be necessary to move this huge structure that had been standing in that same spot for nearly 150 years?

To answer this question we must first consider the location of the lighthouse.  It is located on the tip of Ocracoke Island on the beach.  Now what do we know occurs at the beach?  There is a lot of wave action occurring there and there is also a lot of wind blowing on beaches.

To further explore the question to why it was necessary to translocate Cape Hatteras Lighthouse let's do an activity.

MATERIALS:
- Clear storage box, rectangular baking dish, or bread pan.
- Block of wood
-Modeling clay
-Sand
-Water

PROCEDURE:
-Create and island of sand along one side of the container and place a toothpick on the edge(supposedly where a lighthouse would stand)
-Carefully place the water in the container
-Using the block of wood, create waves that approach the island at an angle from the north
-Continue creating waves for several minutes and record what happens to the beach

What you should have observed is as the waves strike the island and move away from the island each time some of the sand also moved away from the island.  The longer you created waves, the more sand was removed from the island.  Eventually the simulated lighthouse fell because the sand which was holding it up was washed away by the wave action.

Now can you offer an explanation as to why the historical lighthouse is being moved?

Can you offer any way to possibly decrease the rate of erosion to the shoreline and prevent having to move the lighthouse again in later years?


EXPLANATION:

The Cape Hatteras Lighthouse is located on Ocracoke Island, a barrier island off the coast of North Carolina.  A barrier island is defined as a long, offshore, dune covered deposit of sand lying roughly parallel to and separated from the mainland by a shallow sound and or salt marsh and are separated from each other by tidal inlets that are very productive and offer a breeding ground for many animals, many of which are endangered.


 

Barrier islands formed over thousands of years of geological processes involving the melting and formation of glaciers which resulted in the rise and fall of the sea level.

Barrier islands are call such because they create a barrier between the open ocean and the mainland, protecting the main coastline form wind, waves, tides, currents, and storms and hurricanes.  They shelter estuaries that form behind the islands.  They also allow marshes to build up in the quiet waters of the sound.

Barrier islands are constantly changing through the processes of the sea (wind, waves, tides, storms, etc.).  Some may disappear, but if left alone, will rebuild.  This constant changing process of the islands is due to one main factor;  the movement of sand.  The sand of most of the barrier islands of the Atlantic originate from the Appalachian Mountains.  Three hundred million years ago, the Appalachians stood at least three miles high.  soon after their formation and for millions of years since, constant erosion has all but flattened these mountains to what we see today.  The sediments from the mountains were carried by streams to rivers and eventually deposited in the ocean.  as the seas rose and fell with the rise and fall of water due to the glacial advances and retreats, the sands from the Appalachians, were swept back and forth from the edge of the continental shelf to the fall line, creating barrier island ridges that filled the Atlantic coastline.

The sand on today's Atlantic beaches is mostly quartz and mica with deposits of some heavier minerals including ilmenite.  By examining rocks in the Appalachians we see that those are consistent of the same materials.
 
 

Sand Sharing
Barrier Islands are flexible and must remain ina constant state of change in order to survive.  Once the barrier island is formed, the action of the wind, waves, tidal currents, and longshore currents causes drastic changes in it shape and size.

A complex system known as sand sharing is what allows the barrier islands to remain inexistance.  Each island is dependent on the island north of it to maintain.  Once the eroded sand is deposited into the ocean, it is pickedupby the longshore currents and moved south.  The waves then push and pull the sand to and from the beach and fromone island to the next.

When one island looses sand, the next one, the onesouth of the previous, will gain sand.  As sand is pulled from the beaches into the surf zone, it gets swept into the littoral drift.  This current, which moves in a north to south direction, will then deposit the sand to the next island.  In general, the north end of the islands
gain sand and the south end will loose sand.
 
 
 


 
 
 
 

As we said before, the barrier islands are separated by tidal inlets.  These inlets interrupt the flow of the sand sharing system.  As the tidal currents move back and forth between the islands some of the sand becomes permanently trapped in the protected waters of the sounds that are between the island and the mainland.  Once the sand enters the sounds, the finer sand and silt or clay particles settle, creating mud deltas.  These mud deltas build up over many years and create the base for which the marsh grasses grow.  This process adds to the island and moves it toward the mainland.

By understanding how the barrier islands are constantly changing with the motion of the sea, we can see that the island can literally change overnight with the help of a hugh storm or hurricane.  By comparing the coastline from year to year these changes can be observed.
 

Project The Shifting Shores of Sapelo Island
This project will demonstrate the previous lesson regarding the changing barrier islands
-by investigating how the beaches on Sapelo have changed from 1940 to 1992
-investigating how the tidal creeks of Sapelo have changed over time
-explain beach migration using the sand sharing system

Materials
-4 colored pencils or pens
-tracing paper

Procedure
1.  Lay a sheet of tracing paper of a 1940 drawing of Sapelo and color the two black dots.
2.Trace the 1940 map in one color
3.Move the tracing to the 1953 map and match the black circles and trace the 1953 map with a different color.
4.Do the same for the 1974 and the 1992 maps.
5.Discuss the following questions:
    -What changes do you see on the shoreline of Sapelo between 1940 and 1953?  Between 1953 and 1974?  Between 1974 and 1992
    -What changed occurred to the tidal creeks and rivers?
    -From 1940 to 1992 what parts of the island have experienced accretion and erosion?
    -What factors may be responsible for this accretion and erosion?
    -For years, locals have fished and seined in "the big hole" an area between the north end of Nanny Goat Beach and the south end of Cabretta.  In recent years, the fishing has not been as good and the locals say "the big hole is drying up".  Compare the 1974 and the 1992 maps and apply what you have learned about island migration and the sand sharing system.  Explain what is probable happening to decrease the size of "the big hole" and the quality of the fishing there.


ELABORATION:

Now that we have briefly discussed how the barrier islands change shape and form, knowing that the Cape Hatteras Lighthouse is built on a barrier island, can you offer an explanation as to why it is important to relocate this structure?  Also knowing what we know about the ever-changing shape of barrier islands, is it a wise decision to build homes there?  If they are, then knowing that they are building in a high risk area, should they be eligible for homeowners insurance, which if they use, would ultimately increase rates for everyone?  Or should we preserve these valuable resources and use them as protected areas for our ever increasing endangered species and simply leave them to do their job protect the mainland.
Where in Tennessee, Do we see similar situations?  How about when people build on the mountains and get erosion destroying their homes?

Reading Assignment:I will read out loud pages 76-84 from John McPhee's book "A Sense of Where You Are".  This book relates some of the same issues seen on the Atlantic barrier islands to issues in the California Sierra Nevadas in regards to the dangerous and fatal mudslides occurring on the increasing populated hillsides.

Reading Assignment:  Read chapter 19 (pages 117-122) from the book "The Web of Life" regarding the effect of man on nature and the web of life.


EVALUATION:

-Students will be asked to take an examination consisting of multiple choice, short answer, and diagram and discuss the changing processes occurring on a barrier island.
-Complete the project demonstrating how the shores of Sapalo Island have changed from 1942-1992.
-Discuss the reading assignments in class.



 

GLOSSARY OF TERMS

Barrier Islandlong, offshore, durn-covered deposit of sand lying roughly paralles to and separated from the mainland by a shallow sound and/or salt marsh

Salt Marsh:  Type of wetland that consists of salt water and a variety of grassy hydrophytic vegetation

Estuaries:  Type of wetland that consists of a delicated mixture of salt water and freshwater

Tidal Inlet:  Separation between consecutive barrier islands that allow entrance to mainland

Littoral drift:  North to south movement of water in the ocean
 
 
 


                       BIBLIOGRAPHY

Tennessee State Science Framework

Olsen, Margaret M.  "Sapelo Island-Geogria's Coastal Treasure".

http://savethelighthouse.com

http://www.epa.gov/students/

http://inlet.geol.sc.edu/nerrsintro.html

Storer, John H.  "The Web of Life"  p. 117-122.  The New American Library, Inc.  New York, New York 10019.