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Objective

Students will learn to collect and analyze data in a scientific manner. The goal of this project is to identify which geographical areas of a barrier island are affected by stronger wind and water energies by characterizing individual sand samples from different localities across the island transect. Students should hypothesize which areas experience higher wind or water energies by looking for trends in their analyzed sand samples.

 

Major Understandings

Barrier Islands are formed and constantly reshaped by the transport of sand by water and wind.

The type and intensity of these forces vary in different sections of a barrier island. For example, there is more activity on top of s dune than directly behind it.

Sand is made of many different minerals that vary in density.

Sand grains vary in size.

The distribution of minerals and average grain size varies along a beach transect.

More energy is required to move heavier sand grains.

By observing the grain size and mineralogy variations in sand across a barrier island, it is possible to determine which areas are affected by higher energies.

 

Materials Needed

Binocular microscope

Metric scale (preferably digital)

A sieve set containing at least five sieve sizes (Sieve sets available through science catalogues.) Make sure that sets include a wide range of sieve sizes appropriate for the spectrum of grain sizes in your area of study. (I.e., silty sand needs finer sieves.)

Locking sandwich bags

Strong magnets

Glass slides-2 for each group

Plastic cups (small)

Rubber Cement

Tissue paper (thin)

Calculator

Permanent Markers

Tape measure (metric)

Bug repellent/ sunscreen

Screening

 

 

Procedure

Have students read the introduction section and follow up with a pre-lab discussion on wind and water transport of sand. Students should have a basic grasp of the Major Understandings before beginning this project.

Choose a transect to cover. An ideal transect will be unaltered by human activities, yet, not be covered in poison ivy or other potential hazards. The transect should also contain the major zone of a barrier island; Beachface, Berm, Foredune, Backdune and Bay beach.

If this project is to be done on multiple days, try to find a permanent reference point on or near the transect.

Look at the local tide tables. Times of low tide will be better for sampling variety.

Divide class into enough groups to cover all areas to be sampled.

Collect samples

Assist students in graphing and analyzing data

 

Pre-Lab Questions/Discussion guide

1.) In which areas of a barrier island would you expect exposed to larger amounts of energy?

2.) What would you expect to find in the areas of higher energy?

Average grain size?

Percentage of heavy minerals? These include magnetite, garnet, staurolite, and olivine.

3.) What kind of relationship would you expect to find between average grain size and mineral content?

Students should discuss as a class which areas they would like to sample. Be sure they include areas on the beach face, berm and dune (both front and back)

 

Introduction

Barrier Islands

Barrier Islands occur along the length of shorelines that have a lot of sediment. Barrier islands are not stationary structures. They migrate landward or seaward as the sea level changes. There are several different sub-environments across barrier islands. The beachface, also called the intertidal zone, is the area on a beach that extends from the water level of low tide to the berm, a terrace like ridge built by storm waves. The next section is called the backshore, and includes the area from the berm to the dunes on the other side of the barrier island.
 
Sand

Sand comes from rocks. As rock is exposed to the weathering conditions and geological processes, it gradually breaks down into sediments. This idea is a keystone in the geological cycle. What type of minerals make up a certain sand is therefore directly related to the type of rocks from which it originated. (It also depends on the average energies of a particular beach.) Glaciers created Long Island, therefore the sediment that forms the sand is derived from glacial sediment. Most beaches are dominated by quartz, a light colored mineral that is more resistant to weathering than most other minerals. This is why most beaches appear to be white. If you take a closer look at the sand, you will notice that quartz is one of many minerals. On Long Island beaches, among the quartz grains you can see lesser amounts of magnetite, garnet, staurolite, and sometimes olivine.

Sand Transport

A barrier island is affected by both wind and water processes. The effect of these energies varies with different kinds of sand grains. The equation for kinetic energy is E=1/2 mv² . According to this equation, if the wind and water are moving at the same speed, the water, which has a greater mass, will have more kinetic energy. Therefore water has a greater capacity to transport larger and heavier grains. The areas affected by water energy are the beachface, the bay beach and sometimes the berm (during storm weather). The other parts of a barrier island are all shaped by aeolian, or wind processes, which change in intensity over the island zones. Areas subject to stronger forces will have a greater percentage of large and/or heavy mineral grains.
 

Procedure

Data collection

1.) Each group will choose one zone along the beach.
2.) Each student should create their own data sheet that will include
        Date:
        Time:
        Location:
        Distance from reference point:
        Sample #:  
        Comments:
3.) With the meter stick, measure the distance from the ocean or the reference point to your site and scoop sand (about the size of a half-cup) to al least 5 cm. depth. Put the sand in a plastic bag and label the bag with site area, distance from ocean or reference point, and group number using the permanent marker.
4.) Back in the lab, put the samples on a piece of paper away from any drafts. Leave them overnight under a lamp to dry.

Sieving

1.) Once the samples are dry, decide which sieves to use and in what order they should be stacked. Separate the samples by grain size.
2.) Once sediments have been separated, take sieves apart, being careful not to lose too much sand. Dump the sand onto a piece of paper and weigh the different sizes. Calculate the weight percentage of each using chart 1.

Chart 1

Sieve #	Mass (g)	Weight % = 100* mass/total mass
.	.	.
.	.	.
.	.	.
.	.	.
.	.	.
.	.	.
.	.	.
Total:

 

3.) Find the average grain size of your site using the formula:

Sieve grain size (mm)=d

Weight % = p

Average grain size=(d1)(p1)+(d2)(p2)+……(dn)(pn)

For (n) sieve sizes

4.) Data from each group should be publicly posted, so that it can be plotted together. Using a spreadsheet, or by hand on graph paper, students should create a graph plotting average grain size against the location on a beach. Figure 2 is an example of such a plot.

 

Mineralogical Analysis

Before classifying the minerals, students should be able to identify the major minerals found in the sand. Minerals will be separated into heavy and light categories. Light minerals include quartz and feldspar. Heavy minerals include magnetite, garnet, staurolite, and olivine, along with other trace minerals. See Chart 1 below

 

 

If you see:	It might be:
Clear and Colorless, or White	Quartz
Black, Dark Grey	Magnetite
Pink (Light or Dark)	Garnet
Orange, Brown (Light or Dark)	Staurolite
Light green	Olivine
Opaque and Whitish	Feldspar

 

2.) Next, figure out the mineralogy of the samples. This can be done in two ways.

Grain Count:

Use binocular microscope.

a.) Students should first choose a relatively small grain size that is represented in all samples. For example sieve sizes .25mm-.17mm. Note: Larger grain sizes tend to contain a less diverse mineralogy and are less interesting to look at for the students, but distribution trends remain similar. However, if the grains are too small, then the minerals are hard to count. See examples below.

Each group is to create a slide by applying rubber cement to the slide and pouring the sample over the slide. Be sure to hold the slide over a cup to catch the excess sand.

Students should glue a gridded slide onto the sand side on the previous slide. Each student will be responsible for the light and dark grain counts of a particular square slot. Using the supplied chart, each student will count the number of heavy minerals and light minerals.

Chart 2
Student #	Light Minerals	Heavy Minerals	Total	Volume % Heavy minerals
Example	156	102	=156+102=258	=100*102/258=39.5%
.	.	.	.	.
.	.	.	.	.
.	.	.	.	.
.	.	.	.	.
.	.	.	.	.
.	.	.	.	.
.	.	.	.	.

 

 

 

 

 

 

 

Once again, all the class data should be collected and plotted together. This time the plot will be the percent of heavy (dark) minerals against location on the beach. Figure 3 is an example of such a plot.

Physical Separation with Strong Magnets:

This method uses the composition of magnetic minerals such as garnet and magnetite to physically separate the dark and light minerals. If the magnet is not strong enough, it will only pick up magnetite.

a.) Take a part of your sample and pour it on a piece of white paper

b.) Cover the magnet with tissue paper

c.) Use the magnet to remove as much magnetic material as possible by "stamping" the magnet onto and off the sand. Then lift the magnet off the tissue paper, while holding it over a cup or another piece of paper. The magnetic material will fall off the tissue paper.

d.) Weigh both magnetic and non-magnetic sample portions.

e.) Once again, calculate weight percents and post data for the class

f.) Create graph of weight percent of heavy minerals vs. distance from ocean.

 

Discussion Questions

1.) Look at your first graph. Which areas have the largest size grains on average? Why do you think this is?

2.) Look at distribution of heavy minerals. How is this graph similar and different from the first graph?

3.) Do you see any resemblance in the graphs created by grain counts and magnet separations?

4.) What do these graphs suggest about the relative forces of wind on a barrier island? (Where are they strongest and where are they the weakest?)

 

Source: Unknown