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![](/web/20160804011836im_/http://www.unesco.org/csi/unesco3.gif;pv4557de5b2c48eee9) |
Environment
and development
in coastal regions and in small islands |
![](/web/20160804011836im_/http://www.unesco.org/csi/csi.gif;pv90b588ee93b29b06) |
Coastal region and small
island papers 19 |
5
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Beach composition
The powder
white
sand
on this beach at Vlingilli,
Madives, 2003, originates
from the surrounding
coral reefs.► |
![](/web/20160804011836im_/http://www.unesco.org/csi/pub/papers3/sande31.jpg) |
![](/web/20160804011836im_/http://www.unesco.org/csi/pub/papers3/sande32.jpg) |
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Different sizes of material on a
beach in
Rarotonga, Cook Islands, 2003. |
Background
A
beach consists of loose material, of varying
sizes. The actual material itself can tell a lot about the stability of
the beach.
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Activity 5.1 |
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Finding out where beach material comes
from
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Observe and record |
► |
Observe, describe and record the type of beach material. A beach may be
composed of just one type of material, e.g.
sand, or there may be a mixture of
materials, e.g. sand, gravel and boulders. Beach material can be classified into
different sizes (see the table below). Sand is just one size range.
Note and record the colour, size and texture of
the material on the beach. A simple ruler or tape measure can be used to
distinguish between the larger sizes, although obviously not for clay
and silt. Use plastic bags to collect samples of material from different
parts of the beach and label the location, e.g. near
high water
mark,
beneath cliff face and so on.
SEDIMENT SIZES |
Clay |
Less than 0.004 mm |
Less than 0.00015 inches |
Silt |
0.004–0.08 mm |
0.00015–0.003 inches |
Sand |
0.08–4.6 mm |
0.003–0.18 inches |
Gravel |
4.6–77 mm |
0.18–3 inches |
Cobbles |
77–256 mm |
3–10 inches |
Boulders |
Greater than 256 mm |
Greater than 10 inches |
WHAT IS SAND?
Sand consists of small pieces of stone or shell and can be
classified into three main types:
Common components of
mineral
sand include the following:
-
Quartz grains are clear, quartz
is one of the most common
minerals found in
sand and is extremely weather
resistant
-
Feldspar grains are pink, light
brown to yellow
-
Magnetite grains are black and
strongly magnetic
- Hornblende grains are black and
prism-shaped
Common components of biogenic
sand
include the following:
- Coral may be identified by its
many rounded holes
- Shell fragments may come from
scallops, mussels, clams and
be a variety of colours
- Sea urchin spines appear as
small rods or tubes and may be
a variety of colours
Sand samples may also include some
organic material.
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![](/web/20160804011836im_/http://www.unesco.org/csi/pub/papers3/sande33.jpg) |
This black
sand
at Londonderry,
Dominica, 1994, is volcanic and
is transported to the coast
by the rivers. ► |
![](/web/20160804011836im_/http://www.unesco.org/csi/pub/papers3/sande34.jpg) |
▲This
yellow-brown
silica
sand at Walkers Pond, Barbados, 1983,
originates from the
erosion of
inland rocks. |
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Discuss where
the beach material originates |
► |
Back in the classroom, make a sketch map showing
the different features (e.g. river mouth, rocky outcrop,
cliff) on the
beach and the different types of material. Discuss where the different
types of material might originate.
Sand is
composed of small pieces of stone or shell and its colour depends on its
origin. Sand may come from inland rocks and be carried to the coast by
rivers and streams. It may originate from nearby
cliffs, or even far
distant cliffs and be carried to a particular beach by
longshore
currents (see Chapter 10). Or the sand may have its source in the
offshore coral reefs and
seagrass beds.
The pure white sands of many tropical beaches
are derived from coral reefs or coral reef
limestone rocks. Yellow to
brown silica sand found along some coasts comes from the
erosion of
inland rocks, while the black sand beaches of many volcanic islands
consist of grains of
olivine and
magnetite, derived from the erosion of
volcanic rocks.
Ask students to write a story about the life of a grain of sand,
starting perhaps in an inland mountain and travelling to the beach by a
stream, or originating on a
coral reef and being moved by waves and
currents to a beach. Ask them to imagine their life on a beach and what
happens when a storm strikes or a sand miner moves them. A ‘letter from
a grain of sand’ in the accompanying box provides some further ideas.
![](/web/20160804011836im_/http://www.unesco.org/csi/pub/papers3/sande35.jpg) |
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Ernesto Ardisana
Santa (fourth
from right) presenting ‘Letter from
a grain of sand’, Cuba, February
2004. |
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LETTER FROM A GRAIN OF
SAND
Hello friends!
I am a tiny
grain of sand, bathed by the sea spray, created by the waves
of the Caribbean Sea. I live in a marvellous place where,
every morning at sunrise, I listen to the tremulous murmur
of flying fish shooting out of the transparent sea water.
Many birds inhabit this place, particularly the small,
delicate and dark sea swallows which fl y constantly in
search of food.
The sea is
sweet and beautiful, but it can also be cruel and can become
angry all of a sudden. Perhaps you may be surprised at my
referring to the sea in Spanish as if it were feminine. This
is the way we, those that love her, refer to the sea. I
consider her as belonging to the feminine gender and as
someone who concedes or denies big favours, and if she does
perverse deeds, it is because she cannot help it.
My Mom and Dad
are also sand grains, already hundreds of thousands of years
old, since in this beach toxic substances that could have
degraded us have never been used. Those persons who visit us
are sorry to tread on us, which explains their walking
warily and their not leaving food leftovers behind. We are
always tended by children and the young of the local beach
community, who remove the plant litter that comes out of the
sea.
Through this
letter I wish to express my solidarity with all the
suffering grains and tiny grains of sand in this world, and
especially so those of the coasts of Galicia in Spain who
are bearing the effects of an oil spill.
I wish to
invite you all to my unpolluted world. You can find me at
the following e-mail address: letstakecare@everybody.world.
I will receive you with pleasure. I now say goodbye with a
great marine salutation, since it is the time to go to
listen to the classes given by the snail on how to recycle
the trash left daily on the coasts by humans, in order that
this, my small paradise, may remain clean and pure and that
I may be proud to live in my blue planet, helping to make it
liveable for others too.
I am looking
forward to your messages. I will give you my address later,
because it is difficult, very difficult to understand, since
unfortunately you must find your way through the paths of
dreams.
With best
wishes
The happy tiny grain of sand
Source: Instituto Pre Universitario
Vocacional De Ciencias Exactas,
Comandante Ernesto Che Guevara, 2004
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Activity 5.2 |
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Exploring what happens when sand and
stones are removed for construction |
Observe and record |
► |
Visit a beach that has been heavily mined for construction material as
well as a beach that has not been mined. Observe and record the
differences between the two beaches and relate them to the mining
activity. Features to look for and discuss might include the following:
![](/web/20160804011836im_/http://www.unesco.org/csi/pub/papers3/sande36.jpg) |
Mined beach
at
Brighton,
St Vincent and
the Grenadines,
1995. |
- How is the material being extracted – with
heavy equipment or by people using spades?
- Are there vehicle tracks all over the
beach?
- Are there deep holes where material has
been extracted?
- Does the water reach further inland?
- Are there trees that have been undermined
or vegetation that has been trampled?
- Might the deep holes affect baby turtles if
they nest on this beach?
- Does the beach look like a nice place to
visit?
- Are there other sources of construction
material besides the beach?
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Discuss how the
beach material
is used in
construction |
► |
Ask the students to think about the construction
materials used for houses and buildings in their country. Topics to
discuss might include:
- What materials were used to build houses in
the past?
- Compare and contrast the differences
between concrete houses and wooden houses.
- What materials are needed to make concrete?
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Activity 5.3 |
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Measuring beach sand - size, shape and
sorting |
What to measure |
► |
Sand samples can be collected from different parts of the beach and the
size, sorting and shape of the sand grains can be measured. These
characteristics are likely to vary from one part of the beach to
another. |
How to measure |
► |
During a visit to the beach, sand samples can be collected from
different areas, e.g. from a river mouth, from the inter-tidal zone
where the sea is wetting the sand, from the dry sand at the back of the
beach, from a dune behind the beach, or from beneath an eroding rock
face or cliff.Place the sand samples in
clean plastic bags, label each bag and keep notes on exactly where the
sample was collected.
THREE ‘S’S’ OF SAND:
SIZE, SHAPE AND SORTING
Sand size depends on the origin of the sand
and the wave energy. Strong wave action, such as found on
exposed coasts, washes out the finer sand particles leaving
only coarse sand and a steep beach profile. Often stones and
boulders may be present on such beaches. However, on more
sheltered coasts, finer sand is deposited and a gently
sloping beach results. Near mangroves and river mouths,
silt
and organic material also collects.
Sorting relates to the
mixture of sizes, e.g. if all the sand grains are the same
size, then the sample is well sorted. If there are a lot of
different size grains in the sample, then it is poorly
sorted. As sand is moved about by the waves, it tends to get
better sorted, in other words all the sand grains are about
the same size.
The shape of the sand
grains relates to whether the individual grains are angular
and pointed or whether they are smooth and rounded. As the
sand grains are moved about by the waves, they tend to
become rounded with very few sharp points.
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![](/web/20160804011836im_/http://www.unesco.org/csi/pub/papers3/sande37.jpg) |
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Measuring the
shape of sand
grains with a magnifying glass,
St Lucia, 2001. |
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On return to the classroom, the
samples should be spread out on a flat surface to dry (if they are
wet). Then sprinkle some dry grains on to a plastic sheet. Place the
plastic sheet with the sand grains on top of the size charts in
Figure 11. If the sand grains are light coloured use the left hand
chart, while if the grains are dark coloured use the right hand
chart. With a magnifying glass, determine the size category matching
most of the grains and record the results. Then compare the sand
grains on the plastic sheet with the sorting chart, and with the
magnifying glass determine the best-fit sorting category. Finally,
compare the sand grains in the sample with the angularity charts to
determine the shape.
If the beach is made up of
stones only, these can also be measured. Collect at least 20 stones,
picking them randomly, measure the length along the longest axis and
then calculate the average. The chart in Figure 11 can be used for
determining the shape of the stones.
![](/web/20160804011836im_/http://www.unesco.org/csi/pub/papers3/sande38.jpg) |
Figure 11
Sediment analysis charts for size, sorting and shape
(adapted from Kandiko and Schwartz, 1987; and Powers,
1953). |
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When to measure |
► |
You may wish to collect sand samples from different parts of the beach
one time only, and compare the different samples.
Alternatively you may decide to collect and measure
sand samples from the inter-tidal zone, at different times of the year
and after different wave events, e.g. after the summer when the waves
have been relatively calm and then again after a high wave event. Some
beaches show marked differences in composition, having sand in the
summer and stones in the winter. Size comparisons can be made and
related to the wave energy (see Chapter 9).
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What the measurements
show
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► |
Variations in size, sorting and angularity will
provide information about the different zones on the beach and the processes
that shape these zones. For instance,
dunes are formed by the wind lifting dry
sand grains and carrying them to the back of the beach. So, dune sand might be
expected to be smaller in size than sand in the inter-tidal zone. Similarly,
sand near a river mouth might be expected to have more organic material in it
than the sand in the inter-tidal zone.
![](/web/20160804011836im_/http://www.unesco.org/csi/pub/papers3/sande39.jpg) |
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![](/web/20160804011836im_/http://www.unesco.org/csi/pub/papers3/sande40.jpg) |
In the summer months (April
to
October), Bunkum Bay in
Montserrat is a sandy beach; |
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while in the winter months
(December to March) the sand is
replaced by stones. |
Comparisons of sand size over time might be
shown in a bar graph, such as is shown in Figure 12. In this example the
beach consisted of black and grey stones in January 2002, while at other
times of the year, the beach was made up of black sand (see also
photographs of Bunkum Bay in Montserrat where similar changes take
place).
![](/web/20160804011836im_/http://www.unesco.org/csi/pub/papers3/sande41.gif) |
Figure 12
Bar graph showing changes in sediment size. |
Start
Chapter 6
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