aka: Sandy Beaches – Part II
Equipment
Required:
You will need a reasonably accurate set of scales, a one litre
container and a hand lens or magnifying glass.
Background
Beaches are deposition landforms, and are the result of wave
action by which waves or currents move sand or other loose
sediments of which the beach is made as these particles are held in
suspension. Alternatively, sand may be moved by saltation (a
bouncing movement of large particles). Beach materials come from
erosion of rocks offshore, as well as from headland erosion and
slumping producing deposits of scree.
The shape of a beach depends on whether or not the waves are
constructive or destructive, and whether the material is sand or
shingle. Constructive waves move material up the beach while
destructive waves move the material down the beach. On sandy
beaches, the backwash of the waves removes material forming a
gently sloping beach. On shingle beaches the swash is dissipated
because the large particle size allows percolation, so the backwash
is not very powerful, and the beach remains steep. Cusps and horns
form where incoming waves divide, depositing sand as horns and
scouring out sand to form cusps. This forms the uneven face on some
sand shorelines.
Coastal topography, coastal currents, sea level changes and
sediment load in rivers play a major part in shaping beaches. At
Brighton beach sediment derived from eroded schist is transported
down the Clutha and Taieri and longshore currents drag the sediment
to Brighton and other beaches. White coloured quartz from the
schist accounts for the creamy colour of Brighton beach. Headlands
here can act as groynes and the sand is deposited upstream ie
Brighton beach. Forecast sea level rises will change many of the
world’s sandy beaches. Locally, reduced sediment from damming
of rivers such as the Clutha have already been blamed for loss of
beach sand. Southland’s beaches fare worse due to the fact
that the once massive Waiau is now only 1/12 of its original volume
due to its flow being directed through the West Arm power station
on Lake Manapouri.
There are several beaches which are claimed to be the "World's
longest", including Cox's Bazar, Bangladesh (120 km). NZ’s 90
Mile Beach is 88 km long. Brighton beach certainly falls a long way
short!
View along Brighton beach
Logging
Requirements
0. Preface any email with GC23BY8 So Are The Days Of Our
Lives in the subject line and title and clearly note the
question number and answer. All emails will be read but you do not
need to wait for a confirmation email before logging. If your
answers are slim be prepared to supply additional information.
1. As previously stated the sand of Brighton beach is composed
of eroded schist. Using your hand lens examine the sand grains
looking for white coloured quartz. Once you’ve done this
select 20 grains (or however many you like) at random and calculate
the percentage of quartz grains. Email me this percentage.
Upload a photo of the test being done.
2. The density of the sand should roughly reflect that of
schist. The next task is to measure the density of the sand. The
formula for calculating density is
p = m / V
where p = density in grams per cubic centimetre, m = mass in
grams and V = volume in cubic centimetres (or cc, or mL).
Take your 1 litre (ie 1000 mL or 1000 cc) container, tare it on
your scales (or take its weight off your final mass) and fill it
with sand and record the weight of the 1000 cc of sand. Take this
weight and divide it by 1000 cc as per the formula to get the
density in grams per cc. Schist density is roughly 2.8 g per cc.
But, your are finding the density of schist sand, not schist rock.
Email your density of the schist sand and comment on why this is
above or below that of rock. Upload a photo of the test being done,
it must clearly show that you are on Brighton beach.
Key
Sources
Wikipedia article on sand
Wikipedia article on beaches
2010 Stegan’s
EarthCache Masters Programme
Since it is not very feasible for many NZers to easily get more
than two states for the earthcache.org masters programme and
therefore not get past Bronze I’m running my own one on a
number of Earthcaches that I plan to release this year (all things
being equal) with the following points system:
5 points: First to find
3 points: 2nd to find
1 point: Logging a find
1-5 points: Special bonus questions.
Shared points for joint finds.
At the end of 2010, I’ll issue certificates for 1st, 2nd
and 3rd and other prizes might be possible.
Updated information and Leaderboard at: Stegan’s
Earthcache Programme
