Tiny Pebbles in the Sand EarthCache
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Difficulty:
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Here you can see the first stages of how some sedimentary rocks are
formed. Galveston sediment is composed of three main sources of
sediment:
1.inorganic mud & sand eroded from continent
2.organic mud from decaying plants-animals
3.sand-gravel from shell
The wind, waves, and currents sort the sediment making up Galveston
Island. You will notice that very little mud is deposited on the
high-energy Gulf of Mexico side because it is washed away by waves.
To find deposits of mud you need to go to the bay side of the
island, especially in the marshy areas. This is where mud is
produced by decaying vegetation and where some of the mud moving
down the rivers and creeks of the bay is trapped. The marsh
vegetation and relatively sheltered locations allow the deposition
of mud. In many places on the bay side, however, the marsh may have
a shelly beach on the fringe, where bay waves are eroding the marsh
and concentrating oyster shells. Also, near San Luis Pass, strong
tidal currents transport sand along the bay-side shoreline.
Sand and shelly gravel are found on the Gulf beaches and the
island's interior, which is mostly sand because of the way the
island advanced seaward after it formed. So as you walk landward
from the Gulf beach, you are walking across earlier beach deposits.
Most of the sediment on the beach and in the dunes is quartz sand
that was eroded from the continent. Whole shells and shell
fragments made of calcium carbonate add to the variable texture of
the sediment, and small amounts of black, heavy minerals and
organic matter add color.
Wind and waves sort the sediment according to how easily it is
transported. Wind transports small, light grains, so the sand in
the dunes is relatively fine-grained and well-sorted quartz.
Compared with dune sand, you will find that the sand and shelly
gravel moved by waves on the beach is coarser grained and more
poorly sorted because waves can move all grain sizes.
When waves strike the beach, sand may move onshore, offshore, or
along the beach. If waves hit the beach at an angle, which is
almost always the case, then sand will move along the beach. On any
given day, the direction on the beach along which the sand moves
depends on the direction of the waves. Along Galveston Island, sand
can move in either direction, but averaged over the span of a year
or more, you will find that more sand is moved in one direction
than in another.
NOW FOR SOME REAL FUN!! Coordinates given above are for the public
beach on the west end of the island where you can conduct your
testing and to make your observations. There is a wooden walkway
across the dunes to the beach area so it is handicap/stroller
accessible.
To receive credit for completing the earthcache, you will need to
do the following:
1. Dig a small hole at the beach site of your choice 16”-20”deep
with small beach/garden shovel brought from your home.
2. Dig another one in the sand dunes. Notice the difference in the
fine layers the dune's pit reveals. If you would like, you may go
across the island and test the opposite side of the island that
contains more mud settlement. Post picture of you and GPS at the
each test site, and email your observations and don't post
these.
3. At the Public Crossover Sign, you learn about something you
will probably see along the beach. What is this, what size do they
reach when fully grown and what color are they?
After testing, please refill the holes so others will not trip or
fall. Remember to take everything with you as not to leave any
clutter in the area.
Developed by A Platinum EarthCache Master
Congrats to Voodoo Chicken for FTF
Additional Hints
(No hints available.)