The area at and near the coordinates has been devastated by
coastal erosion. The
rocks that you are walking on are mainly
limestone. Over
the centuries water from the
ocean, rain, hurricanes, and tsunamis have beaten a natural
trail into the limestone and other rocks in this area. Also
take notice how the sand and dirt around the trees and rocks
are nearly gone.
To understand Erosion and Tidal Erosion read the
following.
Erosion
Concept
Erosion is a broadly defined group of processes involving the
movement of soil and rock. This movement is often the result of
flowing agents, whether wind, water, or ice, which sometimes
behaves like a fluid in the large mass of a glacier. Gravitational
pull may also influence erosion. Thus, erosion, as a concept in the
earth sciences, overlaps with mass wasting or mass movement, the
transfer of earth material down slopes as a result of gravitational
force. Even more closely related to erosion is weathering, the
breakdown of rocks and minerals at or near the surface of Earth
owing to physical, chemical, or biological processes. Some
definitions of erosion even include weathering as an erosive
process. Though most widely known as a by-product of irresponsible land use by humans and for its
negative effect on landforms, erosion is neither unnatural nor without benefit. Far more erosion
occurs naturally than as a result of land development, and a
combination of weathering and erosion is responsible for
producing the soil from which Earth's plants grow.
How It
Works
Weathering
The first step in the process of erosion is weathering.
Weathering, in a general sense, occurs everywhere: paint peels;
metal oxidizes, resulting in its tarnishing or
rusting; and any number of
products, from shoes to houses, begin to show the effects
of physical wear and tear. The scuffing of a shoe, cracks in a sidewalk, or the chipping of
glass in a gravel-spattered windshield are all examples of physical weathering.
On the other hand, the peeling of paint is usually the result of
chemical changes, which have reduced the adhesive quality of the paint. Certainly oxidation is
a chemical change, meaning that it has not simply altered the
external properties of the item but also has brought about a
change in the way that the atoms are bonded.
Weathering, as the term is used in the geologic sciences, refers
to these and other types of physical and chemical changes in rocks
and minerals at or near the surface of Earth. A mineral is a
substance that occurs naturally and is usually inorganic, meaning that it contains carbon in a form
other than that of an oxide or a
carbonate, neither of which is considered organic. It typically has
a crystalline structure, or one in which the
constituent parts have a simple and definite geometric arrangement
repeated in all directions. Rocks are simply aggregates or combinations of minerals or organic
material or both.
Two and One-Half Kinds
of Weathering
There are three kinds of weathering (or perhaps two and
one-half, since the third incorporates aspects of the first two):
physical or mechanical, chemical, and biological. Physical or
mechanical weathering takes place as a result of such factors as
gravity, friction, temperature, and moisture.
Gravity may cause a rock to drop from a height, such that it falls
to the ground and breaks into pieces, while the friction of
wind-borne sand may wear down a rock surface. Changes in
temperature and moisture cause expansion and contraction of
materials, as when water seeps into a crack in a rock and then
freezes, expanding and splitting the rock.
Minerals are chemical compounds; thus, whereas physical
weathering attacks the rock as a whole, chemical weathering
effects the breakdown of the minerals
that make up the rock. This breakdown may lead to the dissolution
of the minerals, which then are washed away by water or wind or
both, or it may be merely a matter of breaking the minerals down
into simpler compounds. Reactions that play a part in this
breakdown may include oxidation, mentioned earlier, as well as carbonation,
hydrolysis (a reaction with water that results in
the separation of a compound to form a new substance or
substances), and acid reactions. For instance, if coal has been
burned in an area, sulfur
impurities in the air react with water vapor (an example of
hydrolysis) to produce acid rain, which can eat away at rocks.
Rainwater itself is a weak acid, and over the years it slowly
dissolves the marble of headstones in old cemeteries.
As noted earlier, there are either three or two and one-half
kinds of weathering, depending on whether one considers biological
weathering a third variety or merely a subset of physical and
chemical weathering. The weathering exerted by organisms (usually
plants rather than animals) on rocks and minerals is indeed
chemical and physical, but because of the special circumstances, it
is useful to consider it individually. There is likely to be a
long-term interaction between the organism and the geologic item,
an obvious example being a piece of moss that grows on a rock. Over
time, the moss will influence both physical and chemical weathering
through its attendant moisture as well as its specific chemical
properties, which induce decomposition of the rock's minerals.
Unconsolidated
Material
The product of weathering in rocks or minerals is
unconsolidated, meaning that it is in pieces, like gravel, though much less uniform in size. This is called
regolith, a general term that describes a layer
of weathered material that rests atop bedrock.
Sand and soil, including soil mixed with loose rocks, are examples
of regolith. Regolith is, in turn, a type of sediment, material deposited at or near Earth's
surface from a number of sources, most notably preexisting
rock.
Every variety of unconsolidated material has its own angle of repose, or the maximum angle at which it can remain
standing. Piles of rocks may have an angle of repose as high as
45°, whereas dry sand has an angle of only 34°. The addition of
water can increase the angle of repose, as anyone who has ever
strengthened a sand castle by adding water to it knows. Suppose one
builds a sand castle in the morning, sloping the sand at angles that would be impossible
if it were dry. By afternoon, as wind and sunlight dry out the
sand, the sand castle begins to fall apart, because its angle of
repose is too high for the dry sand.
Water gives sand surface tension, the same property that causes
water that has been spilled on a table to bead
up rather than lie flat. If too much water is added to the sand,
however, the sand becomes saturated and will flow, a process
called lateral spreading. On the other hand, with too little
moisture, the material is susceptible to erosion. Unconsolidated
material in nature generally has a slope less than its angle of
repose, owing to the influence of wind and other erosive
forces.
Introduction to Mass
Wasting
There are three general processes whereby a piece of earth
material can be moved from a high out-cropping to the sea:
weathering, mass wasting, and erosion. In the present context, we
are concerned primarily with the last of these processes, of
course, and secondarily with weathering, inasmuch as it contributes to erosion. A few words
should be said about mass wasting, however, which, in its slower
forms (most notably, creep), is
related closely to erosion.
Mechanical or chemical processes, or a combination of the two,
acting on a rock to dislodge
it from a larger sample (e.g., separating a rock from a boulder) is
an example of weathering, as we have seen. If the pieces of rock
are swept away by a river in a valley below the outcropping, or if
small pieces of rock are worn away by high winds, the process is
erosion. Between the out-cropping and the river below, if a rock
has been broken apart by weathering, it may be moved farther along
by mass-wasting processes, such as creep or fall.
Real-Life
Applications
Mass Wasting in
Action
One of the principal sources of erosion is gravity, which is
also the force behind creep, the slow downward movement of regolith
along a hill slope. The regolith begins in a condition of unstable
equilibrium, like a soda can lying on its side rather than
perpendicular to a table's surface: in both cases,
the object remains in place, yet a relatively small disturbance
would be enough to dislodge it.
Changes in temperature or moisture are among the leading factors
that result in creep. A variation in either can cause material to
expand or contract, and freezing or thawing
may be enough to shake regolith from its position of unstable
equilibrium. Water also can provide lubrication, or additional
weight, that assists the material in moving. Though it is slow,
over time creep can produce some of the most dramatic results of
any mass-wasting process. It can curve tree trunks at the base,
break or dislodge retaining walls, and overturn
objects ranging from fence posts to utility poles to
tombstones.
Other Varieties of
Flow
Creep is related to another slow mass-wasting process, known as
solifluction, that occurs
in the active layer of permafrost—that is, the layer that thaws in
the summertime
. The principal difference between creep and solifluction is not the speed at which they take
place (neither moves any faster than about 0.5 in. [1 cm] per year)
but the materials involved. Both are examples of flow, a chaotic
form of mass wasting in which masses of material that are not
uniform move downslope. With the
exception of creep and solifluction,
most forms of flow are comparatively rapid, and some are extremely
so.
Because
it involves mostly dry material, creep is an example of
granular flow, which
is composed of 0% to 20% water; on the other hand,
solifluction, because of the ice
component, is an instance of
slurry flow,
consisting of 20% to 40% water. If the water content is more than
40%, a slurry flow is considered a stream. Types of granular flow
that move faster than creep range from earth flow to
debris avalanche.
Both earth flow and debris flow, its equivalent in slurry form,
move at a broad range of speeds, anywhere from about 4 in. (10 cm)
per year to 0.6 mi. (1 km) per hour. Grain flow can be as
fast as 60 mi. (100 km) per hour, and mud flow is even faster.
Fastest of all is debris
avalanche, which may
achieve speeds of 250 mi. (400 km) per hour.
Other
Types of Mass Wasting
Other
varieties of mass wasting include
slump, slide, and
fall. Slump occurs when a mass of regolith slides over or creates a
concave surface (one
shaped like the inside of a bowl.) The result is the
formation of a small, crescent-shaped
cliff, known as a scarp, at the upper end—rather like
the crest of a wave. Slump often is classified as a variety
of slide, in which material moves
downhill in a fairly
coherent mass (i.e.,
more or less in a section or group) along a flat or
planar surface. These
movements are sometimes called rock slides, debris slides, or, in
common
parlance,
landslides.
In
contrast to most other forms of mass wasting, in which there is
movement along slopes that are considerably less than 90°, fall
occurs at angles almost perpendicular to the ground. The "Watch for
Falling Rock" signs on mountain roads may be
frightening, and rock
or debris fall is certainly one of the more dramatic forms of mass
wasting. Yet the variety of mass wasting that has the most
widespread effects on the
morphology or shape
of landforms is the slowest one—creep. (For more about the
varieties of mass wasting, see Mass Wasting.)
What
Causes Erosion?
As
noted earlier, the influences behind erosion are typically either
gravity or flowing media: water, wind, and even ice in glaciers.
Liquid water is the substance perhaps most readily associated with
erosion. Given enough time, water can wear away just about
anything, as proved by the carving of the Grand Canyon by the
Colorado River.
Dubbed
the universal solvent for its ability to dissolve other
materials, water almost never appears in its pure form, because it
is so likely to contain other substances. Even "pure" mountain
water contains minerals and pieces of the rocks over which it has
flowed, a testament to the power of water in
etching out landforms
bit by bit. Nor does it take a rushing mountain stream or crashing
waves to bring about erosion; even a steady
drip of water is
enough to wear away granite over time.
Moving
Water
Along
coasts, pounding waves continually alter the
shoreline. The sheer
force of those walls of water, a result of the Moon's gravitational
pull (and, to a lesser extent, the Sun's), is enough to wear away
cliffs, let alone beaches. In addition, waves carry pieces of
pebble, stone, and
sand that cause weathering in rocks. Waves even can bring about
small explosions in
pockmarked rock
surfaces by trapping air in small cracks; eventually the pressure
becomes great enough that the air escapes, loosening pieces of the
rock.
In
addition to the erosive power of
saltwater waves on
the shore, there is the force exerted by running water in creeks,
streams, and rivers. As the river moves, pushing along sediment and
other materials eroded from the
streambed or
riverbed, it carves
out deep chasms in the bedrock beneath. These moving bodies of
water continually
reshape the land,
carrying soil and debris downslope, or
from the source of the river to its mouth or delta. A delta is a
region of sediment formed when a river enters a larger body of
water, at which point the reduction in velocity on the part of the
river current leads to the widespread deposition (depositing) of
sediment. It is so named because its triangular shape resembles
that of the Greek letter delta, ?
.
Water
at the bottom of a large body, such as a pond or lake, also exerts
erosive power. Then there is the influence of falling rain.
Assuming ground is not protected by vegetation, raindrops can
loosen particles of
soil, sending them scattering in all directions. A rain that is
heavy enough may dislodge whole layers of
topsoil and send them
rushing away in a swiftly moving current. The land left behind may
be
rutted and scarred,
much of its best soil lost for good.
Just as
erosion gives to the soil, it also can take away. Whereas erosion
on the Nile delta acted to move rich, black soil into the region
(hence, the ancient Egyptians' nickname for their country, the
"black land"), erosion also can remove soil layers. As is often the
case, it is much easier to destroy than to create: 1 in. (2.5 cm)
of soil may take as long as 500 years to form, yet a single
powerful
rainstorm or
windstorm can sweep
it away.
Glaciers
Ice, of
course, is simply another form of water, but since it is solid, its
physical (not its chemical) properties are quite different.
Generally, physical sciences, such as physics or chemistry, treat
as fluid all forms of matter that flow, whether they are liquid or
gas. Normally, no solids are grouped under the heading of "fluid,"
but in the earth sciences there is at least one type of solid
object that behaves as though it were fluid: a
glacier.
A
glacier is a large, typically moving mass of ice either on or
adjacent to a land surface. It does not flow in the same way that
water does; rather, it is moved by gravity, as a consequence of its
extraordinary weight. Under certain conditions, a glacier may have
a layer of melted water surrounding it, which greatly enhances
it mobility. Regardless of whether it
has this
lubricant, however, a
glacier steadily moves forward, carrying pieces of rock, soil, and
vegetation with it.
These
great rivers of ice
gouge out pieces of
bedrock from mountain slopes, fashioning deep valleys. Ice along
the bottom of the glacier pulls away rocks and soil, which assist
it in wearing away bedrock. The fjords of Norway, where high cliffs
surround narrow inlets whose depths extend many thousands of feet
below sea level, are a testament to the power of glaciers in
shaping the Earth. The fact that the fjords came into existence
only in the past two million years, a product of glacial activity
associated with the last ice age, is evidence of something else
remarkable about glaciers: their speed.
"Speed,"
of course, is a relative term when speaking about processes
involved in the shaping of the planet. A "fast" glacier, one whose
movement is assisted by a wet and warm (again, relatively
warm!) maritime climate, moves at the rate of about 980 ft. (300 m)
per year. Examples include not only the glaciers that shaped the
fjords, but also the active Franz Josef glacier in southern New
Zealand. By contrast, in the dry, exceptionally cold, inland
climate of Antarctica, the Meserve
glacier moves at the rate of just 9.8 ft. (3 m) per
year.
Wind
The
erosion produced by wind often is referred to as an
eolian process, the name
being a reference to Aeolus, the Greek god of the winds encountered
in Homer's Odyssey and elsewhere. Eolian processes include the erosion, transport,
and deposition of earth material owing to the action of wind. It is
most pronounced in areas that lack effective ground cover in the
form of solidly rooted, prevalent vegetation.
Eolian
erosion
in some ways is less forceful than the erosive influence of water.
Water, after all, can lift heavier and larger particles than can
the winds. Wind, however, has a much greater frictional component
in certain situations. This is particularly true when the wind
carries sand, every grain of which is like a cutting tool. In some
desert regions the bases of rocks or cliffs have been sandblasted,
leaving a mushroom-shaped formation. The wind could not lift the
fine grains of sand very high, but in places where it has been able
to do its work, it has left an
indelible
mark.
The
Dust Bowl and Human Contribution to Erosion
Though
human actions are not a direct cause of erosion, human
negligence or
mismanagement often
has prepared the way for erosive action by wind, water, or other
agents. Interesting, soil itself, formed
primarily by chemical weathering and enhanced by biological
activity in the sediment, is a product of nature's erosive powers.
Erosion transports materials from one place to another, robbing the
soil in one place and greatly enhancing it in
another.
This is
particularly the case where river deltas are concerned. By
transporting sediment and depositing it in the delta, the river
creates an area of extremely fertile soil that, in some cases, has
become literally the basis for civilizations. The earliest
civilizations of the Western world, in Egypt and
Sumer, arose in the
deltas of the Nile and the Tigris-Euphrates river systems,
respectively.
Erosion
on the Great Plains
An
extreme example of the negative effects on the soil that can come
from erosion (and, ultimately, from human mismanagement) took place
in Texas, Oklahoma, Colorado, and Kansas during the 1930s. In the
preceding years, farmers unwittingly had prepared the way for vast
erosion by overcultivating the land and
not taking proper steps to preserve its moisture against
drought. In some
places farmers alternated between wheat cultivation and livestock
grazing on particular plots of land.
The
soil, already weakened by raising wheat, was damaged further by the
hooves of livestock, and thus when a period of high winds began at
the height of the Great Depression (1929-41), the land was
particularly vulnerable. The winds carried dust to places as far
away as the eastern
seaboard, in some
cases removing topsoil to a depth of 3-4 in. (7-10 cm). Dunes of
dust as tall as 15-20 ft. (4.6-6.1 m) formed, and the economic
blight of the
Depression was compounded for the farmers of the plains states,
many of whom lost everything.
Out of
the Dust Bowl era came some of the greatest American works of art:
the 1939 film Wizard of Oz, John Steinbeck's book The
Grapes of Wrath and the acclaimed motion picture (1939 and
1940, respectively), as well as Dorothea Lange's haunting
photographs of Dust Bowl victims. The Dust Bowl years also taught
farmers and agricultural officials a lesson about land use, and in
later years farming practices changed. Instead of alternating one
year of wheat growing with one year in which a field lay
fallow, or
unused, farmers
discovered that a wheat-sorghum-fallow cycle worked better. They
also enacted other measures, such as the planting of trees to serve
as windbreaks around croplands.
The
Striking Landscape of Erosion
Among
the by-products of erosion are some of the most dramatic landscapes
in the world, many of which are to be found in the United States. A
particularly striking example appears in Colorado, where the
Arkansas River carved out the Royal Gorge. Though it is not nearly
as deep as the Grand Canyon, this one has something the more famous
gorge does not: a bridge. Motorists with the stomach for it can
cross a span 1,053 ft. (0.32 km) above the river, one of the most
harrowing drives in
America.
Another,
perhaps equally taxing, drive is that down California 1, a
gorgeous scenic
highway whose most dramatic stretches
lie between Carmel and San Simeon. Drivers headed south find
themselves pressed up against the edge of the cliffs, such that the
slightest
deviation from the
narrow road would send an automobile and its passengers plummeting
to the rocks many hundreds of feet below. These magnificent,
terrifying landforms are yet another product of erosion, in this
case, the result of the pounding Pacific waves.
Also
striking is the
topography produced
by the erosion of material left over from a volcanic eruption. As
discussed in the Mountains essay, Devils Tower National Monument in
Wyoming is the remains of an extinct volcano whose outer surface
long ago eroded, leaving just the hard lava of the volcanic "neck."
Erosion of lava also can produce mesas. Lava that has settled in a
river valley may be harder than the rocks of the valley walls, such
that the river eventually erodes the rocks, leaving only the lava
platform. What was once the floor of the valley thus becomes the
top of a mesa.
Controlling
Erosion
The
force that shapes valleys and coastlines is certainly enough to
destroy hill slopes, often with disastrous consequences for nearby
residents. Such has been the case in California, where, during the
1990s, areas were dealt a powerful onetwo punch of drought followed by rain. The
drought killed off much of the vegetation that might have held the
hillsides, and when rains came, they brought about mass wasting in
the form of mudflows and landslides.
Over
the surface of the planet, the average rate of erosion is about 1
in. (2.2 cm) in a thousand years. This is the average,
however, meaning that in some places the rate is much, much higher,
and in others it is greatly lower. The rate of erosion depends on
several factors, including climate, the nature of the materials,
the slope and angle of repose, and the role of plant and animal
life in the local environment.
Whereas
many types of plants help prevent erosion, the wrong types of
planting can be
detrimental. The
dangers of
improper land
usage for crops and livestock are illustrated by the Dust Bowl
experience, which highlights the fact that the organism most
responsible for erosion is humanity itself. On the other hand,
people also can protect against erosion by planting vegetation that
holds the soil, by carefully managing and controlling land usage,
and by lessening slope angle in places where gravity tends to erode
the soil.
The trail that leads to the exact coordinates was not man
made. It was created by
the erosion of the land during rainfall, tsunamis, and hurricanes
throughout the centuries.
To get credit for this earthcache email cache owner the answers to
the following questions. And Take photos.
1.
What types
of rocks are on the trail at the posted
coordinates?
2.
How has the
erosion affected the trees?
3.
Give the 3
types of trees within the area.
4.
Take a
photo at the posted cords with GPS in
hand.
Bonus: Take a picture
of the plane, ship w/cannons, or anchor located at the beach. (You
will need an underwater camera and snorkel gear for this) What
effect does erosion have on these items?