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Erosion is the eating or wearing away of land features. It is caused by a variety of factors, some
natural, others man-made. The consequences can he serious both for the natural world and for man
himself.
The natural causes are weathering, water, ice, wind and change of temperature. The changes may
be very gradual, sometimes taking millions of years and dating back to the major
upheavals of the planet
when the earth was very young. Wind and rain driving incessantly against sandstone, formed originally
by immense pressures on early sea-beds and then lifted above sea-level by volcanic eruption or the clash
of land-plates, wears the stone back into sand, thus creating beaches along the seashore. In the case
of harder rock such as granite, surfaces are worn smooth.
Weathering also erodes exposed coastlines in temperate zones. Often cliffs and dunes simply disappear over perhaps a short period of two or three hundred years. The sea encroaches, and sometimes
coastal villages are lost. There is written evidence of English villages having been lost under the waves.
The sea also plays its part in the erosion process. The Netherlands, facing the turbulent North Sea,
have for centuries fought the battle against salt water encroachment due to erosion. Great dikes have
been built to exclude the sea, and gradually the low-lying salt flats have been sweetened and fertilized
for agriculture and bulb-growing. In another way, the sea also erodes rock fragments by friction due
to the tides. The smooth pebbles on northern beaches are the result of their having rubbed together
over millions of years.
The great ice-floes attached to the poles play a conspicuous part in regulating sea levels. In general,
sea levels are thought to be rising, though opinions vary as to the rate. At present, many fear what is
called the greenhouse effect , i.e. the punching of holes in the ozone layer due to industrial gases and
the use of CFCs. Nations are beginning to agree to eliminate these hazards. The result might be the
melting of the ice-caps causing a devastating rise in sea levels. This would put much of the land in
temperature climates under sea-water.
Slow-moving glaciers also have an effect. Their immense power
pulverizes any rocks in their path.
The piles of shale at the foot of many mountains resulted from the pressure of glaciers millions of years ago.
Wind is probably the greatest single cause of erosion. Where there is no protection given to the
soil, and after a period of drought or intense heat, the soil crumbles to dust and literally blows away.
Man himself can either let this happen or take steps to prevent it. Rain, of course, has a dual effect.
In some circumstances, it can wash away the soil into river beds, where it is carried down to
estuaries,
often silting them so that they require dredging. Inland, and on flat territory, rain holds the soil together.
Yet, rain depends on trees and foliage which cause clouds to precipitate. The central plains of North
America from time to time become dust bowls, simply because all vegetarian has been cleared in favor
of large-scale, economic cereal growing. The same clearance of rain forests goes on currently in South
America in favor of cash crops. Conservationists throughout the world are resisting these clearances,
but are fighting vested interests.
The rain forests support a wide variety of animals, birds, insects and plants, many of which can
only exist in their present habitat. This is an added reason for resisting deforestation. Sooner or later
when the forests have gone the climate will change from hot and humid to dry. The soil will crumble
and erode.
Tribes dependent on land for grazing and agriculture lose their herds, flocks and food. They become
nomads or refugees and are exposed to epidemic and starvation. Erosion can cause much human suffering.
Even in temperature countries large-scale farming is now being discouraged, for the foregoing
reasons. In England such farming has meant the destruction of hedges, ditches and trees, again spoiling
traditional landscapes and the habitats of bird, animal and insect species.
Some erosion is natural and inevitable. Much however is caused by man. Long term conservation
is essential if man is to pass on a beautiful planet to future generation. |
