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 be
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 on 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 sea-shore. 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 dykes 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 temperate climates under
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 vegetation 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 not 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 temperate 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, aging 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