.
.
.
.
Geysers
are fountains of hot water and superheated steam that may spout up to a height
of 150 feet from the earth beneath. The phenomena are associated with a thermal
or volcanic region in which the water below is being heated beyond
boiling-point. The jet of water is usually emitted with an explosion, and is
often triggered off by gases seeping out of the heated rocks. Almost all the
world's geysers are confined to three major areas: Iceland, the Rotorua
district of North Island, New Zealand and Yellowstone Park of U.S.A. The
world's best known geyser is perhaps 'Old Faithful' in Yellowstone National
park, Wyoming which erupts at regular intervals- every 63 minutes on the
average.
Hot
springs or thermal springs are more common, and may be found in any part of the
earth where water sinks deep enough beneath the surface to be heated by the
interior forces. The water rises to the surface without any explosion. Such
springs contain dissolved minerals which may be of some medical value. Iceland
has thousands of hot springs. Some of them have been harnessed to heat houses,
swimming pools and for other domestic purposes.
Hot springs and geysers have become tourist attractions e.g in Japan and Hawaii.
The variations of salinity in
the various sea and oceans is affected by the following factors :-
· The rate of evaporation - The water fringing the High Pressure
Belts of the Trade Wing Deserts, between 20 degree and 30 degree N and S, have
salinity because of the high rate of evaporation caused by high temperature and
low humidity. The temperate oceans have lower salinity due to the lower
temperature and a lower rate of evaporation.
· The amount of fresh water added by precipitation streams and
icebergs - Salinity is lower than the average 35% in equatorial waters because
of the heavy daily rainfall and high relative humidity. Oceans into which huge
rivers like the Amazon, Congo, Ganges, Irrawaddy and Mekong frain, have much of
their saltness diluted and have a lower salinity. The Baltic, Arctic and
Antarctic waters have a salinity of less than 32% because of the colder climate
with little evaporation and because much fresh water is added from the melting
of icebergs, as well as by several large poleward-bound rivers, e.g. Ob, Lena,
Yenisey, and Mackenzine.
· The degree of water mixing by currents - In wholly or partially enclosed seas such as the Caspian Sea, Mediterranean Sea, Red Sea and Persian Gulf, the waters do not mix freely with the ocean water and they are not penetrated by ocean currents. Salinity is high, often over 37%. In areas of inland drainage without links with the oceans, continuous evaporation under an almost cloudless sky causes the accumulation of salts around the shores. In the open oceans where currents freely flow, salinity tends to be near the average 35% or even a little lower. The range of salinity is negligible where there is free mixing of water by surface and sub-surface currents.
The term weather should not be confused with climate, though they are very closely related to each other in the study of meteorology and climatology. We don't hear people saying that the climate of the day is warm or cold, but we do talk of warm weather, a cold morning, a sunny afternoon, a rainy day or a chilly night. Any casual remarks about the atmospheric conditions of a certain place at a certain time are about weather. It is never static, and thus cannot be generalized. In the same country, even over a small area, the weather can vary tremendously. It may be sunny in one part of the district, but raining heavily a few miles away. Strong gales may be experienced along the coasts while the interior may be relatively calm. It is important to realise that any place can be subjected to haphazard changes in weather at any time.
When
we speak of climate we mean the average atmospheric conditions of an area over
a considerable time. For climate averages, a minimum period of 35 years is
desirable. This involves the systematic observation, recording and processing
of the various elements of climate such as rainfall, temperature, humidity, air
pressure, winds, clouds and sunshine before any standardization of the climate
means or averages can be arrived at. The climate of Malaysia is described as
hot, wet, equatorial climate which is a summing up of the average everyday
climate of the country throughout the year.
The
degree of variability in the climate or weather of a country also differs.
Generally speaking, the climate of temperate latitudes is far more variable
than that of the tropics, The climate of the the British Isles is so changeable
that many people have commented that ` Britain has no climate, only weather'.
Conversely, the climate of Egypt is so static that it makes a good deal of
sense when people say that ` Egypt has no weather, only climate'.
The earth's crust is
far from stable and it is not surprising that, in the course of a river's
development, parts may be uplifted or depressed, giving rise to certain
characteristics features associated with rejuvenation, i.e. being young again.
If
rejuvenation occurs in the upper-course, the river valleys are deepened and
steep-sided Gorges are formed. In the middle and lower course vertical
corrasion replaces lateral corrasion and the existing meanders are vertically
eroded by the rejuvenated stream. A distinct new inner trench is cut in the old
valley, and the river develops a deep valley with entrenched or incised
meanders. The best developed incised meanders are those of the River Colorado,
U.S.A., where the uplift of 7,000 feet in the tertiary period renewed
down-cutting to a fantastic depth. In some parts of the Grand canyon, the depth
is almost a mile. It is 10 miles wide at the top and 300 miles long. Other
examples are the River Moselle in Germany, the River Wear at Durham, England
and the Wye Valley, Monmouthshire.
A positive movement occurs when there
is a depression of land or a rise in sea level. This submerge the lands along
the coast, `drown' the valleys and weaken the erosive power of the river. The
flow is checked and large quantities of sediment will be dropped. The lower
course of the river may be partly in the sea and features of deposition are
shifted upwards to the middle course. The upper course is little affected when
there is a rise in sea level. In many areas where the sea has risen this was
probably caused by the release of water locked up in the ice masses during the
Quaternary Ice Ages.
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