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Paper
2: Question #3 (pt 2)
Marjorie Henry, Contributor
I
began a discussion on Question 3 from
the June 2009 CSEC examination paper
in the last lesson. I will continue
that discussion today. In part (b)
(i) of the question, you are required
to outline the sequences occurring
in the water cycle. These are as follows:
The
process whereby moisture changes from
a liquid in oceans, lakes and rivers
to a gas in the air (water vapour).
The
process whereby moisture loss from
plants transfers water from land to
air.
The
process whereby moisture changes from
a gas into a liquid in the atmosphere
as clouds.
This
includes all forms of moisture falling
from the air, on both land and sea,
under gravity - rain, ice, snow and
sleet.
- Surface
run-off or percolation
This
includes all water running from the
land into the sea under gravity -
rivers, underground water; unchannelled
water, glaciers.
Your
answer should include all of these
processes. The statement below would
be adequate:
Evaporation
from sea and land forms clouds which
condense into rain that falls to earth
as run-off or percolates to form groundwater,
or is absorbed by plants or evaporated
again to form clouds. The cycle is
repeated when clouds are condensed
to fall as rain.
A
well-labelled diagram similar to the
one below could also be done for this
answer.
(Source:
Certificate Physical and Human Geography
by Goh Cheng Leong)
(b)
(ii) The TWO characteristics of
limestone which make it susceptible
to chemical weathering are its composition
and permeability. Limestone is a rock
which is made up mainly of calcium
carbonate, more than 80 per cent.
It is especially vulnerable to the
chemical weathering process known
as carbonation. Most limestone rocks
contain pores, fissures and joints
which water can pass through. These
are enlarged when rainwater begins
to dissolve the limestone. The limestone
becomes a permeable rock - water can
flow through it easily.
(c)
(i) The formation of pillars:
Carbonated water filters through the
joints, fissures and pores of limestone
rocks. Drop after drop slowly trickles
through cracks in the roof of the
cave. As the water drips from ceiling
to floor, evaporation causes deposition
of thin layers of calcium out of solution.
The deposits on the roof gradually
build up the long, slender column
of calcium bicarbonate which hangs
from the ceiling and grows downwards.
These are stalactites.
The
water from the overhanging stalactite
drips slowly to the floor, through
the hollow centre of the stalactite.
Some of it evaporates, leaving deposits,
which spread out on the floor. These
grow upwards by an accumulation of
calcite, to form stalagmites. Stalactites
and stalagmites may join to form a
pillar.
(ii)
The formation of swallow holes or
sinkholes: The widely fissured
structure of limestone rocks causes
joints and fissures to be widened
and enlarged by solution, forming
holes or funnel-shaped depressions
known as sinkholes or swallow holes.
(iii)
The formation of caves: Large
areas of limestone rocks are corroded
by underground water, containing carbon
dioxide. The slowly moving groundwater
dissolves the rocks along joints and
bedding planes to form tunnels and
irregular passages or caves.
References:
- Certificate
Physical and Human Geography
- Goh Cheng Leong
- Geography
for CSEC
- Jeanette Ottley & Marolyn
Gentles
- New
Caribbean Geography
- Vohn A. M. Rahil
- The
Caribbean Environment
- Mark Wilson
Marjorie
Henry is an independent contributor.
Send questions and comments to kerry-ann.hepburn@gleanerjm.com
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