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Decoding
examination questions (pt 3)
Marjorie Henry, Contributor
Today
I will discuss question two from the
June 2009 CSEC paper, as promised.
This was given in the lesson last
week. For part (a) you were asked
to draw a diagram to show the main
features of a subduction zone. The
diagram similar to the one below would
be required. To realise the full four
marks, the diagram you do must have
the following:
- Arrows
showing the direction of the plates
- The
subduction zone
- Names
of the plates (or at least one)
- A
feature formed, for example, mountains.
Convergent
plates moving towards each other
Source:
New Caribbean Geography by
Vohn A. M. Rahil
(b)(i)
Distinguish between 'extrusive'
and 'intrusive' volcanic features
and give ONE example of EACH.
Magma,
while thrusting its way up to the
surface, may cool and solidify within
the crust, resulting in the formation
of intrusive landforms. One example
of an intrusive feature is sill. Magma
that reaches the surface (lava) and
solidifies forms extrusive landforms.
One example of an extrusive feature
is lava plain.
Here
are other intrusive features - dykes,
laccolith, lopolith, phacolith and
batholith. Basalt plateaux, volcanic
cones - lava domes or shield volcanoes,
ash and cinder cones are other examples
of extrusive features.
(b)(ii)
Describe TWO ways by which intrusive
volcanic landforms may influence the
landscape over time.
Here
are four possible answers:
- Laccolith
-
arches up the overlying strata of
sedimentary rocks, for example,
the laccoliths of the Henry Mountains,
in Utah, USA.
- Batholith
- after
the removal of the overlying rocks,
it forms a massive and resistant
upland region, such as Wicklow Mountains
of Ireland.
- Sill
-
the denudation of the overlying
sedimentary strata of the sill will
expose it and it can form a bold
escarpment like the Great Whin Sill
of north-east England.
- Dykes
- when exposed to denudation,
they may appear as upstanding walls
or shallow trenches, depending on
whether they are more or less resistant
than the rocks in which they are
emplaced. An example of a dyke is
the Cleveland Dyke of Yorkshire,
England.
(c)(i)
Explain how earthquakes are formed
at transform plate boundaries.
Two
plates are sliding pass each other.
The plates move in parallel or in
opposite directions. Friction prevents
the plates from moving smoothly. Since
they have rough edges, they sometimes
become interlocked. The forces are
built up so strongly that the plates
suddenly jerk or snap. This sudden
jerk releases large amounts of energy
which causes vibrations resulting
in earthquakes.
(c)(ii)
Using an example, account for the
formation of fold mountains where
continental plates collide.
Sometimes
two continental plates moving towards
each other collide. Mountain chains
are formed. When the plate carrying
continental materials goes back into
the mantle, the lighter, old rocks
are scraped up and folded on the surface.
They are too light to be subducted
into the dense mantle. The lighter,
continental material 'floats' on top
and becomes compressed in large folds.
This happens when the rocks are relatively
soft (sediments). These large folds
form high mountain areas. Plates moving
or converging towards one another,
such as the Eurasian and African plates,
have formed the Alps. The Himalayas
have been formed by the meeting of
the Eurasian and Australian plates.
(c)(iii)
Explain how lava plateaux are formed.
Molten
lava may issue from the earth's crust
and spread over its surface to form
successive sheets of basaltic lava.
These solidify to form a lava plateau.
An example of a lava plateau is the
Antrim Plateau of Northern Ireland.
References:
- Certificate
Physical and Human Geography
- Goh Cheng Leong
- Geography
for CSEC - Jeanette Ottley and
Marolyn Gentles
- New
Caribbean Geography - Vohn A.
M. Rahil
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St
Elizabeth Technical High School's
captain Gregory McKogg (centre)
lifts the daCosta Cup as his
team celebrates its 1-0 win
over Manchester High in the
final at Jarrett Park. Sharing
in the moment are representatives
of the sponsors who made the
trophy presentation, Digicel's
Paula Pinnock-McLeod (left)
and Pepsi's Denise Dixon.
- Adrian Frater photo
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Marjorie
Henry is an independent contributor.
Send questions and comments to kerry-ann.hepburn@gleanerjm.com
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