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Exam Guide | Model Answer

Leaving Cert Geography (Ordinary) - Model Answer

Question 2000 Question 4
General Comments

The Physical Geography section is always a popular one with Ordinary Level candidates. The Chief Examiner’s Report points out that many candidates regularly select two questions from this section.With regard to diagrams, which appear in part (ii), note that the five marks allocated to each diagram is graded. This means that the examiner must assess on a scale of 0-5 what mark the candidate’s answer merits.

You can include the diagrams as you go through your answer or else include them all at the beginning or end of your work. A composite diagram which includes more than one of the features being discussed is acceptable (see model answer below, where stalactites and swallow holes feature in the same diagram). Diagrams should be drawn in pencil.

“Stalactites, Limestone Pavements, Swallow Holes and Pillars.
(i) State which of the above are overground features and which are underground features.

(20 marks)

Here, you are required to clearly and concisely identify whether the features are overground or underground ones.

No diagrams required. 

Each correct identification earns five marks.

(i) The overground features are:

  1. Limestone Pavement and
  2. Swallow Holes.
The underground features are:
  1. Stalactites and
  2. Pillars.

“Stalactites, Limestone Pavements, Swallow Holes and Pillars.

(ii) Select any three of the features from part (i) above and for each one you select: describe and explain with the aid of a diagram, how it is formed.

(60 marks)

Here, you must select three of the four features given and write in detail on them.

Each feature carries 20 marks (five marks for a diagram) and three points on how the feature has been formed at five marks each.

For each of the features under discussion you should state the process involved in its formation (e.g. erosion or deposition) and you should provide an example (preferably an Irish one) of each feature.

Feature 1: Limestone Pavement.

Example: The Burren in Co. Clare.

As already stated, limestone pavement is an overground feature associated with Karst (limestone) regions. The process involved in its formation is essentially chemical weathering.

These are flat areas of exposed surface limestone. They are broken up in large rectangular-shaped blocks called clints which are separated by long grooves known as grikes. Together they resemble something like large separate paving stones hence the name ‘limestone pavement.’

The limestone was exposed at an earlier stage possibly due to the action of glaciation. Exposed limestone is attacked by the chemical weathering process known as ‘carbonation.’ Essentially this involves rainwater mixing with carbon dioxide in the atmosphere to form a weak carbonic acid which turns the calcium carbonate in limestone into soluble calcium bicarbonate.

Most limestones have vertical ‘joints’ or cracks on their surface. The chemical weathering by the rainwater enlarges these joints to form the grooves known as clints. These clints run parallel to each other and separate the flat limestone surface into large slabs (grikes).

Over time the grikes will continue to get deeper and wider. The clints may contain small quantities of soil which allow unusual plants to flourish.

Example can be given at either the beginning or the end of the section.

Feature 2: Swallow Hole

Example: Pollnagollum (Poll na gColm) in the Burren, Co. Clare.

The process involved in the formation of a swallow hole is again erosion and chemical weathering. In particular, it involves the solution of the limestone as described above and the collapse of the surface limestone.

Swallow holes are also known as sink holes or sluggas. They are openings in the beds of rivers which occur when the surface river flows over an opening and then disappears underground through this swallow hole. The river then winds its way underground through various solution channels.

Originally the river is flowing over some form of impermeable rock. When it reaches the exposed limestone area it flows over joints or grikes on the surface, the river may then enlarge the grike into a hole which causes it to disappear into the underground caverns and solution channels which are a feature of Karst regions. The erosion of this hole while originally caused by solution is helped by the abrasive action of the river itself.

The previous river channel downstream from a swallow hole is called a ‘dry valley.’ The point where the river again reaches the surface is called a ‘resurgence point.’ Swallow holes may be many metres in diameter and up to one hundred metres deep; however, those in the Burren tend to be much smaller.

Remember to always clearly state the process involved in the formation of the feature.

Feature 3: Stalactites.

Example: Denmore Caves, Co. Kilkenny.

Stalactites are formed by water seepage from the roofs of caverns in limestone regions. The processes involved in their formation are solution and evaporation. This water that seeps through the cavern roof from above will contain plenty of calcium carbonate (limestone) in solution. Some evaporation of water will occur and this leads to deposits of calcium carbonate occurring particularly around the edge of the drops of water. These deposits are known as dripstone and when they extend downwards from the roof of the cave they are specifically know as stalactites.

Stalactites are icicle-shaped forms and can grow by about seven or eight millimetres per year. As the water forming these may have many impurities, the colour of the stalactite may vary in accordance with these impurities. A brownish colouring is often found. When the stalactites join with similar features on the floor of the cavern known as stalagmites they often join to form limestone pillars or limestone columns.

Exam Guide | Model Answer


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