Natural systems
Marjorie Henry, Contributor

For the past few weeks, I shared with you on the expected responses for section A, the map reading section, of the last examination paper. Section B of the paper tests that section of the syllabus that is based on natural systems. This will be my focus for the next three or four weeks. There are three questions in this section and you are required to do only ONE.

In reference to the syllabus, Question 2 tested the following objectives:

2 - name and locate the Caribbean and adjacent plates;

3 - distinguish among convergent, divergent and transform plate margins;

4 - explain the formation and distribution of volcanoes, earthquakes and fold mountains;

13 - describe trellis, radial and dendritic drainage patterns;

I stated this deliberately to highlight the fact that several topics are tested in any one question in this section of the question paper.

Let me mention also that for Question 2 through to 10, profile one of these questions, that is, practical skills, is allocated the least marks. This section is given four marks out of a total of 24 marks for the question. There is always some stimulus material at the beginning of the question. This can take the form of maps, diagrams, sketches, tables and graphs. More times than not, you are required to study what is given then answer a series of questions not exceeding four, based on the stimulus material.

Figure 2. Caribbean and adjacent plate boundaries.

Stimulus material

In reference to Question 2, the stimulus material is that of a map. This is shown above, along with the questions.

(a) Study Figure 2 (above), which shows the Caribbean and adjacent plate boundaries and answer the questions that follow.

(I) What type of mountains are located at A? (1 mark)
(II) Name the type of plate boundary indicated by the symbol (1 mark)
(III) Name the plates labelled X and B. (2 marks)

The responses to the questions asked are as follows:

(I) FOLD MOUNTAINS are located at A.

(II) DESTRUCTIVE or CONVERGENT MARGIN is the plate boundary indicated by the symbol.

(111) The plate labelled X is the COCOS PLATE while the one labelled B is the CARIBBEAN PLATE.

A complete sentence is not absolutely necessary in answering this part of the question. The words highlighted in capital would be adequate for your answer.

Section (b) is profile two of the question. It is as follows:

(b) (I) Describe the main features of dendritic and radial drainage patterns and state where each is developed.

(II) Describe the coastal process of longshore drift.

Observe the key verb for the question - DESCRIBE - that is, based on your knowledge, write down the details about what you are asked. Sub-section (b) (I) requires that you do two things for each of the drainage patterns given. First of all, you describe the features, then you say where each is developed. In contrast to Section (a) of the question, full sentences are needed in your response.

(b) (I) Dendritic drainage patterns have several tributaries or branches that converge on the main stream or trunk. This pattern develops on uniform rock types. Radial rivers originate from a central location going out in all directions like the spokes of a wheel. The radial pattern develops on domes and volcanic cones.

(b) (II) In longshore drifts, there is the movement of coastal material in a zig-zag pattern along the coast. The SWASH moves materials diagonally up the beach while the BACKWASH returns the materials at a right angle. The material therefore moves slightly along the beach. When the process is treated, material can travel great distances.

I will complete section (c) in the next lesson. However, reflect on it until then.

(c) (I) Explain how the shape of a volcano is influenced by the type of lava ejected.

(II) Account for the occurrence of earthquakes along transform plate boundaries.

(III) Explain how explosive volcanoes are formed.

Marjorie Henry is an independent contributor.