Geomorphology

Grade 12 geomorphology follows a river from source to mouth, and the patterns rivers make when rock and slope differ.

CAPS

Grade 12 · Geography · Geomorphology

Geography examines physical and human processes, with map skills in both papers.

The papers
Paper 1 is climate and weather, and geomorphology, with geographical skills. Paper 2 is rural and urban settlement, and the economic geography of South Africa, with geographical skills. Each paper is 150 marks.
Map work
Direction, scale, gradient, cross-section and a calculation from the map must show the formula and the substitution. A place you cannot point to on the extract is a guess.
How a marker reads it
A common mix-up is to expect deposition in the steep upper course, or to number stream order by the river’s age in years.

Paragraph questions want causes and effects in sequence. Naming a term without saying how it changes the landscape or the settlement is only the first mark.

Diagram

Worked theory

Worked theory. Two streams on one watershed. The steeper one cuts back, breaks the divide, and the upper part of the other stream now flows into it. The beheaded stream is left smaller. On the map the elbow of capture is a sharp bend, and a wind gap marks the old route. Downstream, the pirate river carries more silt and more flood. A farmer who protects only the lower field, and ploughs the source bare, is fighting the deposited silt that their own upstream caused. The profile, the pattern and the capture are one river system, read from source to mouth.

More worked examples

A dam that silts in twenty years
A farmer ploughs the steep ground at the source. Storms carry the soil into a stream of order 1, then into a larger stream, then into a dam on the main river. The dam, meant to last 50 years, is half full of silt in 20. Downstream the river runs clearer and hungrier, and erodes its own bed. The capture is not the story this time. The catchment is. The silt was always going to arrive. The ploughing decided how fast.
A hillslope after heavy rain
In the 2022 floods in KwaZulu-Natal, rain soaked a steep slope until the weight of the wet soil failed. The slope slid and a road closed. Weathering had loosened material beforehand. The movement itself was mass movement, and the streams that then carried the mud were erosion. A sentence that calls the whole event “weathering” stops before the slope actually moved. The closed road is the evidence of movement.

In ordinary words

Near the source the river is steep and erodes downward. In the middle it starts to curve. Near the mouth it deposits, building floodplains and sometimes a delta. A longitudinal profile is that slope from source to mouth, steep then flat. Drainage patterns copy the rock: branching like a tree on uniform rock, rectangular on joints, radial off a hill. Stream order numbers the tributaries. River capture is one river cutting back and stealing the water of another. People manage catchments because what happens upstream arrives downstream.

In South Africa

A captured stream and a silted dam downstream are the reason catchment management is in this topic.

Part 1 / 4

What it is

Grade 12 geomorphology follows a river from source to mouth, and the patterns rivers make when rock and slope differ.

More worked examples

Board walkthroughs on this topic. Open one, copy the working, then try the next.

Example 1 / 20

Explain how river capture occurs.

How we got there

Read this like a teacher at the board. We go slowly, name every number, and say why we take each step.

Explain in another language · 11

1. What is the question asking?

Read the question twice. Circle the unknown. Underline every number and unit. The paper is asking: Explain how river capture occurs.

Before any working — hunt first

Given

Numbers and units already in the sentence: no numbers yet — only a name, a diagram, or a worded unknown. Copy each one into a column. A name without a number is not given.

Missing

After you copy the given, the letter that still has no number is missing. The paper is pointing at: Explain how river capture occurs. Circle that word — that is the missing variable.

Find

We are required to find: Explain how river capture occurs. Write that as a symbol on the left, with a question mark, before you touch a formula.

Calculate

What we need to calculate: Headward erosion. Then substitute the given, one line at a time, to get Explain how river capture occurs.

In other words — as if you have never seen this before

If you have never seen this before: Headward erosion. We will name a method in words, write the formula with no numbers, then substitute one line at a time.

2. What do we already know?

River capture.

3. Which method — and why this one?

Headward erosion.

4. Step-by-step working

01 / 08
Step A — Read the question twice
Slow down. Circle the word that names the unknown. Underline every number and its unit. Do not grab a formula yet — first decide what the paper is actually asking.
Why this step: If you can say the method in a sentence, you will pick the right formula. First-timers skip this and grab the first equation they remember.
02 / 08
Step A2 — Hunt: Given, Missing, Find, Calculate
Given: Numbers and units already in the sentence: no numbers yet — only a name, a diagram, or a worded unknown. Copy each one into a column. A name without a number is not given. Missing: After you copy the given, the letter that still has no number is missing. The paper is pointing at: Explain how river capture occurs. Circle that word — that is the missing variable. Find: We are required to find: Explain how river capture occurs. Write that as a symbol on the left, with a question mark, before you touch a formula. Calculate: What we need to calculate: Headward erosion. Then substitute the given, one line at a time, to get Explain how river capture occurs.
Why this step: Do not name the letters yet. First hunt: what already has a number (Given), what has no number (Missing), the word the paper wants (Find), and which formula still contains the missing letter (Calculate).
03 / 08
Step B — Write the given in a column
River capture.
Why this step: A column with units stops you mixing cm with m, or minutes with seconds. Markers can also see you started correctly.
04 / 08
Step C — Name the method in words
Headward erosion.
Why this step: If you can say the method in a sentence, you will pick the right formula. First-timers skip this and grab the first equation they remember.
05 / 08
Explain
A more energetic river erodes headwards and captures part of another river; capture creates an elbow of capture, misfit stream and wind gap.
Why this step: We only do one job per line so a marker can follow the marks — and so you can find a slip without starting over.
06 / 08
Step G — Sense-check the size
Ask: is this the kind of number a Grade 10–12 paper would want? A speed of 3 000 ms for a learner walking, or a probability bigger than 1, means a unit or algebra slip. Estimate first: round the numbers and do the sum in your head.
Why this step: Markers write ‘unrealistic’ in the margin when the method is right but the size is wild. A 10-second head check often finds a missing 10² or a unit that never changed.
07 / 08
Step F — Box the answer with its unit
Headward erosion.
Why this step: A number without a unit is half a mark on a Physics paper, and a marker can miss a Maths answer that is buried in working.
08 / 08
Step H — What the marker is looking for
On an NSC memo you usually earn: (1) a method mark for naming the right formula or idea in words, (2) an accuracy mark for substituting the given numbers with units, (3) an accuracy mark for the boxed answer with its unit. Write those three lines even if you are unsure of the arithmetic — blank pages score zero.
Why this step: First-timers chase the final number and leave the method blank. The memo still pays out for the idea and the substitution even when the last line is wrong.

5. The answer

Headward erosion.

Copy onto your answer sheet — in this order

Answer: Headward erosion.

6. Check it like a marker

Captor and captured streams.

7. A trap first-timers fall into

First-timers often grab the first formula they remember, mix units (cm with m, minutes with seconds), or drop a minus sign. Write the formula in words first: “this equals that, because…”

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Rural and urban settlement

Geography

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