Forms of Relief
Senior 1 · Geography
Forms of Relief
Lesson 4 of 4
24 min
Tea is grown on the cool, wet hills of Nyungwe's edge, potatoes on the volcanic slopes of Musanze, rice in valley-bottom marshes, and cattle on the wide eastern plains. Hydroelectric power comes from rivers that tumble down steep slopes, and gorilla trekkers climb the Virungas. In each case, relief is part of the reason.
| Activity | Effect of relief | Rwandan example |
|---|---|---|
| Settlement | People prefer gentle slopes, ridge tops and valley sides above flood level; very steep slopes and wetlands are risky. | Houses line ridges in Nyamagabe; Kigali's wetlands are kept free of houses. |
| Farming | Steep slopes erode unless terraced; valley floors are wet and fertile; volcanic slopes are rich; cooler highlands suit different crops. | Terraces across the hills; rice in marshlands; potatoes and pyrethrum near the Virungas; tea in the highlands; cattle ranches in the east. |
| Transport | Roads on steep land wind with sharp bends, take longer and cost more to build and repair; plains are easier. | The winding roads from Musanze down to Rubavu and from Nyungwe down to Rusizi. |
| Climate | Temperature falls with altitude; highlands force moist air to rise and receive more rain. | Musanze is cooler than Kigali; the west is wetter than the east (Figure 1). |
| Energy | Water falling down a steep slope can turn turbines. | Ntaruka power station uses the 100 m drop between Lakes Burera and Ruhondo. |
| Tourism | Mountains, forests, lakes and plains attract visitors. | Gorilla trekking in the Virungas, Nyungwe's canopy walk, Lake Kivu beaches, Akagera safaris. |
| Communication | Hilltops are good sites for radio and phone masts; hills can also block signals. | Masts on high hills around Kigali serve the valleys below. |
| Hazards | Steep slopes plus heavy rain cause landslides and fast floods. | Landslides in the Western and Northern provinces in rainy seasons. |
Definition
Terracing: cutting a slope into a series of level steps (terraces), each held by a bank or wall, so that rainwater soaks in instead of running downhill and carrying soil away. Radical (bench) terraces are dug level at once; progressive terraces form gradually behind grass strips or hedges planted along the contour.
Definition
Soil erosion: the removal of the top layer of soil by water or wind, faster than new soil can form. It is worst on steep, bare slopes during heavy rain.
Definition
Landslide: a sudden movement of soil, rock and debris down a slope, often after heavy rain soaks the ground and makes it heavy and slippery.
Figure 1. The higher you go, the cooler it gets. Values are estimates from the average fall of 6.5 °C per 1,000 m, starting from 24 °C in the Rusizi valley; real temperatures vary.
Worked example 1: how cold is the top of Karisimbi?
On average, temperature falls by about for every 1,000 m of height. Musanze (1,850 m) has an average temperature of about . Estimate the average temperature at the summit of Karisimbi (4,507 m).
Step 1. Height difference. m.
Step 2. Temperature fall.
Step 3. Summit temperature. , just above freezing.
So what? Near the summit, nights are often below freezing and hail can whiten the top; the name Karisimbi is often explained as "white shell". No crops grow there, but the cold, wet slopes lower down feed streams and give the mountain gorillas their bamboo and giant-plant habitat.
Worked example 2: which route for a new road?
A road must climb 300 m from a valley to a ridge. Route A goes straight up over a horizontal distance of 1.5 km; route B zig-zags over 6 km. Lorries can safely climb a gradient no steeper than about 1 in 12.
Answer. Route A (1 in 5) is far too steep. Route B (1 in 20) is gentle enough, though it is four times longer, costs more to build and has sharp bends. This is exactly why so many roads in Rwanda wind back and forth.
Important
Case study: steep slopes, heavy rain and the floods of May 2023
During the night of 2 to 3 May 2023, very heavy rain fell on the steep hills of Rwanda's Western and Northern provinces. Rivers such as the Sebeya rose fast, and soaked hillsides collapsed. More than 130 people were killed, most of them in Rubavu, Ngororero, Nyabihu and Rutsiro districts, and thousands of houses were destroyed or damaged.
The role of relief: steep slopes send rainwater quickly into narrow valleys, and soaked soil on steep ground slides easily. Responses: moving families away from high-risk zones, terracing and planting trees on bare slopes, keeping houses off river banks, and using Meteo Rwanda's rain warnings. The same hills that make Rwanda beautiful and fertile demand careful planning.
Important
Ocean relief and people, too. Continental shelves are the richest fishing grounds and hold much offshore oil and gas; sheltered coasts with deep water close to shore make good ports; undersea cables follow the gentlest routes across the ocean floor.
Agriculture transformation in Hillsides of Rwanda, by the LWH project of Rwanda's Ministry of Agriculture (MINAGRI) (6 min). Watch how terraces, water harvesting and hillside irrigation are used on steep Rwandan slopes.
Many families live on steep hillsides because that is where their land is. Should the government move people off all slopes steeper than a certain gradient? Discuss the advantages and problems, and suggest a fair solution.
Tip
Exam technique: for "explain how relief affects…", name the relief feature, the effect and a Rwandan example: "Steep slopes (feature) cause fast run-off and soil erosion (effect), so farmers in Nyabihu build terraces (example)."
Practice
Remember
Further reading
Books and resources for this unit
Sources and credits
The lesson text, temperature graph, table, worked examples and practice are written by Ganzaa.
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
