Forms of Relief
Senior 1 · Geography
Forms of Relief
Lesson 1 of 4
22 min
Rwanda is called igihugu cy'imisozi igihumbi, the land of a thousand hills. Look at the hills of Nyamagabe below. Which slopes are steep and which are gentle? Where have people built their houses, and where have they planted crops? The shape of the land is the subject of this unit.
Definition
Relief: the shape of the land surface: its differences in height and steepness, and the landforms (mountains, hills, plateaus, valleys, plains) that result. Example: Rwanda's relief is mostly hilly and mountainous, with flatter land in the east.
Definition
Altitude: the height of a place above sea level, usually given in metres. Example: Kigali lies at about 1,500 m; the summit of Karisimbi is 4,507 m above sea level.
Definition
Slope: a surface of land that rises or falls. Its steepness is its gradient. A slope may be gentle or steep; concave (steep at the top, gentle at the bottom) or convex (gentle at the top, steep at the bottom).
Definition
Relative relief: the difference between the highest and the lowest point in an area. Example: Rwanda's highest point is Karisimbi (4,507 m) and its lowest is the Rusizi River (950 m), so its relative relief is 3,557 m.
Figure 1. A relief profile across Rwanda from west to east. The land rises steeply from Lake Kivu to the Congo–Nile Ridge, then falls gently towards the east.
The profile shows the pattern of Rwanda's relief: the land rises steeply from Lake Kivu to the Congo–Nile Ridge, the highland that divides water flowing west to the Congo from water flowing east to the Nile. East of the ridge the land descends gradually across the hilly central plateau to the eastern lowlands. In the north-west, the Virunga volcanoes rise above everything else.
| Relief region | Approximate altitude | What it is like | Examples |
|---|---|---|---|
| Volcanic region (north-west) | 2,000 to 4,507 m | Tall volcanic cones rising from a lava plain; fertile soils | Karisimbi, Bisoke, Sabyinyo, Gahinga, Muhabura |
| Congo–Nile Ridge (west) | 2,000 to about 3,000 m | High, steep ridges and deep valleys; cool and wet; forest | Nyungwe (Mount Bigugu, 2,921 m), Gishwati |
| Lake Kivu shore and Rusizi valley (far west) | 950 to 1,500 m | Steep slopes down to the lake; flat plain in the far south-west | Rubavu, Karongi, the Bugarama plain |
| Central plateau | 1,500 to 2,000 m | Rounded hills separated by valleys and marshes | Huye, Muhanga, Kigali |
| Eastern lowlands | 1,000 to 1,500 m | Gentle slopes, wide valleys, lakes and swamps; drier savanna | Akagera, Nyagatare, Bugesera |
Important
Measuring a slope: the gradient
The gradient compares how much the land rises (the vertical interval, VI) with the horizontal distance over which it rises (the horizontal equivalent, HE). Both must be in the same units.
The answer is written as "1 in n": the land rises 1 m for every n m you travel. The smaller n is, the steeper the slope.
Worked example 1: a road up from Lake Kivu
A road climbs from the lake shore at 1,460 m to a pass at 2,060 m. The horizontal distance is 12 km. Find the average gradient.
Step 1 VI = 2,060 − 1,460 = 600 m. HE = 12 km = 12,000 m.
Answer. 1 in 20: the road rises 1 m for every 20 m travelled. (Real roads bend back and forth to keep the gradient gentle for lorries.)
Worked example 2: a gradient from a contour map
On a 1:50,000 map, a point on the 1,600 m contour and a point on the 1,800 m contour are 2 cm apart. Find the gradient between them.
Step 1 VI = 1,800 − 1,600 = 200 m.
Step 2 HE = cm = 1,000 m.
Answer. 1 in 5, which is very steep: too steep for normal farming without terraces.
Warning
Same units first. A common mistake is to divide 600 m by 12 km and get "1 in 0.02". Convert both to metres before dividing.
What is Relief? GEOGRAPHY BASICS, by Mr B (4 min). Watch how relief is shown on a map by contours, spot heights and colour, and how the presenter reads steep and gentle slopes.
Kigali lies almost on the Equator, yet its average temperature is about 21 °C, cooler than many coastal cities at the same latitude, such as Mombasa. Using the idea of altitude, suggest why.
Tip
Gradient = Rise over Run. "1 in 5" means a 1-step rise for every 5 steps along. The smaller the second number, the more you puff.
Practice
Remember
Sources and credits
The lesson text, relief profile, table, worked examples and practice are written by Ganzaa. The profile is simplified from general altitudes and is not an exact survey.
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
