Physical Features and Effects of Climate Change
Primary 6 · Social and Religious Studies
Physical Features and Effects of Climate Change
Lesson 2 of 4
15 min
Let's begin
Ishimwe's grandmother tells an old story: long ago the ground in the north-west shook, fire came out of the earth, and the mountains grew. Ishimwe laughs. But his teacher says the story is close to what scientists have found!
Today you will find out how volcanoes, valleys and lakes were made, and why they matter to us.
The outer layer of the Earth is called the crust. It is made of huge pieces of rock that move very slowly, only millimetres or centimetres a year. Under the crust is very hot, melted rock called magma. Over millions of years, these slow movements and this hot rock have built most of the big physical features you learned about.
Magma pushes up through a crack or weak place in the crust. When it comes out onto the surface, it is called lava. Lava, ash and rocks pile up around the opening, layer after layer, and build a cone-shaped mountain: a volcano.
In East Africa the crust is being pulled apart. It cracks along long lines called faults. The land between two faults sinks, leaving a long, deep valley with steep walls. This is a rift valley. Its steep walls are called escarpments.
The Great Rift Valley has two arms. The Eastern Rift runs through Ethiopia, Kenya and Tanzania. The Western (Albertine) Rift runs along the western borders of Uganda, Rwanda, Burundi and Tanzania. Rwanda sits on the edge of the Western Rift.
Rain and rivers fill the deep floor of the rift with water. This makes lakes that are long, narrow and very deep, such as Lake Kivu (almost 500 m deep), Lake Tanganyika (the second-deepest lake in the world), and Lakes Albert, Edward and Malawi.
Sometimes the land between two faults is pushed up instead of sinking. This makes a block mountain. The Rwenzori Mountains between Uganda and the DR Congo are block mountains. Their tops are so high that they have snow and ice, even though they are close to the equator.
Rain and running water slowly wear away soil and rock. This is called erosion. Over millions of years, rivers such as the Nyabarongo have cut valleys between Rwanda's hills.
| Feature | How it helps people | Problems it can bring |
|---|---|---|
| Volcanoes | Fertile volcanic soil for Irish potatoes, beans and pyrethrum; gorilla tourism in Volcanoes National Park | Eruptions and earthquakes |
| Lakes | Fish such as isambaza, water, boat transport, beaches for tourists, and methane gas from Lake Kivu to make electricity | Drowning accidents; flooding on the shores |
| Rivers and waterfalls | Water for homes and irrigation, fishing, hydroelectric power | Floods in the rainy season |
| Mountains and forests | They bring rain, store water, give homes to wild animals and attract tourists | Steep slopes cause landslides and make roads hard to build |
| Valleys and wetlands | Wet, fertile land for rice and vegetables; wetlands soak up floodwater and clean it | Mosquitoes; flooding |
Here is a real example: water drops about 100 m on a short stream called the Ntaruka, flowing from Lake Burera down into Lake Ruhondo. A power station there uses the falling water to make electricity.
Worked example
Mugisha's uncle farms on the lower slopes of the volcanoes in Musanze. Why do his Irish potatoes grow so well?
Step 1 The volcanoes made the soil there from old lava and ash.
Step 2 Volcanic soil is full of minerals that plants need.
Answer: the land has fertile volcanic soil.
Tip
Three ways the Earth builds land
Try it with your hands: put them flat together, then slowly pull them apart. The gap is your rift valley. Fill it with "water" and you have made Lake Kivu!
What is lava?
Answer: magma (melted rock) that has come out onto the Earth's surface.
How did the Rift Valley form?
Answer: the crust was pulled apart and cracked along faults, and the land between the faults sank.
Name two rift valley lakes.
Answer: any two of Kivu, Tanganyika, Albert, Edward and Malawi.
Give one way Lake Kivu helps Rwanda's economy.
Answer: fishing, boat transport, tourism, or methane gas used to make electricity.
Why are steep hillsides dangerous in the rainy season?
Answer: heavy rain can loosen the soil and cause landslides.
What you learned today
Sources and credits
The practice questions were written by Ganzaa.
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
Quick check
Match each kind of volcano to an example from the lesson.
Tap one on the left, then its partner on the right.
