Internal Landform Processes (Tectonic Processes)
Senior 2 · Geography and Environment
Internal Landform Processes (Tectonic Processes)
Lesson 2 of 4
22 min
Rwanda's western border runs along one of the great scars of the Earth's crust: the Albertine Rift, the western branch of the East African Rift. Lake Kivu sits in it. So do Lake Tanganyika, Lake Edward and Lake Albert. The Rwenzori mountains stand beside it. Understanding faulting explains the shape of western Rwanda, why the Lake Kivu region has earthquakes and hot springs, and why the lake is so deep.
When rock is under more stress than it can bend with, it breaks. A fault is a crack in the crust along which the rocks on either side have moved. The block above a sloping fault is the hanging wall; the block below is the footwall. A steep slope formed where one side has moved up is a fault scarp (escarpment).
| Fault type | Stress | Movement |
|---|---|---|
| Normal fault | Tension | The hanging wall moves down relative to the footwall; the crust is stretched |
| Reverse fault | Compression | The hanging wall moves up relative to the footwall; the crust is shortened |
| Thrust fault | Compression | A reverse fault with a gentle slope (less than 45°), so one block rides far over the other |
| Tear (strike-slip) fault | Shear | The blocks slide past each other sideways, with little up or down movement |
There are two explanations. Learn both.
Apply it: scientists studying the 2008 earthquake near Lake Kivu found that it was caused by normal faulting, the same kind of movement that created the Kivu basin. That is evidence that the Albertine Rift is still being stretched today, which supports the tension theory for this rift.
Warping is a gentle up or down bending of the crust over a very wide area, without sharp folds or breaks. Upwarping raises a broad region; downwarping lowers it into a shallow basin.
Tip
Memory hook. Tension tears apart and lets the middle drop: normal faults and rift valleys. Compression crushes together: reverse and thrust faults. Shear slides sideways: tear faults. Warping is wide and gentle, with no break.
Solution: a normal fault; the hanging wall slips down.
Solution: they fill the floor of a rift valley, which is a long, narrow block that has sunk between parallel faults.
Solution: the Rwenzori mountains.
Solution: Lake Victoria fills a broad, shallow basin formed by downwarping; Lake Kivu fills a narrow, deep basin formed by faulting in the rift.
Solution: its great depth traps methane gas that is extracted for electricity (also acceptable: transport and fishing on a large lake).
Summary
Sources and credits
The worked example and practice items are written by Ganzaa.
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
