Chapter 7 - Mass Movement Flashcards
What causes mass movement?
(a) Slope: The steeper the slope, the more likely that mass movement will occur.
(b) Water: Heavy rainfall will make the soil heavier and easier to move downhill - it will act like a lubricant.
(c) Lack of vegetation: The roots of trees and plants hold the soil, so when they are cleared away, mass movement is more likely.
(d) People: Work carried out by people, such as digging and drilling, will disturb the ground and cause mass movement.
Define soil creep.
Soil creep is the very slow movement of soil, about 1cm a year. This is the slowest form of movement. Water and gravity cause the soil to move slowly downhill. This movement is shown in features in the surface.
List the evidence of soil creep.
(a) Fences and trees bend downhill.
(b) Terracettes are formed - natural steps are formed on the slope.
(c) Walls collapse because of pressure building up behind them from soil moving downhill.
Define landslide.
A landslide is a rapid movement of loose rock and soil down a slope. Landslides are caused by undercutting, coastal erosion and earthquakes. Heavy rain can lead to landslides by loosening the soil.
Why are landslides so dangerous?
Buildings such as houses, churches and schools can be buried by the landslide. Many people can be killed and roads can be blocked so that rescuers find it difficult to help.
Define bogbursts.
Bogbursts are fast movements of bog down a slope. The bog may be loosened by heavy rainfall (liquefied) or by work on mountaintop wind turbines when vegetation is removed.
Define mass movement.
Mass movement is the movement of loose earth materials (soil, stones, mud) called regolith down a slope under the influence of gravity.
Define coastal cliff collapse.
Coastal cliffs can collapse very quickly when they have been weakened by the waves. The waves wear away the base if the cliff, causing it to collapse into the sea.
Define mudflows.
Mudflows are fast movements of mud down a slope. These may be caused after heavy rainfall or volcanic activity.
Define lahars.
Lava from volcanoes can melt snow, which will then create a river of mud. This is known as a lahar.
