Mass Movement Flashcards
Mass Movement
The movement of regolith down a slope in response to the pull of gravity, influenced by natural processes, natural disturbances and human activities
Influences: Slope Material
Solid rock, less likely to move, unconsolidated (boulder clay) is more likely
Influences: Gradient
Steeper the slope, the more likely for mass movement
Influences: water content
More water there is, faster the movement
Influences: Vegetation
Slows mass movement, binds soil together and absorbs rainfall
Influences:
Tectonic Activity
Can speed up mass movement e.g volcanic, earthquakes
Influences:
Human activity
Can speed up m. Movement by weakening the slope e.g deforestation or road building
How is m. Movement classified
- Speed it occurs
- Condition of material
- type of material
Slow: Soil Creep
Slowest form, soil + regolith moved slowly downhill under influence of gravity
What is soil creep influenced by
- Periods of heavy rainfall
- Frost heave
Slow: Solifluction
Occurs in high altitudes, underlying layer of permafrost, summer the soil can become saturated, water is unable to percolate in the permafrost layer, saturated soil flows downhill
Fast: Bogburst
Peat bogs on slopes, heavy rain after dry weather, plants don’t bind soil together, explosion, peat flows downhill
E.g August 2008 Co. Kerry
Fast: Mudflow
Steep slopes, deep soils, impermeable rock, rain heavy, mixes with soil, concrete like substance, 100km per hour
Fast: Lahars
Volcanic Mudflows, snow melts due to v. Eruptions, water mixes with lava, ash, soil and rock travelling 100km/h
Rapid: Landslides
Mountainous or coastal, rock and debris move downhill, can be caused by natural and human factors
Natural factors of landslides
- Rainfall lubricates soil making it easier to move, water adds weight
- Weathering
Slope material fractured by weathering processes, more likely to move downslope - Earthquakes
Vibrations can cause soil to slip downhill
Human activities that impact landslides
- Loading
Heavy materials added increases downward force e.g wind farms or dams - Deforestation
Roots can no longer bind soil and stabilise it. - Mining and quarrying
Blasts cause vibrations which encourage sliding
Rapid: Rock Fall
Heavily influenced by gravity and gradient of slope, loose blocks fall, pile ups are called Talus Slopes, occur due to F. Thaw action, E.quakes, undercutting by rivers and waves, plant root wedging
Rapid: Liquefaction
When loose sediment becomes over saturated with water, after heavy 🌧️, rapid melting of ❄️ and 🧊, strong vibrations from high mag. quakes
Rapid: Slump Rotational Slide
Slumping occurs where unconsolidated material such as boulder clay slips downward along c. surface Area, crescent shaped cliff forms with abrupt end called scarp at the top of slope.
Material gathered at bottom is called slump
Rapid: Avalanche
Rapid slow flow, steep slopes, Jan - Mar, heavy snowfall causes weight gain, snow foundations loosen, Deforestation causes instability, earthquakes too, blasting, artillery
Avalanche prediction
Predicting When they can happen using past events
Deliberate start using explosives
