Mass Movements

what is a mass movement?

the downward movement of weathered material on a slope under the influence of gravity

factors needed for mass movements (6 + explanations)

1. steep slopes: rapid movement is more likely

2. stratified rock with varying levels of resistance: impermeable base rock + rain = more saturation

3. sparse vegetation / deforestation: less soil binding

4. heavy rain: adds weight and volume to soil

5. urbanisation / mining: instability

6. earthquakes and volcanoes: trigger mass movements

soil creep (7)

-gradual and continuous process

-steeper slope = faster creep

-soil moves <1cm per year

-occurs when soil expands and contracts due to heating and cooling / wetting and drying / animal burrows

-rainfall required

-forms terracettes on slopes

-indicated by curved poles, trees, etc

-

solifluction (2)

-when topsoil is saturated and slides over frozen ground beneath it

-faster than soil creep (5cm-1m per year)

earthflow (3)

-occurs in clay areas

-saturated soil moves down gentle slopes

-1-15km per year

mudflow (4)

-rapid movement

-streams of mud flow down a steep slope in channels

-occurs after heavy rainfall or volcanic activity (ash turns into mud)

-collects sand and fine silt in process (makes mud form them)

landslide (3)

-mass of land breaks loose and plunges down slope

-occurs along faults / bedding planes / joints where land tilts and move backwards

-triggered by earthquakes

rockfalls (4)

-occurs when rock fragments break of from parent rock due to weathering

-collects at the bottom as a talus

-most rapid form of mass movement

-40 degree incline

impacts of mass movements on people (4)

-death and injury

-property damage

-displacement and home repairs needed

-damage to infrastructure and farmlands

impacts of mass movements on the environment (5)

-destroys farmlands, vegetation and forests

-damages ecosystems

-blocks streams and dams

-removes topsoil = erosion

-changes nature of slopes

human impact on mass movements (6)

-building on slopes

-road cutting and railway construction

-traffic vibrations

-quarrying at hill bases

-mine and rubbish dumps

-hotels, biking, climbing on slopes

strategies to lessen impact of mass movements (7)

1. careful planning and research before you build

2. maintain vegetation

3. add concrete or mesh wire onto slopes

4. insert stakes on slopes

5. restrict development in vulnerable areas

6. add regulations on building

7. risk analysis

mnemonic to remember mass movements in order of speed

Some: Soil creep

Elephants: Earthflow

Sing: Solifluction

Melodies: Mudflow

Like: Landslide

Rainbows: Rockfall