Mass Movement

Mass movement is the downslope movement of lots of regolith due to gravity.

Consolidated is soil stuck together

Unsolidated soil is loosened.

Factors influencing mass movement

Gradient

Gradient means the steepness of a slope. If gradient is steep mass movement is fast eg mudslide. If slope is gentle then mass movement is slow eg soil creep. Diagram = trees tilting etc

Vegetation Cover

In areas with lots of vegetation cover for eg grass, trees. Mass movement is slow. The roots of vegetation holds soil in place. They blind the soil together and slows down mass movement. Rainfall will not then wash the rain away and cause mudslides. people deforest trees because they want wood for furniture, Firewood and paper. Mass movement is fast for eg you've a lot of mudflows there's no roots to hold the soil together and that then washes the soil away.

Tectonic Activity

An earthquake is a sudden shaking of the earth's crust at destructive plate boundaries when 2 plates collide or passive plate boundaries where 2 plates slide past each other. If they're in areas covered in mountains they will cause a rapid downslope movement of snow which causes a avalanche. Volcanoes can also cause mass movement. lava mixes with ash hot magma causing a huge amount of melt water. That meltwater will then mix with the volcanic ash and mud and then moves rapidly downslope then causes a lahar-which is a mudflow. They can move up to 80km/hr

Rainfall

Rain mixes with regolith which becomes a liquid and it moves faster. 30% of regolith becomes a liquid.

Slow form of mass movement

Soil creep

slowest form of mass movement
occurs in areas of gentle slopes/gradient
does not need rainfall (slow and dry type of mass movement)
regolith loosened by weathering or burrowing animals and moves very slowly downslope due to gravity. effects of soil creep are fences, phones tilt slightly down the slope then you'll get ripples of soil forming terracettes.

Fast form of mass movement

Bog Burst

rapid type of mass movement
mass of bog moves downslope after a period of heavy rainfall
bog moves downslope and can block roads, knock down trees ,damage buildings etc.

Mudflows

rapid form of mass movement (100km/h)form on steep slopes
occurs after periods of heavy rain
rain mixes with mud and turns into liquid like constituency •liquid mud/peat flows rapidly downslope and spread out when reaches flat land
A scar left in landscape where mud or peat originated

Lahar

fast and wet type of mass movement steep slopes
wet mudflow heavy rain especially due to climate change this then causes cold season to get colder and wetter in winter and melt ice due to volcanoes
water mixes with mud and silt and ash and becomes a river of mud that can move up to 80km/hr

Landslides

rapid movement of regolith down to a steep slope that has become unstable
causes of landslides include coastal erosion, deforestation and earthquakes.

Avalanches

rapid form of mass movement of snow and ice downslope when weight of snow is too much for the slope to hold.

Effects of Bogbursts

scar left in landscape
crops on fields destroyed.

Case Study

Mudflow

Mocoa Mudslide

· Saturday, 1 April 2017

· Rainfall begun Friday evening

· 127 mm in 2 hours

· 254 people killed

· 400 injured

· 200 missing

· Over 1,100 soldiers and police officers helped dig people in 17 neighbourhoods

· Colombian president pledged 40,000 million pesos in aid of area

Bog Burst

Derrybrien

· Friday, 22 August 2003

· 50 meters in width

· Homeowners left stranded

· Private bog bursts destroyed

· Livelihoods destroyed

· Boil water notices put in place

How can the removal of trees lead to a landslide

The removal of trees which is also known as deforestation causes landslides because the soil on the rock weakens on a slope when the trees are removed. The slope then becomes established by the tree removal.

measures to reduce or prevent mass movement

Plant more vegetation. Eg trees, grass. The roots of vegetation blind the soil together and slowdown mass movement. People could reduce rates of over cropping and overgrazing. The soil wouldn't be exposed and regolith wouldn't move downslope due to gravity.
Stop building roads or quarrying in upland areas because that can make land unstable and then cause mass movement. By stopping doing that you can reduce mass movement.