• Shuffle
    Toggle On
    Toggle Off
  • Alphabetize
    Toggle On
    Toggle Off
  • Front First
    Toggle On
    Toggle Off
  • Both Sides
    Toggle On
    Toggle Off
  • Read
    Toggle On
    Toggle Off
Reading...
Front

Card Range To Study

through

image

Play button

image

Play button

image

Progress

1/29

Click to flip

Use LEFT and RIGHT arrow keys to navigate between flashcards;

Use UP and DOWN arrow keys to flip the card;

H to show hint;

A reads text to speech;

29 Cards in this Set

  • Front
  • Back

Mass movement

Large-scale movement of the Earth’s surface that is not accompanied by a moving agent such as a river, glacier or waves




Move under the force of gravity




On different time and spatial scales




More common when heavy precipitation

Sheer strength and sheer stress

Shear strength - the internal resistance of a body to movement




Shear stress - the force acting on a body that causes movement of the body down slope

Slope failure causes

An increase in shear stress - forces to pull a mass down slope




A decrease in shear strength - resistance to movement




Critical threshold when stress outweighs strength

Factors holding slopes in place

Friction and weight of particles




Cohesive forces e.g. clay




Vegetation roots bind the soil




Human structures e.g. nets

Physical factors that increase shear stress

Removal of support from undercutting or steepening - erosion from rivers and glaciers, wave action, previous mass movements




Sudden shocks - earthquakes




Loading of the slope weight - vegetation, water, sediment

Human factors that increase shear stress

Adding weight to slopes - buildings and walking




Steepening slopes - cuttings, quarries, adding waste

Physical factors that decrease shear strength

Weathering - disintegration of rocks, hydrated of clay




Drainage - wet areas on the slope saturation




Rock type - tilt, impermeable rocks




Animals - burrowing and walking

Human factors that decrease shear strength

Removing vegetation - less roots to hold slope




Drainage - adding water to the ground to saturate it

Water

Many movements happen when increased water




Weaken the slope by increasing shear stress




Adds weight and the slope becomes saturated




Water reduces the cohesion of particles by saturation




Water decreases the amount of friction so decreases shear strength




Increased volume of water


Heavy or prolonged rain


Rising water tables

Types of mass movement

By speed - fast or slow




By types of movement - slide or creep or flow




By type of material - rock or soil or ice




By water content - wet or dry

Slow movements

Creep


Slow and continual process


Soil and low water content


Results in terracettes




Solifluction


Slow downhill flow


Saturated soil so high water content


Periglacial environments


Solifluction lobes

Flows

Mudflow




Soil or weak rock becomes saturated and begins to move downhill


Can be slow but mainly rapid


After heavy rainfall


Volcanic hazards - melted snow and ice can combine with ash to form lahars

Difference between slides and flows

Flows undergo internal derangement




Slides move together and are not affected by internal derangement

Rapid movements

Landslides




Sudden movement of material downslope due to gravity


Range of materials and water contents


In contact with the ground and most are along a bedding plane with impermeable rock below so water lubricates the slide




Rock falls




Spontaneous debris movement on steep slopes


From extreme physical or chemical weathering


Travel through the air


From scree slope below




Slumps




Rotational slides


Rock rotates around a slip plane in the arc of a circle


Plane is concave in shape


Most common in clay where becomes saturated and slips

Slip plane locations

Junction of two layers




At a fault line




Where there is a joint




Along a bedding plane




At the point where shear stress becomes greater than shear strength

Environmental impacts of mass movements

Relief - reduces slope angle, fills in valleys, adds bulges




Drainage - may dam or divert rivers




Vegetation - trees lean or fall




Soil - collects at the base of the slope

Social impacts of mass movements

Buildings collapse




Disasters e.g. Aberfan




Loss of life

Economic impacts of mass movements

Transport - road and rail destroyed, disruption and cost of repair




Power and phone lines lean or fall - disruption and cost of repair




Loss of farmland




Damage to structures - buildings and bridges




Quarrying and mining disasters

Short-term management of mass movements

Plant vegetation to bind the slope and dry it out




Stop walking on the slope to reduce stress

Long-term management of mass movements

Reduce pressure on top of the cliff - limit building




Reduce processes undercutting the cliff - revetements, sea wall




Change slope angle - regrade it to gentler slope




Reduce moisture on the slope - drains

CS - Aberfan disaster

21st October 1966




A coal waste tip slide down a mountainside into the mining village of Aberfan in South Wales

Aberfan causes

The spoil heap was located above a spring and at a steep angle




No management of the tip




Little vegetation in the area to bind to the waste




Prolonged heavy rainfall




100,000 cubic metres of waste travelling up to 30km/hr




Couldn’t alarm them as phone cable was stolen

Aberfan impacts

147 killed - 116 school children




Destroyed the primary school called Pantglas Junior school and 20 houses




Loss of a generation




Huge psychological impact




Cost of clean up

Aberfan short-term responses

Emergency rescue services




100s of people helped in the search for people but no one rescued alive after 11am and took 1 week to find all the bodies

Aberfan long-term responses

Other tips checked and slope angles reduced




1969 Mine and Quarry Act passed to control the siting of tips




Over £20 million in donations




Expensive clean-up of £2 million




No prosecutions

CS - Holbeck Hall

3-5th June 1993




Landslip along the upper section of the boulder clay at the 60m cliffs at Start Bay, Scarborough




Caused the destruction of 4 star Holbeck Hall Hotel




Constructed 1883




One of the most rapidly retreating areas in Britain




Succession of droughts made the area unstable - the boulder clay had become dry and cracked in previous years and then saturated by the rains in early spring and summer - 140mm of rain in the 2 months before




The saturated clay became unstable and slumped along the slip plane causing an earth flow at the base of the slump




Cut the cliff by 70m




Cracks appeared 6 weeks before the main failure and garden had a minor movement so closed the cliff paths below the hotel




Affected tourism in the area as the remains were demolished, owners of the hotel lost money and land




Expensive painting lost from inside the hotel

CS - Venezuelan mudslides

15-16th Dec 1999




Worst disaster in the country for 200 years




Avalanche of rocks and mud began to pour down the 2000m high Mount Avila burying large parts of the 300km stretch of Central Coast




The rains triggered a series of mudslides, landslides and flash floods




Took the lives of 10,000 to 50,000 people in the narrow strip of land from the mountains to the Caribbean sea




Worst hit was state of Vargas - countless mountainside slum dwellings were buried or swept out to sea




Mudslides between 8m - 10m deep

Venezuelan mudslides - physical causes

Northern venezuela has very high mountains over 2000 m just 10km from the sea




Seaward facing slopes are very steep - rapid runoff and high energy streams




Impermeable rocks which have been deeply weathered




Precipitation was 40-50% higher than normal

Venezuelan mudslides - human causes

Severe lack of preparation or education




Corrupt politicians and planners allowed shanty towns to grow on steep valleys and near the coast and capital of Caracas




Widespread deforestation - increased runoff and erosion