Hazardous environments

• what is shear strength and stress


  shear strength- the internal resistance of the slope itself that binds it cohesively together

  
  

  shear stress- the forces acting on the slope
• factors that could increase shear strength


  tree roots binding soil together

  
  

  removing weight from surface
• factors that could decrease shear strength


  weathering that weakens internal structure

  changes in water level or pore pressure

  burrowing animals that remove material

  undercutting of slope
• factors that increase shear stress


  removal of lateral support from slopes, adding weight to slopes, and earthquakes
• why does mass movement occur

  When the forces acting on the slope exceeds the forces supporting it
• what is rock fall


  movement is mainly through the air

  on cliffs above 40 degrees

  rocks may become detached due to weathering

  also triggered by undercutting
• what are slides


  These may be linear, with movement along the slip plane. Rotational slides are known as slumps. undercutting of the base of the cliff removes support for the materials above
• what are landslides


  downslope movement of a large block of material that moves as a coherent mass

  it retains its internal structure until hitting the base of the slope

  move common over wet periods
• what is earthflow


  The downslope movement of water-saturated, clay-rich sediment.

  quite fast

  flow is elongated
• what are mudflows


  a mudflow is an earthflow consisting of material that is wet enough to flow rapidly
• what is a slump


  rock and soil slip down a slope

  marine processes erode and undermine the base

  rainwater infiltrates the cliff through porous material

  this then creates a slip plane

  the weight of the saturated clay causes the material to slump along the slip plane

  
  

  water adds weight and lubricates the clay
• what are the impacts of mass movements


  death

  injuries

  cost of evacuation, investigation and repair

  other indirect costs

  costs of prevention
• how to predict mass movements


  warning signs

  -cracks in buildings/ground

  -tilted structures

  -bulging walls

  -steep slopes with deposited material on them
• how to monitor mas movements

  sloped can be closely monitored for change

  
  

  use of gps and laser surveys to determine exact movement per year

  
  

  rainfall data can determine how much a slope can hold

  
  

  changes in soil moisture can also be monitored

  
  

  boreholes can be monitored as that indicates change in ground water

  
  

  tiltmeters- amount of tilt

  
  

  strain meters- changes in amount of crustal strain
• how to hazard map mass movements


  drawn up using factors that effect slope stability and knowledge of previous movements

  
  

  rocks are classified by susceptibility
• how to prepare for mass movement

  hard engineering strategies
• living with mass movement: usa Bingham copper mine 2023 what happened, why and effect pon lives and property


  what happened

  -two big landslides carrying 145 million tons of waste rock fell into the bottom of an open pit

  -each one lasted 90 seconds

  -no one injured or died

  
  

  human factors

  -undercut the slope

  -quarrying steepened the slope

  -increased weight from waste rock on slope

  
  

  physical factors

  -weak thin sedimentary layer

  -old fault lines decreasing the strength

  
  

  effect on lives and property

  -everyone evacuated

  -interferometric radar system detected movement and instability

  -3million dollars spent on remote control bulldozers to clear rubble
• what is a hazard


  threat that could injure a person and damage the built environment
• what is a disaster


  a hazard that causes so much damage and injury that recovery without help is impossible
• where do earthquakes usually occur


  mainly on plate boundaries

  found on all boundaries

  some intraplate activity at weak points eg hawaii

  found in cluster chains
• where do volcanoes usually occur


  all plate boundaries except collision

  most common is strato at convergent destructive

  also found in chains

  can also be found in intra plate
• what are the 4 types of plate boundaries

  divergent <---- ---->

  
  

  convergent --_<---

  >

  
  

  collision ---><---

  
  

  conservative ^!

  ! !

  ! *
• what is a divergent plate boundary

  plates are moving apart and magma is rising up and forcing its way to the surface

  
  

  as it is rising through the mantle there is more basalt in the lava therefore less silica decreasing the viscosity and the trapped gas and decreasing the explosiveness of a volcano formed here

  
  

  shallow earthquakes
• what is a convergent plate boundary


  oceanic plates are denser so forced under continental plates when they converge, subduction where the plate goers under another

  
  

  volcanoes are quite explosive as basalt + granite = higher silica so more viscosity therefore more trapped gas so higher explosiveness

  
  

  shallow medium and deep earthquakes
• what is the benioff zone


  this is a zone where the oceanic plate is put under intense friction and pressure after subducting leading to faulting and fracturing and therefore earthquakes
• what is a collision plate boundary

  when 2 continental plates converge little subduction occurs

  
  

  no volcanoes

  
  

  shallow earthquakes
• what is a conservative plate boundary


  this is where plates slide past each other

  
  

  no volcanoes

  
  

  shallow but strong earthquakes
• what is an earthquake

  an earthquake is a release of stress that has built up within the earths crust energy is released as seismic waves

  
  

  stress in the crust is widespread therefore earthquakes can happen anywhere
• how to measure earthquake intensity


  the mercalli scale measure the surface damaged by an earthquake
• how to measure earthquake magnitude


  richter scale measure the amount of strain energy released
• what hazards come from earthquakes


  ground shaking and displacement

  liquefaction

  landslides and avalanches

  tsunamis
• how is ground shaking and displacement caused

  vertical and horizontal movement of the ground

  severity depends on the eq
• what is liquefaction


  an area with a surface of fine grained sand alluvium and landfill with a high water content will act like liquids when an eq happens

  
  

  these materials lose their strength

  
  

  slopes collapse and structures tilt and sink as foundations give way
• how are landslides and avalanches caused by eq


  can cause slope failure

  small tremors can cause landslides

  some areas are more prone than others
• how are tsunamis caused


  caused by underwater earthquake forcing the sea bed to rise vertically- this displaces water above which produces powerful waves- height increases as it gets closer to the shore

  
  

  before it breaks water in front in pulled out to sea this is called drawdown
• what are the impact of earthquakes


  loss of life- drowning- building collapse

  
  

  loss of buildings

  
  

  flooding of land

  
  

  total or partial destruction of buildings- destabilisation of buildings which may then collapse in the future

  
  

  interruption of water supplies- broken water pipes

  
  

  loss of public utilities- burst gas pipes can lead to fires

  
  

  floods from collapsed dams- damage to dams from shaking causes dam to collapse and water to rush out

  
  

  spread of illness- water piped can be contaminated with sewage
• what is perception of risk


  influences what people are going to do

  
  

  depends on their experience of hazards, money and personality eg are they a leader
• what is a forecast


  a relatively imprecise statement of time place and nature of event
• what is a prediction


  a relatively precise statement of time place and size of event
• how to predict an earthquake


  very hard to predict earthquakes

  
  

  seismic gap theory- historical records for a particular fault show the period of elapsed time between earthquakes, if the pattern is regular the next earthquake may be predicted

  
  

  applied to a section of a fault which has been quiet for some time

  
  

  -

  patterns are not regular

  it assumes that movement and other forces are constant

  
  

  however can be used to predict if an earthquake is likely