seismicity

• predicting volcanic eruptions

  • history and type of previous activity
  • physically observing
  • infrasound device
  • seismometers and seismograph
  • ground deformation measured with tutometers and lasers
  • magnetometers to measure movement of lava
  • hydrological instrumentation
  • warning signs
• volcanic explosively index (VET)

  measures

  • volume of ejecta
  • height of eruptive column
  • qualitative descriptions
  • style of past activity
  • height of spreading of eruptive plume head
  • doesn't take into account gas emissions or atmospheric impact of emissions
• pyroclastic flows

  hot mixture of rock fragments, gas and ash which travels rapidly away from a volcanic vent or collapsing flow
• lava flow

  varies in speed but can destroy buildings, block roads and trigger pyroclastic flows
• volcanic gases

  co2, carbon monoxide, sulphur dioxide, chloride
• ash cloud

  lava droplets which are blasted into the air and then quickly cool to produce sharp ash
• ash fallout

  distribution of ash from a volcanic eruption
• mud flow

  composed of volcanic ash mixed with water and is a secondary impact
• acid rain

  volcanic gases mix with water vapour which is a secondary impact
• flooding

  when lava flow blocks river channels leading to runoff outside the river channel which is a secondary impact
• fissure eruption

  creates extensive lava plateaus and hollows which are filled to create flat features like basalt plains
• basic shield eruption

  shallow sides and broad formed by pure basalt which cools as it runs down the summit crater
• acid dome eruption

  steep sided convex cones with thick silica rich gaseous lava that solidifies before running too far down the slope
• composite cone eruption

  formed for alternating eruptions of ash, tephra and lava which builds up the volcano in layers which produces weaknesses that can be exploited by magma
• caldera eruption

  result from violent eruptions that blow of the volcanoes summit which empties the magma chamber causing the sides of the volcanoes to collapse inwards
• liquefaction

  ground acts as a liquid due to vibrations of an earthquake when compacted sediment looses strength and stiffness due to an applied stress
• shockwaves

  change of pressure in a narrow region travelling through a medium
• epicentre

  point on the surface directly above the focus where the earthquake is felt
• focus

  the breaking point where the pressure is released and the rock moves
• p waves

  fastest and reach the surface first. Have high frequency and travel through the mantle and core to the opposite side of the earth
• S waves

  half as fast as P waves and reach the surface next. high frequency and travel through the mantle not core
• L waves

  are the slowest and cause most of the damage. move and originate from side to side
• R waves

  radiate from the epicentre in low frequency rolling motions
• causes of tsunamis

  • ocean floor earthquakes
  • submarine volcanic eruptions
  • landslides into the sea
  • submarine debris slides
  • meteor strikes
• Formation of tsunamis

  1. pressure of plates build up due to sticking
  2. plates slip releasing the pressure
  3. ocean floor lifts up
  4. water is displaced
  5. wave forms
• signs of seismic activity

  • microquakes
  • bulging of ground
  • decreasing radon gas concentration in ground water
  • raised groundwater levels
  • increased argon gas concentration in soil
  • curious animal behaviour
  • visible signs
• Earthquake impact depends on

  • magnitude and depth
  • geological conditions
  • distance from epicentre
  • population density, preparedness, education, design and strength of buildings
  • time of day
  • impact of indirect hazards
• Richter scale

  based on amplitude of the largest wave recorded on a seismometer and the distance between the earthquake and seismometer
• Moment magnitude scale (MV)

  based on total movement release of the earthquake. Moment is a production of the distance a fault moves and the force required to move it
• Mercalli scale

  uses the observations of people who experience the earthquake to estimate it's intensity