3.1.2

• shield volcanoes

  • Fluid lava flowas, with low silicone content, build up layers over time
  • eruptions tend to be quiet and no-explosive
  • can grow to hundreds of kilometres in diameter - repeated flows of low viscosity lava spread quickly and over long distances
  • shaped like a warrior's shield - broad with gently sloping sides
  • normally found on constructive plate boundary
• cinder cones volcanoes

  • magma has high silicone content, making it very viscous, or thick
  • eruptions tend to be explosive
  • erupt rock fragements, or cinders - often farm along sides of shield and composite volcanoes
  • tend to be small with steep sides, and have a crater on top
  • formed from a single eruption
• composite volcanoes - stratavolcanoes

  • magma is viscous, or thick, and rich in silica
  • eruptions can be highly explosive
  • alternating eruptions of lava flows and pyroclastic materials like ash, cinders and bombs
  • usually cone shaped with steep sloped sides, can grow to be very tall and wide
• Rhyolitic lava

  temperature - 650 to 800 degrees - coolest

  Formed by melting of lithosphere mantle and slabs of previously subducted plate

  Silica plate - high silica content (70%)

  flow characteristics - thick and stiff, very violent, cataclysmic
• Basaltic lava

  Temperature- 1000 to 1200 degrees - hottest

  Formed by melting of mantle minerals, mostly from upper zone but some from core - mantle boundary

  Silica content - low silica (50%)

  flow characteristics- thin and runny, gentle, effusive

  Normally shield volcanoes
• Andesitic lava

  Temperature - 800 to 1000 degrees

  Formed by subducted oceanic plate melts and mixes with seawater, lithospheric mantle and continental rocks

  Silica content - intermediate silica (60%)

  eruption energy - violent, Moderately explosive
• what are volcanic harzards

  any volcanic proccess that threatend life or detroys land or infastructure

  • tephra, Lahars, pyroclastic flows, lavs - associated with compsote volcano
• Tephra

  rock and ash erupted and flung from a volcano
• lahar

  water mixed with volcanic material
• pyroclastic flows -

  fasts flows, very hot, dense cloud of toxic gas and tephra
• lava

  lava can build up in craters, on shield volcano, lava more hazardous
• ashfall

  fragments of rock produced when magma or rock is ejected during an explosive eruption
• Lahar


  a mixture of water and rock fragments that flows down the slopes of a volcano
• Jokeulhlaups 


  a sudden discharge of glacial meltwater
• volcanic landslides

  large masses of debris that move rapidly down the volcanoes slopes and and are triggered by a variety of proccesses
• toxic gases

  gases within the magma that are released when it rises to the surface and pressure is released
• Eyjafjallajokull - march 2010 eruption

  • very dramatic and powerful
  • lasted for 2 months
  • 30,000 tons of CO2 per day - not thought to make an impact
  • magma broke the crust beneath the glacier
  • March = mostly lava eruptions - little threat to local communties
  • impacted the whole world
  • became an international eruption
  • 14th april - lasted several days - huge amounts of ash where put into the atmosphere - new phase = much more explosive
• Eyjafjallajokull - national impacts

  • decrease in tourism - affects icelands economy - floods - erupted beneath a glacier
  • road transport interuppted - roads washed away
  • reconstruction was expensive
  • agricultural impact - crops covered by a thick layer of ash
• Eyjafjallajokull - local impacts

  • high amount of particles of ash - hundreds of people had to be evacuated - 800 people evacuated
  • home and roads damaged
  • rescuers wore face masks to prevent chocking
  • animals injested floride
  • floods -> erupted beneath a glacier -> 2000 - 3000 $m^3$/ second
  • -> flood defences constructed
  • local water supplies containmented with flouride from ash
• Eyjafjallajokull - location

  located Mid-altantic ridge in iceland -> constructive divergent

  -> north amercan plate - west

  eurasian plate - east

  -> 1cm - 5cm apart per yeaar
• Eyjafjallajokull - international impacts

  • 100,000 flights were cancelled -> losing around 130 million a day

  -> 10 million air passengers affected - people stranded

  • production stopped due to lack of raw materials - raw materials could not been flows -> kenya and other LICS struggled because they couldn't transport their goods abroad - 20% of kenya economy relies on these - over 50,00 farmers temporarily unemployed
  • large amounts of european airspacr closed - sporting events such as the Japanese motercycle grand prix were affected
• Eyjafjallajokull

  40 $km^2$, overall small volcano -> composite volcano -> explosive type

  • at highes point, it is 1651m -> crater 3-4 km
  • ash plume reached 11,000m into the air
• primary hazards of a volcano

  tephra, lahar, pyroclastic flows, lava
• secondary hazards of volcanoes

  acid rain, landslide, earthquakes, lahar
• Hazard

  a percieved natural event which has the potential to threaten both life and property. It can only become hazard if lives are at risk
• Deggs model

  Harzdous geophysical event, for example volcanoes, earthquakes, Tsunami

  vulnerable population: sucsetible to human and/or economic loss because of their location

  
• The diaster Risk equation

  the probabilty of a harzard event occouring and creating loss of lives and livelhood

  level of vulnerability - how exposed you may be or how exposed an area may be. the tendency of place,group or society to have increased losses to harzards

  capacity of population to cope - planning, preperation and evacuation

  
• why has the frequency of reported diasters has changed over time

  increased technologly to detect natural hazards e.g. seismometor which can detect very small earthquakes

  increased reporting of natural harzards due to improved technologly e.g. internet

  population size has increased which means vulnerable populations live in risky locations so are more likely to experience diasters

  climate realted harzards have seen large increases in numbers due to climate change
• monitoring volcanoes and predicting eruptions

  there is a greater opportunity to predict a volcanic eruption because there are usually warning signs before the main eruption

  • monitor gas emmissons, ground deformation, hydrologly, temperature changes and seismic activity
  • but not possible to accurately predict when an eruption will occour or the scale of the eruption
  • satellite imagery- ground shape to understand heat released by volcanoes - trend found that in the years leading to an eruptions the temperature increases
• 10% of worlds population live near active volcanoes
• monitoring techniques

  volcanocams, seismic studies, gas analysis, ground deformation
• Mt Ontake Japan 2014


  A volcanic eruption of mount ontake took place on September 27th 2014

  it was a stratavolcano

  200km southwest of Tokyo

  This eruption was Phreatic, This then ejected hot ash, rocks and steam, eruption of magma within the volcano - so very hard to predict (VEI 3)

  it was being monitored

  total death rate - 60

  2 seismographs were broken and not replaced
• Stromboli - Aeolian islands

  Surveillance camera has been installed on the peak of the vocano -> transmits 'real-time' images of the volcano's activity 24 hours a day
• Volcanic seismic activity

  seismic analysis centre in the vesuvius observatory, naples italy transmisson statiosn that collect seismic data have been set up on vesuvius
• 3 Major types of seismic information

  short-period earthquake - caused by magma forcing its way upwards and fracturing brittle rock in proccess

  Long-period earthquakes - increase gas pressure in the volcano's plumbing system

  Harmonic tremor occours due to sustained movement of magma below the surface often as it is vibrating or pulsating within the feeder pipenor conduit
• major gases given off by volcanoes

  over 80% is water vapour

  Carbon dioxide, Sulphur dioxide, hydrogen, hydrogen sulphite and hydrogen chloride - increase prior to an eruption
• COSPEC

  correlation spectrometer to measure the amount of sulphur dioxide. these may be mounted on a tripod, on a vehicle or attached to a helicopter
• FLYSPEC

  minature version of COSPEC that can be attached to a hard hat or backpack
• LI-COR

  Infra-red analyzer to measure the amount of co2 in a volcanic plume
• FTIR

  Fourier transform infared spectrometer continously sample gas in a volcanic plume