Hazards generated by Volcanic Eruptions

• Lava flows


  • The impacts depend on the type of lava
  • The temperature of lava ranges between 700-1200oC
• Basic (basaltic) lava


  Free flowing and can run for considerable distances
• Lava flows


  • In July 2015 on Hawaii, a lava flow extended for 20km before stopping
  • In August 2015 on Hawaii, a flow was reported to have covered 800m in a day
• Acidic lavas such as rhyolite


  Thick, and pasty so do not flow easily
• Everything in the path of the lava will either be burned, bulldozed or buried
• Although they destroy infrastructure, property and crops, lava flows rarely cause injuries or fatalities
• Pyroclastic flows:

  ·         These are a combination of very hot gasses (500oC+), ash and rock fragments travelling at high speeds (100km/h).

  ·         They follow the contours of the ground and destroy everything in their path.

  ·         The inhalation of such hot and poisonous gas and ash causes almost instant death.

  ·         The Roman town of Pompeii was overwhelmed by a pyroclastic flow from Mt Vesuvius in 79AD.
• Tephra


  Material ejected from the volcano into the air
• Tephra


  • Ranges in size from fine ash to large volcanic bombs (≥6cm) across
  • Includes lighter debris such as pumice
• Tephra is potentially very hazardous, burying farmland in layers of ash and destroying crops
• Transport can be disrupted both on the ground and in the air
• The eruption of Iceland's Eyjafjallajökull volcano in April 2010 led to the cancelation of over 100,000 flights
• Buildings can collapse due to the weight of accumulated ash
• People with respiratory diseases may have trouble breathing
• Toxic gasses:

  ·         Eruptions can emit a wide range of toxic gasses, including CO1, CO2 and SO2.

  ·         These gasses can pose a deadly (and silent) threat to human populations.

  ·         When SO2 combines with atmospheric water, acid rain is produced.

  ·         This enhances weathering, can damage crops and pollute surface water and soils.

   
• Lahars


  A type of mudflow with the consistency of wet concrete
• Formation of lahars


  1. Snow and ice on a volcano summit melt during an eruption

  2. Flow rapidly down the cone

  3. Rock fragments, ash and soil are mixed together
• Lahars


  • Can travel at speeds up to 50km/h
  • Everything in the path is either destroyed or buried under thick layers of debris
• Lahars


  • In 1985, following the eruption of Nevada del Ruiz, the Columbian town of Armero was overwhelmed by lahars, resulting in the deaths of at least 23,000 people. This became known as the Armero tragedy.
• Floods:

  ·         Volcanic eruptions beneath an ice field or glacier can cause rapid melting.

  ·         In Iceland, several active volcanoes lie under the Vatnajӧkull ice field.

  ·         During an eruption vast quantities of water accumulate until they find an exit from under the ice.

  ·         The resulting torrent of water, which can cause devastating floods, is known locally as jӧkulhlaup.
• Tsunami


  • Caused by violent eruption of island volcanoes
  • Capable of travelling at speeds up to 600km/h
• Tsunami in deep water

  • Height usually less than 1m
  • Wavelength up to 200km
• Tsunami approaching the shore

  1. Increase rapidly in height

  2. Break and transfer vast amounts of energy and water along the shore and inland
• Tsunamis created by eruption of Krakatoa in 1883


  • Drowned 36,000 people
• Potential eruption of Cumbre Vieja on La Palmer

  Could lead to the flank of the volcano sliding into the sea and causing a tsunami that could reach the shores of the UK