Primary and secondary houses of volcanoes and measuring them

Primary – volcanic gasses

• least hazardous

• Gases are associated with explosive eruptions and lava flows

• Mix includes water vapour sulphur dioxide, hydrogen carbon monoxide

• Most deaths are due to carbon dioxide

• If gas stays localised, then damage is limited to the immediate area

• If it mixes and condenses with other materials, it can cause problems (Lahars)

  CO2 from Lake Nyos in Cameroon Killed 1700 people

Primary – lava flows

• right, if they are fast moving

• Viscosity is determined by the amount of silicon dioxide

E.g.Nyiragongo in DRC Exploded and destroyed 12,500 homes and 80% of air strips at the airport were covered in lava

Ashfall/ tephra primary

• sometimes eject rock fragments into the atmosphere (tephra)

• Can blanket large areas in ash killing vegetation, collapsing buildings and poisoning water sources

• Occurs at constructive plate boundaries

E.g. E15 Iceland 2010 Was carried in the atmosphere and cancelled flights globally

Pyroclastic flows primary

• most dangerous

• Ash Gas and rock gets up to 800°C

• Travelling 700 km/h down volcanoes

• Result of frothing Magma

• Contains glass, pumice , Crystal and Ash

E.g. Mount Saint Helens 1980

Areal extent

• Area covered by a hazard

Secondary - lahars

• Most dangerous

• When volcanic ash mixes with water or snow

• Melts to create a type of mudflow that varies in viscosity due to the ratio of ash to water

• Rainfall is common after a volcanic eruption Because the as in the atmosphere encourages condensation of water vapour (Condensation nuclei)

E.g. Mount Pinatubo the Philippines- Height was 40 km with a VEI of six

Jokulhlaup glacial burst – secondary

• Volcano erupt under an ice cap and the heat melts some of the ice

• The melt water builds up around the top which melts and lifts overhead ice

• The water from under the ice and flows rapidly

• Anything in the path is wash away or covered in volcanic and glacial deposits

E.g E15 700 were ordered to evacuate

Flowed at 2000 – 3000 m³ per second

Secondary – tsunamis

• 1883 Krakatoa exploded + Collapsed

• Waves reached 41 m high

• And killed over 30,000 people

Measuring volcanic eruptions

• VEI - volcanic explosivity index 0-8

• Volumes of erupted lava

• Areal extent