vulcanicity (unfinished)

• define a volcano


  a vent at the surface of the earth through which magma and other volcanic materials are ejected
• what are volcanoes proof of

  that the earth is active and the plates are in constant motion
• what is are intrusive features


  batholiths

  sills and dikes

  laccoliths
• what are extrusive features


  lava
• where can volcanic activity be found


  most associated with plate boundaries

  
  

  - along oceanic ridges where plates are moving appart

  - rift valleys

  - near subduction zones

  - hot spots
• what might vary in a volcanic eruption

  form

  frequency

  type
• what are the variations in eruption linked to

  different kinds of plate boundaries, the emissions and the lava
• what might be released in an eurption


  basaltic lava (also called basic)

  andesitic (acid) lava

  pyroclastic material

  ash

  lapilli
• characteristics of basaltic lava


  - dominated by iron and manganese

  - low in silica

  - gas bubbles have the freedom to expand as the magma rises to the surface = less violent

  - low viscosity

  - the lava is fluid and free flowing

  
  

  - erupted at temps between 1100 to 1250 degrees c

  
  

  - shield volcanoes are composed almost entirely of basalt
• characteristics of andesitic lava

  - high vicocity so the gas bubbles struggle to escape = more violent due to build up of pressure

  - associated with destructive plate boundaries

  - produced when there is subdution

  - temp of 800 degrees c

  - but moves slowly + solidifies quickly so it might solidify in the central vent which causes a blockage and builds up pressure = violent eruptions

  
  

  produces steep sided volcanoes
• what is pyroclastic material


  all the fragmental material formed by explosive eruptions including bombs, blocks, lapilli and ash

  
  

  most dangerous
• what is a pyroclast


  magma can be forcefully or explosively ejected into the atmosphere as particles called pyroclasts
• what is volcanic activity below the surface

  intrusive
• what is extrusive


  volcanic activity above the surface
• types of volcanos


  shield

  ..
• what is volcanic ash


  has particles as small as 2mm

  consists of rock, minerals and volcanic glass fragments

  
  

  it is abrasive

  doesnt dissolve in water
• what is lapilli


  small pieces of material ranging from 2mm and 64mm across (pea to walnut)
• what are volcanic bombs

  when lava is blasted out of the crater and solidifies in the air and lands on the surface

  they are lava fragments that were ejected while viscous and larger than 64mm diameter
• what are volcanic blocks

  a solid rock fragment greater than 64mm in diameter that was ejected from a volcano during an explosive eruption, the block was once part of the volcanoes cone
• how are volcanoes classified


  according to the nature of eruption

  - base don the degree of violence of the explosion which is a consequence of (check slides)
• how are volcanoes measured


  using the VEI

  - volcano explosivity index
• what is the VEI based on


  how much volcanic material is thrown out in an eruption, to what height and how long it lasts
• what is the VEI scale


  it goes from 0-8

  and is logarithmic
• what is tephra


  Erupted material from a volcano (a general term for it)
• what is the relationship between magnitude and frequency

  negative correlation
• what landforms are linked to basaltic and andesitic lava


  fissures and lava plateaus

  vents

  basic and shield volcanoes

  composite cones

  ash and cinder cones

  calderas
• where are explosive volcanoes located


  at convergent boundaries, particularly around the pacific where the oceanic plate is subducting

  
  

  associated with strato-volcanoes because they consist of layers of lava and pyroclastic deposits
• how do intrusive volcanic features/landforms form


  when magma doesn't reach the surface at an eurption and solidifies in the crust

  
  

  these are later exposed at the surface by erosion
• what are some hazards at volcanoes


  pyroclastic flow

  lava dome collapse

  bombs

  lava flow

  tephra (ash) fall

  acid rain

  lahar (mud or debris flow)

  debris avalanche
• what are the primary hazards of an eruption

  tephra

  lava

  pyroclastic flows

  volcanic gases
• what is tephra


  solid material that varies in size from volcanic bombs to ash
• why is pyroclastic flow a p hazard


  a mix of gas and tephra which is very hot and moves at a high velocity
• why are volcanic gasses a p hazard


  people can suffocate from eg carbon monoxide like in

  1986 when 1.7k people suffocated from lake nyos in cameroon
• secondary hazards of an eruption


  lahar

  flooding

  volcanic landslides

  tsunami

  climate change
• how is lahar a s hazard


  it is volcanic mud
• how is flooding a s hazard

  caused by the heat of lava melting ice caps and glaciers
• how are volcanic landslides a s hazard

  due to the steep gradient on volcano sides land will slide
• how is a tsunami a s hazard

  giant waves which are generated by displaced land
• how is climate change a s hazard


  during major eruptions, huge amounts of volcanic gas and ash are injected into the stratosphere which can cool temps
• what are the hazards of volcanoes


  lava flow - burns and burys crops

  
  

  tsunamis - submarine or coastal eruptions can cause them

  
  

  ash fall - ruins crops and machinary, disrupts transport, pollutes air, causes breathing difficulties

  
  

  dust emissions- endanger air transport, 'seed torrential rainstorms resulting in

  dangerous wet ash and mud lahars.' idk wt this is

  
  

  pyroclastic flow - violent eruptions destroys life and property

  
  

  volcanic melting of snow - creates dangerous lahars

  
  

  volcanic dust- absorbs solar energy + lowers temp