Volcanoes

Question 1

3 principle magma generating processes:

Answer 1

• decompression melting
• addition of volatiles
• addition of heat

Question 2

decompressional melting

Answer 2

• thinning of lithosphere [mid-continental (rift valley) & mid-ocean]
• reduction in pressure (asthenosphere rises)
• hot-spot volcanism

Question 3

addition of volatiles

Answer 3

• lowers melting point by breaking chemical bonds
• voltiles: H2O, CO2, SO2
• melting temp at depth reduced from 1500 to 800oC
• dominant process in subduction zones
• volatile content influences eruption style
• Volatile content increases with increasing silica
  content

Question 4

Addition of heat

Answer 4

• rising asthenosphere partially melts lithosphere
• some minerals more susceptible than others
• crustal melting affects magma chemistry
• different magma comes from different portions of partial melt
• composition influences eruption behaviour

Question 5

soufriere-type formation

Answer 5

• foundation collapse
• eruption column can no longer be sustained (due to loss of pressure)
• column collapses forming pyroclastic flows on the flanks of the volcano
• they tend to be cooler than the others
• widening of the vent = collapse

Question 6

Pelee-type formation

Answer 6

• a dome of viscous magma blocks the conduit
• eventually it explodes under pressure, blasting pyroclastic material down one of the flanks of the volcano
• can produce a lateral rather than vertical blast

Question 7

Merapi-type formation

Answer 7

• dome of viscous magma grows in the crater

- gets so large it collapses under gravity, producing a pyroclastic flow

Question 8

Giachetti et al. 2012

Answer 8

• incredible modelling
• potential impact of 0.28km3 collapse
• tsunami risk and impact

Question 9

Anak Krakatau, 2018

Answer 9

• limited publications currently
• 220 fatalities/800 injured
• modelling was highly accurate for reality of event
• early warning

Question 10

volcanic and seismic monitoring

Answer 10

• earthquakes (seismographs)
• deformation (tiltmeters)
• gas output (sulphur levels)
• remote sensing techniques (GPS)
• relocation if change detected

Question 11

Lahars

Answer 11

• energetic debris flows of pyroclastic material and water
• can be highly destructive traveling at 10s of meters per second
• many potential causes
• anything that mixes pyroclastic material with water and energy
• usually but not always related to an eruption
• glacier melted by an eruption, hot magma meeting mud and water during an eruption, earthquake near a volcano

Question 12

volcanoes as a resource

Answer 12

• fertile volcanic soils (mt pinatobo and st helens)
• mining of mineral resources
• building materials
• tourism
• geothermal energy