Lecture 15 + 16: Eruptive Styles and Landforms

Question 1

volcanic eruption four steps

Answer 1

1. hot solid rock from asthenosphere rises closer to the surface following convection loop
2. change from solid to liquid accompanied by volume expansion (fractures create pathways through which more hot materials rise)
3. volatiles gradually come out of the melt (gas bubbles push magma upward
4. magma fragments (when bubbles >75% magma volume, powerful gas jet magma into the atmosphere)

Question 2

peaceful eruptions

Answer 2

• low viscosity
• low volatile content
• small to large volume of magma

Question 3

icelandic type eruptions

Answer 3

• divergent zones and hot spots
• basaltic composition
• landform: Laval Plateau; small area covered by nearly horizontal layers of solidified lava, surgace supture: fissures: linear fracture (<25km)

Question 4

hawaiian type eruptions

Answer 4

• divergent zone or hot spot
• basaltic magma
• volatiles escape easily and lava flows like water
• large volume of lava
• landform: shield volcano (volcano in the shape of flattened dome built by numerous flows of very fluid lava over a long time)

Question 5

strombolian type eruptions “intermediate” case

Answer 5

• tectonic environment: subduction zones
• basaltic to andesitic
• medium viscosity
• medium volatile content
• small volume
• landform: Scoria cone (volcano in the shape of a conical hill formed by pyroclastic debris piled up next to a central vent)

Question 6

explosive eruptive style

Answer 6

• viscosity - medium/high magma viscosity
• volatiles: high volatile content
• volume: small to very large volume

Question 7

Vulcanian-type eruptions

Answer 7

• mostly subduction zones or hot spots
• basaltic andesitic rhyolitic
• large volume
• landform: stratavolcano

Question 8

Plinian type eruptions

Answer 8

• difference from vulcanian and Plinian type eruptions: height of eruption column
• subduction zones and hot spots
• landform: stratavolcano

Question 9

lava dome

Answer 9

• during final phase of Plinian eruption: landform: lava dome
• volcanic cone with a highly viscous blob of lava forming a half-ball shape over the vent
• lava is too viscous to flow far from the vent

Question 10

Caldera type eruptions

Answer 10

• subduction zones or hot spots
• high viscosity
• large volume
• volcano collapse or cataclysmic explosion

Question 11

volcano collapse

Answer 11

• collapse of existing strata volcano into partially empties magma chamber
• follows a Plinian type eruption that opened void space below the volcano
• piston like action of collapsing volcano cause very large volume of magma to flow outward as pumice rich sheets

Question 12

Cataclysmic explosion

Answer 12

• explosion blows the existing volcano apart completely

Question 13

early phase of eruption

Answer 13

• vulcanian type eruption
• formation of stratovolcano

Question 14

major phase of eruption

Answer 14

• Plinian type eruption
• continued development of stratovolcano

Question 15

final phase of eruption

Answer 15

• Plinian type eruption
• formation of lava form or
• caldera type eruption
• formation of caldera

Question 16

volcanic explosivity index

Answer 16

• metric established to quantify the hazards posed by volcanoes
• three factors: volume of material extruded height of eruption column; duration of major eruptive blast

Question 17

Pyroclastic flows

Answer 17

• hot gases ash and rock fragments moving down the side of a volcano
• responsible for the largest number of fatalities related to volcanism
• highly destructive due to momentum high temperature and great mobility
• highly destructive die to momentum high temperature and great mobility

Question 18

volcanic gas

Answer 18

• volcanic gases come out of the melt during eruption
• main driving force of explosive eruptions
• concentrated near vents

Question 19

Pyroclastic fall

Answer 19

• Ballistic projectiles
• fall close to volcanic ash
• hard abrasive mildly corrosive does not dissolve in water

Question 20

Secondary Hazards

Answer 20

• lahar: mudflow that originates on the slopes of volcanoes when volcanic ash and debris become saturated with water and flow rapidly downslope
• 1-40 m/s
• almost always occur on stratovolcanoes

Question 21

Tertiary hazards

Answer 21

• results from the destabilizing long term effects of the volcanic eruption on society
• famine: extensive crop damage and loss of farm animals
• disease: breakdown of sewage and water systems

Question 22

mitigation

Answer 22

• most difficult natural disaster to mitigate
• timing of events is difficult to predict especially for explosive volcanoes

Question 23

volcanic activity classification

Answer 23

• active: erupted in historical times
• dormant: volcano that has not erupted in historical time but is capable of erupting in the future
• extinct: volcano that is not expected to erupt again

Question 24

Monitoring volcanic activity

Answer 24

• to detect and measure changes in the state of a volcano caused by magma movement
• increased seismic activity
• swelling of summit
• deformation of lanks - release of volcanic gases