Volcanic processes and hazards

Question 1

why are volcanoes both destructive and constructive?

Answer 1

the can destroy human infrastructure but also add material to the Earth’s surface

Question 2

3 things effected by large volcanic eruptions

Answer 2

1. atmosphere composition (addition of gases)
2. bioshpere (kills plants, animals, humans)
3. hydrosphere (tsunamis)

Question 3

define VOLCANO

Answer 3

landform built by volcanic activity

Question 4

define VOLCANISM

Answer 4

process in which magma rises through the Earth’s crust and erupts at the surface as lava flows and/or pyroclastic materials and gases

Question 5

what is a VOLCANIC EDIFICE

Answer 5

part of the volcano above the ground

Question 6

seamount

Answer 6

a volcano under the sea which doesn’t reach the surface

Question 7

______ volcanoes form intra-plate, subduction volcanoes form at _______ margins, and rift volcanoes form at _______ margins.

Answer 7

hot-spot volcanoes form intra-plate, subduction volcanoes form at convergent margins, and rift volcanoes form at divergent margins.

Question 8

Active, dormant and inactive/extinct volcanoes?

Answer 8

active - erupted in historic time.
dormant - haven’t erupted in historic time, but they could.
Inactive - not expected to erupt again

Question 9

Flood basalts form due to gigantic volcanic eruptions of ______ viscosity lava. They erupt due to __________ _______. A single eruption can cover 200,000km^2 and form large ________ ________. They have been cited as the cause of mass-extinction events.

Answer 9

Flood basalts form due to gigantic volcanic eruptions of very_low viscosity lava. They erupt due to continental rifting. A single eruption can cover 200,000km^2 and form large igneous provinces. They have been cited as the cause of mass-extinction events.

Question 10

shield volcanoes

Answer 10

• form from low viscosity lava
• gentle slopes
• build up layers over time
• eruption is effusive (not explosive) and can be continuous.
• e.g. rangitoto

Question 11

cinder cones

Answer 11

• steep, scoria cone
• formed from effusive eruptions of low viscosity lava
• gases can vent long after the end of the eruption
• e.g. mt eden, one tree hill

Question 12

what is scoria and why is it red?

Answer 12

scoria forms from low viscosity, basaltic lava cooling rapidly as it flies through the air. It is red because it gets oxidised by steam.

Question 13

composite/ stratovolcanoes

Answer 13

• tall, conical shaped volcanoes
• explosive eruptions
• form from higher viscosity (than mafic) felsic magma
• no extensive lava flows
• e.g. Mt Taranaki

Question 14

rock types associated with felsic magma

Answer 14

• rhyolite
• dacite
• andesite

Question 15

Volcanic domes

Answer 15

• formed from lava too viscous to flow (high silica content)
• lava accumulates around the vent
• basaltic or rhyolitic
• large pieces of rock (BRECCIA) break off as the dome grows
• may erupt explosively, as gases get trapped and pressure builds up

Question 16

what is the name given to a collapsed volcano? why do they collapse?

Answer 16

caldera. Volcanoes collapse when the magma chamber is emptied and the weight of the edifice is no longer supported.

Question 17

2 mechanisms by which a caldera can forms

Answer 17

1. sudden emptying of the magma chamber in an explosive eruption, causing rapid collapse of the edifice through formation of a ring fault.
2. Gradual emptying of the magma chamber associated with shield volcanoes (low viscosity), causing subsidence of the edifice

Question 18

4 types of volcanic eruption

Answer 18

1. Hawaiian - mostly low viscosity lava, not much gas
2. Plinian - large volume of gas, pumice and ash
3. Strombolian - mixed gas/ pyroclastic material and lava
4. hydrovolcanic - highly explosive, hot magma comes into contact with water in the ground and vaporises it.

Question 19

what is used to measure the size of a volcanic eruption?

Answer 19

Volcanic explosivity index.
Similar to the Richter scale.
Based on ammount of material, duration, and how high ejection is

Question 20

rhyolite, dacite, andesite and trachyte are all ____ viscosity lavas.

Answer 20

high

Question 21

igneous rock found with bubbles (vesicles), would’ve formed from …. why?

Answer 21

formed from high viscosity lava, because since the lava doesn’t really flow, the gases get trapped. (the opposite is the case with low viscosity lava)

Question 22

basalt and andesite are _____ viscosity lavas

Answer 22

low

Question 23

pyroclastic materials

Answer 23

• form from explosive volcanism
• classified as airfall deposits
• range from ash to volcanic bombs (breccia)

Question 24

deposits from a pyroclastic flow are called?

Answer 24

Ignimbrite

Question 25

Ignimbrite composites comprise?

Answer 25

- volcanic ash - pumice - lithics - they can be unconsilidated or welded by heat.

Question 26

do volcanic gases (SO2, HCl, HF, CO2) cause global warming?

Answer 26

no they form global cooling by reflecting sunlight back into space.

Question 27

lahar

Answer 27

fast flowing slurry of water, ash and rock. Occur if the eruption melts a lot of snow or ice or if there is heavy rain after an eruption.

Question 28

whats the most destructive volcanic hazard?

Answer 28

pyroclastic flow - mixture of hot (500 degrees c) gases and ash which travel at several hundred kph, destroying everything in their path

Question 29

5 main hazards of a volcano

Answer 29

1. ash falls 2. airborne ash 3. lava flows 4. pyroclastic flows 5. lahar

Question 30

dangers of ash

Answer 30

- abrasive (especially to aircraft) - corrosive - electrically conductive - suspend in the atmosphere for weeks - ash loading on buildings -- increase the dead-load on the roof (even worse when wet) which may lead to collapse - impact water supplies (change composition, shortages during clean-up)

Question 31

does ash affect water quality?

Answer 31

yes, 55 soluble compounds (mineral acids). can change the pH of water and increase turbidity (addition of flocculants)

Question 32

Mitigation of the volcanic hazards at Mt Ruapehu. | Eastern Ruapehu Lahar Alarm and Early Warning System (ERLAWS)

Answer 32

- installed after 1995 and successfully predicted 2007 lahar - array of geophones detect vibrations - buried tripwires detect dam collapse - water level sensors in crater lake detect sudden emptying - automatic barriers on SH1 if lahar detected

Question 33

other lahar mitigation techniques

Answer 33

- bund preventing flow - overflow channel - sediment retention basin - channelisation of flow

Question 34

main things monitored on a volcano

Answer 34

1. gas monitoring 2. seismic activity (tiltmeters, extensometers and gps) 3. deformation monitoring (large scale bulging)

Question 35

what is the most widespread hazard caused by a volcano?

Answer 35

ash fall