Volcanic Hazards

Question 1

Monogenetic

Answer 1

Volcano erupts once

Question 2

Polygenetic

Answer 2

Volcano erupts many times

Question 3

Explosive

Answer 3

Silica content
Magma temp
Gas content

Question 4

Upper mantle

Answer 4

Fe, Mg, Silicates

1400-3000 degrees C

Question 5

Lower mantle

Answer 5

solid rock at 3000 degrees C

Silicon, magnesium oxides and sulphides

Question 6

Spreading ridge

Answer 6

75%

Question 7

Subduction zone

Answer 7

15%

Question 8

Intraplate volcanism

Answer 8

10%

Question 9

Divergent plate boundary example

Answer 9

Iceland
Low viscosity basalti lava fed by fissures
Non explosive

Question 10

Divergent e.g. submarine volcanoes

Answer 10

75% annual output of magma, 4000 volcanoes per million square km of the Pacific

Question 11

Volcanism at hot spots

Answer 11

Hawaii, Galapagos, Iceland

Question 12

Characteristics of hot spo volcanoes

Answer 12

Shallow, smooth, broad slopes: SHIELD. Non-explosive, basaltic lava

Question 13

Hotspots below continental lava type:

Answer 13

rhyolitic

Question 14

Ocean Islands

Answer 14

island chains e.g. Hawaii. Plate moves over a stationary, hotspot e.g. Galapagos

Question 15

Basaltic Lava

Answer 15

Most common, 2/3rds of Earth is basalt

Question 16

Two types of lava

Answer 16

A’a, Pahoehoe

Question 17

A’a lava [3]

Answer 17

1000-1100. low viscosity, low dissolved gas

Question 18

Pahoehoe

Answer 18

1100-1200

Question 19

Shield Volcanoes [5]

Answer 19

Low viscosity, Low silica, Gently sloping, Large, Spatter Cone

Question 20

Volcanoes at convergent boundaries

Answer 20

Central composite (strato) volcanoes

Question 21

Andesite [3]

Answer 21

53-63% SiO2
Most common on strato
900-1100

Question 22

Dacite [3]

Answer 22

63-68% SiO2
Most common with plinian eruptions
800-1000

Question 23

Rhyolite [2]

Answer 23

> 68% SiO2

700-850

Question 24

Types of volcanic eruption [2]

Answer 24

Effusive (lava) or Explosive (gas)

Question 25

Types of explosive volcanic eruptions [3]

Answer 25

Strombolian Vulcanian Plinian

Question 26

Strombolian eruption [5]

Answer 26

``` Basaltic low viscosity Explosive with gas Volcanic bombs Cinder cone Mt Etna ```

Question 27

Vulcanian eruption [4]

Answer 27

Viscous High gas pressure Columns 5-20km high Andesitic to dacitic material

Question 28

Plinian eruption

Answer 28

``` Si-rich magma High dissolved gas >20km columns Dacitic to rhyolitic materia Pumice and pyroclastic Mt St Helens ```

Question 29

Volcanic Explosivity Index

Answer 29

Intensity of eruption | Increase a number, increases by a factor of 10

Question 30

Cinder Cone

Answer 30

Pyroclastic cone or cinder cone from tephra deposits around the vent

Question 31

Lava dome

Answer 31

Steep round mounds from eruption of high viscosity, low gas content magma Subduction zone related

Question 32

Caldera

Answer 32

Large circular depression at the summit of a volcano from collapse of centre of a volcano