Volcanoes

Question 1

Where do volcanoes occur?

Answer 1

On divergent and destructive boundaries

Question 2

What happens at a divergent boundary?

Answer 2

Plates move apart
Magma rises through crust
Magma cools and forms new crust
Repeats

Question 3

What happens at a destructive boundary?

Answer 3

Oceanic crust is subducted
Pressure builds in continental, folds then cracks
Magma rises through cracks

Question 4

What volcano forms at a divergent boundary?

Answer 4

Shield

Normally underwater

Question 5

What volcano forms at a destructive boundary?

Answer 5

Strato

Question 6

What are the primary effects?

Answer 6

Lava flows
Pyroclastic flows
Tephra/ash falls
Gas eruptions

Question 7

What are the secondary effects?

Answer 7

Jokulhlaup

Lahars

Question 8

What are lava flows?

Answer 8

Sheets of liquid rock expelled from an erupting volcano

Question 9

What are pyroclastic flows?

Answer 9

Gas and lava that flow down the side of the volcano

Question 10

What are tephra/ash falls?

Answer 10

Volcanoes project ash and it covers the ground

Question 11

What are gas eruptions?

Answer 11

Water vapour, CO2, sulphur dioxide and sulphur trioxide are released

Question 12

What are jokulhlaup?

Answer 12

Water/ice melted from glaciers leading to mud flows

Question 13

What are lahars?

Answer 13

Volcanic mud flows, ash mixed with snow and ice

Question 14

What are the features of a shield volcano?

Answer 14

Wide base- 180km
Slopping sides
Solidified layers of lava

Question 15

What are the features of a strato volcano?

Answer 15

Narrower base- 18km
Steep sides
Solidified layers of ash and pyroclastic materials

Question 16

How is volcanic eruption measured?

Answer 16

Volcanic explosivity index- 1-8

Question 17

Composition of basaltic lava

Answer 17

1000-2000 degrees- hottest
Low silica content- 50%
Low gas content- 0.5-2.0%
Low viscosity

Question 18

How is basaltic lava formed?

Answer 18

Melting of the mantle

Question 19

What is the eruption energy like of basaltic lava?

Answer 19

Effusive

Question 20

Where is basaltic lava found?

Answer 20

Ocean hotspots
Mid-ocean ridges
Shield volcanoes

Question 21

What is an example of a volcano with basaltic lava?

Answer 21

Mauna Loa, Hawaii

Question 22

Composition of andesitic lava

Answer 22

800- 1000 degrees- middle
Intermediate silica content- 60%
Medium gas content- 3-4%
Intermediate viscosity

Question 23

How is andesitic lava formed?

Answer 23

Subduction of oceanic plate

Question 24

Where is andesitic lava found?

Answer 24

Subduction zones + strato volcanoes

Question 25

What is an example of a volcano with andesitic lava?

Answer 25

Chances Peak, Montserrat

Question 26

Composition of rhyolitic lava

Answer 26

650-800 degrees- coolest
High silica- 70%
Gas content- 4-6%
High viscosity

Question 27

What is the eruption energy like of andesitic lava?

Answer 27

Moderately explosive

Question 28

What is the eruption energy like of rhyolitic lava?

Answer 28

Cataclysmic

Question 29

How is rhyolitic lava formed?

Answer 29

Melting of the lithosphere

Question 30

Where is rhyolitic lava found?

Answer 30

Super volcanoes and strato volcanoes

Question 31

What is an example of a volcano with rhyolitic lava?

Answer 31

Yellowstone, USA

Question 32

How are hotspots formed?

Answer 32

Mantle plum is stationary
Rises as less dense than surroundings
Oceanic crust is mobile
Carries volcano away from plume
Seamounts form
Leads to hotspot track

Question 33

Why does a bend sometimes occur in a hotspot track?

Answer 33

Due to a change in the direction of the plate