Volcanic hazards (intro)

Question 1

What is the definition of a volcano?

Answer 1

A vent in the earth’s surface where lava, rock, vapour, and gases erupt. A mountain formed by volcanic material.

Question 2

What is magma?

Answer 2

Molten rock in the earth’s core

Question 3

What is lava?

Answer 3

Magma that erupts onto the earth’s surface

Question 4

What are pyroclasts?

Answer 4

Solid fragments released from a volcano

Question 5

What is tephra?

Answer 5

All pyroclasts that fall onto the ground from eruptions

Question 6

What are the four eruption types?

Answer 6

Monogenetic
Polygenetic
Gentle
Voilent/Explosive

Question 7

Why do volcanoes erupt?

Answer 7

Magma is buoyant, less dense than the surrounding rocks and rises through the crust to erupt on the surface

Question 8

Eruption with lots of entrapped gas

Answer 8

Very viscous and brittle lava doesn’t flow as quickly, explosive eruption

Question 9

What does a volcanic eruption depend on?

Answer 9

Level of viscosity and gas content

Question 10

Eruption with little entrapped gas

Answer 10

Not very viscous and slow moving lava, effuisve eruption

Question 11

______ is a function of magma viscosity

Answer 11

Explosiveness

Question 12

What is viscosity determined by?

Answer 12

Silica content (composition)
Temperature
Gas content

Question 13

What causes plumes to rise to the earth’s surface?

Answer 13

Primordial heat- outer mantle convecting, bringing about temperature variations causing plumes to rise from the core-mantle up to the earth’s surface

Question 14

What is the lower mantle?

Answer 14

Solid rock composed of silicon, magnesium oxides and sulphides

Question 15

What is the upper mantle?

Answer 15

Not liquid but a ‘plastic’ so it can deform and flow, lots of heat by convention

Question 16

What is the crust?

Answer 16

Formed by melting of the mantle. Higher silicone and less magnesium and sulphides

Question 17

Fundamental relationship between volcanic activity and ____________ ___________

Answer 17

Plate tectonics

Question 18

Where does the majority of volcanic activity occur?

Answer 18

On or along constructive or destructive plate boundaries

Question 19

What does plate melting occur due to?

Answer 19

Heating e.g. hot spots
Decompression e.g. mid ocean ridge
Hydration

Question 20

What is the Wilson cycle?

Answer 20

The process of ocean formation at spreading ridges and subduction back into the mantle at convergent margins

Question 21

What % of active volcanism is spreading ridge (mid-ocean ridge)?

Answer 21

75

Question 22

What % of active volcanism is subduction zone?

Answer 22

15

Question 23

What % of active volcanism is intraplate?

Answer 23

10

Question 24

How do hotspot volcanoes form?

Answer 24

Very hot plumes of material ascend from deep in the mantle and encroach on the base of the lithosphere causing melting

Question 25

What do hotspot volcanoes look like?

Answer 25

Shallow, smooth, shield volcanoes

Question 26

How do hotspot volcanoes erupt?

Answer 26

Non-explosive basaltic lava flow- if related to oceanic crust

Question 27

What is basalt?

Answer 27

Most common rock type in earth's crust 2/3 of surface

Question 28

Shield volcanoes- lava viscosity, magma type and shape

Answer 28

Low viscosity lava flows (aa and pahoehoe) Low silica magma- basalt Gentle sloping flanks

Question 29

Volcanism with oceanic and continental plates

Answer 29

Subduction of oceanic crust below continental crust, forming a deep trench

Question 30

Volcanism with oceanic and oceanic plates

Answer 30

Subduction of oceanic plate below another oceanic plate, forming deep trench

Question 31

Volcanism with continental and continental plates

Answer 31

Collision of two continents, forming a mountain range

Question 32

Decreasing ability to flow = _______ viscosity

Answer 32

Increased

Question 33

How does gas affect viscosity?

Answer 33

Decreasing chance of bubble to escape is what leads to explosive eruption, build up and up until it is able to escape

Question 34

What is the VEI?

Answer 34

Volcanic explosivity index Intensity of eruption 1 number= 10x increase

Question 35

What is a strombolian eruption?

Answer 35

Low viscosity lava Explosive basaltic eruption (loud blast) Cinder cone forms

Question 36

What is a vulcanian eruption?

Answer 36

High viscosity lava High gas pressure 5-20 km high andesitic and dacitic eruption

Question 37

What is a Plinian eruption?

Answer 37

High viscosity lava >20km high dacitic and rhyolitic eruption Large pyroclastic flows

Question 38

What are the three rock types from subduction zone related volcanism?

Answer 38

Andesite Dacite Rhyolite |- Increasing silicone content, increasing viscosity