Introduction to Volcanology (1)

Question 1

Where does most volcanism arise from?

Answer 1

Plate tectonics

Question 2

What is the outer layer of the Earth called?

Answer 2

the Lithosphere

Question 3

What is the lithosphere split up into?

Answer 3

Plates

Question 4

The movement of what causes volcanism?

Answer 4

Tectonic plates

Question 5

Explain the four stages of Subduction zone Volcanism

Answer 5

1. More dense oceanic crust subjects beneath less dense continental crust
2. At a certain depth the subjecting plate begins to melt.
3. Batches of magma rise through the continental crust
4. Magma may collect in storage zones before rising through a conduit and resulting in an eruption.

Question 6

Explain the two stages of Intra Plate (“Hot spot”) Volcanism

Answer 6

1. A mantle plume rises from the core-mantle boundary

2. Over time it will penetrate the oceanic crust and erupt to form a shield volcano

Question 7

What are the two main types of volcano?

Answer 7

Stratovolcanoes and Shield Volcanoes

Question 8

What is a stratovolcano?

Answer 8

These are built from layers of viscous lava flows and pyroclastic rocks from explosions. The concave profile can produce a “postcard volcano”.

Question 9

What are shield volcanoes?

Answer 9

Layers of fluid lava flows, convex profile and can be enormous.

Question 10

Give an example of a Shield Volcano and an interesting fact

Answer 10

Mauna Kea has a volume 100 times greater than a typical stratovolcano

Question 11

Give an example of a stratovolcano

Answer 11

Mayon Volcano in the Philippines

Question 12

What are the two types of Magmas?

Answer 12

Low viscosity and high visocity

Question 13

Give an example of low viscosity magma

Answer 13

Basalt

Question 14

What type of volcano does Basalt give rise to?

Answer 14

Basaltic

Question 15

What type of volcano does low viscosity magma create?

Answer 15

Shield Volcanoes

Question 16

Give two examples of high viscosity magma

Answer 16

Andesite and Rhyolite

Question 17

What type of volcanism do high viscosity magmas give rise to?

Answer 17

Silicic Volcanism

Question 18

Where is high visocity magma most commonly produced?

Answer 18

Subduction zone settings

Question 19

What type of volcanoes does high visocity magma create?

Answer 19

Stratovolcanoes

Question 20

Which compound defines the viscosity of magmas?

Answer 20

Silicate

Question 21

What is the chemical formula for silicate? What does it mean?

Answer 21

SiO4. One silicon atom with four oxygen atoms surrounding it.

Question 22

What is formed when silicate combines?

Answer 22

A lattice

Question 23

How does the lattice affect the magma?

Answer 23

It makes it more viscous.

Question 24

Which type of magma has more SiO4? High or low visocity?

Answer 24

Silicic. High Viscosity

Question 25

Which type of magma has less SiO4? High or low visocity?

Answer 25

Basaltic. Low viscosity

Question 26

What happens to gas flow in silicic magmas?

Answer 26

It is impeded

Question 27

What happens to gas flow in basaltic magmas?

Answer 27

It can move more freely

Question 28

What causes explosively in volcanism?

Answer 28

Gases within the magma

Question 29

What three elements make up magma?

Answer 29

Melt (molten rock), Crystals (solid rock) and Gas

Question 30

What temperature can the gas within the magma reach?

Answer 30

1000*C

Question 31

Where does the gas come from?

Answer 31

A solution (it exsolves) from the magma as pressure decreases during magma ascent

Question 32

What is the term used for when gas is released at the surface?

Answer 32

Degassing

Question 33

How can gas within magma be compared to a champagne bottle?

Answer 33

Both have explosive potential

Question 34

What can changes in degassing cause?

Answer 34

Abrupt transitions in activity

Question 35

Why is it important to understand which gas is being emitted?

Answer 35

In order to determine how we measure and detect gas

Question 36

What are the three major constituents to Volcanic gas?

Answer 36

1. Water Vapour (H2O) 2. Carbon Dioxide (CO2) 3. Sulphur Dioxide (SO2)

Question 37

Where are gases usually emitted from?

Answer 37

Summit craters or calderas from a volcanic conduit

Question 38

Which two ways can gases be emitted from a volcano?

Answer 38

1. Quiescently during passive degassing | 2. More violently during explosive degassing

Question 39

Is it easier or more difficult for gases to move independently within high viscosity magma?

Answer 39

More difficult

Question 40

Where can gas sometimes escape from?

Answer 40

Through fractures in a volcano or through networks of other bubbles

Question 41

What can degassing cause changes to?

Answer 41

The magma chemistry

Question 42

Does degassing increase or decrease viscosity?

Answer 42

Increase

Question 43

What happens if gas can't escape from a conduit?

Answer 43

It will pressurise and cause explosions

Question 44

What happens when gas rises faster than magma?

Answer 44

Bubbles can form and coalesce

Question 45

What happens when bubbles coalesce within the magma?

Answer 45

They grow in size and can lead to passive degassing, lava flows or Strombolian volcanism

Question 46

What happens when gas rises at the same rate as the magma?

Answer 46

The mixture is ejected into the atmosphere to form a low explosivity "lava fountain".

Question 47

What happens when gas emits without lava?

Answer 47

The magma and gas rises, the gas is passively emitted, the magma then sinks back down the conduit during convection

Question 48

What are the three distinct behaviours of degassing in basaltic volcanism?

Answer 48

1. Gas rises faster than magma 2. Gas and magma rise at the same rate 3. Gas emission without lava