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New Horizons > Introduction to Volcanology (1) > Flashcards

Introduction to Volcanology (1) Flashcards

1
Q

Where does most volcanism arise from?

A

Plate tectonics

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2
Q

What is the outer layer of the Earth called?

A

the Lithosphere

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3
Q

What is the lithosphere split up into?

A

Plates

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4
Q

The movement of what causes volcanism?

A

Tectonic plates

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5
Q

Explain the four stages of Subduction zone Volcanism

A
  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.
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6
Q

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

A
  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

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7
Q

What are the two main types of volcano?

A

Stratovolcanoes and Shield Volcanoes

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8
Q

What is a stratovolcano?

A

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

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9
Q

What are shield volcanoes?

A

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

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10
Q

Give an example of a Shield Volcano and an interesting fact

A

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

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11
Q

Give an example of a stratovolcano

A

Mayon Volcano in the Philippines

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12
Q

What are the two types of Magmas?

A

Low viscosity and high visocity

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13
Q

Give an example of low viscosity magma

A

Basalt

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14
Q

What type of volcano does Basalt give rise to?

A

Basaltic

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15
Q

What type of volcano does low viscosity magma create?

A

Shield Volcanoes

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16
Q

Give two examples of high viscosity magma

A

Andesite and Rhyolite

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17
Q

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

A

Silicic Volcanism

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18
Q

Where is high visocity magma most commonly produced?

A

Subduction zone settings

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19
Q

What type of volcanoes does high visocity magma create?

A

Stratovolcanoes

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20
Q

Which compound defines the viscosity of magmas?

A

Silicate

21
Q

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

A

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

22
Q

What is formed when silicate combines?

A

A lattice

23
Q

How does the lattice affect the magma?

A

It makes it more viscous.

24
Q

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

A

Silicic. High Viscosity

25
Q

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

A

Basaltic. Low viscosity

26
Q

What happens to gas flow in silicic magmas?

A

It is impeded

27
Q

What happens to gas flow in basaltic magmas?

A

It can move more freely

28
Q

What causes explosively in volcanism?

A

Gases within the magma

29
Q

What three elements make up magma?

A

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

30
Q

What temperature can the gas within the magma reach?

A

1000*C

31
Q

Where does the gas come from?

A

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

32
Q

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

A

Degassing

33
Q

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

A

Both have explosive potential

34
Q

What can changes in degassing cause?

A

Abrupt transitions in activity

35
Q

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

A

In order to determine how we measure and detect gas

36
Q

What are the three major constituents to Volcanic gas?

A
  1. Water Vapour (H2O)
  2. Carbon Dioxide (CO2)
  3. Sulphur Dioxide (SO2)
37
Q

Where are gases usually emitted from?

A

Summit craters or calderas from a volcanic conduit

38
Q

Which two ways can gases be emitted from a volcano?

A
  1. Quiescently during passive degassing

2. More violently during explosive degassing

39
Q

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

A

More difficult

40
Q

Where can gas sometimes escape from?

A

Through fractures in a volcano or through networks of other bubbles

41
Q

What can degassing cause changes to?

A

The magma chemistry

42
Q

Does degassing increase or decrease viscosity?

A

Increase

43
Q

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

A

It will pressurise and cause explosions

44
Q

What happens when gas rises faster than magma?

A

Bubbles can form and coalesce

45
Q

What happens when bubbles coalesce within the magma?

A

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

46
Q

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

A

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

47
Q

What happens when gas emits without lava?

A

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

48
Q

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

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

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