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Geography paper 3: hazardous earth > 14.2 Types of volcanic eruption > Flashcards

14.2 Types of volcanic eruption Flashcards

1
Q

What is viscosity?

A

An indication of how well a substance flows

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2
Q

What causes volcanic eruptions to produce diverse landforms?

A
  • Where the eruption occurs
  • The type of lava
  • Variety of materials produced eg ash, gases
  • How the eruption takes place
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3
Q

What are the two types of volcanic eruption?

A

Effusive and explosive

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4
Q

Effusive eruptions: where do they occur?

A

Divergent plate boundaries

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5
Q

Effusive eruptions: what type of lava?

A

Basalt

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6
Q

Effusive eruptions: characteristics of the lava?

A

Basic (low % silica), low viscosity, higher temperature at eruption

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7
Q

Effusive eruptions: style of eruption?

A

Gas bubbles expand freely, limited explosive force

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8
Q

Effusive eruptions: materials erupted?

A

Gas, lava flows

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9
Q

Effusive eruptions: frequency?

A

Tend to be more frequent and can continue for many months

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10
Q

Effusive eruptions: shape of volcano?

A

Gently sloping sides, shield volcanoes

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11
Q

Explosive eruptions: where do they occur?

A

Convergent plate boundaries

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12
Q

Explosive eruptions: type of lava?

A

Rhyolite (more acid), andesite (less acid)

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13
Q

Explosive eruptions: characteristics of the lava?

A

Acid (high % silica), high viscosity, lower temperature at eruption

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14
Q

Explosive eruptions: style of eruption?

A

Violent bursting of gas bubbles when magma reaches the surface, highly explosive, vent and top of cone often shattered

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15
Q

Explosive eruptions: materials erupted?

A

Gas, dust, ash, lava bombs, tephra

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16
Q

Explosive eruptions: frequency of eruption?

A

Long periods with no activity

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17
Q

Explosive eruptions: shape of volcano?

A

Steep-sided stratovolcanoes, caldera

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18
Q

What type of eruptions does Iceland owe itself to?

A

Effusive eruptions

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19
Q

Two products of explosive eruptions?

A

Calderas and stratovolcanoes

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20
Q

What are stratovolcanoes?

A

Also known as composite cone volcanoes – made up of layers of ash and acid lava with concave symmetrical profiles – associated with explosive eruptions

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21
Q

What are the complex internal networks of lava called inside a stratovolcano?

A

Sills and dykes

22
Q

What is the difference between a sill and a dyke?

A 
Sill = horizontal protrusion of magma into surrounding older rocks
Dyke = vertical protrusion of magma into surrounding older rocks
23
Q

What are the vents like in stratovolcanoes + why + what can this lead to?

A

The vents are often filled with a mass of solidified magma because acid magma does not flow easily = build-up of pressure causing explosive eruption

24
Q

What is a caldera?

A

A large-scale volcanic crater formed because of an explosive eruption which emptied the magma chamber causing the volcano sides to subside

25
Q

Example of a caldera:

A

1883 eruption of Krakatoa in Indonesia left a 7km wide caldera

26
Q

What do convergent plate boundaries and explosive eruptions often give rise to?

A

Chains of stratovolcanoes eg Indonesia has 130 active stratovolcanoes along its archipelago

27
Q

Two products of effusive eruptions:

A

Lava plateaux and shield volcanoes

28
Q

How do lava plateaux form?

A

When basic magma erupts from multiple fissures, vast areas can be covered by free-flowing lava – flood basalts

29
Q

Example of a flood basalt?

A

Deccan Plateau in central India covers more than 500,000 km2

30
Q

What is a shield volcano?

A

A volcano with a broad base and gently sloping sides

31
Q

How did the Hawaiian chain of islands form?

A

Due to the formation of a hotspot, thousands of kilometres from the nearest plate boundary

32
Q

What is a hotspot?

A

A fixed area of intense volcanic activity where magma from a rising mantle plume reaches the Earth’s surface

33
Q

Two examples of places with a hotspot:

A

Hawaii and East African Rift Valley

34
Q

Most common type of volcano formed at a hotspot:

A

Shield volcano

35
Q

Why do volcanoes of Hawaii become extinct?

A

Over millions of years the pacific plate moves northwest away from the hotspot, so the volcanoes lose their source of magma eg Kauai

36
Q

How quickly does the Pacific plate move over the Hawaiian hotspot?

A

Moves northwest at a rate of 10cm/year

37
Q

Two examples of active volcanic peaks in Hawaii:

A

Mauna Loa and Mauna Kea = both reach over 4000m above sea level

38
Q

What Hawaiian volcano is currently rising?

A

Loihi is directly over the hotspot and is currently 970km below sea level

39
Q

How long is the rift valley running through East Africa?

A

4000 km long

40
Q

How have active volcanoes been created in East Africa?

A

As a result of rifting – magma has forced its way to the surface

41
Q

Example of a volcano formed through rifting:

A

Mount Kilimanjaro

42
Q

What is a super-volcano + what do they exist as?

A

A volcano that erupts more than 1000km3 of material in a single eruption
They exist as giant calderas

43
Q

Example of a super volcano:

A

The Yellowstone super volcano in Wyoming has a caldera measure 75km in diameter

44
Q

When was the most recent super-volcano eruption?

A

27,000 years ago – Taupo, North Island, New Zealand

45
Q

When did volcanic activity start in Yellowstone?

A

2 million years ago – when the giant caldera formed

46
Q

When did Yellowstone last erupt?

A

70,000 years ago

47
Q

What two key factors need to be considered when measuring and assessing a volcano?

A
  • Magnitude = amount of material erupted

- Intensity = speed at which the material is erupted

48
Q

What scale are volcanoes measured on?

A

Volcanic Explosivity Index
Scale is 0-8
Combines magnitude and intensity

49
Q

What factors are considered when measuring explosivity?

A

Volume of erupted material, heigh of ejected material, duration

50
Q

What VEI was Eyjafjallajökull in 2010?

A

VEI of 4

Geography paper 3: hazardous earth (14 decks)

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