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A2 plate tectonics and associated hazards > Vulcanicity > Flashcards

Vulcanicity Flashcards

1
Q

What is vulcanicity

A

Refers to all volcanic activities related to magma being forced into the crust,usually at plate margins but not always

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2
Q

Distribution of volcanic activity

A

Mainly along plate margin in belts

  • along oceanic ridge-plates apart
  • on/near subduction zones
  • over hot spots
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3
Q

What is a volcano

A

Openings in the earths crust through which lava, ash and gas erupt. Mark the presence of magma in crust

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4
Q

What is magma

A

Molten rock beneath the surface

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5
Q

What is lava

A

When the molten rock beneath the surface is ejected at the surface it is called lava

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6
Q

What type of magma occurs at constructive plate margins

A

Basaltic

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7
Q

What are the characteristics of lava at constructive plate margins

A

Runny
Less viscous
Low in silica

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8
Q

Type of eruption that occurs at constructive plate margins

A

One of little violence as the gases can easily escape

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9
Q

What sort of materials are erupted at constructive plate margins

A

Mainly lava

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10
Q

Frequency of eruption at constructive plate margins

A

Regular , can be continuous

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11
Q

Form of the volcano at constructive plate margins

A

Lava plateau
Shield volcano
Lava only

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12
Q

Type of lava at a destructive plate margins

A

Acidic (andesitic and rhyolite )

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13
Q

Lava characteristics at destructive plate margins

A

Slow flowing
Viscous
High in silica

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14
Q

Type of eruption at destructive plate margins

A

Potentially explosive ; lava shatters into pieces

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15
Q

Materials erupted at a destructive plate margin

A

Lava bombs, ash , dust

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16
Q

Frequency of eruption at destructive plate margins

A

From time to time ; long dormant periods

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17
Q

Form of the volcano at destructive plate margins

A

Acid lava dome
Composite come
Layers of ash and lava

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18
Q

What is intrusive volcanic activity

A

Take place beneath the earths surface. They may become part of the landscape once later erosion removes overlying rock.

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19
Q

What is extrusive volcanic activity

A

Takes place on the earths surface when magma reaches the surface

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20
Q

What are the 3 types of lava

A

Basaltic
Andesitic
Rhyolithic

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21
Q

Characteristic of basaltic lava

A

Common along spreading ridges - constructive plate margin
Low in silica
Low viscosity
Prevents sudden explosive activity

22
Q

Characteristics of andesitic lava

A

Formed at destructive plate margins
Very viscous , silica rich
Violent explosion as solidifies before reaching the surface

23
Q

Characteristics of rhyolithic lava

A

Formed at destructive and collision margins.

Same characteristics of andesitic lava

24
Q

What are the major extrusive landforms?

A

Volcanos

25
Q

Describe a shield volcano

Eg Mauna Loa, Hawaii

A

Made of basaltic rock, often occur at constructive margin
Layers of lava
Gently sloping side (5- 10)
Cover large area

26
Q

Describe a composite (strato) volcano

Eg Mt Etna

A

Andesitic rock at destructive margin
Pyramid shaped
Layers of ash and lava
Angle slope ( 6-10) 30 at top

27
Q

Describe a acid/dome volcano

Eg puy de dome , France

A

Destructive margins
Steep sided convex cone - viscous lava cools quickly
Rhyolithic

28
Q

Describe a caldera volcano

A

Often at destructive margins
Wide circular crater
Build up of gas so big explosions occur and remove peak of cone

29
Q

Describe a fissure volcano eg heimaey Iceland

A

No central crater at all, giant cracks open in ground and expel lava.
Basaltic lava and has gentle persistent eruptions
Found around spreading ridges
Produces lava plateau

30
Q

Which type of volcanoes have explosive and unpredictable eruptions

A

Composite cone
Acid or dome volcanos
Caldera

31
Q

What type of eruption does a shield volcano have

A

Gentle and predictable

32
Q

What sort of eruptions happen at constructive margins and what type of lava

A

Icelandic and Hawaiian - least violent and have basaltic lava

33
Q

What sort of eruptions happen at destructive margins and what type of lava

A

Vulcanian -plinian often andesitic and rhyolitic lava - much more violent eruptions

34
Q

What are the minor forms of volcanic activity

A

Geysers
Hot springs and boiling mud
Fumaroles

35
Q

What is a geyser

A

Intermittent, forceful discharge of superheated water ejected from surface. Water heated at depth in crust by magma chambers and escape as steam / hotwater. Pressure builds up until eruption and vent refills with water

36
Q

Example of geysers

A

Stokkur Iceland

37
Q

What are fumaroles

A

Low pressure outlets of steam found where superheated water turns to steam as it condenses on the surface.
If sulphurous known as solfataras

38
Q

Describe hot thermal springs

A

Not under pressure, don’t explode from surface. Common in Iceland eg blue lagoon.
Where hotwater on its way upwards mixes with mud and minerals near surface, bubbling boiling mud volcano may form.

39
Q

What happens to magma in intrusive features

A

It cools,crystallises and solidifies into igneous rocks below surface.resulting features become part of landscape once later erosion removes overlying rocks

40
Q

Types of intrusive volcanic landforms

A

Batholiths
Sills
Dykes

41
Q

Describe batholiths

A

Formed deep below surface when large masses of magma cool and solidify.
Often domed shape and exposed by later erosion
Eg Dartmoor and isle of arran

42
Q

What is intrusive volcanic activity

A

Takes place beneath earths surface

Includes magma being forced into crust

43
Q

What is extrusive volcanic activity

A

Takes place on earths surface

44
Q

Describe dykes

A

Vertical intrusions with horizontal cooling cracks, they cut across bedding planes, often occur in groups where they are known as dyke swarms erosion of surrounding rocks can leave dykes exposed as low ridges

45
Q

Where do dykes occur place example

A

Scottish islands mull and Skye

46
Q

Describe sills

A

Horizontal intrusions along lines of bedding plane of pre existing rock. They have vertical cooling cracks
Examples ;great whin sill (hadrians wall) , drumadoon on isle of Arran

47
Q

Primary effects of volcanic events

A

Tephra
Pyroclastic flows
Lava flows
Volcanic gases eg carbon dioxide,carbon monoxide,hydrogen sulphide

48
Q

Secondary effects of a volcanic event

A 
Lahars-volcanic mudflows 
Flooding
Tsunamis
Volcanic landslides
Climatic change
49
Q

When do volcanic effects become a hazard

A

When they impact upon human and built environment, killing, injuring people, buildings collapsing infrastructure destroyed

50
Q

Prediction of a way of managing volcanoes

What’s involved

A

Hazard mapping
Analysing seismic shockwave patterns
Sampling gas and lava emissions
Remote sensing - changes in topography,heat and gas emissions by satellite
- tiny earthquakes and changes in shape of volcanos eg bulge -likely eruption

51
Q

What’s involved in protection in volcano hazard management

A
  • Warnings issued
  • Instructions given on how to react
  • Hazard mapping and land use planning to avoid development in at risk areas
  • Buildings strengthened to withstand weight of ash
  • divert lava flow away using barriers if there’s warning and slow moving lava eg in Etna in 1983

A2 plate tectonics and associated hazards (5 decks)

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