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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?

25
Describe a shield volcano Eg Mauna Loa, Hawaii
Made of basaltic rock, often occur at constructive margin Layers of lava Gently sloping side (5- 10) Cover large area
26
Describe a composite (strato) volcano Eg Mt Etna
Andesitic rock at destructive margin Pyramid shaped Layers of ash and lava Angle slope ( 6-10) 30 at top
27
Describe a acid/dome volcano Eg puy de dome , France
Destructive margins Steep sided convex cone - viscous lava cools quickly Rhyolithic
28
Describe a caldera volcano
Often at destructive margins Wide circular crater Build up of gas so big explosions occur and remove peak of cone
29
Describe a fissure volcano eg heimaey Iceland
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
Which type of volcanoes have explosive and unpredictable eruptions
Composite cone Acid or dome volcanos Caldera
31
What type of eruption does a shield volcano have
Gentle and predictable
32
What sort of eruptions happen at constructive margins and what type of lava
Icelandic and Hawaiian - least violent and have basaltic lava
33
What sort of eruptions happen at destructive margins and what type of lava
Vulcanian -plinian often andesitic and rhyolitic lava - much more violent eruptions
34
What are the minor forms of volcanic activity
Geysers Hot springs and boiling mud Fumaroles
35
What is a geyser
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
Example of geysers
Stokkur Iceland
37
What are fumaroles
Low pressure outlets of steam found where superheated water turns to steam as it condenses on the surface. If sulphurous known as solfataras
38
Describe hot thermal springs
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
What happens to magma in intrusive features
It cools,crystallises and solidifies into igneous rocks below surface.resulting features become part of landscape once later erosion removes overlying rocks
40
Types of intrusive volcanic landforms
Batholiths Sills Dykes
41
Describe batholiths
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
What is intrusive volcanic activity
Takes place beneath earths surface | Includes magma being forced into crust
43
What is extrusive volcanic activity
Takes place on earths surface
44
Describe dykes
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
Where do dykes occur place example
Scottish islands mull and Skye
46
Describe sills
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
Primary effects of volcanic events
Tephra Pyroclastic flows Lava flows Volcanic gases eg carbon dioxide,carbon monoxide,hydrogen sulphide
48
Secondary effects of a volcanic event
``` Lahars-volcanic mudflows Flooding Tsunamis Volcanic landslides Climatic change ```
49
When do volcanic effects become a hazard
When they impact upon human and built environment, killing, injuring people, buildings collapsing infrastructure destroyed
50
Prediction of a way of managing volcanoes | What's involved
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
What's involved in protection in volcano hazard management
- 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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