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Physical Geography: Dynamic Landscapes > Volcanoes > Flashcards

Volcanoes Flashcards

1
Q

Which boundaries do volcanoes form on

A

Constructive and destructive
Aswell as hotspots in the Centre of some plates

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2
Q

How do volcanoes form

A

-the upwelling of hot molten material from the core/mantle boundary
- OR from the top of a huge mantle plume just under the crust

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3
Q

Fill in:
The shape of volcanoes is mainly related to the __ _ __ erupted

A

Type Of Lava

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4
Q

what type of volcanoes are yellowstone and taupa

A

Super volcanoes

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5
Q

what happens to volcanic hazards when magnitude increases

A

volcanic hazards increases

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6
Q

TRUE OR FALSE are composite cones more dangerous than shield volcanoes

A

TRUE

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7
Q

what factor causes the shape of volcanoes

A

the type of lava

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8
Q

characteristics of composite volcanoes

A

composite volcano rises higher with a greater gradient than shield volcanoes
Produces a much greater ash cloud than shield
Has a quick eruptions
Has a longer period of time between eruptions
Narrow base
The magma is andesitic and likely melted from oceanic crust
Crate can be blocked causing violent eruptions

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9
Q

what are the characteristics of shield volcanoes

A

Wide base
Gentle slope, less than 10 degrees
Magma rises directly from asthenosphere
Magma is basaltic
Gentle eruption - mainly lava occasionally ash from rare explosive eruptions

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10
Q

define primary hazard

A

when a volcano erupts (immediate)

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11
Q

what are the 4 primary hazard of volcanic eruptions

A

Lava flows
Emissions of gases and steam
Pyroclasts/tephra - ash, volcanic bombs
Pyroclastic flows

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12
Q

define secondary hazard

A

a hazard that occurs after the eruption

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13
Q

what are the 2 secondary hazards of volcanoes

A

jokulhaup
lahar

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14
Q

what does the speed of flow of lava depend on

A

viscosity, temperature, silica content, and the volcanoes incline

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15
Q

what lava is associated with composite volcanoes

A

andesitic lava

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16
Q

what type of lava is associated with shield volcanoes

A

basaltic lava

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17
Q

what type of lava is associated with super volcanoes

A

rhyolitic lava

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18
Q

what is the hottest type of lava

A

basaltic lava

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19
Q

what are the flow characteristics of andesitic lava

A

slow, intermediate viscosity, traps gases

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20
Q

what are flow characteristics of basaltic lava

A

runny, low viscosity, thin, gases escape

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21
Q

what are the flow characteristics of rhyolitic lava

A

thick, high viscosity, slow, gases are trapped

22
Q

the eruption energy of basaltic lava

A

gentle, effusive

23
Q

the eruption energy of andesitic lava

A

violent, moderately explosive

24
Q

the eruption energy of rhyolitic lava

A

very violent, cataclysmic

25
Q

is it true that gases can still be released even years after the volcanic eruption

A

TRUE
Gases are released in and around volcanoes before, during and for many years after volcanic eruptions.

26
Q

what are the 2 main gases released by volcanoes

A

water vapour
sulphur dioxide

27
Q

what can water vapour cause during eruptions

A

heavy rainfall or even lahars in some situations

28
Q

what can sulphur dioxide cause during eruptions

A

Forms fine particles that get carried as high as the stratosphere. These solid particles reflect radiation from the Sun back into space, so cooling the Earth.

29
Q

what are the gases released by volcanoes

A

water vapour
sulphur dioxide
fluorine gas
carbon dioxide

30
Q

what can fluorine gas cause during eruptions

A

can be poisonous in high concentrations and can contaminate farmland or water supplies.

31
Q

what are pyroclasts

A

volcanic materials that are solid

32
Q

what are the 3 groups of pyroclasts

A

volcanic ash
lapilli
volcanic bombs/blocks

33
Q

how are the 3 groups of pyroclasts catagorised

A

via size of the pyroclasts

34
Q

what size is volcanic ash

A

less than 2mm

35
Q

what size is lapilli

A

2mm - 64mm

36
Q

what size are volcanic bombs/blocks

A

greater than 64mm

37
Q

how can ash cause hazards

A

its disruptive rather than devastating. Heavy ash can collapse roofs, damage crops and vegetation and affect people’s breathing.

38
Q

what are pyroclastic flows

A

a dense mixture of superheated tephra and poisonous gases moving rapidly down the sides of a composite cone volcano

39
Q

how fast can pyroclastic flows travel

A

at speeds of up to 700 km/h

40
Q

an example of pyroclastic flows

A

for example, Chances Peak on Montserrat in 1997

41
Q

what can pyroclastic flows cause

A

leave behind thick layers of volcanic deposits (ignimbrite), up to 200 m thick

may cause secondary hazards such as river flooding if they temporarily dam them

example Pinatubo, Philippines 1991

42
Q

what are lahars

A

consist of water mixed with volcanic deposits flowing rapidly along existing valleys.

43
Q

how are lahars caused

A

heavy rainfall
- a result of humid air being seeded with volcanic ash which accelerates condensation, the formation of clouds and rain

emptying of a crater lake; or through the melting of snow and ice due to the heat from an eruption at high altitude

44
Q

what are the dangers of lahars

A

their fast velocity, the amount of material carried and the great distances they can travel.

45
Q

what is a jokulhlaup

A

A jokulhlaup is a flood of meltwater from underneath an ice cap or glacier.

46
Q

how does a jokulhlaup form

A

This happens when a volcano erupts underneath the ice and melts the ice so that it forms a lake, either in a crater or at the crater side where it is dammed by the ice.

The warm meltwater will have sufficient volume to lift the ice away from the bedrock. When this happens the water bursts out underneath the ice carrying with it glacial moraines and blocks of ice.

47
Q

dangers of Jokulhlaup

A

The speed and volume of the event will wash away anything in its path and change the route of river channels.

48
Q

how do scientists measure eruptions

A

VEI (volcanic explosivity index)

49
Q

what factors does VEI use to measure a volcanoes eruption

A

Amount and height of volcanic material erupted
How long the eruption lasts
Qualitative descriptive terms (e.g gentle, explosive)

50
Q

what scale does VEI use

A

logarithmic
0 (non explosive) to 8 ( extremely explosive)

51
Q

how do scientists predict eruptions, what signs do they look for

A

Small earthquakes
Changes to the volcanoes surface
Changes to the volcanoes tilt

52
Q

a problem with predicting eruptions

A

they are never 100% accurate

Physical Geography: Dynamic Landscapes (10 decks)

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