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Geohazards And Earth Resources > Volcanic Hazards > Flashcards

Volcanic Hazards Flashcards

1
Q

Monogenetic

A

Volcano erupts once

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2
Q

Polygenetic

A

Volcano erupts many times

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3
Q

Explosive

A

Silica content
Magma temp
Gas content

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4
Q

Upper mantle

A

Fe, Mg, Silicates

1400-3000 degrees C

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5
Q

Lower mantle

A

solid rock at 3000 degrees C

Silicon, magnesium oxides and sulphides

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6
Q

Spreading ridge

A

75%

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7
Q

Subduction zone

A

15%

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8
Q

Intraplate volcanism

A

10%

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9
Q

Divergent plate boundary example

A

Iceland
Low viscosity basalti lava fed by fissures
Non explosive

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10
Q

Divergent e.g. submarine volcanoes

A

75% annual output of magma, 4000 volcanoes per million square km of the Pacific

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11
Q

Volcanism at hot spots

A

Hawaii, Galapagos, Iceland

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12
Q

Characteristics of hot spo volcanoes

A

Shallow, smooth, broad slopes: SHIELD. Non-explosive, basaltic lava

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13
Q

Hotspots below continental lava type:

A

rhyolitic

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14
Q

Ocean Islands

A

island chains e.g. Hawaii. Plate moves over a stationary, hotspot e.g. Galapagos

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15
Q

Basaltic Lava

A

Most common, 2/3rds of Earth is basalt

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16
Q

Two types of lava

A

A’a, Pahoehoe

17
Q

A’a lava [3]

A

1000-1100. low viscosity, low dissolved gas

18
Q

Pahoehoe

A

1100-1200

19
Q

Shield Volcanoes [5]

A

Low viscosity, Low silica, Gently sloping, Large, Spatter Cone

20
Q

Volcanoes at convergent boundaries

A

Central composite (strato) volcanoes

21
Q

Andesite [3]

A

53-63% SiO2
Most common on strato
900-1100

22
Q

Dacite [3]

A

63-68% SiO2
Most common with plinian eruptions
800-1000

23
Q

Rhyolite [2]

A

> 68% SiO2

700-850

24
Q

Types of volcanic eruption [2]

A

Effusive (lava) or Explosive (gas)

25
Q

Types of explosive volcanic eruptions [3]

A

Strombolian
Vulcanian
Plinian

26
Q

Strombolian eruption [5]

A 
Basaltic low viscosity
Explosive with gas
Volcanic bombs
Cinder cone
Mt Etna
27
Q

Vulcanian eruption [4]

A

Viscous
High gas pressure
Columns 5-20km high
Andesitic to dacitic material

28
Q

Plinian eruption

A 
Si-rich magma 
High dissolved gas
>20km columns
Dacitic to rhyolitic materia
Pumice and pyroclastic
Mt St Helens
29
Q

Volcanic Explosivity Index

A

Intensity of eruption

Increase a number, increases by a factor of 10

30
Q

Cinder Cone

A

Pyroclastic cone or cinder cone from tephra deposits around the vent

31
Q

Lava dome

A

Steep round mounds from eruption of high viscosity, low gas content magma
Subduction zone related

32
Q

Caldera

A

Large circular depression at the summit of a volcano from collapse of centre of a volcano

Geohazards And Earth Resources (20 decks)

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