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SOES2003 > Volcanic hazards (intro) > Flashcards

Volcanic hazards (intro) Flashcards

1
Q

What is the definition of a volcano?

A

A vent in the earth’s surface where lava, rock, vapour, and gases erupt. A mountain formed by volcanic material.

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2
Q

What is magma?

A

Molten rock in the earth’s core

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3
Q

What is lava?

A

Magma that erupts onto the earth’s surface

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4
Q

What are pyroclasts?

A

Solid fragments released from a volcano

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5
Q

What is tephra?

A

All pyroclasts that fall onto the ground from eruptions

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6
Q

What are the four eruption types?

A

Monogenetic
Polygenetic
Gentle
Voilent/Explosive

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7
Q

Why do volcanoes erupt?

A

Magma is buoyant, less dense than the surrounding rocks and rises through the crust to erupt on the surface

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8
Q

Eruption with lots of entrapped gas

A

Very viscous and brittle lava doesn’t flow as quickly, explosive eruption

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9
Q

What does a volcanic eruption depend on?

A

Level of viscosity and gas content

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10
Q

Eruption with little entrapped gas

A

Not very viscous and slow moving lava, effuisve eruption

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11
Q

______ is a function of magma viscosity

A

Explosiveness

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12
Q

What is viscosity determined by?

A

Silica content (composition)
Temperature
Gas content

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13
Q

What causes plumes to rise to the earth’s surface?

A

Primordial heat- outer mantle convecting, bringing about temperature variations causing plumes to rise from the core-mantle up to the earth’s surface

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14
Q

What is the lower mantle?

A

Solid rock composed of silicon, magnesium oxides and sulphides

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15
Q

What is the upper mantle?

A

Not liquid but a ‘plastic’ so it can deform and flow, lots of heat by convention

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16
Q

What is the crust?

A

Formed by melting of the mantle. Higher silicone and less magnesium and sulphides

17
Q

Fundamental relationship between volcanic activity and ____________ ___________

A

Plate tectonics

18
Q

Where does the majority of volcanic activity occur?

A

On or along constructive or destructive plate boundaries

19
Q

What does plate melting occur due to?

A

Heating e.g. hot spots
Decompression e.g. mid ocean ridge
Hydration

20
Q

What is the Wilson cycle?

A

The process of ocean formation at spreading ridges and subduction back into the mantle at convergent margins

21
Q

What % of active volcanism is spreading ridge (mid-ocean ridge)?

A

75

22
Q

What % of active volcanism is subduction zone?

A

15

23
Q

What % of active volcanism is intraplate?

A

10

24
Q

How do hotspot volcanoes form?

A

Very hot plumes of material ascend from deep in the mantle and encroach on the base of the lithosphere causing melting

25
Q

What do hotspot volcanoes look like?

A

Shallow, smooth, shield volcanoes

26
Q

How do hotspot volcanoes erupt?

A

Non-explosive basaltic lava flow- if related to oceanic crust

27
Q

What is basalt?

A

Most common rock type in earth’s crust
2/3 of surface

28
Q

Shield volcanoes- lava viscosity, magma type and shape

A

Low viscosity lava flows (aa and pahoehoe)
Low silica magma- basalt
Gentle sloping flanks

29
Q

Volcanism with oceanic and continental plates

A

Subduction of oceanic crust below continental crust, forming a deep trench

30
Q

Volcanism with oceanic and oceanic plates

A

Subduction of oceanic plate below another oceanic plate, forming deep trench

31
Q

Volcanism with continental and continental plates

A

Collision of two continents, forming a mountain range

32
Q

Decreasing ability to flow = _______ viscosity

A

Increased

33
Q

How does gas affect viscosity?

A

Decreasing chance of bubble to escape is what leads to explosive eruption, build up and up until it is able to escape

34
Q

What is the VEI?

A

Volcanic explosivity index
Intensity of eruption
1 number= 10x increase

35
Q

What is a strombolian eruption?

A

Low viscosity lava
Explosive basaltic eruption (loud blast)
Cinder cone forms

36
Q

What is a vulcanian eruption?

A

High viscosity lava
High gas pressure
5-20 km high andesitic and dacitic eruption

37
Q

What is a Plinian eruption?

A

High viscosity lava
>20km high dacitic and rhyolitic eruption
Large pyroclastic flows

38
Q

What are the three rock types from subduction zone related volcanism?

A

Andesite
Dacite
Rhyolite
|- Increasing silicone content, increasing viscosity

SOES2003 (21 decks)

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