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Geology > Volcanoes > Flashcards

Volcanoes Flashcards

0
Q

What makes a volcano explosive?

A

High silica –> viscous –> has is trapped –> pressure builds up

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1
Q

Define volcano

A

A vent at the earths surface through which magma and other volcanic materials are ejected

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2
Q

Some gases released by volcanoes?

A

Water vapour, CO2, SO2, N2,

Bit of H, Cl, F, CO, Ar, S

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3
Q

Impacts of volcanic gases

A

Asphyxiation, acid rain, global decrease in temperature

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4
Q

Define viscosity of a magma

A

Measure of a resistance to flow. Determined by silica content

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5
Q

What do magic lavas cool to form?

A 
Aa lava flows (rough, blocky and jagged surface)
Pahoehoe flows (ropey and smooth)
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6
Q

Define pyroclastic rocks

A

Forms when pyroclastic material is compacted into a solid rock

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7
Q

Describe ash

A

The smallest particles smaller than 2mm and forms the pyroclastic rock “tuff” when consolidated

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8
Q

Describe lapilli

A

Particles between 2-64mm and form a “lapilli tuff”

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9
Q

Describe volcanic bombs

A 
Coarsest particles (>64). 
Form the pyro clastic rock agglomerate and form nearest to the crater of the volcano
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10
Q

Define pyroclastic flows

A

Super-heated, fast-flowing, turbulent cloud of gas and ash

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11
Q

What do pyroclastic flows cool to form?

A

The rock ignimbrite

Contains pieces of pumice known as fiame

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12
Q

What are lahars?

A

Unconsolidated ash, rock, and pyroclastic deposits which become saturated from water from lakes and rivers or melted snow or ice to produce a fast flowing cement like mudflow

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13
Q

What is an isopachyte?

A

A map where there is a line joining points of equal thickness of deposit. Resultant map is called an isopach map.

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14
Q

What will effect the distribution of volcanic products?

A 
Grain size,
Wind,
Energy / type of blast
Viscosity of lavas
Topography determining lahar distribution
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15
Q

Are mafic eruptions frequent or not?

A

Yes they are frequent

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16
Q

Do mafic magmas have a high or low viscosity?

A

Low viscosity

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17
Q

What type of volcanoes do mafic eruptions create?

A

Shield volcanoes

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18
Q

Which type of eruptions are effusive?

A

Mafic eruptions

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19
Q

What does effusive mean?

A

Used to describe the fluid, non explosive nature of basaltic lava

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20
Q

Which types of plate boundaries do mafic eruptions take place at?

A

Divergent and hot spots

21
Q

Shield volcano example?

A

Mauna Loa in Hawaii (from the sea floor is 150km wide at the base)

22
Q

What is the gradient of the slope of shield volcanoes?

A

10 degrees

23
Q

Why are the flanks of volcanoes slightly steeper?

A

As the magma travels it cools and the viscosity increases

24
Q

What are fissure eruptions?

A

Where the magma reaches the surface along long linear cracks or fissures.
They are basaltic and effusive eruptions

25
Q

Which type of boundaries do explosive volcanoes accurate at?

A

Convergent

Particularly around the Pacific Ocean - ring of fire

26
Q

Do explosive eruptions have high or low viscosity magma?

A

High viscosity

27
Q

Two examples of thick magmas?

A

Andesite and rhyolite

28
Q

Gradient of slope of composite / strato volcanoes?

A

Over 30 degrees

29
Q

Size of explosive volcanoes on the VEI scale?

A

2 - 8

30
Q

What percent of the material ejected is pyroclastic in explosive eruptions?

A

50%

31
Q

Eruption style of explosive volcanoes can be described as?

A

Strombolian, volcanian, Orleans, Plinian

32
Q

What percentage of volcanoes are composite volcanoes?

A

60%

33
Q

What’s a dormant volcano?

A

When there is a period of no activity (magma chamber filling with magma)

34
Q

When will there be a volcano?

A

Pressure inside the volcano exceeds the weight of the overlying rock creating an explosion

35
Q

How do calderas form?

A

Magma chamber empties due to a series of explosive eruptions
Volcano begins to collapse into weakened area. The compression makes more violent eruptions.
Entire volcano collapses. Can cause tsunamis if on island or coast

36
Q

What does superheated mean?

A

Very hot but pressure prevents liquids from turning into gasses

37
Q

Define geyser

A

Hot springs from which a column of superheated water is explosively discharged at regular intervals

38
Q

Define an active volcano

A

Shows eruptive activity within recorded history.

39
Q

Define an extinct volcano

A

Not shown any historic activity and is usually deeply eroded

40
Q

Active volcano example?

A

My St. Helens

41
Q

Dormant volcano example?

A

Yellowstone

42
Q

Extinct volcano example?

A

Borrowdale

43
Q

Methods of predicting earthquakes?

A

Historic patterns of activity - how frequent and composition

44
Q

What does studying the distribution of volcanic material tell us about the volcano?

A

The type of eruption eg lateral blast
Strength or magnitude.
Volume of it gives explosivity

45
Q

Swelling of the ground can indicate a volcano will erupt. What is it measured with?

A

Tiltmetres and GPS

46
Q

How can gas emissions indicate a volcano will erupt?

A

As magma bears the surface it’s pressure decreases and pressure escapes. Increasing amounts of gasses eg SO2 being released suggest that magma is nearing the surface

47
Q

Earthquakes commonly provide the earliest warning of eruptions. Which are the 3 types of earthquakes?

A

Short period
Long period
Harmonic tremors

48
Q

What are short period earthquakes caused by?

A

Fracturing of brittle rock as magma forces it’s way upwards

49
Q

What are long period earthquakes caused by?

A

Increasing gas pressure in the magma chamber

50
Q

What are harmonic tremor earthquakes caused by?

A

Magma vibrating in the feeder pipe as it moves upwards

51
Q

What is Nuée ardentes?

A

Gaseous magma that forms the fast moving pyroclastic flows and cools to form the rock ignimbrite

Geology (4 decks)

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