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Geological natural hazards > Pre-reading > Flashcards

Pre-reading Flashcards

1
Q

What is a seismic hazard?

A

potential for dangerous earthquake related natural phenomona i.e. shaking, soil fracture or liquefaction

  • leon reiter (1990)
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2
Q

How can seismic hazards affect society?

A

Potential destrution of buildings or loss of life

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3
Q

What is seismic risk?

A

probability of occurence of the consequences of seismic hazards

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4
Q

What is needed to calculate seismic risk?

A

Need to know the seismic hazard

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5
Q

When does an earthquake occur?

A

When there is sudden movement along a new or pre-existing fracture or fault

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6
Q

What is a ‘Maximum earthquake’?

A

Upper bound to qauke size determined by earthquake processes no matter how unlikely
or
Max historic quake

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7
Q

How are seismic waves and their ground motion divided?

A

2 levels
Weak/ small amplitude (distant or small earthquake)
Strong/ large amplitude (nearby or large earthquakes)

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8
Q

What is the difference between continental and ocean flood basalt volumes?

A

Oceanic flood basalts are usually 10 times greater in volume

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9
Q

What is the amount of melt associated to a mantle plume proportional to?

A

The amount of decompressionthe plume experiences where the temp is equal to or above the solidus

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10
Q

Where do temperatures above the solidus begin to occur?

A

200km depth or shallower

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11
Q

What is the extent of melting in a mantle plume primarily controlled by?

A

Thickness of lithosphere

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12
Q

What is a diapir?

A

An upwelling of material or intrusion into the overlying surface

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13
Q

What is a magma resevoir?

A

domain of fluid filled matrix that can store and transmit magma

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14
Q

definition and characteristics

What is the magma chamber?

A

The top of the magma reservoir
- fluid rich
- sill like

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15
Q

What is neutral bouyancy?

A

Where melt density and in-situ country rock density are equal

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16
Q

What is the horizon of neutral bouyancy (HNB)?

A

Layer of narrow vertical extent and wide lateral extent where melt has mechanical equillibrium

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17
Q

What is negative bouyancy?

A

When melt density is greater than insitu country rock

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18
Q

Where is the zone of negative bouyancy located?

A

Above horizon of neutral bouyancy

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19
Q

What is positive bouyancy?

A

When the density of insitu country rock is greater than the melt density

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20
Q

Where is the zone of positive bouyancy?

A

Bounded below the site of magma generation and bounded above the horizon of neutral bouyancy

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21
Q

What is contractancy?

A

progressive reduction in macri and microscopic pore spaces produced by progression increase in pressure with depth

22
Q

What is present in every slope?

A

stresses which will promote movement (shear stress) and opposing forces which resist movement

23
Q

What are the best 3 states to view slopes in for classification?

A

Stable
Unstable (marginally stable)
Actively unstable

24
Q

There are 3

What are the destabalising factors that affect slopes?

A

Preparatory factors
Triggering factors
Controlling (perpetuating)

25
Q

What are preparatory factors for slope destabalisation?

A

Factors which make the slope susceptable to movement without intitiating it
Make slope marginally unstable

26
Q

What are triggering factors for slope destabalisation?

A

Initiate movement
Move slope from marginally unstable to actively unstable

27
Q

What are cintrolling factors for slope destabalisation?

A

Dictate conditions of movement as it happens
Control:
- form
- rate
- duration

28
Q

What must happen for a slope to move from stable ro marginally unstable to actively unstable?

A

Changes that affect the distribution of resistance and shear stresses

29
Q

Where are the most active orogenic belts in the world found?

A

convergent crustal plate boundaries along which folding produces mountain ranges

30
Q

How can the costs of landslide activity be classified?

A

Personal - death injury etc
Economic - individual or public
Environmental

31
Q

Why is rhyolitic lava typically more viscous?

A

Their internal structure is highly polymerised with large intertwined silicate molecules which dont readily move

32
Q

What is a Plinian eruption?

A

When an umbrella cloud forms from a rhyolitic eruption and there is a ‘pumice rain’
Very explosive

33
Q

What are the characteristics of andesitic eruptions?

A

Highly explosive
Viscous
Intermittent

34
Q

what is the composition of basaltic lavas?

A

Less: silica
More: magnesium, calcium and iron

35
Q

What is the viscosity of basaltic lava like compared to rhyolitic?

A

A lot runnier

36
Q

What is the name of the bubbly rock produced from basaltic eruptions?

A

Scornia

37
Q

What type of eruption leads to pyroclatic density currents?

A

Plinian

38
Q

What affects the transport distance of pyroclastic flows?

A

The slope angle and the amount of material supplied by the volcano

39
Q

What is ignimbrite?

A

A deposited layer of ash and pumice following a pyroclastic flow

40
Q

What controls the depth of ignimbrite deposits?

A

Quickness of deposition i.e. how quickly the cloud decelerates

41
Q

When does a pheonix plume form?

A

When a pyroclastic cloud has depsoited a vast proportion of pumice and rock that an ash-laden cloud rises again

42
Q

How did the pheonix plume get its name?

A

As the cloud rises due to the heat of the hot ash rather then from the volcano

43
Q

What are vesicles?

A

Bubbles of gas that have become ‘frozen’ in the lava

44
Q

What are carbonatites?

A

Lime-rich lavas that is very runny and forms minature lava flows (1cm thick) but 500-600*c

45
Q

What is a Pahoehoe?

A

a winkled like lava formation that occurs as lava advances and cools on top of itself

46
Q

What is another name for the ropey variety of pahoehoe?

A

Toothpaste lava

47
Q

How does toothpaste lava form?

A

As the surface winkles and shears

48
Q

What are flood basalts?

A

Fast flowing almost wave like lava flows which travelled 10’s-100’s of km

49
Q

What can happen if a pahoehoe reaches a slope which overwhelms its viscosity?

A

Cause it to tear itself apart

50
Q

What is the name given by hawiians to the rubbly lava flow?

A

a’a

51
Q

What happens when pahoehoe turns into a’a?

A

It is irriversable with a rubbly front and a still fluid interior

52
Q
A

Geological natural hazards (20 decks)

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