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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
What are preparatory factors for slope destabalisation?
Factors which make the slope susceptable to movement without intitiating it Make slope marginally unstable
26
What are triggering factors for slope destabalisation?
Initiate movement Move slope from marginally unstable to actively unstable
27
What are cintrolling factors for slope destabalisation?
Dictate conditions of movement as it happens Control: - form - rate - duration
28
What must happen for a slope to move from stable ro marginally unstable to actively unstable?
Changes that affect the distribution of resistance and shear stresses
29
Where are the most active orogenic belts in the world found?
convergent crustal plate boundaries along which folding produces mountain ranges
30
How can the costs of landslide activity be classified?
Personal - death injury etc Economic - individual or public Environmental
31
Why is rhyolitic lava typically more viscous?
Their internal structure is highly polymerised with large intertwined silicate molecules which dont readily move
32
What is a Plinian eruption?
When an umbrella cloud forms from a rhyolitic eruption and there is a 'pumice rain' Very explosive
33
What are the characteristics of andesitic eruptions?
Highly explosive Viscous Intermittent
34
what is the composition of basaltic lavas?
Less: silica More: magnesium, calcium and iron
35
What is the viscosity of basaltic lava like compared to rhyolitic?
A lot runnier
36
What is the name of the bubbly rock produced from basaltic eruptions?
Scornia
37
What type of eruption leads to pyroclatic density currents?
Plinian
38
What affects the transport distance of pyroclastic flows?
The slope angle and the amount of material supplied by the volcano
39
What is ignimbrite?
A deposited layer of ash and pumice following a pyroclastic flow
40
What controls the depth of ignimbrite deposits?
Quickness of deposition i.e. how quickly the cloud decelerates
41
When does a pheonix plume form?
When a pyroclastic cloud has depsoited a vast proportion of pumice and rock that an ash-laden cloud rises again
42
How did the pheonix plume get its name?
As the cloud rises due to the heat of the hot ash rather then from the volcano
43
What are vesicles?
Bubbles of gas that have become 'frozen' in the lava
44
What are carbonatites?
Lime-rich lavas that is very runny and forms minature lava flows (1cm thick) but 500-600*c
45
What is a Pahoehoe?
a winkled like lava formation that occurs as lava advances and cools on top of itself
46
What is another name for the ropey variety of pahoehoe?
Toothpaste lava
47
How does toothpaste lava form?
As the surface winkles and shears
48
What are flood basalts?
Fast flowing almost wave like lava flows which travelled 10's-100's of km
49
What can happen if a pahoehoe reaches a slope which overwhelms its viscosity?
Cause it to tear itself apart
50
What is the name given by hawiians to the rubbly lava flow?
a'a
51
What happens when pahoehoe turns into a'a?
It is irriversable with a rubbly front and a still fluid interior
52

Geological natural hazards (21 decks)

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