Pre-reading Flashcards
What is a seismic hazard?
potential for dangerous earthquake related natural phenomona i.e. shaking, soil fracture or liquefaction
- leon reiter (1990)
How can seismic hazards affect society?
Potential destrution of buildings or loss of life
What is seismic risk?
probability of occurence of the consequences of seismic hazards
What is needed to calculate seismic risk?
Need to know the seismic hazard
When does an earthquake occur?
When there is sudden movement along a new or pre-existing fracture or fault
What is a ‘Maximum earthquake’?
Upper bound to qauke size determined by earthquake processes no matter how unlikely
or
Max historic quake
How are seismic waves and their ground motion divided?
2 levels
Weak/ small amplitude (distant or small earthquake)
Strong/ large amplitude (nearby or large earthquakes)
What is the difference between continental and ocean flood basalt volumes?
Oceanic flood basalts are usually 10 times greater in volume
What is the amount of melt associated to a mantle plume proportional to?
The amount of decompressionthe plume experiences where the temp is equal to or above the solidus
Where do temperatures above the solidus begin to occur?
200km depth or shallower
What is the extent of melting in a mantle plume primarily controlled by?
Thickness of lithosphere
What is a diapir?
An upwelling of material or intrusion into the overlying surface
What is a magma resevoir?
domain of fluid filled matrix that can store and transmit magma
definition and characteristics
What is the magma chamber?
The top of the magma reservoir
- fluid rich
- sill like
What is neutral bouyancy?
Where melt density and in-situ country rock density are equal
What is the horizon of neutral bouyancy (HNB)?
Layer of narrow vertical extent and wide lateral extent where melt has mechanical equillibrium
What is negative bouyancy?
When melt density is greater than insitu country rock
Where is the zone of negative bouyancy located?
Above horizon of neutral bouyancy
What is positive bouyancy?
When the density of insitu country rock is greater than the melt density
Where is the zone of positive bouyancy?
Bounded below the site of magma generation and bounded above the horizon of neutral bouyancy
What is contractancy?
progressive reduction in macri and microscopic pore spaces produced by progression increase in pressure with depth
What is present in every slope?
stresses which will promote movement (shear stress) and opposing forces which resist movement
What are the best 3 states to view slopes in for classification?
Stable
Unstable (marginally stable)
Actively unstable
There are 3
What are the destabalising factors that affect slopes?
Preparatory factors
Triggering factors
Controlling (perpetuating)
What are preparatory factors for slope destabalisation?
Factors which make the slope susceptable to movement without intitiating it
Make slope marginally unstable
What are triggering factors for slope destabalisation?
Initiate movement
Move slope from marginally unstable to actively unstable
What are cintrolling factors for slope destabalisation?
Dictate conditions of movement as it happens
Control:
- form
- rate
- duration
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
Where are the most active orogenic belts in the world found?
convergent crustal plate boundaries along which folding produces mountain ranges
How can the costs of landslide activity be classified?
Personal - death injury etc
Economic - individual or public
Environmental
Why is rhyolitic lava typically more viscous?
Their internal structure is highly polymerised with large intertwined silicate molecules which dont readily move
What is a Plinian eruption?
When an umbrella cloud forms from a rhyolitic eruption and there is a ‘pumice rain’
Very explosive
What are the characteristics of andesitic eruptions?
Highly explosive
Viscous
Intermittent
what is the composition of basaltic lavas?
Less: silica
More: magnesium, calcium and iron
What is the viscosity of basaltic lava like compared to rhyolitic?
A lot runnier
What is the name of the bubbly rock produced from basaltic eruptions?
Scornia
What type of eruption leads to pyroclatic density currents?
Plinian
What affects the transport distance of pyroclastic flows?
The slope angle and the amount of material supplied by the volcano
What is ignimbrite?
A deposited layer of ash and pumice following a pyroclastic flow
What controls the depth of ignimbrite deposits?
Quickness of deposition i.e. how quickly the cloud decelerates
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
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
What are vesicles?
Bubbles of gas that have become ‘frozen’ in the lava
What are carbonatites?
Lime-rich lavas that is very runny and forms minature lava flows (1cm thick) but 500-600*c
What is a Pahoehoe?
a winkled like lava formation that occurs as lava advances and cools on top of itself
What is another name for the ropey variety of pahoehoe?
Toothpaste lava
How does toothpaste lava form?
As the surface winkles and shears
What are flood basalts?
Fast flowing almost wave like lava flows which travelled 10’s-100’s of km
What can happen if a pahoehoe reaches a slope which overwhelms its viscosity?
Cause it to tear itself apart
What is the name given by hawiians to the rubbly lava flow?
a’a
What happens when pahoehoe turns into a’a?
It is irriversable with a rubbly front and a still fluid interior
