Volcanics Flashcards
(53 cards)
what is an ‘isopleth’?
a line of constant maximum clast size
what is an ‘isopach’?
a line of constant deposit thickness
Name the explosive eruption styles in order of increasing explosiveness
Strombolian, Vulcanian, Vesuvian, Plinian, Ultra-plinian
How can pyroclastic flows be formed?
destabilisation of lava flow fronts and lava domes or by collapsing plumes(larger volumes)
What are the 3 main ways of producing melt
- increasing temperature (e.g hotspots)
- decreasing pressure
- lowering the melting temperature (e.g volatiles)
Magma steps to reach the surface. (page 55)
- extraction
- migration
- magma chamber pooling (feed volcanic edifices)
What would cause the opening of a new conduit?
When the critical pressures inside the magma chamber exceed the tensile strength of the overlying rock (maybe due to new magma supply as well as exsolving gas)
When does ‘fragmentation’ occur?
When the pressure inside the bubbles becomes so large that it breaks the magma fills around it.
Controls whether an eruption is explosive or effusive.
(page 57)
eruption regime diagram: what are the 3 regimes from left to right?
Extrusive (meaning effusive??) , Gas-pyroclast dispersion (explosive) , Gas segregation (Strombolian burps)
Eruption precursors:
changes in seismic activity rate, character and location
volcanic tremor
dome-style uplift or other deformation
changes in amount/ composition of released gas
changes in gravitational/ magnetic field over volcano (direct expressions of magma movement)
changes in hydrology
What are ‘tsunami earthquakes’?
earthquakes that produce tsunami that are particularly large relative to the magnitude estimated form earthquake waves (page 62)
produce a relatively large amount of low-frequency waves
What is the energy of a tsunami source equal to?
the potential energy of the uplifted water =mgh
How much of the produced magma beneath a volcano eventually erupts?
20-50%
Give values for the time scales on which magma rises from the source to the subvolcano chamber, and velocities of movement. (2011 5 mark exam question)
velocities: cm’s to 100s m’s per year (from crust to mantle) , km’s a day-km’s per hour in brittle crust (through diking)
*time scales: 1000s of years in deeper crust
10-100s of years in shallow magma chamber
What depth are magma chambers located beneath the surface?
10-20km
When do fire fountains develop?
As the mixture of gas and magma first leaves the vent using its momentum which is slowly exhausted, if insufficient additional buoyancy is gained.
Can reach a max of a few km’s tall
When do clasts fall out of the plume?
when their terminal falling velocity exceeds the velocity with which the plume carries them upwards (page 51)
What effect do volatiles in the magma have on column buoyancy?
plumes with larger volatile content require lower exit velocities to become stable (relationship breaks down when water content is 10 wt % or higher due to additional mass of plume) . (page 51)
For achieving buoyancy what effect does a larger vent radius have on the required exit velocities?
exit velocities must be higher
3 types of calderas
Basaltic type (due to summit collapse of shield volcanoes), crater-lake type (due to collapse of stratovolcanoes) and resurgent (have no single localised vent)
What are the velocities of plate motions?
cm/year
What are the velocities of slow creep landslides?
0.1 m/year
What are the velocities of slow debris flows
10 m/hour
What are the velocities of mudflows?
10 km/hr
