Flashcards in Variations in the type and frequency of volcanic activity Deck (13):
What is a volcano?
Geological land form.
Created magma intrusion into the crust.
Extrusive magma eruption onto the surface through a vent.
Where can volcanoes be found? 4
1. Oceanic ridges (divergent plate boundaries) e.g. Mid Atlantic Ridge.
2. Rift valleys e.g. African rift valley - Mount Kenya.
3. Subduction zones - 'Ring of Fire'.
4. Hot spots e.g. Hawaiian islands.
What are active volcanoes?
Constantly erupting volcanoes.
Usually quiet, sometimes be violent.
E.g. Stromboli, Italy.
What are dormant volcanoes?
Inactive volcanoes that have not erupted for an amount of time but can't be called extinct.
What are extinct volcanoes?
Inactive volcanoes which have not erupted since the beginning of recorded history are extinct volcanoes.
Will never erupt again unless mistaken (dormant).
What are intermittent volcanoes?
Erupt at fairly regular time periods.
E.g. Mount Etna.
What is an example of a Plinean (explosive) eruption?
Mount Vesuvius, AD79 - buried Pompeii.
High gas/silica content.
Magma emerges - depressurises - gas expands.
Propels pyroclastic material as high as 45 km in the air.
Can last for days.
Tall/sustained eruption plume.
Hugh tephra amount.
Extremely fast moving lava flows.
What is an example of a Hawaiian (gentle) eruption?
Low viscosity, gas pressures, silica content.
Fows over large areas.
Gentle shield volcanoes/lava plateaus.
Fire fountains - lava thrusted 50m for many hours.
Steady lava flow from a central vent.
Produce wide lava lakes - forms in craters/depressions.
What happens in a Strombolian eruption?
High viscosity, high gas pressure.
Small amounts of lava 15-90m in the air - very short bursts.
Impressive booming sounds, but the eruptions are relatively small.
Small ash amounts.
NO lava flows.
What are the different types of magma?
Basaltic - 48-52% - low viscosity (fluid) - 1,160C.
Andesitic - 52-63%,
Dacite - 63-68%.
Rhyolitic - 68-77% silicon - high viscosity (thick) - 900C.
What are the different types of eruption and where are they on the VEI?
Hawaiian, 0, effusive, Kilauea.
Strombolian, 1, Nyiragongo.
Vulcanian/Pelean, 3, severe, every few months, Soufriere Hills.
Plinian, 5, Mt St Helens (1980).
Ultra-Plinian, 7, Tambora (1815).
Supervolcanic, 8, Yellowstone.
What are the volcanic primary hazards?
+ when do they occur?
Tephra - solid material of varying grain size (volcanic bombs to ash particles) ejected into the atmosphere.
Pyroclastic flows - hot high velocity flows made up of gases and tephra (800C).
Volcanic gases - CO2, carbon monoxide etc. e.g. CO2 from Lake Nyos in Cameroon, 1986 killed 1,700.