Variations in the type and frequency of volcanic activity

Question 1

What is a volcano?

Answer 1

Geological land form.
Created magma intrusion into the crust.
Extrusive magma eruption onto the surface through a vent.

Question 2

Where can volcanoes be found? 4

Answer 2

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.

Question 3

What are active volcanoes?

Answer 3

Constantly erupting volcanoes.
Usually quiet, sometimes be violent.
E.g. Stromboli, Italy.

Question 4

What are dormant volcanoes?

Answer 4

Inactive volcanoes that have not erupted for an amount of time but can’t be called extinct.

Question 5

What are extinct volcanoes?

Answer 5

Inactive volcanoes which have not erupted since the beginning of recorded history are extinct volcanoes.
Will never erupt again unless mistaken (dormant).

Question 6

What are intermittent volcanoes?

Answer 6

Erupt at fairly regular time periods.

E.g. Mount Etna.

Question 7

What is an example of a Plinean (explosive) eruption?

Answer 7

Mount Vesuvius, AD79 - buried Pompeii.
Highly viscous.
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.

Question 8

What is an example of a Hawaiian (gentle) eruption?

Answer 8

Hawaiian islands.
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.

Question 9

What happens in a Strombolian eruption?

Answer 9

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.

Question 10

What are the different types of magma?

Answer 10

Basaltic - 48-52% - low viscosity (fluid) - 1,160C.
Andesitic - 52-63%,
Dacite - 63-68%.
Rhyolitic - 68-77% silicon - high viscosity (thick) - 900C.

Question 11

What are the different types of eruption and where are they on the VEI?

Answer 11

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.

Question 12

What are the volcanic primary hazards?

+ when do they occur?

Answer 12

Initial eruption.
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).
Lava flows.
Volcanic gases - CO2, carbon monoxide etc. e.g. CO2 from Lake Nyos in Cameroon, 1986 killed 1,700.

Question 13

What are the volcanic secondary hazards?

+ when do they occur?

Answer 13

AFTER the initial eruption.
Lahars (mudflows) - mixture of rain and ash.
Flooding - melting of glaciers/ice caps.
Tsunamis - Krakatoa in 1883 - drowned 36,000.
Volcanic landslides.
Climate change - vast amounts of volcanic debris into the atmosphere can reduce global temperatures.