Hazardous Earth Flashcards
Where are explosive eruptions found and what types of lava are associated with them?
Convergent boundaries, rhyolite and andesite lava
Where are effusive eruptions found and what type of lava is associated with them?
Divergent boundaries, basalt lava
Give characteristics of rhyolitic/andesitic lava and the style of eruption it produces.
- Highly acidic/silica content 70%, high viscosity, 750-900ºC
- Violent, gas bubbles burst at surface, highly explosive, vent and cone often shattered
Give characteristics of basaltic lava and the style of eruption it produces.
- Less acidic/silica content 50%, low viscosity, 1100-1200ºC
- Bubbles expand freely, limited explosive force
What are the materials erupted by an explosive eruption?
Gas, dust, ash, lava bombs, tephra
What materials are erupted by an effusive eruption?
Gas, lava flows
How frequently do explosive eruptions occur?
Not often, tend to have long periods with no activity
How frequently do effusive eruptions occur?
More often, tend to be more frequent and can continue for many months
What shape of volcano is associated with explosive eruptions?
Steep-sided strato-volcanoes, caldera
What shape of volcano is associated with effusive eruptions?
Gently sloping sides, shield volcanoes; lava plateaux
Give an example of a group of islands produced by a hot spot.
The Hawaiian islands
What are lava flows?
Streams of molten rock from an erupting vent
How are lava flows hazardous?
As lava is extremely hot (1000ºC) flows can cause fires and destroy crops and infrastructure
Do lava flows often cause injuries and fatalities?
No as even low viscosity lava does not move that rapidly
What are pyroclastic flows?
A dense, fast-moving flow of solidified lava pieces, volcanic ash, and hot gases
