3.1.2:Volcanoes, processes,hazards,impacts Flashcards
VEI
Volcano explosivity index
-volume of ejected product
-duration of main eruption
scale from 0 - 8
Limitations of VEI
- all types of ejected material are treated alike
- no account of emissions eg: SO2 so impact on climate change hard to measure
Recurrance
how often an event occurs
Inverse relationship
The larger the event the less likely it is to occur regularly
Areal extent
Area covered by the tectonic event
Duration
Length of time the hazard exists for
Speed of onset
Amount of warning that event may occur
Predictability of occurrence
Earthquakes and volcanoes both have random temporal distribution which can add to their potential impacts
Gap theory
Length of time between past events
Can help prepare communities
Types of volcanic eruptions
6
- Fissure
- Shield
- Acid/dome
- Composite/strato
- Ash/cinder
- Calderas
Pyroclastic flows and surges
primary volcanic hazard
Bubbles in the magma burst and eject a mix of gases and material, the bursts surge downhill
- results of frothing magma in the volcano vent
- responsible for most volcanic deaths (to date)
Lava flows
2 types
(primary volcanic hazard)
more threat to property than human life
- A’a
- Pahoehoe
lava flows: Pahoehoe
Most liquid lava, wrinkled surface, moves quickly downhill
lava flows: A’a
Lava tends to form blocks, rough surface, moves slowly downhill
Airfall Tephra
primary volcanic hazard
Composed of fragmented material ejected by the volcano which then falls to the ground
-ash falls/clouds
Volcanic gases
primary volcanic hazard
Complex gas mixture:
- water vapour
- hydrogen
- carbon monoxide/ dioxide
- hydrogen sulphate
- sulphur dioxide
- chlorine
- hydrogen chloride
more on volcanic gases
CO causes deaths as its toxic
most deaths from CO2
Primary volcanic hazards
4
- pyroclastic flows+surges
- lava flows
- airfall tephra/ash falls
- volcanic gases
Secondary volcanic hazards
3
- Lahars
- volcanic landslides
- Jokulhlaups
Lahars
secondary volcanic hazard
Volcanic mud flows composed mainly of silt-sized sediments
- 2nd biggest volcanic risk to human life
- consist of ash, rock and torrential rain
- dense, viscous
- occur on steep volcanic flanks in tropical,humid or monsoon climates
Volcanic landslides
secondary volcanic hazard
Landslides and debris avalanches
Gravity driven slides of masses of rock+volcanic material
occur during an eruption
Ground deformation
Rising magma deforms volcanic slopes by bulging and triggering instability + landslides
pre eruption
Jokulhlaups
secondary volcanic hazard
Water produced by melting ice is trapped in a lake between volcano + overlying glacier then water is released = violent flood
-in most sub-glacial eruptions
