Hazards - Volcanic Hazards Flashcards
What are the four types of volcanoes?
1) Shield - low and wide cone with gently sloping sides e.g. Mauna Loa.
2) Fissure - magma rises through deep fractures e.g Ejyafjallajokull.
3) Composite - consist of alternating layers of ash and lave e.g. Mt Etna. 4) Cinder - composed of cinder fragments or volcanic bombs e.g. Paracutin
Where does basaltic lava form?
Basaltic lava forms at constructive plate boundaries. Very hot with low viscosity (runny) so it flows easily and quickly. Basaltic lava eruptions are frequent but not violent.
Where does andesitic and rhyolitic lava form?
Andesitic and rhyolitic lava forms at destructive plate boundaries. Cooler and more viscous (thicker) so they flow slowly and less easily. These eruptions tend to occur intermittently.
What is a pyroclastic flow?
Mix of super-heated gas, ash and volcanic rock flowing down side of volcano at over 450mph. Deposits ignimbrite. Instant death.
What is a lava flow?
Often from vent on side of volcano. Low viscosity can run fast and far depending on gradient. Most are slow giving time to evacuate.
What are volcanic gases?
Potentially deadly toxic gases e.g. carbon dioxide and sulfur dioxide released into atmosphere upon eruption.
What is tephra?
Material ejected during eruption. Mostly ash – ash fallout. Can travel thousands of km from site, killing vegetation and hindering air transport as well as causing breathing difficulty. Volcanic bombs are large particles of tephra which can damage buildings and hurt people.
What is a lahar?
Tephra mixes with water from rainfall or snow melt, flowing very quickly and far. Thick cement-like lahar can bury people and settlements.
What is acid rain?
Volcanic gas react with water vapor in atmosphere.
What three things are used to predict volcanic activity?
1) Tilt meters
2) Gas emission
3) Remote sensing
How are tilt meters used to predict volcanic activity?
When pressurized magma enters chamber it expands and creates deformities in the ground above. Before an eruption the magma rises up and chamber deflates causing a reversal in tilt direction.
How is gas emissions used to predict volcanic activity?
Samples collected from active vents. Changes in gas composition or emission rate of SO2 and other gases may be related to variation in magma supply rate, change in magma type or magma movement.
How is remote sensing used to predict volcanic activity?
Satellites can identify thermal anomalies in volcanoes caused by rising magma and temperature increase prior to eruption. Infra-red detectors provide a reliable early warning system.
How is prepardness used in response to volcanic hazards?
Warnings – authorities install alert systems supported by the info given by scientists predicting eruptions e.g. New Zealand implemented 5 stage alert to inform the public about an eruption.
Hazard mapping – history of past volcanic activity can help identify threats to certain areas and prioritize protection and evacuation there.
How is mitigation/adaptation used in response to volcanic hazards?
1) Build trenches or barriers to prevent damage from oncoming lahars.
2) Pouring water on lava flow front.
3) Capitalise on opportunities for tourism and farming industries.
