Volcano hazards Flashcards
What is a lahar?
-mixture of hot and cold water with rock fragments
How do lahars form?
-when erupted volcanic material gets saturated
Where are lahars most common?
-on stratovolcanoes
(Due to their greater gradients)
What makes lahars so dangerous?
-they are capable of setting like concrete
-they grow as the travel
-they will destroy anything in their path
-have been known to move car-sized objects
What is ashfallout?
-term for aash and tephra that falls to the earths surface
What can happen to ash and tephra during eruptions?
-it can be sent up to incredible heights
-can travel many kilometres
What problems can ash fallout cause?
-health problems
-disrupt air travel
-damage machinery
-contaminate water supplies
-collapse structures
What is a mudflow?
-form of mass movement involving fast-moving flow of debris
What speeds can a mudflow reach?
-ranges from 3 metres/minute to 5 metres/second
How can mudflows travel so far?
-they contain significant amounts of clay
-are a secondary effect of a volcanic eruption
What triggers a mudflow?
-heavy rainfall
-snowmelt
-groundwater flowing through cracked bedrock
-form after an eruption
Why are mudflows so dangerous?
-can carry large boulders and trees
-damage water supplies
-damage gas pipes
-damage electrical infrastructure
-can cause secondary effects such as disease
What are volcanic gases?
-gases that are released during volcanic activity or an eruption
What are some examples of volcanic gases?
-sulphur dioxide
-carbon dioxide
-hydrogen chloride
-hydrogen fluoride
-hydrogen sulphide
Why are volcanic gases so dangerous?
-they are hazardous to human health
-cause respiratory problems
-can lead to death
-air quality alerts
-health warnings
What makes volcanic gases difficult to be aware of?
-they are invisible
-they are denser than air so tend to pool in depressions surrounding the volcano
What is an example of gases being deadly?
-lake Nyos in Cameroon
-killed 1700 people
-massive amounts of carbon dioxide released in lake Nyos
What are pyroclastic flows?
-dense, fast moving flow of solidified lava pieces, hot ash and hot gases expelled from a volcano during an eruption
How does a pyroclastic flow form?
-mainly happens with explosive eruptions
How are pyroclastic flows so dangerous?
-move at speeds of up to 200m/s
(Impossible to escape from)
-cover the ground in solidified lava and ash
-water levels are made to rise
-causes secondary flooding
What is an example of a pyroclastic flow?
-Pompeii and Herculaneum when Vesuvius erupted in 79AD
What is acid rain?
-precipitation that has elevated levels of hydrogen ions
What does acid rain effect?
-trees
-freshwater sources
-soil
-insects and aquatic life forms
-corrosion of metal bridges and structures
-impacts human health
How is acid rain created?
-sulfur dioxide gas can lead to acid rain and air pollution downwind of a volcano
What is tephra?
-rock fragments and participles ejected by a volcanic eruption
(Also referred to as pyroclasts)
What happens to tephra once it hits the ground?
-remains as tephra unless its hot enough to fuse into pyroclastic rock or tuff
What dangers does tephra pose?
-can trigger fires if falling on ignitable material
-reduces visibility
-causes complete blackout
-hazards for driving
-contaminates water
what are lava flows?
-a stream of molten rock that pours out of a volcano during an eruption
Which eruption motivated the first systematic epidemiological and toxicological research?
-Mount St Helens in 1980
What happens to lava once it’s out of the volcano?
-it remains molten and flows across the ground until it cools and hardens into rock
(Because it’s so hot = over 1,100 degrees C)
Are lava flows a major threat?
-no
-they can be very destructive but are rarely a threat to humans directly
-they move very slowly so people can outrun it
What is an example of a lava flow?
-lava flows at Etna volcano in Italy
-destroyed up to 12 villages and part of the city Catania
What does ‘nuees ardente’ mean?
-glowing cloud
What is a nuees ardente?
-turbulent, fast-moving cloud of hot gas and ash erupted from a volcano
What is an example of a nuees ardente?
-1902 eruption of Mount Pelee
-killed 29,000 people
-destroyed the city of St.Pierre
How do nuees ardentes form?
-during explosive eruptions as columns of material collapse
-or when volcanic rock collapses in non-explosive eruptions
Why are nuees ardentes so dangerous?
-flow into valleys at speeds up to 50mph
-range from 204-704 degrees C
-accompanied by large boulders
