Volcanic hazards Flashcards
What are the main volcanic hazards
- Pyroclastic flows
- Ashfall
- Lahars
- Lava flows
- Toxic gases
- Volcanic landslides
- Jokualhaps
What are pyroclastic flows and why are they bad
Pyroclastic flows are high-density mixes of hot volcanic gases, volcanic fragments, pumice and ash, which moves at high speeds down volcanic slopes
They are considered the worst volcanic hazard because the lava flow can reach 1000 degrees c, people caught in flows die immediately, can travel many metres
How do pyroclastic flows form
-The eruption column collapses
- Boiling over (material travels downslope quickly)
- Collapse of a lava dome ( slopes of volcanoes are so steep the collapse)
What is a eruption Column
The eruption column is a cloud of hot volcanic ash suspended in volcanic gas from an explosive eruption
What is an example pyroclastic flows
1982 eruption of El Chichon in Mexico killed up to 2,300 and made 20,000 homeless as a result of pyroclastic flows
What are lava flows and why are they bad
Lava flows are streams of molten rock pouring from an erupting vent
Least dangerous because people have time to move away, but building, farms and infrastructure can be destroyed so secondary impacts can be significant
What are the two types of lava flows
Aa lava
- Thick lava
- High lava flow
- Rough
Pahoehoe Lava
- Less thick lava
- Low lava flow
- Smooth
What are Ashfalls and why are they dangerous
Tephra emitted during an explosive eruption includes volcanic ash, consisting of fragments of pulverised rock and volcanic glass less than 2mm in diameter
- Most frequent volcanic acid but only accounts for 5% of volcanic related deaths, through respiratory issues
- Large quantities of ash can travel thousand of kilometres via wind
- Weight of ash collapses building, even heavier if wet
Whare are Lahars and why are they dangerous
A lahar is a mixture of volcanic ash, debris and water that travels down a volcanic slope usually a long valley
- Increases in size the further it travels
- Greatest risk to human life after pyroclastic flows
1985 eruption of Nevada Del Ruiz in Colombia 60km/h lahar destroyed town of Amero killing over 20,000 inhabitants
What are Jokulhaups and why are they dangerous
Translated directly from Icelandic it becomes glacial run
Subglacial volcanic activity causes melting at the base of an overlying glacier, results in brief but significant floods.
1966 eruption of Grimsvotn in Iceland drained 3.2km cubed of water in 40 hours travelling at 5,000 metres per second
Jokulhaups usually occur in scarlessly populated areas so little risk
What are volcanic landslides and why are they dangerous
Is a mass of volcanic rock or debris that moves rapidly under the force of gravity
Bury areas of in debris many metres thick destroying buildings
Can help create Lahars
1980 eruption of Mt St Helens in the USA involved a landslide triggered by an earthquake 2.9km of material moved at 170-250 km/h for 20 km
What are toxic gases and why are the dangerous
Magma rises to the surface the pressure drops and gases are released reaching the atmosphere
Harmless water vapour is most present but carbon dioxide and sulphur dioxide can be released
Carbon dioxide is denser than air so it builds up in dips in surface and suffocates animals and humans
Sulphur dioxide can create acid rain and is a greenhouse gases so contributes to global warming
Primary impact on environment of Volcanic hazards
Destruction of vegetation
reshaping land because of lahars
increased precipitation due to increase water vapour released
All occur on a local scale
Primary impact on demographic of Volcanic hazards
Over 91,000 people died to volcanic hazards between 1900 and 2016
Secondary impact on environment of volcanic hazards
emissions of greenhouse gases- global temperature rise
Emissions of sulphur- increased risk of acid rain
both occur globally
