3.1.5.3 - Volcanic Hazards Flashcards
How are volcanoes formed at oceanic ridges and what is a key example of this
When the plates move apart magma forces its way up to the surface where it cools and forms a new crust - as the plates move the new crust moves further away
- Eyjafjallajokull
How volcanoes formed on or near subduction zones, why are the volcanoes viscous and explosive and what is an example where lots occur
- the heat generated from the inside of the earth and from the friction between the two plates causes the oceanic plate to melt.
- as its less dense it rises as plutons of magma until reaching the surface and forms volcanoes
- andesitic lava causes viscous and explosive volcanoes
- e.g. ring of fire
How are volcanoes formed at rift valleys and a key example
- when the continental plates move apart areas of the brittle crust drop between forming rift valleys
- this crust is thinner meaning magma can force its way to the surface easily forming volcanoes
- e.g. Mount Nyrigongo
What are hot spots, how do they cause volcanoes and a key example
- = concentration of radioactive elements
- causes plumes of magma to rise and eat into the plate above
- when the magma breaks through, active volcanoes form above the spot
- plates moves along the hot spot forming a chain of islands e.g. Hawaiian islands
Why are volcanoes formed at hot spots cause shield volcanoes and how have the old volcanoes been reduced to seamounts
- basaltic lava flows slowly and forms huge flattish volcanoes = shield volcanoes
- due to marine erosion and subsidence caused by the pressure the volcanoes puts on the crust
Where are three key places that volcanoes are found
- ring of fire (surrounding pacific ocean)
- Rift in Africa
- Hawaiian hot spots
What is used to measure the magnitude of volcanoes and what is used to determine the magnitude
- volcanic explosivity index
- the volume of erupted material
How can volcanologists track the frequency of a volcanoes eruption
- a volcanoes previous history of activity is tracked using deposits associated with the volcano and how old or deep they are
What are 6 ways volcanologists can predict when a volcano is going to erupt or close to erupting
- monitor land swelling - could mean magma is moving to the main chamber
- changes in the groundwater levels - if groundwater levels rise then magma could be forcing its way toward the surface
- chemical composition of groundwater - poisonous gases can seep from the ground, water can get hotter so thermal monitoring is used
- Shock waves caused from magma moving towards the surface
- mass movements like landslides suggests upwelling of magma
- magma movement can be tracked using magnometres
What are 3 ways we can protect from volcanoes
- monitoring allows for prediction which allows for evacuation
- studying the nature and extent of deposits from lahars and lavas which allow to identify places at great risk and therefore influence land use planning
- viscous lava can be diverted through digging trenches or splashing seawater on it to solidify it
What are the 4 primary effects of volcanoes and how do they impact people
- tephra = solid material of varying grain size (vary from volcanic bombs to ash) - climate change, aviation, breathing issues
- pyroclastic flows = very hot, gas charged flows containing a mixture of gas and tephra - can flow up to 700kmph so are a high cause of death as they hard to escape
- Lava flows - destroy buildings and can cause death
- Volcanic gases (e.g. CO2, carbon monoxide and Sulphur dioxide )- can cause climate change and acid rain
6 secondary effects of volcanoes and how do they occur
- Lahars (volcanic mud flows) = when snow or ice melts caused by an eruption and they combine with volcanic ash to form fast flowing mud flows
- Flooding - when an eruption causes glaciers or ice to melt
- Volcanic landslides - the shaking from the eruption causes rocks to move and mass movements to occur
- Tsunami’s - from violent eruptions the ground shakes causing a tsunami to occur
- Acid rain - Sulphur emitted from volcanic eruption combines with the moisture in the air
- Climate change - the emission of CO2 contributes to global warming
Case study
- Where is Mt Nyiragongo located, what is it associated with and when did it erupt
- Democratic republic of congo
- the african rift valley
- January 2002
Case study
- What were the 3 characteristics of the main crater of the volcano
- 250m deep
- 2km wide
- ‘lava lake’
Case study
What encouraged many people to settle down in Goma despite the risk of the volcano
It was a fertile agricultural region because :
- It has an extended growing season
- the volcanic soils are very fertile
Case study
What are people from Goma particularly vulnerable to that the local people call ‘Mazuku’
Poisonous carbon dioxide seeping from the ground
Case study
What are 4 economic primary effects of the eruption and 2 social primary effects of the eruption
Economic-
- lava flows destroyed 1/3 of Goma
- covered the northern third of the runway at airport Goma
- Commercial centre and water and power facilities were destroyed
- 3 health centres and 1 hospital were destroyed
Social-
- The death toll = 147
- 350,000 people had to be evacuated/fled to Rwanda where they struggled for food and shelter
Case study
3 social secondary effects and 2 economical secondary effects
Social-
- Thousands were injured and required medical attention from eye irritation, respiratory problems or even from drinking contaminated water
- looting of houses and commercial properties - many people died when a petrol station they were looting blew up
- Large unemployment through destroyed businesses
Economical-
- Several earthquakes followed the eruption one on Richter scale 5 which caused industrial damage
- Destroyed businesses which caused unemployment
Case study
- How did sulphorous lave entering lake kivu have a social and environmental secondary effect
- Environmental = contaminated lake kivu killing wildlife as well
- Social = it was a major drinking source so it was difficult for many people to access clean water
Case study
What was an immediate short term response and what 4 things did the UN provide that cost around $15m
- authorities issued a red alert for Goma and surrounding areas enabling for a full evacuation and was a big reason for such a low death toll
- UN provided : emergency rations, set up camps for displaced people, health care and water
Case study
What is a long term response and why is it both expensive and difficult
- rebuilding homes, infrastructure and livelihoods
- expensive as much of Goma was destroyed
- difficult as the loss of businesses meant large unemployment which made it hard to rebuild livelihoods
Case study 2
Why was vulnerability to Eyjafjallajökull very low
- not many people live in that part of iceland
Case study 2
What is a key characteristic of the volcano and what is the 3 step process of it causing large ash clouds
- covered by an ice cap
- 1) When magma hits the ice cap it suddenly cools forming a glass-like material which instantly disintegrates
2) Explosions of gas from the main vent pulverise this glass-like material into very tiny particles
3) These particles are carried in the ash and as it gets further away from the volcano it becomes invisible - can be sucked into engine
Case study 2
When did the volcano erupt and and what was it on the VEI
- April 14th 2010
- 4 on the scale
