Volcanoes and mt nyiragongo Flashcards
1
Q
What is the spatial distribution of volcanoes?
A
- clustered around destructive and constructive plate margins, particularly around the ring of fire
- none at conservative margins
- can occur in the centre of plates eg. Hawaiian hotspots and along rift valleys
2
Q
What is a volcano?
A
- vents in the earth’s crust through which lava, tephra and gases erupt
- when the vents become blocked pressure builds up
- fissures create lower pressure areas that cause rocks to become molten and rise
3
Q
How do different volcano shapes change the characteristics of the materials erupted?
A
- shield volcanoes are less steep and less viscous lava is more common, they often explode releasing ash
- composite volcanoes are composed of tephra, pyroclastic flows and viscous lava
4
Q
What are the 2 types of lava?
A
basaltic:
- hot and runny, produces gently sloping landforms and gentle eruptions
- found at constructive margins
andesitic:
- viscous and cooler, violent eruptions due to gas build up
- found at destructive margins
5
Q
How is the magnitude of volcanic eruptions measured?
A
- using the VEI (volcanic explosivity index), which is a measurement of the volume of erupted materials
- each individual eruption is given a mark on the scale rather than each volcano
- logarithmic scale from 0-8, 8 is very bad
6
Q
What are the advantages and disadvantages of using the VEI?
A
+
- easy comparison of eruptive strength
- logarithmic so each number is 10x more powerful - true representation of strength
-
- doesnt account for secondary hazards
- not suitable for all volcanoes eg. in Hawaii, less explosive but still destructive
7
Q
What are the characteristics of composite volcanoes?
A
- found at destructive margins - very violent eruptions which force bombs out of vents
- very steep-sided, thick and viscous lava
8
Q
What are the characteristics of shield volcanoes?
A
- basaltic magma
- gentle sided as lava flows long distances before cooling and solidifying
- less violent eruptions
9
Q
What are the secondary impacts of volcanic hazards?
A
- lahars - melted snow and ice combine with volcanic ash to form mud flows that flow down river valleys at high speeds
- flooding - eruption melts glaciers and ice caps
- landslides - common on volcanic cones because they are tall, steep and weakened by the rise and eruption of molten rock, magma releases gases which dissolve into groundwater and weaken rock, and the thousands of layers of lava leave to faults that can be easily exploited
10
Q
What are the factors affecting the intensity of the effects of volcanic eruptions?
A
- viscosity of magma - higher viscosity = greater explosivity
- plate margins - more violent eruptions at destructive margins
- materials ejected
- proximity to population centres
- frequency of eruptions and risk perceptions pf population
- prediction
11
Q
How can volcanoes be predicted?
A
- monitoring seismic activity by looking at shockwaves that result from magma moving towards the surface using seismometers
- monitoring land swelling (using tiltometers), changes in groundwater levels and gas emissions
- overall can be predicted, but difficult to predict when an eruption will actually take place as it can occur very suddenly
12
Q
Where is mount nyiragongo located?
A
- lies on the eastern border of the democratic republic of the Congo in the Virunga mountains and is associated with the African Rift Valley
- lies 7 miles south of the city of Goma
13
Q
Why did nyiragongo erupt and why were the effects so damaging?
A
- lies on a divergent plate boundary within the East African Rift Valley
- eruption was caused by tension being released along a series of faults along the East African Rift Valley
- stratovolcano erupted from 3 different craters and lava was very runny with low silica - allowed it to travel rapidly to the city of Goma
- very difficult to monitor due to remote location
14
Q
Why was the population of Goma so vulnerable?
A
- very high population density (over 2 million) and located just 12km from the crater - lava travelled 40mph reaching the city very quickly therefore leaving little time to prepare
- LIC so little access to education, healthcare, stable housing etc, so fewer means to prepare for and recover from a disaster
- Goma volcano observatory lost funding in 2020 - limited early warnings due to corruption
- low government capacity to cope due to lack of infrastructure etc - communication of risk was poor
15
Q
What were the immediate responses and how effective were they?
A
- 300,000 evacuated from Goma to Rwanda within hours - saved many lives however evacuation camps quickly became overcrowded with poor sanitation and pressure on services, forcing many to return to Goma despite the risks
- USAID worked with NGOs and UN to provide $5 million in aid
- community resilience and prior experience helped people to act fast and international aid arrived quickly
16
Q
What were the primary impacts of the eruption?
A
- 30% infrastructure was destroyed
- major roads and airport runways destroyed which disrupted aid delivery and movement
- 350,000 displaced and ended up in overcrowded refugee camps
- long-lasting social and economic impacts due to low capacity to recover
17
Q
What were the secondary impacts?
A
- death toll reached 147 due to spread of cholera and inhalation of poisonous gases
- 120,000 left homeless
- followed by a large number of earthquakes continuing for 3 months after the eruption, caused even more collapse of buildings and hindered recovery hugely
- unemployment now at 95% compared to 80%
- 350,000 still dependent on aid 3 months after the eruption
- had much longer lasting effects on health, education and the economy which deepened vulnerability and poverty therefore more severe than primary impacts
18
Q
What were the long-term responses?
A
- homes/roads/schools reconstructed, was difficult as solidified lava made construction extremely difficult
- GVO received new equipment and international funding to monitor seismic activity to improve early warnings, however funding problems continued
- NGOs introduced public awareness campaigns and evacuation drills - limited in reach to poorer informal settlements
- exclusion zones created - however many returned to high-risk areas due to poverty and lack of alternatives so unsuccessful
- long-term resilience limited by poverty, political instability and weak governance
19
Q
What made it a disaster rather than just a hazard?
A
- very high population density and rapid flowing lava which had to travel only 12km to Goma
- destruction was very widespread not just concentrated in one area
- poor capacity to cope due to poverty and weak governance
- GVO underfunded so inaccurately predicted which delayed evacuation
- very fast moving lava at 60km/h so little time to react
20
Q
Relate this disaster to HMC
A
- very limited mitigation due to poverty, conflict and weak governance
- low preparedness and limited warnings/awareness
- some successful responses however slow and self-led showing local resilience, weakly coordinated
- slow and incomplete recovery and many returned to high-risk areas - minimal long-term planning
- OVERALL: useful as it shows why the disaster was so severe due to lack of preparation and struggles in long-term recovery. However assumes all stages are equally developed which is inaccurate for LICs like DRC
21
Q
Relate to the PM
A
- takes account for the fact that QOL was low before the disaster due to conflict and poverty
- shows rapid decline in QOL and slow recovery time
- OVERALL: can visualise depth of impacts and slow recovery, however predicts linear and steady recovery which was inaccurate in Goma
22
Q
Negatives of the models
A
- assume linear recovery
- more effective for HICs - assumes all stages are equally developed but much harder for LICs to implement mitigation
- don’t account for secondary hazards eg. earthquakes
- doesn’t address deep-rooted issues that contribute to greater vulnerability eg. poverty and instability
- no spatial patterns - more remote areas has more severe impacts due to lack of coordinated response
