Volcanic eruptions Flashcards
Frequency and regularity of volcanic eruptions?
Over past 10 years 600 people have died as a direct result of volcanic eruptions.
Large volcanic eruptions are rare has only been 1 eruption over a VEI of 5 in past 10 years (Chile eruption 2011- VEI 5).
Volcanos at constructive plate boundaries erupt frequently but VEI is only 0-1.
Predictability of eruptions?
More predictable than earthquakes as the often exhibit characteristics before eruption:
- Small earthquakes as magma rises
- Large earthquakes as gas builds up in magma chamber
- Ground deformation
- Gas emissions due to magma building up
- Ground heating up due to magma rising.
Many ways of monitoring this now with modern technology.
What hazards are created when a volcano erupts?
- Lava flow (leads to fires)
- Ash fallout
- Pyroclastic explosion
- Gas/ acid rain
Mitigation to reduce the impacts of the hazards created by volcanos?
Prevention is impossible so mitigation is important, can be done through:
- Monitoring the volcano
- Diverting lava away from population using concrete blocks
- Creating evacuation plans along with practice drills
- Creating risk/hazard maps of risk zones by using past eruptions and flows to map high risk areas
Spatial distribution of volcanos:
Edge of the pacific ocean:
- Destructive plate boundary where magma rises as magma plutons at the Benioff melting zone. (Galeras volcano, columbia)
Atlantic ocean:
- Constructive plate boundary volcano caused at point of ridge push where magma rises. (Eyjafjallajokull, Iceland)
Africa:
- Along west African rift valley where the earth drops magma pushes through to create volcano. (Nyiragongo, Domincian Republic of Congo)
Centre of the pacific ocean:
- Destructive plate boundary magma creates islands and then still needs somewhere to escape to (Mt Ontake, Honshu Island, Japan).
- Magma plume causes magma to create island and rises through to create volcanoes (Kilavea, Hawaii).
Nyiragongo volcanic eruption, Democratic Republic of Congo, 2002:
- Erupted in January 2002, in the West African rift valley in the Democratic Republic of Congo. Was a strato volcano containing a lava lake.
- African plate pulling apart (C v C), had a VEI 1, caused lava flow (fast, runny lava) and CO2 gas leaking.
Primary impacts:
- 147 died
- Lava flow destroyed 1/3 of Goma.
- Lava entered into the lake, feared toxic gas could be released.
Secondary impacts:
- Earthquakes caused structural damage
- Thousands needed medical attention from smoke and contaminated water.
- 12,000 homeless and 35,000 fled to Rwanda.
- Eco systems damaged and altered.
Fact file about DR of Congo and responses:
Fact file:
- LE= 59 years
- GDP per capita= $737
- Infant mortality rates= 74.5/ 1000 births
- 77% below the poverty line (earn below $1.90 per day)
- Allegations of a corrupt government.
Short term responses:
- Full evacuation of 400,000 people after red alert issued (reduced death rate).
- UN brought in humanitarian aid 3 days after.
Long term responses:
- Rebuilt Goma infrastructure
- UN later sent food and water supplies worth $15 million.
- Updated the volcanic observatory.
How did development of the DR of Congo affect impacts and responses of the Jan 2002:
Economic:
- 77% below the poverty line so people cannot mitigate homes.
- Government also has little money to mitigate so no emergency services respond, no warning for citizens, water contaminated etc.
- Due to poor infrastructure aid could not be distributed quickly.
Political:
- Corrupt president meant little money was spent on protecting from impacts.
Social:
- Struggled to prepare for the hazard which means resilience may be hard.
- Little/no knowledge on mitigation and adaptation, fatalistic attitude as result.
Eyjaffjallajokull eruption, Iceland 2010:
- VEI of 4, fissure volcano, constructive margin (C v C)
- Subglacial eruption as lava melted glacier above which created huge ash cloud.
Impacts:
- Population evacuated (inc. animals)
- No deaths or injury
- Vast ash cloud over Northern Europe and Atlantic
- 10,000 cancelled flights and 10 million people left stranded
- $1.7b to US airlines
Magma plumes (Oceanic crust):
- Overactive radio-decay in the inner core causes strong convection currents.
- Creates a stationary magma plume underneath the crust.
- Magma collects in the top of the plume head which melts crust, magma rises through crust and cools eventually creates islands.
- Create island chain as gravitational sliding causes plate to move overtime.
- Magma rises through weaknesses in the new island, creates shield volcano.
Hawaiian island chain e.g. Hawaii (youngest), Maui.
Shield volcanos = Maunaloa, Kilavea
Magma plumes (Continental crust):
- Overactive radio-decay in the inner core causes strong convection currents.
- Creates a stationary magma plume underneath continental crust.
- Magma will build up in the magma chamber until eventually pressure becomes too great and it forms a super volcano.
- Once erupted a caldera (depression) forms due to the extreme force.
- Plate moves over the plume so a string of extinct volcano and calderas are formed where it has previously been.
- Geysers also created here where water is heated by magma under surface.
Yellowstone national park, North America.
Caldera can be seen here as well as previous calderas e.g. Idaho caldera.
Geyser called Old Faithful
