Volcanic hazards (with case studies) Flashcards
What is an Ocean Ridge?
- Formed when plates move apart (constructive) in oceanic areas
- Space between plates fills with basaltic lava from ridge below
- Volcanic activity occurs from these ridges forming underground volcanoes which sometimes rise above sea level
What is a Rift Valley?
- Formed when plates move apart (constructive) on continental areas
- Areas of the crust fall down between the fault lines a rift valley is formed, part between 2 valleys is called the horst
e. g East Africa
What are Deep Sea Trenches?
- Where oceanic and continental plates meet, the denser oceanic plate goes under the continental (subduction)
- Downwarping of oceanic plates forms a deep trench
e. g Peru/Chile trench
What are Young Fold Mountains?
- Formed when 2 continental plates come together
- Their edges and the sediments between them are forced up into fold mountains
- Material is also forced downwards to form deep mountain roots
e. g Himalayas
What is Constructive plate margins?
2 plates moving apart
What is Destructive plate margins?
2 plates moving towards each other
What is Conservative plate margins?
2 plates moving alongside each other.
What are Island Arcs?
- As one plates goes under the other its get hotter due to friction and surrounding and melts
- The material becomes less dense and rises to surface as pluntons of magma
- When reach surface form volcanoes and a line of volcanoes form
What is Ridge push?
- Force that acts away from the ocean ridge
- Result of gravity acting down the slope of the ridge
What is Slab pull?
-Pulling force exerted by cold, dense oceanic plunging into mantle due to its own weight
What is Tephra?
Solid matter ejected by volcano e.g volcanic bombs, ash
What is a Pyroclastic flow?
- Know as ‘nuees ardentes’
- Mixture of hot gas and tephra (over 800C)
- Flow down sides of mountain of up to 700 km per hour
What are the layers of the earth
Crust (lithosphere)
Mantle (asthenosphere)
Outer core (liquid)
Inner core (solid)
Where can volcanoes occur?
- Ocean ridges
- Subduction zones (island arcs)
- Rift valleys
- Hot spots
What is a hot spot?
- In certain places the concentration of radioactive elements causes a hot spot to develop
- From this a plume of magma rises to eat into the plate above to form active volcano
- As the plates moves the hot spots stays forming a line of volcanoes
e. g Hawaiian islands
Name the primary effects of volcanic activity
- Tephra
- Pyroclastic flows
- Lava flows
- Volcanic gases
What gases are released by a volcano eruption
- Carbon dioxide
- Sulphur dioxide
- Carbon monoxide
- Hydrogen sulphide
- Chlorine
Name the secondary effects of volcanic activity
- Lahars (volcanic mudflows)
- Flooding (melts glaciers)
- Volcanic landslides
- Tsunamis
- Acid rain (from gases)
- Climate change
What are impacts upon humans by volcanic activity?
- Death and injury
- Destroying infrastructure
- Ruining agriculture
- Blocking roads and airlines
Which LIC was affected by a volcanic event?
Congo
Mt Nyiragongo, (African rift valley)
January 2002
What were effects of the Congo eruption?
- 147 died, contaminated water, collapsing buildings, inhaling smoke
- Thousands required medical attention
- 350,000 people fled
- Destroyed 1/3 of Goma which has over 200,000 inhabitants
- Covered northern third of runway at Goma airport
- Water and power supplies shutdown
- Destroyed businesses (led to massive unemployment)
Response to Congo eruption
- ‘red alert’ (full evacuation)
- 2 days in the UN ferried humanitarian aid e.g food, water, shelter, blankets, healthcare (cost $15 million)
- UN set up camps to house people
Which HIC was affected by a volcanic hazard?
Iceland
Eyjafjallajokull (mid-Atlantic ridge)
April 2010
Effects of Iceland eruption?
- Huge amounts of ice were melted causing floods to rush to nearby rivers, 1000 people evacuated
- Large quantities of ash poured from volcano
- Jet stream carried ash over Europe shutting down air traffic (cost £130 mil per day for 6 days)
- Largest shutdown since world war 2
Risks of Iceland eruption
- Little risk as few lived in this part of Iceland
- Threat came from ash
