Volcanic hazards (with case studies)

Question 1

What is an Ocean Ridge?

Answer 1

• 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

Question 2

What is a Rift Valley?

Answer 2

• 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

Question 3

What are Deep Sea Trenches?

Answer 3

• 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

Question 4

What are Young Fold Mountains?

Answer 4

• 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

Question 5

What is Constructive plate margins?

Answer 5

2 plates moving apart

Question 6

What is Destructive plate margins?

Answer 6

2 plates moving towards each other

Question 7

What is Conservative plate margins?

Answer 7

2 plates moving alongside each other.

Question 8

What are Island Arcs?

Answer 8

• 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

Question 9

What is Ridge push?

Answer 9

• Force that acts away from the ocean ridge

- Result of gravity acting down the slope of the ridge

Question 10

What is Slab pull?

Answer 10

-Pulling force exerted by cold, dense oceanic plunging into mantle due to its own weight

Question 11

What is Tephra?

Answer 11

Solid matter ejected by volcano e.g volcanic bombs, ash

Question 12

What is a Pyroclastic flow?

Answer 12

• Know as ‘nuees ardentes’
• Mixture of hot gas and tephra (over 800C)
• Flow down sides of mountain of up to 700 km per hour

Question 13

What are the layers of the earth

Answer 13

Crust (lithosphere)
Mantle (asthenosphere)
Outer core (liquid)
Inner core (solid)

Question 14

Where can volcanoes occur?

Answer 14

• Ocean ridges
• Subduction zones (island arcs)
• Rift valleys
• Hot spots

Question 15

What is a hot spot?

Answer 15

• 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

Question 16

Name the primary effects of volcanic activity

Answer 16

• Tephra
• Pyroclastic flows
• Lava flows
• Volcanic gases

Question 17

What gases are released by a volcano eruption

Answer 17

• Carbon dioxide
• Sulphur dioxide
• Carbon monoxide
• Hydrogen sulphide
• Chlorine

Question 18

Name the secondary effects of volcanic activity

Answer 18

• Lahars (volcanic mudflows)
• Flooding (melts glaciers)
• Volcanic landslides
• Tsunamis
• Acid rain (from gases)
• Climate change

Question 19

What are impacts upon humans by volcanic activity?

Answer 19

• Death and injury
• Destroying infrastructure
• Ruining agriculture
• Blocking roads and airlines

Question 20

Which LIC was affected by a volcanic event?

Answer 20

Congo
Mt Nyiragongo, (African rift valley)
January 2002

Question 21

What were effects of the Congo eruption?

Answer 21

• 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)

Question 22

Response to Congo eruption

Answer 22

• ‘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

Question 23

Which HIC was affected by a volcanic hazard?

Answer 23

Iceland
Eyjafjallajokull (mid-Atlantic ridge)
April 2010

Question 24

Effects of Iceland eruption?

Answer 24

• 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

Question 25

Risks of Iceland eruption

Answer 25

• Little risk as few lived in this part of Iceland

- Threat came from ash