3.1.5.3 Volcanic hazards Flashcards
What is the nature and predictability of volcanoes
- volcanoes tend to form on plat boundaries
- concentrated around the Pacific ring of fire
- can form in the middle of plates at hotspots (Hawaiian islands)
Characteristics of volcanoes formed on ocean ridges
- gentle gradients
- low viscosity
- basaltic lava
- frequent but gentle eruptions
Characteristics of volcanoes formed in subduction zones
- viscous lava
- composite volcanoes
- violent eruptions
Characteristics of volcanoes formed in rift valleys
- thin crust where magma forces its way to the surface
Characteristics of volcanoes formed over hotspots
Similar to ocean ridges
How is the magnitude of volcanoes measured
- volcanic explosivity index (VEI)
- logarithmic scale running from 0-8
What are the primary effects of volcanic eruptions (4)
- tephra
- pyroclastic flows (nuees ardentes)
- lava flows
- volcanic gases
What are the secondary effects of volcanic eruptions (5)
- lahars
- flooding
- tsunamis
- acid rain
- climate change
Define tephra
Solid material ejected into the atmosphere
Define pyroclastic flows (nuees ardentes)
- over 800 degrees, high velocity flows made from gas and tephra
- up to 700km per hour
- destroyed Pompeii
Define volcanic gases + example
- carbon dioxide/monoxide and sulfur dioxide are the most common
- 1986, carbon dioxide emissions killed 1,700 people in the crater of Nyos (Cameroon)
Define lahars + example
- volcanic mudflows
- melted snow and ice combines with volcanic ash
- 1985, a Lahar from Nevada del Ruiz destroyed Colombian town Armero killing roughly 20,000
Define flooding (in reference to volcanoes) + example
- when an eruption melts glaciers and ice caps
- happened in 1996 in Iceland when Grimsvotn erupted
Define tsunamis
- sea waves generated by violent eruptions
- after the eruption of Krakatoa (Indonesia), 1883 it killed an estimated 36,000 people
Define acid rain
- volcanoes emit gases including sulfur
- when sulfur combines with rain, acid rain occurs
How is climate change a secondary effect of volcanic eruptions
The ejection of ash and debris into the atmosphere can cool temperatures
How can you predict volcanic activity
- it is difficult to predict exactly when a major event will take place
- past lahar flows can be studied to predict potential flow paths
- volcanologists can monitor groundwater levels and gases being emitted
What happened for the Colombian eruption of Nevada del Ruiz in 1985 which shows the difficulty of prediction
Small scale activity continued for months before the major event. This meant that people were not prepared to evacuate as they did not see any threat. 20,000 died
How can you protect against volcanic activity (4)
- monitoring the volcano (New Zealand 5-stage alert)
- strengthening buildings against ash
- planning and education
- foreign aid in lower income countries
Social primary impacts of Mount Pinatubo eruption (2)
- 850 people died
- 60,000 people evacuated (saved a lot of people)
Social secondary impacts of Mount Pinatubo eruption (econ, social)
- 650,000 lost their jobs
- 1.2 million lost their homes and had to relocate in Manilla shanty towns
Environmental primary impacts of Mount Pinatubo eruption
- volcanic ash spread thousands of kms
- lahars caused erosion
Environmental secondary impacts of Pinatubo
Cooled global temperatures by 0.6 degrees
Economic primary impacts of Pinatubo
- bridges destroyed
- airport closed
Economic secondary impacts of Pinatubo
- 650,000 lost their jobs
- farmland covered in ash and unusable for years
- $700mn in damage
Short term responses to Pinatubo (social x2)
- 200,000 people relocated
- charities provided food and blankets in camps
Long term response to Pinatubo (econ, social)
- President Ramos created theMount Pinatubo Commission which raised almost $200 million
- new houses built on stilts to avoid being destroyed by lahars
When did Mount Pinatubo erupt
1991
When did Mount St. Helen’s (MSH) erupt
1980
Social impacts of MSH (3)
- almost all buildings and vegetation destroyed in a 30km radius
- 57 people killed
- 2000 people evacuated
Economic impact of MSH
- $1.1bn in damages
- airports were temporarily closed
- timber industry affected by the deforestation
- ships were stranded due to sediment deposits
Environmental impact of MSH
- over 200 square kms of forest destroyed
- 12 million salmon
Responses to MSH
- over 18 million trees replanted
- declared as a national monument in 1982 for research and tourism
