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Hazards > 3.1.5.3 Volcanic hazards > Flashcards

3.1.5.3 Volcanic hazards Flashcards

1
Q

What is the nature and predictability of volcanoes

A
  • 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)
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2
Q

Characteristics of volcanoes formed on ocean ridges

A
  • gentle gradients
  • low viscosity
  • basaltic lava
  • frequent but gentle eruptions
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3
Q

Characteristics of volcanoes formed in subduction zones

A
  • viscous lava
  • composite volcanoes
  • violent eruptions
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4
Q

Characteristics of volcanoes formed in rift valleys

A
  • thin crust where magma forces its way to the surface
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5
Q

Characteristics of volcanoes formed over hotspots

A

Similar to ocean ridges

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6
Q

How is the magnitude of volcanoes measured

A
  • volcanic explosivity index (VEI)
  • logarithmic scale running from 0-8
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7
Q

What are the primary effects of volcanic eruptions (4)

A
  • tephra
  • pyroclastic flows (nuees ardentes)
  • lava flows
  • volcanic gases
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8
Q

What are the secondary effects of volcanic eruptions (5)

A
  • lahars
  • flooding
  • tsunamis
  • acid rain
  • climate change
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9
Q

Define tephra

A

Solid material ejected into the atmosphere

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10
Q

Define pyroclastic flows (nuees ardentes)

A
  • over 800 degrees, high velocity flows made from gas and tephra
  • up to 700km per hour
  • destroyed Pompeii
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11
Q

Define volcanic gases + example

A
  • carbon dioxide/monoxide and sulfur dioxide are the most common
  • 1986, carbon dioxide emissions killed 1,700 people in the crater of Nyos (Cameroon)
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12
Q

Define lahars + example

A
  • 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
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13
Q

Define flooding (in reference to volcanoes) + example

A
  • when an eruption melts glaciers and ice caps
  • happened in 1996 in Iceland when Grimsvotn erupted
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14
Q

Define tsunamis

A
  • sea waves generated by violent eruptions
  • after the eruption of Krakatoa (Indonesia), 1883 it killed an estimated 36,000 people
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15
Q

Define acid rain

A
  • volcanoes emit gases including sulfur
  • when sulfur combines with rain, acid rain occurs
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16
Q

How is climate change a secondary effect of volcanic eruptions

A

The ejection of ash and debris into the atmosphere can cool temperatures

17
Q

How can you predict volcanic activity

A
  • 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
18
Q

What happened for the Colombian eruption of Nevada del Ruiz in 1985 which shows the difficulty of prediction

A

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

19
Q

How can you protect against volcanic activity (4)

A
  • monitoring the volcano (New Zealand 5-stage alert)
  • strengthening buildings against ash
  • planning and education
  • foreign aid in lower income countries
20
Q

Social primary impacts of Mount Pinatubo eruption (2)

A
  • 850 people died
  • 60,000 people evacuated (saved a lot of people)
21
Q

Social secondary impacts of Mount Pinatubo eruption (econ, social)

A
  • 650,000 lost their jobs
  • 1.2 million lost their homes and had to relocate in Manilla shanty towns
22
Q

Environmental primary impacts of Mount Pinatubo eruption

A
  • volcanic ash spread thousands of kms
  • lahars caused erosion
23
Q

Environmental secondary impacts of Pinatubo

A

Cooled global temperatures by 0.6 degrees

24
Q

Economic primary impacts of Pinatubo

A
  • bridges destroyed
  • airport closed
25
Q

Economic secondary impacts of Pinatubo

A
  • 650,000 lost their jobs
  • farmland covered in ash and unusable for years
  • $700mn in damage
26
Q

Short term responses to Pinatubo (social x2)

A
  • 200,000 people relocated
  • charities provided food and blankets in camps
27
Q

Long term response to Pinatubo (econ, social)

A
  • President Ramos created theMount Pinatubo Commission which raised almost $200 million
  • new houses built on stilts to avoid being destroyed by lahars
28
Q

When did Mount Pinatubo erupt

A

1991

29
Q

When did Mount St. Helen’s (MSH) erupt

A

1980

30
Q

Social impacts of MSH (3)

A
  • almost all buildings and vegetation destroyed in a 30km radius
  • 57 people killed
  • 2000 people evacuated
31
Q

Economic impact of MSH

A
  • $1.1bn in damages
  • airports were temporarily closed
  • timber industry affected by the deforestation
  • ships were stranded due to sediment deposits
32
Q

Environmental impact of MSH

A
  • over 200 square kms of forest destroyed
  • 12 million salmon
33
Q

Responses to MSH

A
  • over 18 million trees replanted
  • declared as a national monument in 1982 for research and tourism

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