Volcanic hazards.

Question 1

The nature of vulcanicity and its relation to tectonic plates:

Answer 1

• Most active volcanoes occur near plate boundaries.
• Approximately 75% occur around the ring of fire, surrounding the pacific ocean
  -Vulcanicity is focused on constructive and destructive plate margins.

Question 2

Constructive margins (plates diverging):

Answer 2

• Small eruptions
• Basaltic lava is formed here and is very hot and low viscosity (runny).
• If the margin is underwater ocean ridges form
• If margin is on land rift valleys are formed.
• Basaltic magma allows the gas to escape easily, preventing the build up of pressure which is why eruptions are smaller.

Question 3

Destructive plate margins (converging):

Answer 3

• Bigger eruptions but less frequent.
• Andesitic and rhylotic lava is formed here, cooler but more viscous.
• At subduction zones because the lava is viscous it forms blockages in volcanic vents causing pressure to build, greater eruption.

Question 4

Quick fact:

Answer 4

A few volcanoes form away from hotspots above magma plumes, forming shield volcanoes.
- Divergent plate boundaries

Question 5

What is a nuée ardentes (pyroclastic flow): (4 marks)

Primary hazard

Answer 5

Mixture of superheated gas, ash and volcanic rocks which flows down the side of a volcano.
- High speeds of 80-700 km/h, can usually travel around 10-15km.
- Cause widespread destruction as they give little time for warning.
e.g Fuego volcano in Guatemala (2018), pyroclastic flows destroyed several nearby towns.

Question 6

What is a lava flow (4 marks)

Primary hazard

Answer 6

Can flow from a volcano vent at the side of a volcano.
Speed and distance travelled depends on the temperature and viscosity of the lava and the gradient of the slope.
- Travels 10’s of Km
- Roughly 10Km/h speed.

Question 7

Volcanic gases (4 marks)

Primary hazard.

Answer 7

• Lava contains carbon dioxide and sulphur dioxide which are released into the atmosphere when the volcano erupts.
• Sulphur dioxide is hazardous to human and animal health e.g Kilauea in Hawaii released large volumes of sulphur dioxide which led to air quality alerts and health warnings for residents.

Question 8

Pyroclastic and ash fallout (4 marks)

Primary Hazard.

Answer 8

pyroclastic fallout is material ejected during an eruption and falls back to the ground.
When fallout mainly consists of ash this is called ash fallout.
Ash and material can travel many Km by being carried by the wind, this can cause threat to death, damage and respiratory problems.
e.g E15, 2010

Question 9

Tephra (4 marks)

Primary hazard

Answer 9

• Solid material of varying size ejected by the volcano.
• Travel tens of Km
• Damage buildings and kill people.

e.g 108 people died in villages from collapsing roofs due to tephra from the Tarawera volcano 1886.

Question 10

What are mudflows (lahars:
(4 marks)

Secondary hazard.

Answer 10

Form when volcanic material mixes with rainfall or melted snow.
- Flow over 80km/h
- Travel around 100km
- Flow down a valley side and feed into a river channel
- Destroy anything in their path.

Question 11

Acid rain (4 marks)

Secondary Hazard

Answer 11

Sulphur dioxide emitted from a volcano reacts with water vapour in the atmosphere to create sulphuric acid.

Damages ecosystems and crops, can increase soil acidity.

Typically with a PH below 5.6

Mitigate - promote renewable energy sources.

Question 12

Spatial distribution of volcanic hazards:

Answer 12

• Common at constructive and destructive plate margins but absent at conservative plate margins.
• 40,000km Pacific ring of fire has high densities of volcanoes.

Hotspots, occur over magma plumes e.g Hawaii islands.

Question 13

Magnitude of volcanic hazards:

Answer 13

Vulcanicity is measured using the Volcanic Explosivity Index(VEI). The more
powerful, the more explosive. The scale (0-8) is logarithmic from VEI 2 and onwards.
Multiple features are considered when calculating the VEI, including how much
tephra is erupted, how long it lasts, how high the tephra is ejected etc.
Intense high magnitude eruptions are explosive whereas calmer, lower
magnitude eruptions are effusive.

Question 14

Frequency of volcanoes:

Answer 14

• Impossible to measure frequency.
• Less frequent eruptions are more damaging and larger in magnitude.
• Estimated 50-60 volcanoes erupt every month worldwide
• Higher frequency = effusive.

Question 15

Regularity of volcanoes:

Answer 15

• Some volcanoes erupt at regular intervals, whereas others are domant for hundreds of thousands of years e.g Mount St Helens.
• Volcanic eruptions are regular in that the eruptions on each type of boundary
  are similar (e.g. eruptions on destructive boundaries will regularly be explosive)

Question 16

Predictability of volcanic events:

Answer 16

• Volcanic eruptions tend to follow weeks of seismic activity.
• Regularity of eruptions can help scientists predict future eruptions.
  e.g IMO, reduce impacts.
  Gases released.

Question 17

Primary impacts of volcanic events:

Answer 17

Environmental - Ecosystems can be damaged by flows or fallout of volcanic material. Volcanic gases enhance the
Clouds of ash block sunlight in warm areas

Economic - Business and industries destroyed/disrupted. e.g E15.
Infrastructure repair can be costly.
Eruptions, boost tourism.
Social - People killed.
Buildings damaged by flows and fallout.

Political - Spend on repairing infrastructure, and education, the country may not develop as quickly.

Question 18

Secondary impacts of volcanic hazards:

Answer 18

Environmental - - Water acidified by acid rain, can harm water systems and wildlife. Volcanic gases contribute to greenhouse effect (global warming.)

Economic - Jobs lost. Profit from increased tourism

Social - Fires can start which puts lives at risk, mudflows or floods and homelessness.

Political - Government response regarding food shortages and insurance.

Question 19

Short term and Long term responses to volcanic hazards:

Answer 19

Prevention - Volcanic eruptions cannot be prevented. Only the risk to people can be prevented e.g preventing the land area the volcano from being developed on.

Preparedness (monitoring before an eruption to prevent vulnerability or minimise risk e.g sending out warnings). Evacuation plans, education and search and rescue teams.

Mitigation (direct intervention to the volcano). Steer lava away from areas which are at risk.

Adaptation - being able to live with the challenges. e.g reinforcing buildings are benf=efiting from fertile soil from volcanic ash for farming industry.