2.4.2 Volcanic hazards

Question 1

Hazards associated with volcanic eruptions

Answer 1

1. tephra
2. volcanic gases
3. lava flows
4. pyroclastic flows
5. lahars
6. volcanic landslides

Question 2

(1) tephra

Answer 2

• any type/ size of rock fragment that is forcibly ejected from the volcano and travels an airborne path during an eruption
• forms ash and volcanic bombs

Question 3

(1) impacts of tephra on ecosystems

Answer 3

• Ash can be carried thousands of kilometres by prevailing winds, polluting huge areas of forests, rivers and other habitats, and destroying ecosystems.
• Ash can suffocate and kill wildlife.
• Ash can cause blindness to birds, with their eyelids getting gummed together.

Question 4

(1) Impacts of tephra on human systems

Answer 4

• Volcanic bombs, ranging from a few cm to the size of vehicles, can hit properties, damaging them.
• Ashfall can accumulate on roofs of buildings.
• When saturated with water, the weight of ash can double, causing building roofs to collapse.
• Ash is corrosive hence it weakens building structures, making them more likely to collapse
• Thick blankets of ash can damage farmland, suffocating crops and destroying livelihoods.
• Ash particles can damage plane engines, leading to closure of airspaces, and disrupting air transportation services.
• Volcanic bombs can hit people, causing injuries and loss of lives.
• Ashfall can cause respiratory problems, like asthma, eye irritation and suffocate people.

Question 5

(1) Examples of tephra

Answer 5

1991 Mount Pinatubo eruption in the Philippines:
- Emitted huge amounts of ash.
- Buried more than 180km of forests in ash of about 25cm.
- Destroyed 800km² of rice fields, affecting the livelihoods of many farmers.
- 7 airports in the Philippines had to be closed and many flights were cancelled, disrupting transport.
- Some planes were also damaged.

Question 6

(2) Volcanic gases

Answer 6

• Volcanic eruptions can release large amounts of toxic gases such as sulfur dioxide and carbon dioxide

Question 7

(2) Impacts of volcanic gases on ecosystems

Answer 7

• Sulfur dioxide results in acid rain when it reacts with water in the air, which can damage vegetation, soil and kill wildlife.
• Cold carbon dioxide is heavier than air, so it can become concentrated in low-lying volcanic areas such as river valleys.
• Large amounts of carbon dioxide in the air can kill wildlife, and in the soil, can destroy vegetation.

Question 8

(2) Impacts of volcanic gases on human systems

Answer 8

• Sulfur dioxide results in acid rain, which can corrode buildings and infrastructure.
• Sulfur dioxide irritates skin, eyes, nose and throat.
• Air containing over 3% carbon dioxide can cause headaches and breathing difficulties, and when it exceeds 15%, may cause death.

Question 9

(2) Example of volcanic gases

Answer 9

Dieng volcano eruption in Indonesia in 1979:
-Released deadly amounts of carbon dioxide and killed about 150 people.

Question 10

(3) Lava Flows

Answer 10

• Lava flows are extremely hot and can travel over some distances within the geographic region of the volcano.
• However, deaths caused directly by lava flows are uncommon as people can easily move out of their way.

Question 11

(3) Impacts of lava flow on ecosystems

Answer 11

• Hot, low-silica lava can travel over some distances, destroying forests, other habitats and ecosystems in them.

Question 12

(3) Impacts of lava flow on human systems

Answer 12

• Lava can burn through homes, properties and infrastructure
• Lava can destroy electricity and communication cables, and water and gas pipes, disrupting supply of these services.

Question 13

(3) Examples of lava flow

Answer 13

2018 Kilauea eruption in Hawaii:
- Far-reaching lava flows destroyed more than 600 homes.
- Destroyed huge areas of forests and ecosystems.
- Telephone and power lines were damaged, causing widespread communication outages.

Question 14

(4) Pyroclastic flows

Answer 14

• pyroclastic flow is a hot cloud of gas, ash and rocks travelling down the stopes of a volcano at great speeds (more than 200km/hour)
• pyroclastic flows occur when a column of hot ash and gas gets thrown up into the air, and falls back to the ground under the pull of gravity.
• with temperatures of up to 700°C, it is perhaps the most devastating of all volcanic hazards.
• Typically travels several kilometres.

Question 15

(4) impacts of pyroclastic flows on ecosystems

Answer 15

• Huge areas of forests may be destroyed, resulting in biodiversity loss.
• Thick layers of ash cover the path of the flows, polluting huge areas of forests.

Question 16

(4) Impacts of pyroclastic flow on human systems

Answer 16

• The hot flows can burn through all homes, properties and infrastructure in their path.
• The hot flows can destroy electricity and communication cables, and gas pipes, disrupting supply of these services.
• The extreme temperatures can burn, and kill people in a fraction of a second.

Question 17

(4) Examples of pyroclastic flows

Answer 17

2010 Merapi eruption in Indonesia:
- Blasted a series of pyroclastic flows down the slopes of the volcano, which were inhabited by many villagers.
- About 350 people were killed, mostly due to burns and blast injuries.
- Huge areas of forest were burnt.

Question 18

(5) Lahars

Answer 18

• Lahars are mudflows comprising water and volcanic ash.
• Formed when huge amounts of ash and rocks ejected during an eruption mix with water.
  ———
  Can occur when:
• Pyroclastic flows melt snow and ice, and mix with the water on the volcanic cone as they travel down.
  Intense rainfall washes down the ash.
• Lahars are capable of flowing at high speeds (up to 200km/h), and over considerable distances within the geographic region of the volcano.

Question 19

(5) Impacts of lahars on ecosystems

Answer 19

• Lahars can cover forests and other ecosystems with thick mud which hardens like concrete, destroying them.
• Lahars can pollute rivers, killing aquatic life.

Question 20

(5) Impacts of lahars on human systems

Answer 20

• Lahars can bury houses and buildings, destroying them.
• Lahars can cover farms with thick mud, which hardens like concrete, damaging them.
• Roads and railways can be blocked by debris, making it difficult to rescue people or supply emergency aid.
• Lahars can damage communication cables, and water and gas pipes, disrupting supply of these services.
• Lahars can bury houses and its residents, resulting in loss of lives.

Question 21

(5) Examples of lahars

Answer 21

1985 Nevado Del Ruiz eruption in Colombia:
- Released huge amounts of ash and volcanic rocks which melted snow and ice.
- The meltwater mixed with ash and rocks to form lahars.
- Fast-moving lahars buried more than 20,000 people in the nearby town of Armero within seconds.
- Rivers were highly muddied by the lahars, killing many fish.

Question 22

(6) Volcanic landslides

Answer 22

• Volcanic landslides are common on tall and steep volcanic cones which comprise thousands of solidified lava layers and loose tephra.
• The blast from an explosive eruption can trigger the downward movement of loose volcanic material, causing a landslide.
• The high velocity and great momentum of landslides allow them to travel considerable distances within the geographic region of the volcano.

Question 23

(6) Impacts of volcanic landslides on ecosystems

Answer 23

• Fast-moving debris can bury huge areas of forest and wetlands.
• Debris from landslides pollutes rivers, killing aquatic life.
• Debris blocks rivers, causing floods that can damage nearby ecosystems and properties.

Question 24

(6) Impacts of volcanic landslides on human systems

Answer 24

• Debris buries villages and farms, destroying properties and infrastructure.
• Debris can snap electricity and communication cables, and water and gas pipes, disrupting supply of these services.
• Debris blocks roads and railways, making it difficult to rescue people or supply emergency aid.
• Debris can bury people or hit them, causing injuries and loss of lives.
• Debris blocks rivers, resulting in floods, which can drown people.

Question 25

(6) Examples of volcanic landslides

Answer 25

1980 Mt St Helens eruption in USA:
- North face of the volcanic cone collapsed.
- Caused volcanic landslides that traveled as far as 23km from the volcano.
- Destroyed huge areas of land and killed many wildlife.

Question 26

Benefits of volcanic eruptions and living near volcanoes

Answer 26

1. Farming with fertile soil.
2. Extracting precious minerals and fossil fuels.
3. Harnessing geothermal energy.
4. Tourism activities.

Question 27

Farming with fertile soil

Answer 27

• Over thousands of years, volcanic rocks break down and undergo weathering to form fertile soils.
• They are suitable for agriculture as they can produce higher crop yields.
• Locals benefit from growing a variety of crops or earning more from higher crop yields.
  —————
  Example:
• The best rice-growing regions in Indonesia are near volcanoes, such as in Bali, which has several volcanoes such as Mount Agung.
• Despite their continuous use, soils in Bali are more fertile than most non-volcanic areas of Indonesia.

Question 28

Extracting precious minerals and fossil fuels

Answer 28

• Some magma may cool and solidify beneath volcanoes, forming precious minerals such as copper, silver and gold.
• Locals living near volcanoes can be employed to mine these minerals, which provides them with a source of income.
• Governments may sell these precious minerals to generate revenue, which can in turn be used to provide social services to locals such as education and healthcare.
• Volcanic materials, such as ash and sand, may also be mined and used as construction materials.
  —————
  Example:
• Thousands of locals living on Mount Merapi are employed to mine volcanic sand as it is suitable for constructing buildings.

Question 29

Harnessing geothermal energy

Answer 29

• Geothermal energy is derived from heat in the Earth’s crust.
• It can be harnessed in tectonically active areas.
• Beneath Earth’s surface, hot rocks heat up groundwater.
• Steam that is formed is harnessed to generate electricity.
• Locals benefit from cheaper electricity produced locally.
• Locals can also be employed to work in the geothermal power plants.
  —————
  Examples:
• Most of Iceland’s electricity is generated from geothermal power because of the large number of volcanoes in the country.
• In Northern California, the Geysers geothermal field produces enough electricity to meet the power demands of San Francisco.

Question 30

Tourism activities

Answer 30

• Tectonic environments can be attractive to tourists.
• Different volcanic features like the crater appeal to tourists.
• Tourists can engage in various activities, such as hiking and sightseeing.
• Tourism provides locals with employment opportunities, such as tour guides, providing tourist accommodation and selling food and souvenirs.
• Tourism thus boosts local economic development.
  —————
  Example:
• The Hawaiian islands are popular tourist locations for its scenic volcanic landscapes.
• Tourism generates an annual income of about US$88 million and provides locals with thousands of jobs.