2.4.2 Volcanic hazards Flashcards
Hazards associated with volcanic eruptions
- tephra
- volcanic gases
- lava flows
- pyroclastic flows
- lahars
- volcanic landslides
(1) tephra
- 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
(1) impacts of tephra on ecosystems
- 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.
(1) Impacts of tephra on human systems
- 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.
(1) Examples of tephra
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.
(2) Volcanic gases
- Volcanic eruptions can release large amounts of toxic gases such as sulfur dioxide and carbon dioxide
(2) Impacts of volcanic gases on ecosystems
- 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.
(2) Impacts of volcanic gases on human systems
- 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.
(2) Example of volcanic gases
Dieng volcano eruption in Indonesia in 1979:
-Released deadly amounts of carbon dioxide and killed about 150 people.
(3) Lava Flows
- 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.
(3) Impacts of lava flow on ecosystems
- Hot, low-silica lava can travel over some distances, destroying forests, other habitats and ecosystems in them.
(3) Impacts of lava flow on human systems
- 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.
(3) Examples of lava flow
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.
(4) Pyroclastic flows
- 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.
(4) impacts of pyroclastic flows on ecosystems
- 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.
(4) Impacts of pyroclastic flow on human systems
- 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.
(4) Examples of pyroclastic flows
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.
(5) Lahars
- Lahars are mudflows comprising water and volcanic ash.
- Formed when huge amounts of ash and rocks ejected during an eruption mix with water.
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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.
(5) Impacts of lahars on ecosystems
- Lahars can cover forests and other ecosystems with thick mud which hardens like concrete, destroying them.
- Lahars can pollute rivers, killing aquatic life.
(5) Impacts of lahars on human systems
- 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.
(5) Examples of lahars
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.
(6) Volcanic landslides
- 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.
(6) Impacts of volcanic landslides on ecosystems
- 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.
(6) Impacts of volcanic landslides on human systems
- 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.
(6) Examples of volcanic landslides
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.
Benefits of volcanic eruptions and living near volcanoes
- Farming with fertile soil.
- Extracting precious minerals and fossil fuels.
- Harnessing geothermal energy.
- Tourism activities.
Farming with fertile soil
- 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.
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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.
Extracting precious minerals and fossil fuels
- 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.
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Example: - Thousands of locals living on Mount Merapi are employed to mine volcanic sand as it is suitable for constructing buildings.
Harnessing geothermal energy
- 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.
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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.
Tourism activities
- 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.
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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.
