Earthquake and Volcanic Hazards and Impacts

This section outlines the primary hazards associated with earthquakes and volcanic activity, along with their impacts. It is designed for A-Level Geography students studying the 9696 syllabus.

Earthquake Hazards

Ground-Shaking

Ground-shaking is the most direct and widespread hazard associated with earthquakes. It occurs when seismic waves travel through the Earth's crust, causing the ground to move. The intensity of ground-shaking is measured using the Modified Mercalli Intensity Scale.

• Intensity varies depending on the earthquake's magnitude, distance from the epicenter, and local geological conditions.
• Strong shaking can cause buildings to collapse, infrastructure damage (roads, bridges, pipelines), and significant casualties.
• Frequency of shaking and duration are key factors in the severity of damage.

Liquefaction

Liquefaction is a phenomenon where saturated, unconsolidated soils lose their strength and behave like a liquid during an earthquake. This can lead to catastrophic ground failure.

1. Occurs in areas with loose, water-saturated sediments (e.g., river deltas, coastal plains).
2. Ground shaking causes the soil particles to become displaced and lose contact, reducing friction.
3. Consequences include building settlement, tilting, and sinking; roads cracking; and infrastructure damage.

Landslides

Earthquakes can trigger landslides, especially in mountainous regions or areas with steep slopes.

• Weakened slopes due to ground shaking can become unstable.
• Saturated soils from rainfall or previous earthquake activity increase the risk.
• Types of landslides include rockfalls, debris flows, and mudslides.
• Can block roads, damage buildings, and cause loss of life.

Tsunami

Large undersea earthquakes, particularly those occurring at subduction zones, can generate tsunamis – powerful ocean waves with devastating coastal impacts.

1. Generated by vertical displacement of the seafloor.
2. Long wavelengths and low amplitude in the open ocean make them difficult to detect.
3. As they approach shallow coastal waters, their height increases dramatically.
4. Causes widespread flooding, destruction of coastal communities, and significant loss of life.
5. Warning systems are crucial for mitigating tsunami impacts.

Aftshocks

Aftshocks are smaller earthquakes that occur after the mainshock. They can be unpredictable and can cause further damage to already weakened structures.

• Can be of varying magnitudes and occur over days, weeks, or even months.
• Increase the risk of collapse of damaged buildings.
• Can disrupt rescue and recovery efforts.

Volcanic Hazards

Lava Flows

Lava flows are streams of molten rock that can travel at considerable speeds, destroying everything in their path.

• Slow-moving lava flows can be overtaken by people and vehicles.
• Fast-moving flows are extremely dangerous and can cause complete destruction.
• Composition of lava affects its flow rate and destructive power.

Pyroclastic Flows

Pyroclastic flows are fast-moving currents of hot gas and volcanic debris (ash, pumice, rock fragments).

1. Extremely dangerous and can travel at speeds exceeding 100 km/h.
2. Often occur during explosive volcanic eruptions.
3. Cause widespread destruction through impact and heat.
4. Ashfall associated with pyroclastic flows can collapse roofs and contaminate water supplies.

Ashfall

Volcanic ash is fine particles of volcanic rock and glass that can be carried by the wind over long distances.

• Can disrupt air travel and cause respiratory problems.
• Can collapse roofs due to its weight.
• Can contaminate water supplies and damage crops.
• Can cause infrastructure damage by clogging drainage systems.

Lahars

Lahars are mudflows composed of volcanic ash, rock, and water.

1. Can be triggered by rainfall, melting snow and ice, or crater lake breaches.
2. Travel at high speeds and can bury entire communities.
3. Can occur far from the volcano, following river valleys.

Volcanic Gases

Volcanoes release various gases, including sulfur dioxide (SO2), carbon dioxide (CO2), and hydrogen sulfide (H2S).

• SO2 can cause respiratory problems and acid rain.
• CO2 can accumulate in low-lying areas and displace oxygen, leading to suffocation.
• H2S is toxic and can be fatal in high concentrations.

Volcanic Explosions

Violent eruptions can release large volumes of ash, gas, and rock high into the atmosphere.

• Can cause widespread disruption to air travel and climate.
• Can trigger other hazards such as pyroclastic flows and lahars.

Comparison Table

Hazard	Earthquake	Volcano
Ground-Shaking	Primary	Not Applicable
Liquefaction	Secondary	Not Applicable
Landslides	Secondary	Not Applicable
Tsunami	Secondary	Not Applicable
Aftshocks	Secondary	Not Applicable
Lava Flows	Not Applicable	Primary
Pyroclastic Flows	Not Applicable	Primary
Ashfall	Not Applicable	Primary
Lahars	Not Applicable	Primary
Volcanic Gases	Not Applicable	Primary
Volcanic Explosions	Not Applicable	Primary