Describe the social, economic and environmental impacts of earthquakes and volcanic eruptions, and distinguish primary from secondary effects

What this dot point is asking

This outcome asks you to describe the impacts of earthquakes and volcanic eruptions on people, the economy and the environment, and to tell apart the immediate (primary) effects from the knock-on (secondary) effects. The central idea is that a tectonic event causes harm in stages: the shaking or eruption does direct damage first, and that damage then triggers further problems that can be just as serious.

The answer

Primary and secondary effects

Impacts are often split into two stages:

• Primary effects happen immediately and directly because of the event itself, such as buildings collapsing from shaking, or land buried by lava and ash.
• Secondary effects happen afterwards as a result of the primary effects, such as fires from broken gas pipes, disease from damaged water supplies, a tsunami triggered by an undersea earthquake, or food shortages.

Telling these apart clearly is a common exam requirement.

Social impacts

These affect people directly:

• Deaths and injuries from collapsing buildings, falling debris, ash, gas or fast-moving hot flows.
• Homelessness, as homes are destroyed and people must evacuate.
• Disruption to daily life, including loss of schooling, fear and stress, and difficulty getting clean water, food and medical care.

Economic impacts

These affect money, jobs and infrastructure:

• High rebuilding costs for homes, roads, bridges and services.
• Lost income and jobs as businesses, farms and factories are damaged or forced to close.
• Damage to infrastructure such as power, water and transport, which slows recovery and the wider economy.

Environmental impacts

These affect the natural surroundings:

• Damage to land and ecosystems, as lava and ash bury crops and habitats and pollute air and water.
• Landslides and ground cracking that reshape the land.
• A long-term benefit in volcanic areas: ash eventually breaks down into very fertile soil, which is one reason people return.

Examples in context

Example 1. The 2004 Indian Ocean tsunami. The undersea earthquake off Sumatra caused primary shaking damage, but its deadliest impact was the secondary tsunami that flooded coasts across the region, killing very large numbers and destroying homes and livelihoods. It shows how secondary effects can far outweigh the primary ones, especially for a coastal, undersea earthquake.

Example 2. Eruptions and farming in Indonesia. When volcanoes such as those on Java erupt, the primary effects include ash burying crops and forcing evacuations, with serious social and economic harm. Yet over the long term the ash weathers into fertile soil, which is why dense farming communities live on volcanic slopes despite the danger, linking impacts to why people stay.

Try this

Q1. State whether a fire caused by a broken gas pipe after an earthquake is a primary or secondary effect, and explain why. [2 marks]

• Cue. Secondary, because it is caused by the earthquake damage (the broken pipe), not directly by the shaking itself.

Q2. Describe two social impacts of a major earthquake. [2 marks]

• Cue. Deaths and injuries from collapsing buildings; homelessness as homes are destroyed and people must evacuate (also loss of schooling, fear and stress).

Q3. Explain one long-term environmental benefit of a volcanic eruption. [2 marks]

• Cue. Volcanic ash breaks down over time into very fertile soil, which improves farming on the slopes around the volcano.