A physical event is what the Earth does: shaking, an eruption, a tsunami. Exposure is how many people, buildings and services are in the way. The same event can have a small or large human impact depending on exposure and vulnerability.
This lesson follows linking a process to a landform and prepares you to compare impacts from case evidence.
How do you separate the two ideas?
- Describe the physical event with measurable facts: type, size, depth, location, duration.
- Describe exposure: population, building density and key services inside the affected area.
- Describe vulnerability: building strength, warning time, access to help, income and preparation.
- Link them: the event sets the hazard, and exposure and vulnerability set the impact.
- Use rates when comparing places of different sizes.
Worked example
All data are invented for practice. Two towns each feel an earthquake of the same size.
| Town A | Town B | |
|---|---|---|
| People within 30 km | 20,000 | 2,000 |
| People injured | 40 | 10 |
Step 1, exposure: Town A has 20,000 ÷ 2,000 = 10 times as many people in range.
Step 2, totals: Town A has more injuries, 40 against 10.
Step 3, rate per 1,000: Town A: 40 ÷ 20,000 × 1,000 = 2 per 1,000. Town B: 10 ÷ 2,000 × 1,000 = 5 per 1,000.
Step 4, interpret: Town A has more injuries because more people were exposed. Town B has the higher injury rate. The data do not say why, but a possible reason to test is that its buildings or warning time differ.
Answer: “The physical event was the same, so the difference comes from exposure and vulnerability. Town A’s total is higher because more people were exposed. Town B’s rate is higher, which suggests greater vulnerability, though more evidence is needed.”
The mistake to watch for
A common slip is to explain a bigger impact by the size of the event alone.
Mistaken answer: “Town A had more injuries because the earthquake was stronger there.”
The question says both towns felt the same size. The student ignored exposure.
The correction is to check the data first. If the event is equal, the explanation must come from people, buildings or preparation. Then say which part of the data supports the claim.
Check yourself
1. A coastal village has 500 residents and a city nearby has 50,000. Both are in an eruption’s ash zone. How many times greater is the city’s exposure?
Show answer
50,000 ÷ 500 = 100 times greater.
2. In a different invented case, 30 people were harmed out of 15,000 exposed. What is the rate per 1,000?
Show answer
30 ÷ 15,000 × 1,000 = 2 per 1,000. Check: 2 × 15 = 30.
3. Give one factor that adds to vulnerability and one that adds to exposure.
Show answer
Vulnerability: weak buildings or little warning time. Exposure: a dense population or a hospital located in the hazard zone. Either answer must be linked to harm.
Where this leads next
Carry the idea into comparing impacts from supplied case evidence. The statistics and distribution explorer lets you practise rates with your own numbers.
A teacher who sees your first draft can show when exposure is being confused with the event. That is a practical use of online one-to-one Geography tuition.