Hazard risk and vulnerability practice questions.

Tens of thousands of farmers work the flanks of Merapi in Java, Indonesia, inside mapped hazard zones, and return after each eruption. Which factor best explains why they remain?

• Geothermal power stations on the flanks provide most local employment
• The government pays each household a subsidy to stay in the hazard zone
• The volcano is dormant, so the mapped hazard zones are precautionary
• Weathered volcanic ash gives fertile soils for intensive farming

Answer: Weathered volcanic ash gives fertile soils for intensive farming

Andosols weathered from tephra hold nutrients and moisture, so yields are high enough to outweigh a risk that materialises only every few years; a perceived benefit, not ignorance, keeps people in place.

The Mw 8.8 Chile earthquake of February 2010 killed about 525 people, while the Mw 7.0 Haiti earthquake of January 2010 killed well over 100 000. Which factor best explains the contrast in death tolls?

• Chile enforces a seismic building code, while most housing in Port-au-Prince was unreinforced
• Haiti lies on a subduction margin, whereas Chile lies on a conservative transform margin
• The Haitian earthquake released roughly 500 times more energy at the surface
• Shaking in Chile lasted only a few seconds because its focus was extremely shallow

Answer: Chile enforces a seismic building code, while most housing in Port-au-Prince was unreinforced

Vulnerability rather than magnitude decided the outcome: Chile's enforced seismic code kept most structures standing, whereas heavy unreinforced masonry in a densely built capital collapsed onto its occupants.

Four settlements each experience an earthquake of Mw 6.5. In which case is the death toll likely to be greatest?

• A city with an enforced building code, focus 12 km deep, event at 14:00
• A city of unreinforced brick housing, focus 12 km deep, event at 03:00
• A city with an enforced building code, focus 280 km deep, event at 03:00
• A farming district with 40 people km-2, focus 12 km deep, event at 14:00

Answer: A city of unreinforced brick housing, focus 12 km deep, event at 03:00

Losses peak where a shallow focus meets weak buildings and a night-time event that keeps people asleep indoors; a deep focus weakens the shaking at the surface, while enforced codes and low population density reduce how many people are caught in collapsing buildings.

Two earthquakes of similar magnitude strike a high-income and a low-income country. Deaths are far higher in the low-income country. Which explanation is most consistent with the risk equation?

• Higher vulnerability and lower capacity to cope, not a larger hazard
• A larger hazard, because seismic waves travel further in poorer countries
• Greater population density, which is always higher in low-income countries
• Lower building quality alone, independent of any other factor

Answer: Higher vulnerability and lower capacity to cope, not a larger hazard

Risk combines the hazard with vulnerability and divides by capacity, so an identical hazard produces very different outcomes. Building standards matter, but so do enforcement, emergency services, health care and income to rebuild - which is why the answer is not building quality alone.

Despite repeated eruptions, the flanks of Mount Merapi in Indonesia remain densely farmed and settled. Which factor best explains why people stay?

• Fertile volcanic soils and established livelihoods outweigh an intermittent risk
• The population is unaware that the volcano has ever erupted
• The government legally prohibits residents from moving elsewhere
• Eruptions there have never caused any casualties or damage

Answer: Fertile volcanic soils and established livelihoods outweigh an intermittent risk

Hazardous places are often also productive places, and the benefits are certain and daily while the hazard is uncertain and occasional. Explanations built on ignorance rarely survive contact with the residents, who usually know the hazard better than the planners do.

In the Park model of the disaster response curve, which stage immediately follows the drop in quality of life caused by the event?

• Relief, dominated by search, rescue and emergency aid
• Reconstruction, in which infrastructure is rebuilt to a new standard
• Rehabilitation, in which services are restored to their former level
• Mitigation, in which future losses are designed out

Answer: Relief, dominated by search, rescue and emergency aid

The curve runs relief, rehabilitation, reconstruction, and the model's value is that it shows recovery can end above, at, or below the pre-event level. The shape of the curve, not the stages themselves, is what distinguishes cases.