Hazards
Senior 1 · Geography
Hazards
Lesson 1 of 4
22 min
Figure 1 marks four events that struck Rwanda or its borders in the last twenty years. Study it before you read on. Which part of the country appears most often? Which event came out of the ground, which from the sky, and which from a living thing?
Figure 1. Some recent disasters in and around Rwanda. Outlines from Natural Earth; lakes from OpenStreetMap. Markers for the 2023 floods show the worst-hit districts, not exact sites.
Three of the four events began in nature, but none of them would have been a disaster if nobody had lived nearby. A volcano erupting on an empty island harms no one; the same eruption beside a city of two million people is a crisis. Geographers therefore separate the event (the hazard) from its result (the disaster).
Definition
Hazard: an event or situation that could cause loss of life, injury or damage to property and the environment. It is a threat, not yet the damage. Example: very heavy rain falling on steep, soaked slopes in the Western Province.
Definition
Disaster: a hazard that actually strikes a community and causes deaths, injuries and damage so great that the people affected cannot cope using only their own resources. Example: the floods and landslides of 2–3 May 2023, which killed at least 135 people in Rwanda and destroyed thousands of homes.
Definition
Catastrophe: a disaster of extreme size: sudden and overwhelming, causing very great loss of life and destruction over a wide area, beyond what a whole country or region can manage alone. Example: the Indian Ocean earthquake and tsunami of 26 December 2004, which killed about 228,000 people in 14 countries.
Definition
Vulnerability: how easily people, buildings and livelihoods are harmed by a hazard. It is raised by poverty, weak buildings, crowded or unsafe sites and lack of warning, and lowered by preparation. Example: a mud-brick house at the foot of a bare, steep slope is highly vulnerable to landslides.
Figure 2. A disaster happens only where a hazard meets vulnerable people. Drawn by Ganzaa.
Figure 2 gives a rule that disaster planners all over the world use. To make a disaster less likely, you can rarely stop the hazard (nobody can stop the rain or a volcano), but you can nearly always reduce the vulnerability and build capacity: warnings, safer houses and sites, terraces and trees on slopes, and people who know what to do.
| Group | Origin | Examples |
|---|---|---|
| Natural: geological | Movements and heat inside the Earth, and gravity acting on slopes | Earthquakes, volcanic eruptions, landslides |
| Natural: weather and climate | Too much or too little rain, strong winds and storms | Floods, drought, strong winds, hailstorms, lightning |
| Natural: biological | Germs spreading among people, animals or crops | Epidemics such as cholera or Marburg virus disease; crop pests |
| Human-made | People's actions, mistakes or conflicts | Wars, famine, road and mining accidents, fires, pollution |
Many hazards are mixed: a landslide is triggered by rain but made worse by cutting trees; a famine usually follows a drought, but is made deadly by war, poverty or poor planning.
Worked example 1: classifying hazards
Classify each event: (a) the Nyiragongo eruption of 2021; (b) the Marburg outbreak of 2024; (c) a bus crash on a mountain road; (d) the floods of May 2023.
Step 1 Ask where the event comes from: inside the Earth, the weather, germs, or people.
Step 2 (a) Magma from inside the Earth: natural, geological. (b) A virus spreading between people: natural, biological. (c) A human error or a mechanical fault: human-made (accident). (d) Very heavy rain: natural, weather, made worse by bare, crowded slopes.
Check. For (d), notice that the answer has two parts: the trigger was natural, but the size of the disaster depended on human choices.
Worked example 2: one night in a bad year
From January to April 2023, Rwanda's Ministry of Emergency Management (MINEMA) recorded 60 deaths from weather-related disasters. On the single night of 2–3 May, at least 135 more people died. What percentage of the deaths in these five months happened on that one night?
Answer. About 69%, more than two thirds. Rain had soaked the ground for weeks, so when the heaviest rain came the slopes failed all at once. Most disaster deaths come from a few extreme events.
Important
Case study: why Rwanda's hazards cluster in the west
MINEMA names the hazards it plans for: volcanic activity, floods, earthquakes, landslides and mudslides, storms, fire and drought. Three of the four events in Figure 1 struck the west, and there are clear reasons.
The east faces a different hazard: it is lower and drier, so its main threat is drought.
Warning
A hazard is not a disaster. Heavy rain, an earthquake or an eruption is a hazard. It becomes a disaster only when it strikes vulnerable people. In an answer, never write "the hazard killed 135 people": the disaster did.
Understanding Disaster Risk, by the Global Facility for Disaster Reduction and Recovery (GFDRR) at the World Bank (2 min). Watch for the three things that combine to make risk, and match them to Figure 2.
Some geographers say: "There is no such thing as a natural disaster; there are only natural hazards." Using Figure 2 and the floods of May 2023, say whether you agree, and give one reason on each side.
Tip
H + V = D. Hazard plus vulnerability equals disaster. Remove either one, and there is no disaster. That is why prevention works on vulnerability.
Practice
Remember
Sources and credits
The lesson text, map, diagram, table, worked examples and practice are written by Ganzaa.
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
