Cambridge IGCSE Environmental Management (0680): Natural hazards – Study Guide

A natural hazard becomes a disaster when it meets vulnerable people. The same earthquake can cause modest damage in a country with strict building rules and great loss of life in a place without them, so this topic is as much about preparation and management as it is about physical processes. You need to explain why each hazard happens, what its primary and secondary effects are, and how people reduce the risk.

Where this fits in the course

In Cambridge IGCSE Environmental Management (0680) this topic has four sub-topics: earthquakes and volcanoes, tropical cyclones, flooding and drought. Each follows the same shape, which you can use as a revision template: cause, distribution, impacts, then monitoring, prediction, preparation and response.

Two terms are used throughout. Primary effects are the immediate result of the hazard itself, such as collapsed buildings. Secondary effects follow later, such as fires, disease, or loss of income.

Earthquakes and volcanoes

The Earth’s crust is split into tectonic plates that move slowly. Most earthquakes and volcanoes occur at plate boundaries.

• At destructive (convergent) boundaries, one plate is forced beneath another. This can produce powerful earthquakes and explosive volcanoes, often in chains such as those around the Pacific.
• At constructive (divergent) boundaries, plates move apart and magma rises, giving smaller earthquakes and generally gentler eruptions.
• At conservative boundaries, plates slide past each other; stress builds up and is released as earthquakes, with no volcanoes.

The point inside the Earth where an earthquake starts is the focus; the point on the surface directly above is the epicentre. Magnitude is measured with the Richter or moment magnitude scales. Intensity of shaking at a location is described by the Mercalli scale.

Effects

Primary effects: buildings and bridges collapse, people are killed or injured, and roads and pipes are broken. Volcanoes add lava flows, ash fall and pyroclastic flows. Secondary effects: fires from broken gas pipes, landslides, tsunamis after undersea quakes, contaminated water and disease, homelessness, and economic loss.

Management

Earthquakes cannot be reliably predicted, so measures concentrate on preparation: earthquake-resistant buildings, strict building codes, public drills, emergency supplies and land-use planning. Volcanoes can often be monitored with seismometers, gas sensors and ground-deformation measurements, which allows evacuation zones and warnings. Fertile volcanic soils and geothermal energy explain why some people choose to live near volcanoes, which is a useful point for balanced answers.

Tropical cyclones

Tropical cyclones, also called hurricanes or typhoons depending on the region, form over warm oceans, typically where sea-surface temperature is at least about 26.5 degrees Celsius, away from the equator itself so that the Earth’s rotation can make the system spin. Warm moist air rises, condenses and releases heat, which drives the storm. When the cyclone moves over land or colder water it loses its energy supply and weakens.

Effects

• Very strong winds damage buildings, trees and power lines.
• Torrential rain causes flooding and landslides.
• A storm surge, a rise in sea level driven by wind and low pressure, can flood coasts; this is often the cause of the greatest loss of life.
• Secondary effects include disease, loss of crops and disrupted supplies.

Management

Satellites and radar track storms, giving days of warning. Preparation includes evacuation plans, cyclone shelters, strengthened buildings, mangrove protection and coastal defences, and education so that people respond to warnings. Wealthier countries can invest in forecasting and sturdier infrastructure, while poorer countries often rely on community preparedness.

Flooding

Floods occur when a river exceeds its channel capacity. Causes include prolonged or intense rainfall, rapid snowmelt, saturated or impermeable ground, urbanisation that sends water quickly to rivers, deforestation, and coastal flooding from surges. Impacts include loss of life, damaged property, ruined crops and contaminated water, though floods also deposit fertile silt on floodplains.

Management falls into two groups:

Type	Examples	Points to make
Hard engineering	Dams, embankments, flood walls, channel straightening	Effective but costly and can move the problem downstream
Soft engineering	Floodplain zoning, afforestation, wetland restoration, warning systems	Cheaper and more sustainable but may take time or land

A hydrograph shows how river discharge changes after rainfall. The lag time is the delay between peak rainfall and peak discharge. Urban surfaces shorten lag time and increase the peak.

Drought

Drought is a long period of below-average rainfall that causes water shortage. Causes include persistent high-pressure systems, changes in ocean and atmospheric patterns, and climate change, while overuse of water and poor land management can make the effects worse. Impacts include crop failure and food shortages, loss of livestock, reduced water supply, wildfires, migration and conflict over resources.

Management options include water conservation, rainwater harvesting, drip irrigation, drought-resistant crops, storage reservoirs, treated wastewater reuse and early warning from rainfall monitoring. Many are low-cost and suited to communities with few resources.

Worked example 1: comparing magnitudes

On the Richter scale each whole number rise means the recorded ground motion is ten times larger, and the energy released increases by about 32 times. Compare an earthquake of magnitude 7.4 with one of magnitude 5.4.

1. Difference = 7.4 - 5.4 = 2 units.
2. Ground motion ratio = 10 x 10 = 100 times larger.
3. Energy ratio = 32 x 32 = about 1,000 times larger (the exact value is 31.6 squared, close to 1,000).

Worked example 2: lag time

Heavy rain peaks at 04:45 on a Monday. The river discharge peaks at 11:15 the same day. Lag time = 11:15 - 04:45 = 6 hours 30 minutes. After the catchment is built over with roads and roofs, the same storm gives a peak at 07:15, so the new lag time is 2 hours 30 minutes. The reduction is 4 hours, which leaves less time to warn communities.

Common mistakes

• Saying earthquakes can be predicted precisely.
• Mixing up focus and epicentre.
• Describing a tropical cyclone as forming over land or cold water.
• Listing flood defences without saying whether they are hard or soft, or without any disadvantage.
• Forgetting that effects can be both primary and secondary, and that level of development changes the outcome.

Exam technique

Learn at least one named example for each hazard so that you can add place, date and numbers when asked for a case study; if you are unsure of a figure, give a general statement rather than an invented number. For describe-and-explain questions, give a cause and its consequence in the same sentence. For evaluation questions, compare cost, effectiveness and who is protected, then reach a conclusion. Always show units and working in calculations.

Check your understanding

1. Distinguish focus from epicentre. (The focus is where the quake begins underground; the epicentre is the point on the surface directly above.)
2. Why do volcanoes occur at destructive boundaries? (One plate is forced down and melts, producing magma that rises.)
3. State two conditions needed for a tropical cyclone to form. (Warm sea surface, at least about 26.5 degrees Celsius, and sufficient distance from the equator for rotation.)
4. Why can a storm surge cause more deaths than the wind? (It floods low-lying coasts rapidly with sea water.)
5. Give one hard and one soft engineering flood response. (Embankment or dam; floodplain zoning or afforestation.)
6. How much larger is the ground motion in a magnitude 8.0 quake than in a magnitude 6.0 quake? (100 times.)
7. Rain peaks at 09:20 and the river peaks at 13:05. What is the lag time? (3 hours 45 minutes.)
8. Name two drought management methods suited to a low-income farming community. (For example rainwater harvesting and drought-resistant crops.)

Frequently asked questions

When does a natural hazard become a disaster? A natural hazard becomes a disaster when it meets vulnerable people. The same event can cause modest damage in one place and catastrophic loss in another, depending on how prepared and protected people are.

Can earthquakes be predicted? No. Earthquakes cannot be reliably predicted, so management concentrates on preparation, such as earthquake-resistant buildings, strict building codes, public drills, emergency supplies and land-use planning. Volcanoes, by contrast, can often be monitored.

What conditions are needed for a tropical cyclone to form? Tropical cyclones form over warm oceans, typically where sea-surface temperature is at least about 26.5 degrees Celsius, and away from the equator itself so that the Earth’s rotation can make the system spin. They weaken over land or colder water.

What is the difference between hard and soft engineering for floods? Hard engineering, such as dams, embankments and flood walls, is effective but costly and can move the problem downstream. Soft engineering, such as floodplain zoning, afforestation, wetland restoration and warning systems, is cheaper and more sustainable but may take time or land.

What is lag time on a hydrograph? Lag time is the delay between peak rainfall and peak river discharge. Urban surfaces shorten the lag time and increase the peak.