---
title: "Natural Hazards"
book: "Primary & Middle School Earth and Space Sciences"
subject: earth
language: en
chapter: 12
exercises: 11
source: https://one-course.com/books/earth/1/en/chapter/12-natural-hazards
license: CC-BY-NC-SA-4.0
credit: "One Earth and Space Sciences Book, One Course (one-course.com)"
---

# Chapter 12 — Natural Hazards

It is Friday evening. On the radio, the music stops and a calm voice reads a warning: a strong [storm](#def-g5-natural-hazards-storm) will reach the [coast](https://one-course.com/books/earth/1/en/chapter/2-landscapes-around-us#def-g1-landscapes-around-us-water) tonight, with very strong winds and heavy [rain](https://one-course.com/books/earth/1/en/chapter/7-clouds-rain-and-snow#def-g4-clouds-rain-snow-precipitation). People are asked to stay indoors from nine o’clock and to tie down or bring in anything the wind could carry away.

Lena’s family gets to work. Her father brings the garden chairs and the table into the shed. Her mother checks that the torches work and puts spare batteries on the kitchen table. Lena fills two big bottles with water. By nine o’clock, everyone is inside, and the wind is already howling.

![A family listens to a storm warning on the radio, with torches and spare batteries ready.](https://one-course.com/images/onecourse/chapters/earth-1/g5-natural-hazards/img-8332732d135a.jpg)

*A family listens to a [storm](#def-g5-natural-hazards-storm) warning on the radio, with torches and spare batteries ready.*

**You already know.**

A [volcano](https://one-course.com/books/earth/1/en/chapter/8-volcanoes-and-earthquakes-a-first-look#def-g4-volcanoes-earthquakes-first-look-volcano) can erupt, throwing out [lava](https://one-course.com/books/earth/1/en/chapter/8-volcanoes-and-earthquakes-a-first-look#def-g4-volcanoes-earthquakes-first-look-eruption), ash and gas; an [earthquake](https://one-course.com/books/earth/1/en/chapter/8-volcanoes-and-earthquakes-a-first-look#def-g4-volcanoes-earthquakes-first-look-earthquake) is a sudden shaking of the ground; in an [earthquake](https://one-course.com/books/earth/1/en/chapter/8-volcanoes-and-earthquakes-a-first-look#def-g4-volcanoes-earthquakes-first-look-earthquake), we drop, cover and hold on ([Chapter 8](https://one-course.com/books/earth/1/en/chapter/8-volcanoes-and-earthquakes-a-first-look#ch-g4-volcanoes-earthquakes-first-look)). A [river](https://one-course.com/books/earth/1/en/chapter/2-landscapes-around-us#def-g1-landscapes-around-us-water) that receives more water than its channel can hold [floods](https://one-course.com/books/earth/1/en/chapter/10-water-shapes-the-land#def-g5-water-shapes-the-land-flood) its [floodplain](https://one-course.com/books/earth/1/en/chapter/10-water-shapes-the-land#def-g5-water-shapes-the-land-flood) ([Chapter 10](https://one-course.com/books/earth/1/en/chapter/10-water-shapes-the-land#ch-g5-water-shapes-the-land)). Each place has its own [climate](https://one-course.com/books/earth/1/en/chapter/11-weather-and-climate#def-g5-weather-and-climate-climate), and the hot, temperate and cold zones go round the [globe](https://one-course.com/books/earth/1/en/chapter/6-the-globe-continents-and-oceans#def-g3-continents-and-oceans-globe) ([Chapter 11](https://one-course.com/books/earth/1/en/chapter/11-weather-and-climate#ch-g5-weather-and-climate)).

## 12.1 What a natural hazard is

Nature is not always calm. The wind can blow strongly enough to break trees, [rivers](https://one-course.com/books/earth/1/en/chapter/2-landscapes-around-us#def-g1-landscapes-around-us-water) can [flood](https://one-course.com/books/earth/1/en/chapter/10-water-shapes-the-land#def-g5-water-shapes-the-land-flood), the ground can shake. These events are part of how the Earth works: they happened long before there were people, and they will go on happening.

**Definition 12.1 (Natural hazard).**

A *natural hazard* is a natural event that can harm people or damage what they have built: a [storm](#def-g5-natural-hazards-storm), a [flood](https://one-course.com/books/earth/1/en/chapter/10-water-shapes-the-land#def-g5-water-shapes-the-land-flood), a [drought](#def-g5-natural-hazards-drought), an [earthquake](https://one-course.com/books/earth/1/en/chapter/8-volcanoes-and-earthquakes-a-first-look#def-g4-volcanoes-earthquakes-first-look-earthquake), a volcanic [eruption](https://one-course.com/books/earth/1/en/chapter/8-volcanoes-and-earthquakes-a-first-look#def-g4-volcanoes-earthquakes-first-look-eruption), a [landslide](#def-g5-natural-hazards-landslide)…

We can sort [natural hazards](#def-g5-natural-hazards-hazard) by where they come from: from the air, from water, or from the ground.

![The natural hazards, sorted by where they come from.](https://one-course.com/images/onecourse/chapters/earth-1/g5-natural-hazards/fig-a4f8289ab95b.svg)

*The [natural hazards](#def-g5-natural-hazards-hazard), sorted by where they come from.*

## 12.2 Hazards from the air

**Definition 12.2 (Storm).**

A *storm* is a time of very strong wind, usually with heavy [rain](https://one-course.com/books/earth/1/en/chapter/7-clouds-rain-and-snow#def-g4-clouds-rain-snow-precipitation) or [snow](https://one-course.com/books/earth/1/en/chapter/7-clouds-rain-and-snow#def-g4-clouds-rain-snow-precipitation), and sometimes with thunder and lightning.

A strong [storm](#def-g5-natural-hazards-storm) breaks branches, knocks down trees, tears tiles off roofs, and can throw garden chairs through windows. On the [coast](https://one-course.com/books/earth/1/en/chapter/2-landscapes-around-us#def-g1-landscapes-around-us-water), its wind piles the [sea](https://one-course.com/books/earth/1/en/chapter/3-water-on-earth#def-g2-water-on-earth-ocean) up against the shore and sends huge waves over the [sea](https://one-course.com/books/earth/1/en/chapter/3-water-on-earth#def-g2-water-on-earth-ocean) walls.

The most powerful [storms](#def-g5-natural-hazards-storm) on Earth form over warm tropical [seas](https://one-course.com/books/earth/1/en/chapter/3-water-on-earth#def-g2-water-on-earth-ocean). They are huge, spinning [storms](#def-g5-natural-hazards-storm): from space, they look like a giant spiral of [clouds](https://one-course.com/books/earth/1/en/chapter/7-clouds-rain-and-snow#def-g4-clouds-rain-snow-cloud), with a calm, clear hole in the middle, the eye. Around the eye blow the strongest winds. The same kind of [storm](#def-g5-natural-hazards-storm) has different names in different [oceans](https://one-course.com/books/earth/1/en/chapter/3-water-on-earth#def-g2-water-on-earth-ocean): it is called a *hurricane* in the North Atlantic and in the eastern Pacific, a *typhoon* in the north-west Pacific, and a *tropical cyclone* in the South Pacific and the Indian [Ocean](https://one-course.com/books/earth/1/en/chapter/3-water-on-earth#def-g2-water-on-earth-ocean).

![Looking down into the eye of Hurricane Isabel, over the Atlantic Ocean in September 2003, from the International Space Station: a wall of cloud around a calmer centre. Photograph: NASA (public domain).](https://one-course.com/images/onecourse/chapters/earth-1/g5-natural-hazards/img-ea8bce09d541.jpg)

*Looking down into the eye of Hurricane Isabel, over the Atlantic [Ocean](https://one-course.com/books/earth/1/en/chapter/3-water-on-earth#def-g2-water-on-earth-ocean) in September 2003, from the International Space Station: a wall of [cloud](https://one-course.com/books/earth/1/en/chapter/7-clouds-rain-and-snow#def-g4-clouds-rain-snow-cloud) around a calmer centre. Photograph: NASA (public domain).*

Some hazards from the air are slow and quiet. A *heat wave* is a period of several days and nights that are much hotter than usual. It is dangerous above all for very old people, babies and the sick.

**Definition 12.3 (Drought).**

A *drought* is a long period, of months or even years, with much less [rain](https://one-course.com/books/earth/1/en/chapter/7-clouds-rain-and-snow#def-g4-clouds-rain-snow-precipitation) than usual for that place. The soil dries out, [rivers](https://one-course.com/books/earth/1/en/chapter/2-landscapes-around-us#def-g1-landscapes-around-us-water) and [lakes](https://one-course.com/books/earth/1/en/chapter/2-landscapes-around-us#def-g1-landscapes-around-us-water) shrink, crops wilt and die.

A [drought](#def-g5-natural-hazards-drought) creeps up slowly: no one can say on which day it starts. But a long [drought](#def-g5-natural-hazards-drought) can leave farmers without a harvest and towns short of water.

![A field in a long drought: the earth is cracked, the crops are yellow and the pond has dried up.](https://one-course.com/images/onecourse/chapters/earth-1/g5-natural-hazards/img-76a9add04e28.jpg)

*A field in a long [drought](#def-g5-natural-hazards-drought): the earth is cracked, the crops are yellow and the pond has dried up.*

## 12.3 Hazards from water

You already know the [floods](https://one-course.com/books/earth/1/en/chapter/10-water-shapes-the-land#def-g5-water-shapes-the-land-flood) of [rivers](https://one-course.com/books/earth/1/en/chapter/2-landscapes-around-us#def-g1-landscapes-around-us-water) ([Chapter 10](https://one-course.com/books/earth/1/en/chapter/10-water-shapes-the-land#ch-g5-water-shapes-the-land)). After days of [rain](https://one-course.com/books/earth/1/en/chapter/7-clouds-rain-and-snow#def-g4-clouds-rain-snow-precipitation), or when the [snow](https://one-course.com/books/earth/1/en/chapter/7-clouds-rain-and-snow#def-g4-clouds-rain-snow-precipitation) melts fast, a [river](https://one-course.com/books/earth/1/en/chapter/2-landscapes-around-us#def-g1-landscapes-around-us-water) rises above its banks and covers its [floodplain](https://one-course.com/books/earth/1/en/chapter/10-water-shapes-the-land#def-g5-water-shapes-the-land-flood). Some [floods](https://one-course.com/books/earth/1/en/chapter/10-water-shapes-the-land#def-g5-water-shapes-the-land-flood) come very fast: a violent downpour on a steep [valley](https://one-course.com/books/earth/1/en/chapter/2-landscapes-around-us#def-g1-landscapes-around-us-landform) can turn a quiet stream into a roaring torrent within an hour. Others come from the [sea](https://one-course.com/books/earth/1/en/chapter/3-water-on-earth#def-g2-water-on-earth-ocean), when a [storm](#def-g5-natural-hazards-storm) pushes the water up onto a low [coast](https://one-course.com/books/earth/1/en/chapter/2-landscapes-around-us#def-g1-landscapes-around-us-water).

## 12.4 Hazards from the ground

You already know [earthquakes](https://one-course.com/books/earth/1/en/chapter/8-volcanoes-and-earthquakes-a-first-look#def-g4-volcanoes-earthquakes-first-look-earthquake) and volcanic [eruptions](https://one-course.com/books/earth/1/en/chapter/8-volcanoes-and-earthquakes-a-first-look#def-g4-volcanoes-earthquakes-first-look-eruption) ([Chapter 8](https://one-course.com/books/earth/1/en/chapter/8-volcanoes-and-earthquakes-a-first-look#ch-g4-volcanoes-earthquakes-first-look)). There is a third hazard from the ground, and water often triggers it.

**Definition 12.4 (Landslide).**

A *landslide* is a mass of [rock](https://one-course.com/books/earth/1/en/chapter/5-stones-pebbles-and-sand#def-g3-stones-pebbles-sand-rock), earth or [mud](https://one-course.com/books/earth/1/en/chapter/5-stones-pebbles-and-sand#def-g3-stones-pebbles-sand-sand) that suddenly slides or falls down a slope.

A steep slope soaked by long [rains](https://one-course.com/books/earth/1/en/chapter/7-clouds-rain-and-snow#def-g4-clouds-rain-snow-precipitation) becomes heavy and slippery, and it can let go all at once. An [earthquake](https://one-course.com/books/earth/1/en/chapter/8-volcanoes-and-earthquakes-a-first-look#def-g4-volcanoes-earthquakes-first-look-earthquake) can also shake a slope loose. A [landslide](#def-g5-natural-hazards-landslide) can bury a road, block a [river](https://one-course.com/books/earth/1/en/chapter/2-landscapes-around-us#def-g1-landscapes-around-us-water), or carry houses away.

![A large landslide in Washington State, in the United States, in 2014, seen from an aircraft. The hillside on the right has collapsed; its mud has spread across the whole valley, covered a road and blocked the river, which has flooded the woods upstream. Photograph: Mark Reid, U.S. Geological Survey (public domain).](https://one-course.com/images/onecourse/chapters/earth-1/g5-natural-hazards/img-94597ae3bafe.jpg)

*A large [landslide](#def-g5-natural-hazards-landslide) in Washington State, in the United States, in 2014, seen from an aircraft. The hillside on the right has collapsed; its [mud](https://one-course.com/books/earth/1/en/chapter/5-stones-pebbles-and-sand#def-g3-stones-pebbles-sand-sand) has spread across the whole [valley](https://one-course.com/books/earth/1/en/chapter/2-landscapes-around-us#def-g1-landscapes-around-us-landform), covered a road and blocked the [river](https://one-course.com/books/earth/1/en/chapter/2-landscapes-around-us#def-g1-landscapes-around-us-water), which has flooded the woods upstream. Photograph: Mark Reid, U.S. Geological Survey (public domain).*

## 12.5 From a hazard to a disaster

A [storm](#def-g5-natural-hazards-storm) over the open [ocean](https://one-course.com/books/earth/1/en/chapter/3-water-on-earth#def-g2-water-on-earth-ocean), an [earthquake](https://one-course.com/books/earth/1/en/chapter/8-volcanoes-and-earthquakes-a-first-look#def-g4-volcanoes-earthquakes-first-look-earthquake) in an empty [desert](https://one-course.com/books/earth/1/en/chapter/11-weather-and-climate#def-g5-weather-and-climate-desert), a [flood](https://one-course.com/books/earth/1/en/chapter/10-water-shapes-the-land#def-g5-water-shapes-the-land-flood) in a [valley](https://one-course.com/books/earth/1/en/chapter/2-landscapes-around-us#def-g1-landscapes-around-us-landform) where no one lives: these are [natural hazards](#def-g5-natural-hazards-hazard), but they harm no one. The same events become dangerous when they strike where people live.

**Definition 12.5 (Natural disaster).**

A *natural disaster* happens when a [natural hazard](#def-g5-natural-hazards-hazard) strikes a place where people live and does great harm: people are hurt or killed, homes are destroyed, roads, water and electricity are cut.

![The same flood twice. In the empty valley it harms no one; where a village has been built on the floodplain, it fills the houses. The house on the high ground stays dry.](https://one-course.com/images/onecourse/chapters/earth-1/g5-natural-hazards/fig-2937bd0febec.svg)

*The same [flood](https://one-course.com/books/earth/1/en/chapter/10-water-shapes-the-land#def-g5-water-shapes-the-land-flood) twice. In the empty [valley](https://one-course.com/books/earth/1/en/chapter/2-landscapes-around-us#def-g1-landscapes-around-us-landform) it harms no one; where a village has been built on the [floodplain](https://one-course.com/books/earth/1/en/chapter/10-water-shapes-the-land#def-g5-water-shapes-the-land-flood), it fills the houses. The house on the high ground stays dry.*

We cannot stop a [storm](#def-g5-natural-hazards-storm) or an [earthquake](https://one-course.com/books/earth/1/en/chapter/8-volcanoes-and-earthquakes-a-first-look#def-g4-volcanoes-earthquakes-first-look-earthquake). But we can do a great deal to keep a hazard from becoming a disaster: build away from [floodplains](https://one-course.com/books/earth/1/en/chapter/10-water-shapes-the-land#def-g5-water-shapes-the-land-flood) and from the foot of unstable slopes, make buildings strong, watch the [weather](https://one-course.com/books/earth/1/en/chapter/1-watching-the-weather#def-g1-watching-the-weather-weather) and the ground, warn people in time, and teach everyone what to do.

### Warnings

[Weather](https://one-course.com/books/earth/1/en/chapter/1-watching-the-weather#def-g1-watching-the-weather-weather) services watch the sky day and night. When a [storm](#def-g5-natural-hazards-storm), a heat wave or a [flood](https://one-course.com/books/earth/1/en/chapter/10-water-shapes-the-land#def-g5-water-shapes-the-land-flood) is coming, they send out warnings by radio, television, phone and the internet. Many countries use colours, from the calmest to the most serious.

![A ladder of warning colours. The exact meanings differ from one country to another: always listen to the instructions given with the warning.](https://one-course.com/images/onecourse/chapters/earth-1/g5-natural-hazards/fig-c44948917d67.svg)

*A ladder of warning colours. The exact meanings differ from one country to another: always listen to the instructions given with the warning.*

**Safety.**

**In a [storm](#def-g5-natural-hazards-storm).** Stay indoors, away from windows. Do not go out to look, and keep away from trees, which can fall, and from fallen electric wires.

**In a [flood](https://one-course.com/books/earth/1/en/chapter/10-water-shapes-the-land#def-g5-water-shapes-the-land-flood).** Move to higher ground or to an upper floor. Never walk, cycle or ride in a car through [flood](https://one-course.com/books/earth/1/en/chapter/10-water-shapes-the-land#def-g5-water-shapes-the-land-flood) water: a little fast water is enough to knock you over or carry a car away.

**In a heat wave.** Drink water often, stay in the shade or in a cool room during the hottest hours, and check on elderly neighbours.

**In an [earthquake](https://one-course.com/books/earth/1/en/chapter/8-volcanoes-and-earthquakes-a-first-look#def-g4-volcanoes-earthquakes-first-look-earthquake).** Drop, cover, hold on ([Chapter 8](https://one-course.com/books/earth/1/en/chapter/8-volcanoes-and-earthquakes-a-first-look#ch-g4-volcanoes-earthquakes-first-look)).

**Always.** Listen to the warnings and do what the people in charge say, at once.

## 12.6 Exercises

**Exercise 12.1 ★.**

[Natural hazard](#def-g5-natural-hazards-hazard) only, or [natural disaster](#def-g5-natural-hazards-disaster)?

1. [(a)] An [earthquake](https://one-course.com/books/earth/1/en/chapter/8-volcanoes-and-earthquakes-a-first-look#def-g4-volcanoes-earthquakes-first-look-earthquake) shakes an empty [desert](https://one-course.com/books/earth/1/en/chapter/11-weather-and-climate#def-g5-weather-and-climate-desert) .
2. [(b)] A [storm](#def-g5-natural-hazards-storm) tears the roofs off many houses in a town.
3. [(c)] A [landslide](#def-g5-natural-hazards-landslide) falls into a [mountain](https://one-course.com/books/earth/1/en/chapter/2-landscapes-around-us#def-g1-landscapes-around-us-landform) [valley](https://one-course.com/books/earth/1/en/chapter/2-landscapes-around-us#def-g1-landscapes-around-us-landform) where no one lives.
4. [(d)] A [river](https://one-course.com/books/earth/1/en/chapter/2-landscapes-around-us#def-g1-landscapes-around-us-water) [floods](https://one-course.com/books/earth/1/en/chapter/10-water-shapes-the-land#def-g5-water-shapes-the-land-flood) a village and fills its houses with water.

**Solution of Exercise 12.1.**

(a) A [natural hazard](#def-g5-natural-hazards-hazard) only: no one is harmed. (b) A [natural disaster](#def-g5-natural-hazards-disaster): homes are damaged. (c) A [natural hazard](#def-g5-natural-hazards-hazard) only. (d) A [natural disaster](#def-g5-natural-hazards-disaster).

**Exercise 12.2 ★.**

Sort these hazards into three families (from the air, from water, from the ground): a [landslide](#def-g5-natural-hazards-landslide); a heat wave; a [flood](https://one-course.com/books/earth/1/en/chapter/10-water-shapes-the-land#def-g5-water-shapes-the-land-flood); a volcanic [eruption](https://one-course.com/books/earth/1/en/chapter/8-volcanoes-and-earthquakes-a-first-look#def-g4-volcanoes-earthquakes-first-look-eruption); a [storm](#def-g5-natural-hazards-storm); a [drought](#def-g5-natural-hazards-drought); an [earthquake](https://one-course.com/books/earth/1/en/chapter/8-volcanoes-and-earthquakes-a-first-look#def-g4-volcanoes-earthquakes-first-look-earthquake).

**Solution of Exercise 12.2.**

From the air: a heat wave, a [storm](#def-g5-natural-hazards-storm), a [drought](#def-g5-natural-hazards-drought). From water: a [flood](https://one-course.com/books/earth/1/en/chapter/10-water-shapes-the-land#def-g5-water-shapes-the-land-flood). From the ground: a [landslide](#def-g5-natural-hazards-landslide), a volcanic [eruption](https://one-course.com/books/earth/1/en/chapter/8-volcanoes-and-earthquakes-a-first-look#def-g4-volcanoes-earthquakes-first-look-eruption), an [earthquake](https://one-course.com/books/earth/1/en/chapter/8-volcanoes-and-earthquakes-a-first-look#def-g4-volcanoes-earthquakes-first-look-earthquake).

**Exercise 12.3 ★.**

What is a [drought](#def-g5-natural-hazards-drought)? Give two ways in which a long [drought](#def-g5-natural-hazards-drought) harms people.

**Solution of Exercise 12.3.**

A [drought](#def-g5-natural-hazards-drought) is a long period, of months or years, with much less [rain](https://one-course.com/books/earth/1/en/chapter/7-clouds-rain-and-snow#def-g4-clouds-rain-snow-precipitation) than usual. It can leave farmers without a harvest, because the crops wilt and die, and it can leave towns short of drinking water, because [rivers](https://one-course.com/books/earth/1/en/chapter/2-landscapes-around-us#def-g1-landscapes-around-us-water) and [lakes](https://one-course.com/books/earth/1/en/chapter/2-landscapes-around-us#def-g1-landscapes-around-us-water) shrink.

**Exercise 12.4 ★.**

The radio announces a red [storm](#def-g5-natural-hazards-storm) warning for tonight. Give three things your family should do.

**Solution of Exercise 12.4.**

For example: bring in or tie down anything the wind could carry away (garden chairs, toys, bins); check the torches and keep spare batteries and water ready; stay indoors, away from the windows, during the [storm](#def-g5-natural-hazards-storm); keep listening to the radio for news.

**Exercise 12.5 ★.**

A great spinning [storm](#def-g5-natural-hazards-storm) with an eye forms over a warm tropical [sea](https://one-course.com/books/earth/1/en/chapter/3-water-on-earth#def-g2-water-on-earth-ocean). What is it called if it strikes (a) the [coast](https://one-course.com/books/earth/1/en/chapter/2-landscapes-around-us#def-g1-landscapes-around-us-water) of Florida, in the North Atlantic; (b) Japan, in the north-west Pacific; (c) the [coast](https://one-course.com/books/earth/1/en/chapter/2-landscapes-around-us#def-g1-landscapes-around-us-water) of India, on the Indian [Ocean](https://one-course.com/books/earth/1/en/chapter/3-water-on-earth#def-g2-water-on-earth-ocean)?

**Solution of Exercise 12.5.**

(a) A hurricane. (b) A typhoon. (c) A tropical cyclone.

**Exercise 12.6 ★.**

Put the four warning colours in order, from the calmest to the most serious. What should you do at the most serious level?

**Solution of Exercise 12.6.**

Green, yellow, orange, red. At the red level, there is great danger: act at once and follow the instructions of the people in charge.

**Exercise 12.7 ★★.**

Look at the photograph of the [landslide](#def-g5-natural-hazards-landslide) on page [76](#fig-g5-natural-hazards-landslide). Describe what the [landslide](#def-g5-natural-hazards-landslide) did to the [valley](https://one-course.com/books/earth/1/en/chapter/2-landscapes-around-us#def-g1-landscapes-around-us-landform): to the hillside, to the road and to the [river](https://one-course.com/books/earth/1/en/chapter/2-landscapes-around-us#def-g1-landscapes-around-us-water). Why is the land upstream now under water?

**Solution of Exercise 12.7.**

Part of the hillside on the right broke away and slid down, leaving a bare scar. Its [mud](https://one-course.com/books/earth/1/en/chapter/5-stones-pebbles-and-sand#def-g3-stones-pebbles-sand-sand) spread right across the [valley](https://one-course.com/books/earth/1/en/chapter/2-landscapes-around-us#def-g1-landscapes-around-us-landform) floor, covering the road. It also blocked the [river](https://one-course.com/books/earth/1/en/chapter/2-landscapes-around-us#def-g1-landscapes-around-us-water) like a dam: the [river](https://one-course.com/books/earth/1/en/chapter/2-landscapes-around-us#def-g1-landscapes-around-us-water) water, which can no longer flow away, has piled up behind it and flooded the woods upstream.

**Exercise 12.8 ★★.**

Tom says: “[Floods](https://one-course.com/books/earth/1/en/chapter/10-water-shapes-the-land#def-g5-water-shapes-the-land-flood) are natural, so nothing can be done about them.” Lena says: “We cannot stop a [river](https://one-course.com/books/earth/1/en/chapter/2-landscapes-around-us#def-g1-landscapes-around-us-water) from flooding, but we can stop a [flood](https://one-course.com/books/earth/1/en/chapter/10-water-shapes-the-land#def-g5-water-shapes-the-land-flood) from becoming a disaster.” Who is right? Explain with two examples.

**Solution of Exercise 12.8.**

Lena is right. We cannot stop the [rain](https://one-course.com/books/earth/1/en/chapter/7-clouds-rain-and-snow#def-g4-clouds-rain-snow-precipitation) or the [river](https://one-course.com/books/earth/1/en/chapter/2-landscapes-around-us#def-g1-landscapes-around-us-water), but we can keep people out of harm’s way. For example: build houses on higher ground instead of on the [floodplain](https://one-course.com/books/earth/1/en/chapter/10-water-shapes-the-land#def-g5-water-shapes-the-land-flood); warn people in time with [flood](https://one-course.com/books/earth/1/en/chapter/10-water-shapes-the-land#def-g5-water-shapes-the-land-flood) warnings, so that they move to higher ground; teach everyone never to walk or drive through [flood](https://one-course.com/books/earth/1/en/chapter/10-water-shapes-the-land#def-g5-water-shapes-the-land-flood) water.

**Exercise 12.9 ★★.**

In an imaginary farming region, about 60 millimetres of [rain](https://one-course.com/books/earth/1/en/chapter/7-clouds-rain-and-snow#def-g4-clouds-rain-snow-precipitation) usually fall each month. During a [drought](#def-g5-natural-hazards-drought), only a quarter of the usual [rain](https://one-course.com/books/earth/1/en/chapter/7-clouds-rain-and-snow#def-g4-clouds-rain-snow-precipitation) fell in each of four months.

1. [(a)] How much [rain](https://one-course.com/books/earth/1/en/chapter/7-clouds-rain-and-snow#def-g4-clouds-rain-snow-precipitation) usually falls in four months?
2. [(b)] How much fell during the [drought](#def-g5-natural-hazards-drought) , in the four months?
3. [(c)] How much [rain](https://one-course.com/books/earth/1/en/chapter/7-clouds-rain-and-snow#def-g4-clouds-rain-snow-precipitation) was missing?

**Solution of Exercise 12.9.**

(a) $4 \times 60 = 240$ millimetres. (b) A quarter of 60 is 15; in four months, $4 \times 15 = 60$ millimetres. (c) $240 - 60 = 180$ millimetres were missing: three quarters of the usual [rain](https://one-course.com/books/earth/1/en/chapter/7-clouds-rain-and-snow#def-g4-clouds-rain-snow-precipitation).

**Exercise 12.10 ★★.**

An imaginary town has 1 200 homes. A quarter of them stand on the [floodplain](https://one-course.com/books/earth/1/en/chapter/10-water-shapes-the-land#def-g5-water-shapes-the-land-flood) of its [river](https://one-course.com/books/earth/1/en/chapter/2-landscapes-around-us#def-g1-landscapes-around-us-water).

1. [(a)] How many homes stand on the [floodplain](https://one-course.com/books/earth/1/en/chapter/10-water-shapes-the-land#def-g5-water-shapes-the-land-flood) ?
2. [(b)] The town helps the owners of a third of those homes to move to higher ground. How many homes are still on the [floodplain](https://one-course.com/books/earth/1/en/chapter/10-water-shapes-the-land#def-g5-water-shapes-the-land-flood) ?

**Solution of Exercise 12.10.**

(a) $1\,200 \div 4 = 300$ homes. (b) A third of 300 is 100; so $300 - 100 = 200$ homes are still on the [floodplain](https://one-course.com/books/earth/1/en/chapter/10-water-shapes-the-land#def-g5-water-shapes-the-land-flood).

**Exercise 12.11 ★★★.**

Two villages, far apart, are hit by [storms](#def-g5-natural-hazards-storm) of the same strength on the same night. In the first, no one is hurt and the damage is small. In the second, many houses are destroyed. Give at least three different reasons that could explain the difference.

**Solution of Exercise 12.11.**

Possible reasons: the first village had been warned in time and people had prepared (shutters closed, objects brought in), the second had not; the houses of the first are solidly built, those of the second are fragile; the second village lies on a low [coast](https://one-course.com/books/earth/1/en/chapter/2-landscapes-around-us#def-g1-landscapes-around-us-water) or a [floodplain](https://one-course.com/books/earth/1/en/chapter/10-water-shapes-the-land#def-g5-water-shapes-the-land-flood), where the [storm](#def-g5-natural-hazards-storm) also brought a [flood](https://one-course.com/books/earth/1/en/chapter/10-water-shapes-the-land#def-g5-water-shapes-the-land-flood), while the first stands on higher ground; trees close to the houses fell on them in the second village. The same hazard does not cause the same harm everywhere: it depends on where and how people live, and on how well they are prepared.