Fig. 4.1: Illustration of the impact of natural disaster such as earthquakes, tsunami, floods, landslides, cyclones on human activities and infrastructures.
    Key unit Competence

    By the end of the unit the learner should be able to relate physics concepts to earthquakes, Tsunami landslide and cyclone occurrences and impact on environment.

    My goals

    • Anaylse earthquakes, landslides, floods, and tsunami  

    • Describe natural and human made seismic occurrences  

    • Describe earthquake causes as: geological faults, volcanic activity, landslides, mine blasts, and nuclear weapon tests.  

    • Relate Physics concepts to natural disasters impact.  

    • Explain causes of earthquakes, tsunami, landslide and floods.  

    • Outline impacts of earthquakes on buildings and other structures.

    Introductory activity:

    Using the information collected from the above Fig. 4.1, answer the following questions related to natural disasters due to underground earth’s movements. Your answers have to reflect the role of Physics in explaining the origin, causes and impact of these natural disasters. Also describe how their impacts on the environment can be reduced.

    • To what extend is the human activities and environment are affected by natural disaster?  

    • What are the measures to minimize their impacts or prevent them from occurring? 

    • What makes buildings to collapse during such disturbance? What can be done to minimize the impact on buildings and other properties? 

    • What happen to the ocean when such underground disturbances occur?

    • By learning this unit, each student will realize the need for better understanding of the basic physics concepts behind the occurrence of natural disasters such as earthquake, landslide, tsunami, flood and cyclone. The unit focuses on the physics and dynamic of those natural disasters.

     4.1 The earthquake

    Activity4.1: Physical concept behind the earthquake. 

    1. Brainstorm the physics concepts behind the occurrence of earthquakes. 

    2. Write a summary of the main physics concepts in the occurrence of the earthquake.

    An earthquake also known as a quake, tremor or temblor is the shaking or trembling of the ground caused by the sudden release of energy. This is usually associated with faulting or breaking of rocks followed by continuing adjustment of their positions with the later resulting in aftershocks. 

    This continuing shaking or trembling of the ground with unexpected energy is usually associated with perturbation of ground’s medium in different direction that causes the ground to be compressed and stretched. The stretching and compression of the ground medium will result in the emission of waves that propagate in all directions. 

    During the ground’s shaking, the elastic strain energy is released and waves radiate from where ground is disturbed. An element of the ground therefore moves in simple harmonic motion.

    It is said that earthquakes has created seismic waves. Those waves can range in size from those that are so weak that they cannot be felt to those that are violent enough to toss people around and destroy entire cities.

    The seismicity or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time. The place where an earthquake begins underground is called the focus or hypocenter, and the area on the earth’s surface directly above the hypocenter is called the epicenter. This epicenter region receives normally the most powerful shock waves.


                                                              Fig.4. 2: A region where Earthquakes begin.

    4.1.1 Origin of earthquakes 

    Earthquake originates from a high pressure region at the hypocenter. This high pressure increases gradually the temperature and the increase in temperature inside the earth and consequently the increase in heat finally makes rocks to be in molten state.

    As pressure keeps on increasing due to strong heat effect, molten rocks try to get rid of the excess pressure and explode. The explosion induces elastic energy release at the hypocenter and a wave spread out as result of the shifting of the plates and internal disturbances. The wave propagates away from the source. In additional to that, the disturbance that moves away from the hypocenter makes the earth to vibrate. So quakes are accompanied with shock waves. 

    To better understand this phenomenon, let take an example a covered sauce pan filled with milk and heated up. As the pressure increases inside the saucepan, the temperature also increases and the milk starts to boil. As the milk boils due to increased temperature, the excess pressure in milk eject the cover of the saucepan and the sound of the boiling milk is heard at a certain distance from where the phenomenon occurred.

    Major earthquakes have generated into tsunamis that destroyed entire cities and affected whole countries. Relatively minor earthquakes can also be caused by human activity, including extraction of minerals and the collapse of large buildings.

    4.1.2 Intensity of earthquakes 

    The earthquake size is a quantitative measure of the size of the earthquake at its source. The Richter magnitude scale measures the amount of seismic energy released by an earthquake. 

    This magnitude is related to the amount of seismic energy released at the hypocenter of the earthquake. It is based on the amplitude of the earthquake waves recorded on instruments which have identical calibrations called seismographs. The magnitude of an earthquake is translated in the reading on the Richter scale.

    The severity of an earthquake can be expressed in terms of both the intensity and magnitude. However, the two terms are quite different and are often confused. Intensity is based on the observed effects of ground shaking on people, buildings, and natural features. It varies from place to place within the disturbed region depending on the location of the observer with respect to the earthquake’s epicenter. The amplitude and energy measured by the Richter scale are objective and quantitative while intensity is more subjective and qualitative as it depends on the judgment of the observers.

    Earthquakes are recorded by instruments called seismographs or seismometer and their recordings produce a seismogram as represented on fig.4.3. The fig. 4.2 shows a typical seismograph used to measure the magnitude of earthquakes. It has a base that is set firmly on the ground and a heavy weight that hangs free. 

    When an earthquake causes the ground to shake, the base of the seismograph shakes too, but the hanging weight does not. Instead the spring or the string that it is hanging from absorbs all the movement. The difference in position between the shaking part of the seismograph and the motionless part of it is what is recorded. 


                          Fig.4. 3: Instrument used to measure earthquakes: seismographs or seismometer

    4.1.3 Measurement of the size of earthquakes

    The size of an earthquake depends on the size of the fault and the amount of slip on the fault, but that’s not something scientists can simply measure since faults are many kilometers deep beneath the earth’s surface. So how do they measure an earthquake? They analyse the seismograms recorded at the surface of the earth to determine how large the earthquake was. A typical seismogram is shown on the Fig.4.3.


                                                                 Fig.4. 4: intensity or size of Earthquakes.
    A short wiggly line that doesn’t wiggle very much means a small earthquake, and a long wiggly line that wiggles a lot means a large earthquake. The length of the wiggle depends on the size of the fault, and the size of the wiggle depends on the amount of slip.

    4.1.4 Types of earthquake waves 

    They are two types of earthquakes. Those are body and surface waves 

    Body waves are subdivided into P waves or Primary waves and S wave or secondary waves. P and S waves shake each the ground in different ways as they travel through it. The P waves, or compression waves, alternately compresses and expands medium in the direction of propagation.  They are fastest waves and travel through solids, liquids, or gases.

    The surface waves or S waves are slower than P waves and travel through solids only. They are shear waves and the direction of propagation of such waves is perpendicular to the direction of vibration of the medium. The surface waves just travel below or along the ground’s surface and their side-to-side movement and the rock vibration reduce with depth into the earth. They are the main cause of damage to buildings. 

    To understand how this works, let’s compare P and S waves to lightning and thunder. Light travels faster than sound, so during a thunderstorm you will first see the lightning and then after hear the thunder. If you are too close to where the lightning happens, the thunder will boom right after the lightning, but if you are far away from the lightning, you can count several seconds before you hear the thunder. 

    4.1.5 Causes of earthquake 

    The shaking motion of an earthquake is the result of a sudden release of energy. This situation is observed when stress, building up within rocks of the earth’s crust, is released in a sudden jolt. Rocks crack and slip past each other causing the ground to vibrate. The causes are both natural and man- made.

    • Volcanic activity: The combining effects of increase of pressure, temperature and heat inside the volcano results in volume increase and increase in energy. This makes rocks inside the volcanoes to be in molten rocks and as the heat keeps on increasing the molten rocks become sticky hot liquid. As the volume increase further within that sticky liquid it will reach a boiling point and start ejecting gases at high temperature. The ejection of such gases makes the ground to vibrate resulting in earthquakes. Finally the molten liquid is ejected out in an explosion. Earthquakes related to volcanic activity may produce hazards which include ground cracks or deformation.

    • Nuclear weapon testing: The process of underground nuclear testing is rather straightforward. The rocks in the surrounding area of the thermonuclear device are scattered by the passage of explosion shock waves. This sudden release of the elastic strain energy that was stored in the rock will cause the ground to vibrate. 

    • Underground mining: In mining depending on the amount of materials that are removed from the ground, people use deep well injection and shift the stress on underlying rocks. At some point the extractions of minerals will cause the ground to vibrate. 

    There are other causes such as water pumping, collapse of roofs of caverns or even heavy trucks that can cause the ground to shake.

    4.1.6 Effects of earthquakes

    Activity 4.2: Effects of earthquakes


                              Fig.4. 5: illustration of impact of earthquakes on human activities.

    The above pictures A, B and C describe what happened in a certain region after an earthquake. Observe them carefully and answer the following questions: 

    1. In your own words, discuss what you are observing. 

    2. Think of what people can do before, during and after an earthquake.

    The earthquake environmental effects are effects caused by an earthquake on the natural environment. These include surface faulting, ground deformation and subsidence tsunamis, ground resonance, landslides and ground failures. They are either directly linked to the earthquake source or provoked by the ground shaking. 

    Geological effects such as soil liquefaction, landslides etc., that are related to both surface deformation, faulting and ground shaking, not only leave permanent imprints in the environment, but also dramatically affect human lives and infrastructures. Moreover, underwater fault ruptures and seismically triggered landslides can generate devastating tsunami waves. 

    Earthquakes environmental effects are categorized into two main types: 

    • Primary effects: which are the surface expression of the seismogenic source (e.g., surface faulting), normally observed for crustal earthquakes above a given magnitude threshold. 

    • Secondary effects: basically those effects are related to ground. It includes landslides, soil liquefaction, fires, floods etc. they play an important role in the destructions produced by earthquakes.

    The direct shaking effects as damage or collapse of buildings, bridges, elevated roads, railways, water towers, water treatment facilities, utility lines, pipelines, electrical generating facilities and transformer stations , are not the only hazard associated with earthquakes.

    Depending on the vulnerability of the affected community, people may lose their lives get traumatized or become homeless in the aftermath of an earthquake. The table below shows the Richter magnitude of earthquakes and impacts they have on people and infrastructures.


                                             Table 4.1: Richter magnitude of earthquakes.

    4.1.7 Safety measures on earthquakes

    Before an earthquake 

    • You should secure all items that could fall or move and cause injuries or damage (e.g. bookshelves, mirrors, light fixtures, televisions, computers, hot water heaters etc). 

    • Move beds away from windows and secure any hanging items over beds, other places people sit or lie.

    • Protect yourselves: Cover your head and neck with your arms. 

    • Create a strategies plan that you will use to communicate with family members. 

    • Consult a structural engineer to evaluate your home and ask about updates to strengthen areas that would be weak during an earthquake. 

    • In searching buildings to rent or buy, verify whether its materials have earthquake standards.

    During an earthquake

    • Lay down onto your hands and knees so the earthquake doesn’t knock you down.  

    • Cover your head and neck with your arms to protect yourself from falling debris. 

    • If you are in danger from falling objects, and you can move safely, crawl for additional cover under a sturdy desk or table. 

    • If no sturdy shelter is nearby, crawl away from windows, next to an interior wall. Stay away from glass, windows, outside doors and walls, and anything that could fall, such as light fixtures or furniture. 

    • Hold on to any sturdy covering so you can move with it until the shaking stops. 

    • Stay where you are until the shaking stops. Do not run outside. Do not get in a doorway as this does not provide protection from falling or flying objects, and you may not be able to remain standing.

    If you are in bed: 

    • Stay there and Cover your head and neck with a pillow. At night, hazards and debris are difficult to see and avoid; attempts to move in the dark result in more injuries than remaining in bed.

    If you are outside: 

    • If you are outdoors when the shaking starts, move away from buildings, streetlights, and utility wires. Once in the open, “Drop, Cover, and Hold On.” Stay there until the shaking stops. 

    If you are in a moving vehicle: 

    • It is difficult to control a vehicle during the shaking. If you are in a moving vehicle, stop as quickly and safely as possible and stay in the vehicle. Avoid stopping near or under buildings, trees, overpasses, and utility wires. Proceed cautiously once the earthquake has stopped. Avoid roads, bridges, or ramps that the earthquake may have damaged.

    After an earthquake 

    • When the shaking stops, look around. If the building is damaged and there is a clear path to safety, leave the building and go to an open space away from damaged areas. 

    • If you are trapped, do not move about or kick up dust. 

    • If you have a cell phone with you, use it to call or text for help.

    • Tap on a pipe or wall or use a whistle, if you have one, so that rescuers can locate you.

    • Once safe, monitor local news reports via battery operated radio, TV, social media, and cell phone text alerts for emergency information and instructions. 

    • Check for injuries and provide assistance if you have training. Assist with rescues if you can do so safely, etc.

     4.1.8 Checking my progress

    1. What do you understand by the term Earthquake? 

    2. Outline the impact do earthquakes human activities and infrastructure? 

    3. How nuclear weapons testing cause earthquakes? 

    4. What can you do when you are inside  a house during ground shaking?  

    4.2. LANDSLIDES.

     Activity 4.3: Description of landslides 


                            Fig.4.6: illustration of landslide and the impact on environment.

    Observe carefully the above figure and answer the following questions. 

    a. What do you think could have happened to the area shown in the above figure? 

    b. Can you think of the major causes this kind situation? 

    c. Discuss the possible effects of such disaster on human activities and on the environment. 

    d. Suppose that you are living in a region that is likely to be affected by such disaster, discuss what would do you to prevent it from occurring. How will you behave if it happens?

    4.2.1 Definition of landslide 

    A landslide, also known as slope movement, mass movement or mass wasting, is the movement by which soil, sand, and rock move down the slope, typically as a mass, largely under the force of gravity. It is frequently caused by the soil’s water content which acts as a lubricating agent for failure to occur.


                         Fig.4.7: illustration of landslide event with soil, sand and rocks being moved down the slope.

    4.2.2 Causes of landslide

    Several factors can increase a slope’s susceptibility to a landslide event. The following are some the causes:

    • Water (rainfall or the movement of the sea) this acts as a grease to the material increasing the likelihood that it will slip and also adds extra weight to the rock 

    • Erosion processes such as coastal erosion and river erosion 

    • Steepness of slope

    • Rock: soft rock such as mudstone or hard rock such as limestone 

    • Shape of the rock ‘grains’ 

    • Jointing and orientation of bedding planes 

    • Arrangement of the rock layers 

    • Weathering processes for example freeze-thaw reduces the stickiness (cohesion) between the rock grains. 

    • Lack of vegetation which would help bind material together 

    • Flooding 

    • Volcanoes and earthquake activity nearby man’s activity mining, traffic vibrations or urbanization which changes surface water drainage patterns.

    4.2.3. Effect of landslides 

    Due to the movement of rocks, soils, sand mixed with water under the force of gravity, landslides produce both positive and negative effects: Among the positive effects we can mention: 

    • Promotion of mining activities. 

    • Building of fertile flood plains for agriculture  

    • Promotion of tourism due to land forms of mass wasting 

    • Promotion of research or study purposes 

    • Soil formation due to the exposure of fresh rocks.

    Negative effects

    Activity 4.4: Puzzle or cross words.

    To do this activity, check the words in the puzzle then after fill it in the missing sentence such that it will have meaning.  It is related to the negative impact of landslide.


    • Loss of…….. 

    • ………… of people

    • ………of agriculture, land and crops

    • Destruction of ……….. 

    • Alteration of …… ( e.g. damming rivers)

    • …….of vegetation 

    • Increase in ………. expenditures

    4.2.4 Safety measures of landslides 

    Whenever landslide occurs, it damages many things in different area (eg environment, people, buildings, roads etc. Some actions are required:
    Before a landslide 

    • Do not build your house near steep slope, drainage ways or natural erosion. 

    • Ask information to local officials or geologist on vulnerable area to landslides and corrective measures you can take if necessary. 

    • Make an evacuation plans for your area how you will communicate with other people.etc

    During landslide 

    • Stay alert and awake. Many debris-flow fatalities occur when people are sleeping. Be aware that intense, short bursts of rain may be particularly dangerous, especially after longer periods of heavy rainfall and damp weather.

    • If you are in areas susceptible to landslides and debris flows, remember that driving during an intensive storm can be dangerous. 

    • Listen for any unusual sounds that might designate moving debris, this can flow quickly and sometimes without warning that precede a large landslide.  

    • When you are near a steam or channel of water flow, be aware if it increase or decrease, such changes may indicate landslide activity upstream, so be prepared to move quickly. 

    • Inform affected neighbors. Your neighbors may not be aware of potential hazards. Advising them of a potential threat may help save lives. Help neighbors who may need assistance to evacuate. Etc

    After landslide 

    • Report quickly the potential hazards as possible for prevention of further hazard and injury. 

    • Look for and report broken utility lines and damaged roadways and railways to the authorities 

    • Search advice for geologist/geotechnical expert for evaluating and best ways to prevent or reduce landslide risk, without creating further hazard 

    • Look around and check whether the building foundation, chimney, and surrounding land have damaged. 

    • Help your neighbor who may require individual support, aged people and people with disabilities, because they may require additional assistance. The same as people who care for them or who have large families may need a special assistance in emergency situations.

    4.2.5 Checking my progress 

    1. Copy the table into your exercise books and fill it in with the sentences below. 

    • Man’s activity mining brought traffic vibrations which changes surface water drainage patterns. 

    • Ground deformation due to the fact that rocks and debris are swapped by water. 

    • Plant the ground cover on slopes and build retaining walls. 

    • Earthquakes create stresses that make weak slopes fail.

    • Rainfall or the movement of the sea.

    • Listen to local radio or television stations for the latest emergency information. 

    • Erosion.


    4.3. TSUNAMI 

    Activity 4.5: Tsunami event

    Fig.4.8: illustration of the devastating effects of Tsunami. 

    The above figures shows scenarios that where  observed during and after a Tsunami had affected a certain region. Study the picture above carefly these pictures and answer the following questions:
     What are the main observations?

     II. What do you think could have caused such situations?

     III. From your analysis, to what extent this natural disaster affects human activities and environment?

     IV. Imagine your family in such situations as shown above, which advice would you provide to them? 

    4.3.1 Definition of Tsunami. 

    A sudden offset changes the elevation of the ocean and initiates a water wave that travels outward from the region of sea-floor disruption.  Such water waves are called Tsunamis waves and can travel long distances across the ocean. As an example, large earthquakes in Alaska or Chile have generated waves that caused damage and deaths in regions as far away as California, Hawaii and Japan. 

    The world tsunami comes from two Japanese words: Tsu mean “Harbor” and Nami means “wave” so Tsunami mean a “Harbor wave”. A tsunami is a series of waves in a water body caused by the displacement of a large volume of water, generally in large lake, volcanic eruptions and other underwater explosions, landslide, and other disturbances above and below all have a potential to generate a tsunami.

    Generally a tsunami consists of a series of waves with periods ranging from minutes to hours, a small amplitude (wave height) offshore, and a very long wavelength hundreds of kilometers long, whereas in normal ocean waves have a wavelength of only 30 or 40 meters. This is why they generally pass unnoticed at sea, as they form only a slight swell usually about 300 mm above the normal sea surface. They grow in height when they reach shallower water. 

    Tsunamis are sometime referred to as tidal waves. This once popular term from the most common appearance of tsunami which is that of an extraordinarily high tidal bore, both produce waves of water that move internal (inland) but in the case of tsunami the inland movement of water may be much greater, the impression of an exceedingly high and forceful tide. In recent years, the term “tidal wave” has fallen out of favour, especially in the scientific community, because tsunamis have nothing to do with tides which are produced by the gravitational pull of the moon and sun rather than the displacement of water finally tidal wave is discouraged by oceanographers and geologists.

                              Fig.4. 9: illustration of how Tsunami waves increase in amplitude as they approach the shore.

    In deep water tsunamis are not large and pose no danger. They are very broad with horizontal wavelengths of hundreds of kilometers and surface heights much smaller, about one meter. Tsunamis pose no threat in the deep ocean because they are only a meter or so high in deep water. But as the wave approaches the shore and the water shallows, all the energy that was distributed throughout the ocean depth becomes concentrated in the shallow water and the wave height increases, its wavelength diminishes and its amplitude grows enormously.

    Development of Tsunami

    Everybody knows that what goes up must come down. This is particularly true for water which always forms a nice flat surface. So once a disturbance has risen up an amount of water the next step is for the sea to level itself out and bring it back down. 

    This pushes the water that was underneath it to spread outwards and thus creating a wave. As this wave travels through the ocean it may eventually reach the shore. As the sea becomes shallower close to the shore, the energy carried in the water wave remains unchanged. It compresses the small amount water upwards resulting in Tsunamis. The stages of process of the development of tsunami are shown on the figure 4.9. The numbers on the figure correspond to the stage number. 

    As one plate subducts below another the pressure builds up progressively. After many years this will result in a section of the megatrust giving way. 

    Stage 2: As the section gives way it ruptures the ocean floor causing a massive displacement of water. 

    Stage 3:  stage 2 can develop due to an earthquake that create a landslide under the sea floor which in turn would have generated a swell 

    Stage 4: A Tsunami wave is barely noticeable as a ripple of water near the epicenter 

    Stage 5: As the wave reaches the cost and the water becomes shallower the size of the wave increases drastically.


                                   Fig.4. 10: Different stage of Tsunami development process 

    4.3.2 Causes of Tsunami 

    The principal cause of tsunami is the displacement of a substantial volume of water or perturbation of the sea, this displacement of water is usually attributed to either Earthquake, landslide, volcanic eruption, etc. The waves formed in this way are sustained by full of gravity. 

    The rapid displacement of water for a large volume, as energy transfers to the water at a rate faster than the water can be absorbed, the wave did not travel far as it strike land immediately and generate the landslide. The people fishing in the bay were killed, and another board managed to ride the wave .

    Volcanoes cause tsunami when there is an eruption. The volcano can either be on land or under the sea, in which case it is known as a submarine volcano. Violent volcanic eruptions represent also impulsive disturbances, which can displace a great volume of water and generate extremely destructive tsunami waves in the immediate source area. The water in the sea then breaks into waves which travel across the ocean until they come into contact with a coast. Here, a tsunami is formed.

    4.3.3 Effects of Tsunami 

    They are many effect of Tsunami most of them are: 

    • Loss of lives 

    • Death of marine life( aquatic animals) 

    • Famine 

    • Coastal erosion (the wearing a way of coastal land or beaches) 

    • Structural damage through destruction of people’s properties. 

    • Higher  risks of diseases( eg Malaria) 

    • Severe flooding 

    • Displacement of people 

    • Trauma (Psychological effects.) 

    • Government expenditure, etc. 

    4.3.4 Prevention of tsunami 

    Unfortunately nothing can be done to prevent Tsunamis. However, there are several organizations that use complex technology to monitor movement of the earth’s plates and sudden changes in water movement. There are also warning and evacuation procedures in place around countries with higher risks like Japan and Hawaii where Tsunamis are frequent.

    Any sudden earthquake that happens underwater will be detected in the same manner of an on-shore earthquake. These are recorded on the Richter scale and depending on its magnitude then warning systems can be activated to evacuate people.

    4.3.5 Checking my progress.


    4.4. FLOODS. 

    4.4.1 concept of flood

    Activity 4.6:


               Fig.4.11: Illustration of the impact of floods on human activities and on environments.

    a. Critically, analyze the pictures shown in the figure above and write down what is happening. 

    b. What technical term that describes the scenario. Define the term you have mentioned 

    c. What are the end results after the occurrence of the disaster shown in the figure above?. 

    d. Suppose that you are living in the area that is always affected by the disaster, what you would do to prevent it from occurring again?

    Many of us try to generate the process of water cycle in dairy life and rains falling around our environment cause too much water around our house. People think of what they can do during rainfall. 

    Flooding occurs mostly from heavy rainfall when natural watercourses do not have the capacity to convey excess water. However, floods are not always caused by heavy rainfall.


                                    Fig.4.12: Heavy rain can cause flooding in some areas

    4.4.2 Types of floods 

    There are three major types flood: Flash floods, rapid on-set floods and slow on-set floods: 

    a. Flash floods 

    This type of flood occurs within a very short time (2-6 hours, and sometimes within minutes) and is usually a result of heavy rain, dam break or snow melt. Sometimes, intense rainfall from slow moving thunderstorms can cause it.  Flash floods are the most destructive and can be fatal, as people are usually taken by surprise. There is usually no warning, no preparation and the impact can be very swift and devastating. 

    b. Rapid on-set floods 

    Similar to flash floods, this type of flood takes slightly longer to develop and the flood can last for a day or two only. It is also very destructive, but does not usually surprise people like flash floods. With rapid on-set floods, people can quickly put a few things right and escape before it gets very bad. 

    c. Slow on-set floods 

    This kind of flood is usually a result of water bodies over flooding their banks. They tend to develop slowly and can last for days and weeks. They usually spread over many kilometers and occur more in flood plains (fields prone to floods in low-lying areas). The effect of this kind of floods on people is more likely to be due to disease, malnutrition or snakebites.

    4.4.3 Causes of floods 

    Here are a few events that can cause flooding: 

    Rains: Each time there are more rains than the drainage system can take, there can be floods. Sometimes, there is heavy rain for a very short period that results in floods. In other times, there may be light rain for many days and weeks and can also result in floods.

    River overflow: Rivers can overflow their banks to cause flooding. This happens when there is more water upstream than usual, and as it flows downstream to the adjacent low-lying areas (also called a floodplain), there is a burst and water gets into the land.

    Strong winds in coastal areas: Sea water can be carried by massive winds and hurricanes onto dry coastal lands and cause flooding. Sometimes water from the sea resulting from a tsunami can flow inland and cause damages. 

    Dam breaking:  Dams are man-made blocks mounted to hold water flowing down from a highland and this water can be used to generate electricity. Sometimes, too much water held up in the dam can cause it to break and overflow the area. Excess water can also be intentionally released from the dam to prevent it from breaking and that can also cause floods. 

    Ice and snow-melts:  In many cold regions, heavy snow over the winter usually stays
    un-melted for some time. There are also mountains that have ice on top of them. Sometimes the ice suddenly melts when the temperature rises, resulting in massive movement of water into places that are usually dry. This is usually called a snowmelt flood.

    4.4.4 Consequences of floods 

    Floods can have devastating consequences and can have serious impact on the country’s economy, the environment, people and animals 

    a. Economic 

    During floods, especially flash floods, roads, bridges, farms, houses and automobiles are destroyed. All these come at a heavy cost to people and the government. It usually takes years for affected communities to rebuild and business to come back to normalcy.

    b.  Environment

    The environment also suffers when floods happen. Chemicals and other hazardous substances end up in the water and eventually contaminate the water bodies that floods. Additionally, flooding kills animals and others insects in the affected areas, distorting the natural balance of the ecosystem. 

    c. People and animals 

    Many people and animals may get killed   during flash floods. Many more are injured and others made homeless. Water supply and electricity are disrupted. In addition to this, flooding brings a lot of diseases and infections and sometimes insects and snakes make their ways to the area and cause a lot of havoc. 

    However, there is also something good about floods, especially those that occur in floodplains and farm fields. Flood water carries lots of nutrients that are deposited in the plains. Farmers love such soils, as they are perfect for cultivating any kinds of crops.

    4.4.5 Floods and safety measures 

    Sometimes there is no warning of flash floods, and that is why it is important to think of them and prepare for them before they happen. Here are a few things you can do. 

    Before the floods

    • Know about your local relief centers and evacuation routes. 

    • Keep emergency numbers and important information handy, as well as emergency supplies, kits, first aid items. These may include water, canned food; can opener, battery-operated radio, flashlight and protective clothing. 

    • Fold and roll up anything onto higher ground (or upper floors of your home), including chemicals and medicines. 

    • Make sure everything that is of importance is secured (jewelry, documents, pets, and other valuables).

    • Plant trees and shrubs and keep a lot of vegetation in your compound if you are in a low-lying area as that can control erosion and help soften the speed of the flowing water. 

    During the floods 

    • Flash floods occur in a short spate of time. As soon as they start, be quick, keep safe and ensure that children and elderly are safe by leaving the house to a higher ground. 

    • Turn off all electrical appliances, gas, heating and the like if there is a bit of time.

    • Leave the area before it gets too late. Do not drive through the water as moving water can sweep you away. 

    • Stay away from power lines or broken power transmission cables.  

    • Try to keep away from flood water as it may contain chemicals or other hazardous materials. 

    • Don’t walk, swim or drive through floodwater. Just six inches of fast-flowing water can knock you over and two feet will float a car.

    After the floods 

    • Make sure you have permission from emergency officers to get back inside your house.

    • Keep all power and electrical appliance off until the house is cleaned up properly and electrical personnel has confirmed that it is OK to put them on. 

    • Make sure you have photographs, or a record of all the damage, as it may be needed for insurance claims. 

    • Clean the entire home, together with all the objects in it very well before you use them again. They may be contaminated.

    • Keep children and pets away from hazardous sites and floodwater. 

    • Let friends and family know you’re safe. Register yourself as safe on the Safe and Well website.

    4.4.6 Checking my progress 

    1. Explain how the flood is formed? 

    2. Draw diagrams showing 

        I. Infrastructures affected by floods 

       II. People trying to save their lives by clinging on a security line to cross a flooded road.


    Activity 4.8: focused on cyclone


                                                         Fig.4.14: illustration of a cyclone and an anticyclone.

    Describe the above figure and then after answer the following question: 

    a. Which direction does the winds moves?

    b. Relate hemispheres with these winds. 

    c. Describe the characteristics of each and their corresponding whether 

    d. Imagine that such kind of wind comes at certain area/ region, what impact does it have to the area?

    Cyclones can be the most intense storms on Earth. A cyclone is a system of winds rotating counterclockwise in the Northern Hemisphere around a low pressure center. The swirling air rises and cools, creating clouds and precipitation. Low pressure systems are also known as depressions

    These are systems of air masses forming an oval or circular shape, where pressure is low in the center and increases towards the periphery.


                                                          Fig.4.15: Illustration of the cyclone formation 

    4.5.1 Types of cyclones 

    There are two types of cyclones: Temperate cyclones or depressions and Tropical cyclones

    a. Temperate cyclones or depressions 

    They rise in the belt of westerly winds and are caused by the mixing of cold air from the Polar Regions with warm and humid air from tropical regions. They are dominantly located in temperate regions between 40- 60 degrees North and South of the equator. The temperate cyclone is also known as middle latitude (mid-latitude)cyclones e.g.  North West Europe, British Columbia, Alaska and the coasts of Chile.

    Characteristics of temperate depressions 

    1. Lowest  pressure is near the center of the depression 

    2. Highest pressure is at the periphery of the system 

    3. Air circulate around the point of low pressure 

    4. The circulation is clockwise in the southern hemisphere 

    5. And anti-clock wise in the northern hemisphere 

    6. Winds blow towards the center, which is a zone of low pressure 

    7. They develop over sea or ocean water 

    8. They affect small area which may not reach 150 km off the coast 

    9. It is a cyclic form of circulation capable of movement, growth and decay.

    Weather associated with temperate cyclones or depressions 

    • It causes rainfall which begins as light showers and progressively become heavier as the warm front passes 

    • The winds blow in easterly or southeasterly direction

    • Much of precipitation starts to fall as snow 

    • With the passage of the warm front and arrival of the warm sector, rain ceases apart from drizzles, temperatures rise and stable stratiform clouds prevail.  

    • Advection fog is common in winter and reduces visibility.

    b. Tropical cyclones/ tropical depressions 

    It is a large scale storm with heavy rainfall and winds which rotate anti-clock wise in the northern hemisphere and clockwise in the southern hemisphere around and towards a low pressure atmospheric pressure center.

    Characteristics of Tropical cyclones/ tropical depressions 

    • They are among the most destructive storms on the earth’s surface.  

    • They are given name where they occur and affect a small area. 

    • They develop on either side of equator between 10 and 20 degrees of latitude rarely between if ever between 5 degrees N and S of the equator. 

    • They originate over sea and oceans water surfaces never over land surfaces 

    • They mainly occur over the western regions of the oceans with a speed of 120km/h 

    • winds which rotate anti-clock wise in the northern hemisphere and clockwise in the southern hemisphere 

    • In northern hemisphere they are most active in August and early September 

    • While in southern hemisphere they are most active in February and March 

    4.5.2 Effect of Cyclone 

    Depending on the location in the world, cyclone takes different name depending on where they develop so their effects are varied according to   the locations.


                 Table 4.2: The effects, names and location of cyclone.

    4.5.3 Safety and emergency measures of cyclones.


    Before Cyclone 

    • Check whether your home has been built to cyclone standards. 

    • Keep a list of emergency phone numbers on display 

    • Be sure trees around your home are well trimmed. 

    • If you are living away from the floodplain, make plans to secure your property. 

    • Check that the walls, roof and eaves of your home are secured. 

    • Ensure that there is no possibly cause injury or damage during extreme winds.

    During the cyclone 

    • Leave the center if it is possible to move. 

    • If you are unable to quit, go to your safe room. 

    • Close all interiors doors and support exterior doors. 

    • Lie on the floor under a table or another powerful object. 

    After the cyclone 

    • If you are inside the room, don’t go outside until officially advised it is safe. 

    • Don’t use electric appliances if wet. 

    • Listen to local radio for official warnings and advice. 

    • Be careful of damaged power lines, bridges, buildings, trees, etc.

    4.5.4 Anticyclone

    Activity 4.10:  Description of anticyclone 

    a. What do you understand by the term “anticyclone”? 

    b. Categorize the types of anticyclone and explain them. 

    c. Compare and contrast cyclones and anticyclones. You can even use illustrations to clarify your answers. 

    d. Ask your friend whether he/she has ever experienced this disaster in their place? Let him him/her support his/her answer.

    An anticyclone is the opposite of a cyclone. An anticyclone’s winds rotate clockwise in the Northern Hemisphere around a center of high pressure. Air comes in from above and sinks to the ground. High pressure centers generally are associated with fair weather.


                                                     Fig.4. 16: illustration of an anticyclone development

    4.5.5 Types of anticyclones

    a. Cold anticyclones: are relatively shallow features related to the surface chill(coldness) of the polar regions. 

    b. Warm anticyclones: they are characterized by cold dense air in the lower troposphere with relatively warm air above. 

    Characteristics of anticyclones 

    • Winds blow from the center to the periphery 

    • Many move slowly and remain stationary for a long time before fading out. 

    • They move northwards 

    • They affect large area( larger than cyclones). 

    • etc

    Weather associated with anticyclones

     • High pressure systems bring clear skies.

     • Winds are usually light, and blow out of the high pressure area.

     • Some few clouds giving rise to little rain and drizzle.

     • High pressure in winter gives us light clouds or clear skies, very low temperatures, calm or light winds.

     • etc.

    Difference of characteristics between a cyclone and anticyclone 


                                                Table 4.3: Difference between cyclone and anticyclone

    4.5.6 Checking my progress 

    1. Explain the cause of cyclone.


    4.6.1 Multiple choices.

    What will happen when the pressure keeps on increasing and the temperature gets higher inside the ground? 

               a. The volume decreases and heat  energy decreases. 

               b. The volume increases and  heat energy decreases. 

                c. The volume increases and heat  energy increases. 

                d. The volume and heat energy remain constant. 

    2. The intensity of an earthquake is measured with a 

                 a. Barometer 

                  b. Polygraph 

                  c. Hydrometer

                  d. Seismograph

    3. Richter scale is used to measure Temperature of bodies Magnitude of earthquake Intensity of wind Intensity of earthquake

    4.6.2 Structured Questions 

    1. Copy and complete the sentence below and use your prior knowledge to fill in. Calm weather and soft winds is associated with….…. the main difference between a cyclone and an anticyclone is that cyclone has a ………… and anticyclone has …………. The winds blow from the center to the periphery. This is the …………. of anticyclone 

    2. Distinguish landslide to the erosion. 

    3. Why, during earthquakes, tall building and small building are shaken differently? Explain your answer. 

    4. Discuss the impact of floods on human activities and suggest ways of minimizing their negative impact? 

    5. Explain how floods develop. 6. Why does the earth shake when there is an earthquake?

    4.6.3 Essay type questions

    1. Explain how erosion, earthquakes and water increase the possibility of landslide to occur? 

    2. Volcanic activity is one of the causes of the earthquake. What people can do in order to prevent it? 

    3. Elaborate more on the role of water in landslide. 

    4.  Describe different ways of reducing the impact of landslides