Natural hazards & disaster management

NATURAL HAZARDS

AND

DISASTER MANAGEMENT

A Supplementary Textbook in Geography for Class XIon

UNIT 11 : Natural Hazards and Disasters

CENTRAL BOARD OF SECONDARY EDUCATIONPREET VIHAR, DELHI - 110092

FIRST EDITION 2006

© CBSE, DELHIPrice:

Published By: The Secretary, Central Board of Secondary Education,2, Community Centre, Preet Vihar, Delhi-110092

Design, Layout and Illustration By: Chandu Press, D-97, Shakarpur, Delhi-110092

Printed By: Chandu Press, D-97, Shakarpur, Delhi-110092

ACKNOWLEDGEMENTS

❖❖❖❖❖ CBSE Advisors:

ο Shri Ashok Ganguly, Chairman, CBSE.

ο Shri G. Balasubramanian, Director (Academics), CBSE.

❖❖❖❖❖ Editor:

ο Shri M.P Sajnani, Advisor Disaster Management & Dy. National Project Director,GOI-UNDP, DRM Programme.

❖❖❖❖❖ Authors:

ο Ms. Balaka Dey, Programme Associate, GoI – UNDP, DRM Programme.

ο Dr. R.B Singh, Reader, Dept. of Geography, Delhi School of Economics,University of Delhi, Delhi – 110007.

❖❖❖❖❖ Review Team:

ο Prof. Noor Mohammad, Dept. of Geography, Delhi School of Economics,University of Delhi, Delhi – 110007.

ο Shri S.S Rastogi, Retd. Principal, Directorate of Education, Delhi

❖❖❖❖❖ Coordinator: Ms. Sugandh Sharma, Education Officer (Commerce), CBSE

CONTENTS

Foreword (i)

For Students (ii)

Chapter 1: 1

Introduction to Disaster Management

Chapter 2:

Natural Hazards: causes, distribution pattern,consequences and mitigation measures for :

❖❖❖❖❖ Earthquake 10

❖❖❖❖❖ Tsunami 17

❖❖❖❖❖ Cyclone 23

❖❖❖❖❖ Flood 30

❖❖❖❖❖ Drought 34

❖❖❖❖❖ Landslide 39

Page Nos.

FOREWORD

The recurrent occurrences of various natural and manmade disasters like the December2004 Tsunami, the bomb blasts in the cinema halls of Delhi and many such incidenceshave diverted our focus towards safety of one’s own life. In the previous class of VIII, IXand X as students you must have read about various natural and manmade hazards –their preparedness and mitigation measures. In class XI, the Board had introduced frontlinecurriculum on Disaster Management in Unit 11 of the Geography syllabus. In supplementarytextbook on Disaster Management in Geography the Board intends to explain in detailvarious concepts used in Disaster Management and discussed about the causes, distributionpattern, consequences and mitigation measures for various natural hazards like earthquake,tsunami, flood, cyclone, landslide and drought which are a recurrent phenomena in ourcountry.

I hope this book will help all students of Geography, who are the future citizens, to have abetter understanding of the subject so that they are well prepared to combat it. Beingsenior students of the school I would appreciate if all of you (including teachers) asresponsible citizens and as volunteers take up the initiative of preparing the school disastermanagement plan and also educate the younger students of the school on various safetymeasures that need to be taken up for a better living.

I would like to thank Ministry of Home Affairs for their support and guidance in the preparationof the course material and helping the Board in carrying out training programmes for theteachers across the country. I would also like to extend my sincere thanks to the GeographyDepartment, University of Delhi for the support they have extended to come up with thecourse outline for the Board and also helping in the development of the textbook. Mysincere thanks to the UNDP team who have contributed the most and have tirelessly putall their effort in development of the textbook and also carrying out training programmesfor the teachers and the school principals across the country without whose support theinitiative would have been difficult to continue. I am grateful to the teachers who haveplayed a key role in making the subject so interesting and demanding. Their understandingand interest have made teachers, students and other staff members of the school designthe school disaster management plans which have made the schools a better and saferplace.

Last but not the least my sincere thanks and appreciation to Shri G. Balasubramanian(Director, Academics) who has always guided the team while developing the textbook andintroducing innovative ways to make the subject as a necessary life skill than a meresubject.

Ashok GangulyChairman, CBSE

(i)

For the Students………………Some of you must have encountered one or the other natural or manmade hazard whichhas caused a huge loss to life and property and have disrupted the normal life of thepeople. Those who have had the opportunity to undergo certain training on safety like firstaid or search and rescue would have helped those in misery but then all of you are not wellequipped with both theoretical and practical knowledge. As a young responsible citizenyou can take up initiatives to prepare the community and make the community a saferplace to live.

The Board in its endeavor to make the students good managers and volunteers and effec-tive carrier of messages, have introduced Disaster Management at various levels startingfrom Standard VIII with effect from the academic year 2003. The Standard VIII textbook on“Together Towards a Safer India – Part I” focuses on various natural and manmadehazards and its preparedness measures. Taking it forward the Standard IX textbook “To-gether Towards a Safer India – Part II” explains explicitly on the mitigation measuresthat need to be taken up to save lives, livelihood and property. Apart from understanding itas a subject, CBSE has felt the need to understand the subject as a necessary life skill.Standard X textbook “Together Towards a Safer India – Part III” looks disaster manage-ment from a different perspective of making the students and teachers help in preparationof Disaster Management Plans for the school and the community and also making themunderstand the various First Aid and Search and Rescue techniques and also on the roleof government, NGOs and others in managing disasters.

Those who have had the opportunity to read these books are by now better equipped but,as a student the Board doesn’t refrain you from gaining knowledge and have a basicunderstanding of the subject. In this textbook we have tried to give some basicunderstanding about various natural hazards from the geography point of view. Apart fromvarious concepts the chapter tries to analyse various hazards prevalent in our country.Understanding the causes, distribution pattern, consequences and mitigation measureswill help you to get better prepared.

(ii)

Natural Hazards & Disaster Management

1

Objectives of the chapter:

The main objective of this chapter is tohave a basic understanding of variousconcepts used in Disaster Management.The concepts explained here are:Disaster, Hazard, Vulnerability, Capacity,Risk and Disaster Management Cycle.Apart from the terminologies, the chapteralso tries to explain various types ofdisasters. In standard VIII, IX and Xmany of you have already beenintroduced to some of these concepts.This chapter has been designedto upgrade your knowledge and skillso as to have a better understanding ofnatural hazards, disasters and theirmanagement.

After reading this chapter thestudents and the teachers will beable to have a basic understandingof the concepts and should be ableto differentiate between them withsuitable examples.

Chapter 1INTRODUCTION TO DISASTER MANAGEMENT

Background:

The global context:

Disasters are as old as human history butthe dramatic increase and the damagecaused by them in the recent past havebecome a cause of national and internationalconcern. Over the past decade, the numberof natural and manmade disasters hasclimbed inexorably. From 1994 to 1998,reported disasters average was 428 per yearbut from 1999 to 2003, this figure went up toan average of 707 disaster events per yearshowing an increase of about 60 per centover the previous years. The biggest rise wasin countries of low human development,which suffered an increase of 142 per cent.

The figure 1.1 shows the deadliest disastersof the decade (1992 – 2001). Drought andfamine have proved to be the deadliestdisasters globally, followed by flood,technological disaster, earthquake, winds-torm, extreme temperature and others. Globaleconomic loss related to disaster eventsaverage around US $880 billion per year.

Fig : 1.1 World Scenario: Reported Deaths from allDisasters (1992-2001)


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Indian scenario:

The scenario in India is no different fromthe global context. The super cyclone ofOrissa (1999), the Gujarat earthquake(2001) and the recent Tsunami (2004)

Table 1.1 Major disasters in India since 1970

Sl. No Disaster ImpactCyclone

1 29th October 1971, Orissa Cyclone and tidal waves killed 10,000people

2 19th November, 1977, Cyclone and tidal waves killed 20,000Andhra Pradesh people

3 29th and 30th October 1999, Cyclone and tidal waves killed 9,000 andOrissa 18 million people were affectedEarthquake

4 20th October 1991 Uttarkashi An earthquake of magnitude 6.6 killed723 people

5 30th September 1993 Latur Approximately 8000 people died andthere was a heavy loss to infrastructure

6 22 May 1997 Jabalpur 39 people dead7 29th March 1997, Chamoli 100 people dead8 26th January, 2001, Bhuj, More than 10,000 dead and heavy loss

Gujarat to infrastructureLandslide

9 July 1991, Assam 300 people killed, heavy loss to roadsand infrastructure

10 August 1993, Nagaland 500 killed and more than 200 housesdestroyed and about 5kms. Roaddamaged.

11 18th August 1998, Malpa 210 people killed. Villages were washedaway

Flood12 1978 Floods in North East India 3,800 people killed and heavy loss to

property.13 1994 Floods in Assam, More than 2000 people killed and

Arunachal Pradesh, Jammu and thousands affectedKashmir, Himachal Pradesh,Panjab, Uttar Pradesh, Goa,Kerala and Gujarat

affected mill ions across the countryleaving behind a trail of heavy loss of life,property and livelihood. Table 1.1 showsa list of some of the major disasters thathave caused colossal impact on thecommunity.


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While studying about the impact we need tobe aware of potential hazards, how, whenand where they are likely to occur, and theproblems which may result of an event. InIndia, 59 per cent of the land mass issusceptible to seismic hazard; 5 per cent ofthe total geographical area is prone to floods;8 per cent of the total landmass is prone tocyclones; 70 per cent of the total cultivablearea is vulnerable to drought. Apart from thisthe hilly regions are vulnerable to avalanches/landslides/hailstorms/cloudbursts. Apart fromthe natural hazards, we need to know aboutthe other manmade hazards which arefrequent and cause huge damage to life andproperty. It is therefore important that we areaware of how to cope with their effects.

We have seen the huge loss to life, propertyand infrastructure a disaster can cause butlet us understand what is a disaster, whatare the factors that lead to it and its impact.

What is a Disaster ?

Almost everyday, newspapers, radio andtelevision channels carry reports on disasterstriking several parts of the world. But whatis a disaster? The term disaster owes its

origin to the French word “Desastre” whichis a combination of two words ‘des’ meaningbad and ‘aster’ meaning star. Thus the termrefers to ‘Bad or Evil star’. A disaster canbe defined as “A serious disruption in thefunctioning of the community or a societycausing wide spread material, economic,social or environmental losses which exceedthe ability of the affected society to copeusing its own resources”.

A disaster is a result from the combinationof hazard, vulnerability and insufficientcapacity or measures to reduce the potentialchances of risk.

A disaster happens when a hazard impactson the vulnerable population and causesdamage, casualties and disruption. Fig: 1.2would give a better illustration of what adisaster is. Any hazard – flood, earthquakeor cyclone which is a triggering event alongwith greater vulnerability (inadequate accessto resources, sick and old people, lack ofawareness etc) would lead to disastercausing greater loss to life and property. Forexample; an earthquake in an uninhabiteddesert cannot be considered a disaster, nomatter how strong the intensities produced.

Fig: 1.2


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An earthquake is disastrous only when itaffects people, their properties and activities.Thus, disaster occurs only when hazardsand vulnerability meet. But it is also to benoted that with greater capacity of theindividual/community and environment toface these disasters, the impact of a hazardreduces. Therefore, we need to understandthe three major components namely hazard,vulnerability and capacity with suitableexamples to have a basic understanding ofdisaster management.

What is a Hazard ? How is it clas-sified ?

Hazard may be defined as “a dangerouscondition or event, that threat or have thepotential for causing injury to life or damageto property or the environment.” The word‘hazard’ owes its origin to the word ‘hasard’in old French and ‘az-zahr ’ in Arabicmeaning ‘chance’ or ‘luck’. Hazards can begrouped into two broad categories namelynatural and manmade.

Table 1.2: Various types of hazards

Types HazardsGeological Hazards 1. Earthquake 4. Landslide

2. Tsunami 5. Dam burst3. Volcanic eruption 6. Mine Fire

Water & Climatic Hazards 1. Tropical Cyclone 6. Cloudburst2. Tornado and Hurricane 7. Landslide3. Floods 8. Heat & Cold wave4. Drought 9. Snow Avalanche5. Hailstorm 10.Sea erosion

Environmental Hazards 1. Environmental pollutions 3. Desertification2. Deforestation 4. Pest Infection

Biological 1. Human / Animal Epidemics 3. Food poisoning2. Pest attacks 4. Weapons of Mass

Destruction

1. Natural hazards are hazards which arecaused because of natural phenomena(hazards with meteorological, geological oreven biological origin). Examples of naturalhazards are cyclones, tsunamis, earth-quake and volcanic eruption which areexclusively of natural origin. Landslides,floods, drought, fires are socio-naturalhazards since their causes are both naturaland man made. For example flooding maybe caused because of heavy rains, landslideor blocking of drains with human waste.

2. Manmade hazards are hazards whichare due to human negligence. Manmadehazards are associated with industries orenergy generation facilities and includeexplosions, leakage of toxic waste, pollution,dam failure, wars or civil strife etc.

The list of hazards is very long. Many occurfrequently while others take placeoccasionally. However, on the basis of theirgenesis, they can be categorized asfollows:


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What is vulnerability ?

Vulnerability may be defined as “The extentto which a community, structure, servicesor geographic area is likely to be damagedor disrupted by the impact of particularhazard, on account of their nature,construction and proximity to hazardousterrains or a disaster prone area.”

Vulnerabilities can be categorized intophysical and socio-economic vulnerability.

Physical Vulnerability: It includes notions ofwho and what may be damaged ordestroyed by natural hazard such as earth-quakes or floods. It is based on the physicalcondition of people and elements at risk,such as buildings, infrastructure etc; and their

proximity, location and nature of the hazard.It also relates to the technical capability ofbuilding and structures to resist the forcesacting upon them during a hazard event.

Figure 1.3 shows the settlements which arelocated in hazardous slopes. Many landslideand flooding disasters are linked to what yousee in the figure 1.3. Unchecked growth ofsettlements in unsafe areas exposes thepeople to the hazard. In case of an earth-quake or landslide the ground may fail andthe houses on the top may topple or slideand affect the settlements at the lower leveleven if they are designed well for earthquakeforces.

Socio-economic Vulnerability: The degreeto which a population is affected by a hazard

Chemical, Industrial and 1. Chemical disasters 3. Oil spills/FiresNuclear Accidents 2. Industrial disasters 4. Nuclear

Accident related 1. Boat / Road / Train 3. Building collapse

accidents / air crash 4. Electric Accidents

Rural / Urban fires 5. Festival related

Bomb /serial bomb disasters

blasts 6. Mine flooding

2. Forest fires

Types Hazards

Figure 1.3 : Site after pressures from population growth and urbanization


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will not merely lie in the physical componentsof vulnerability but also on the socio-economic conditions. The socio-economiccondition of the people also determines theintensity of the impact. For example, peoplewho are poor and living in the sea coast don’thave the money to construct strong concretehouses. They are generally at risk andloose their shelters when ever there isstrong wind or cyclone. Because of theirpoverty they too are not able to rebuild theirhouses.

What is capacity ?

Capacity can be defined as “resources,means and strengths which exist inhouseholds and communities and whichenable them to cope with, withstand,prepare for, prevent, mitigate or quicklyrecover from a disaster”. People’s capacitycan also be taken into account. Capacitiescould be:

Physical Capacity: People whose houseshave been destroyed by the cyclone or cropshave been destroyed by the flood cansalvage things from their homes and fromtheir farms. Some family members haveskills, which enable them to find employmentif they migrate, either temporarily orpermanently.

Socio-economic Capacity: In most of thedisasters, people suffer their greatest lossesin the physical and material realm. Richpeople have the capacity to recover soonbecause of their wealth. In fact, they areseldom hit by disasters because they live in

safe areas and their houses are built withstronger materials. However, even wheneverything is destroyed they have thecapacity to cope up with it.

Hazards are always prevalent, but thehazard becomes a disaster only when thereis greater vulnerability and less of capacityto cope with it. In other words the frequencyor likelihood of a hazard and the vulnerabilityof the community increases the risk of beingseverely affected.

What is risk ?

Risk is a “measure of the expected lossesdue to a hazard event occurring in a givenarea over a specific time period. Risk is afunction of the probability of particularhazardous event and the losses eachwould cause.” The level of risk dependsupon:

❖ Nature of the hazard

❖ Vulnerability of the elements which areaffected

❖ Economic value of those elements

A community/locality is said to be at ‘risk’when it is exposed to hazards and islikely to be adversely affected by itsimpact. Whenever we discuss ‘disastermanagement’ it is basically ‘disaster riskmanagement’. Disaster risk managementincludes all measures which reduce disasterrelated losses of life, property or assets byeither reducing the hazard or vulnerabilityof the elements at risk.


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Disaster Management Cycle

Disaster Risk Management includes sumtotal of all activities, programmes andmeasures which can be taken up before,during and after a disaster with the purposeto avoid a disaster, reduce its impact orrecover from its losses. The three key stagesof activities that are taken up within disasterrisk management are:

1. Before a disaster (pre-disaster).

Activities taken to reduce human andproperty losses caused by a potentialhazard. For example carrying out aware-ness campaigns, strengthening the existingweak structures, preparation of the disastermanagement plans at household and

community level etc. Such risk reductionmeasures taken under this stage are termedas mitigation and preparedness activities.

2. During a disaster (disasteroccurrence).

Initiatives taken to ensure that the needs andprovisions of victims are met and suffering isminimized. Activities taken under this stageare called emergency response activities.

3. After a disaster (post-disaster)

Initiatives taken in response to a disasterwith a purpose to achieve early recovery andrehabilitation of affected communities,immediately after a disaster strikes. These arecalled as response and recovery activities.

Disaster Risk Reduction can take place in the following ways:

1. Preparedness

This protective process embraces measures which enable governments, communitiesand individuals to respond rapidly to disaster situations to cope with them effectively.Preparedness includes the formulation of viable emergency plans, the developmentof warning systems, the maintenance of inventories and the training of personnel.It may also embrace search and rescue measures as well as evacuation plans forareas that may be at risk from a recurring disaster.

Preparedness therefore encompasses those measures taken before a disaster eventwhich are aimed at minimising loss of life, disruption of critical services, and damagewhen the disaster occurs.

2. Mitigation

Mitigation embraces measures taken to reduce both the effect of the hazard and thevulnerable conditions to it in order to reduce the scale of a future disaster. Thereforemitigation activities can be focused on the hazard itself or the elements exposed tothe threat. Examples of mitigation measures which are hazard specific include watermanagement in drought prone areas, relocating people away from the hazard proneareas and by strengthening structures to reduce damage when a hazard occurs.

In addition to these physical measures, mitigation should also aim at reducing theeconomic and social vulnerabilities of potential disasters


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Reference: Are you prepared? Learning from the Great Hanshin-AwajiEarthquake Disaster - Handbook for Disaster Reduction and Volunteer activities

Figure 1.4 : Disaster Management

In the subsequent chapters we woulddiscuss in detail some of the major hazardsprevalent in our country its causes, impact,preparedness and mitigation measures thatneed to be taken up.

Reference for further reading:

1. Reading materials of 11th Community BasedDisaster Risk Management Course,Bangkok, Thailand July 21 – August 1, 2003.

2. Anderson, M. and P. Woodrow. 1989. Risingfrom the Ashes: Development Strategies in

Times of Disaster. UNESCO and West viewPress, Inc., Colorado.

3. Anderson M. Vulnerability to Disaster andSustainable Development: A GeneralFramework for Assessing Vulnerability.

4. UNDP Disaster Management TrainingProgramme.1992. An Overview of DisasterManagement.

5. International Federation of Red CrescentSocieties World Disaster Report: Focus onCommunity resilience.

6. http://www.unisdr.org/eng/l ibrary/l ib-terminology


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Exercise

1) Explain with examples the differencebetween hazard, and vulnerability. Howdoes capacity influence vulnerability?

2) Explain in detail the vulnerabilityprofile of our country.

3) Define risk and suggest two ways ofreducing risk with appropriateexamples.

4) Briefly discuss the DisasterManagement Cycle with suitableexamples.


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The discussion on various terminologies hashelped us in having a basic understandingof disaster management. However, eachhazard has its own characteristics. Tounderstand the significance and implicationsof various types of hazards we must have abasic understanding about the nature,causes and effects of each hazard type andthe mitigation measures that need to betaken up. In this chapter, we would discussthe following hazards namely earthquake,tsunami, landslide, flood, cyclone anddrought that we normally face in our country.

Chapter 2NATURAL HAZARDS - CAUSES, DISTRIBUTIONPATTERN, CONSEQUENCE, AND MITIGATION

MEASURES

kilometers under the sea to 65 kilometersunder the continents. The crust is not onepiece but consists of portions called ‘plates’which vary in size from a few hundred tothousands of kilometers (Fig 2.1.1). The‘theory of plate tectonics’ holds that theplates ride up on the more mobile mantle,and are driven by some yet unconfirmedmechanisms, perhaps thermal convectioncurrents. When these plates contact eachother, stress arises in the crust (Fig 2.1.2).

These stresses can be classified accordingto the type of movement along the plate’sboundaries:

a) pulling away from each other,

b) pushing against one another and

c) sliding sideways relative to each other.

All these movements are associated withearthquakes.

The areas of stress at plate boundarieswhich release accumulated energy byslipping or rupturing are known as 'faults'.The theory of 'elasticity' says that the crustis continuously stressed by the movementof the tectonic plates; it eventually reachesa point of maximum supportable strain. Arupture then occurs along the fault and therock rebounds under its own elastic stressesuntil the strain is relieved. The fault rupturegenerates vibration called seismic (from theGreek 'seismos' meaning shock or

2.1 Earthquake

Earthquake is one of the most destructivenatural hazard. They may occur at any timeof the year, day or night, with sudden impactand little warning. They can destroy buildingsand infrastructure in seconds, killing orinjuring the inhabitants. Earthquakes notonly destroy the entire habitation but mayde-stabilize the government, economy andsocial structure of the country. But what isan earthquake? It is the sudden shaking ofthe earth crust. The impact of an earthquakeis sudden and there is hardly any warning,making it impossible to predict.

Cause of Earthquake :

The earth’s crust is a rocky layer of varyingthickness ranging from a depth of about 10


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Fig. : 2.1.1 : Tectonic Plates

Seven major plates and several minor ones- They move a few inches a year,riding on semi-molten layers of rock underneath the crust

Fig. : 2.1.2 : Tectonic Plates


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San Andreas fault,California, U.S.A

Table 2.1.1 Different types of plate movement

Plate Motions Examples Illustrations

Divergent - where newcrust is generated as theplates pull away from eachother.

The Mid-Atlantic Ridge,which splits nearly the entireAtlantic Ocean north tosouth, is probably the best-known and most-studiedexample of a divergent-plateboundary. The rate ofspreading along the Mid-Atlantic Ridge averagesabout 2.5 centimeters peryear (cm/yr), or 25 km in amillion years.

2. Convergent - wherecrust is destroyed as oneplate dives under another.

Ring of Fire and TheHimalayan mountain rangedramatically demonstratesone of the most visible andspectacular consequencesof plate tectonics.

3. Transformational - wherecrust is neither producednor destroyed as the platesslide horizontally past eachother.

The San Andreas faultslicing through the CarrizoPlain in the Temblor Rangeeast of the city of San LuisObispo

Mid Atlantic Ridge


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Body waves (P and S waves) penetratethe body of the earth, vibrating fast. ‘P’waves travel about 6 kilometers per hourand ‘S’ waves travel with a speed of 4kilometers per hour.

Surface waves vibrate the groundhorizontally and vertically. These longperiod waves cause swaying of tall buildingsand slight waves motion in bodies of watereven at great distances from the epicenter.

earthquake) waves, which radiates from thefocus in all directions.

The point of rupture is called the 'focus' andmay be located near the surface or deepbelow it. The point on the surface directlyabove the focus is termed as the 'epicenter'of the earthquake (see Fig 2.1.3).

Fig 2.1.3

General characteristics

Earthquake vibrations occur in a variety offrequencies and velocities. The actualrupture process may last for a few secondsto as long as one minute for a majorearthquake. The ground shaking is causedby ‘body waves’ and ‘surface wave’.

♦ Deep:- 300 to 700 kms from the earthsurface

♦ Medium:- 60 to 300 kms

♦ Shallow: less than 60 kms

The deep focus earthquakes are rarelydestructive because by the time the wavesreach the surface the impact reduces.Shallow focus earthquakes are morecommon and are extremely damagingbecause of their proximity to the surface.

Measuring Earthquakes

Earthquakes can be described by the useof two distinctively different scales ofmeasurement demonstrating magnitudeand intensity. Earthquake magnitude oramount of energy released is determinedby the use of a seismograph’ which is aninstrument that continuously records groundvibration. The scale was developed by aseismologist named Charles Richter. Anearthquake with a magnitude 7.5 on theRichter scale releases 30 times the energythan one with 6.5 magnitudes. An earthquakeof magnitude 3 is the smallest normally feltby humans. The largest earthquake that hasbeen recorded with this system is 9.25(Alaska, 1969 and Chile, 1960).

The second type of scale, the earthquakeintensity scale measures the effects of anearthquake where it occurs. The most widelyused scale of this type was developed in 1902by Mercalli an Italian seismologist. The scalewas extended and modified to suit the moderntimes. It is called the Modified Mercalli Scale ,which expresses the intensity of earthquakeeffect on people, structure and the earth’ssurface in values from I to XII. With an intensityof VI and below most of the people can feelthe shake and there are cracks on the walls,

Earthquakes can be of three types basedon the focal depth:


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Fig 2.1.4 shows the adverse effect s of an earthquake

but with an intensity of XII there is generalpanic with buildings collapsing totally and thereis a total disruption in normal life.

Predictability : Although some scientists claimability to predict earthquakes, the methods arecontroversial. Accurate and exact predictionsof such sudden incidents are still not possible.

Typical adverse effects

Physical damage:

down of communication facilities. The effectof an earthquake is diverse. There are largenumber of casualties because of the poorengineering design of the buildings andclose proximity of the people. About 95 percent of the people who are killed or who areaffected by the earthquake is because ofthe building collapse. There is also a hugeloss to the public health system, transportand communication and water supply in theaffected areas.

Distribution pattern of Earthquakesin India

India falls quite prominently on the 'Alpine -Himalayan Belt'. This belt is the line alongwhich the Indian plate meets the Eurasianplate. This being a convergent plate, theIndian plate is thrusting underneath theEurasian plate at a speed of 5 cm per year.The movement gives rise to tremendousstress which keeps accumulating in therocks and is released from time to time inthe form of earthquakes.

Fig 2.1.5: Fault line in India

Damage occurs to human settlement,buildings, structures and infrastructure,especially bridges, elevated roads, railways,water towers, pipelines, electrical generatingfacilities. Aftershocks of an earthquake cancause much greater damage to alreadyweakened structures.

Secondary effects include fires, dam failureand landslides which may block water waysand also cause flooding. Damage may occurto facilities using or manufacturingdangerous materials resulting in possiblechemical spills. There may also be a break

Fig 2.1.5 Fault lines in India


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The seismic zoning map of India is dividedinto four zones namely Zone II, III, IV and V,with zone V shown in red colour infigure 2.1.6 being most vulnerable to

earthquakes. Much of India lies in zone III.New Delhi the capital city of India lie in zoneIV where as big cities like Mumbai andChennai are in zone III.

Table 2.1.2: List of significant Earthquakes in India

Year Location Magnitude of 6+

1950 Arunachal Pradesh - China Border 8.5

1956 Anjar, Gujarat 7.0

1967 Koyna, Maharashtra 6.5

1975 Kinnaur, Himachal Pradesh 6.2

1988 Manipur - Myanmar Boarder 6.6

1988 Bihar - Nepal Border 6.4

1991 Uttarkashi - Uttar Pradesh Hills 6.0

1993 Latur - Maharashtra 6.3

1997 Jabalpur, Madhya Pradesh 6.0

1999 Chamoli, Uttar Pradesh 6.8

2001 Bhuj, Gujarat 6.9

2005 Muzaffarabad (Pakistan) Impact in 7.4

Jammu & Kashmir

Fig: 2.1.6


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Possible risk reduction measures:

Community preparedness: Communitypreparedness is vital for mitigatingearthquake impact. The most effective wayto save you even in a slightest shaking is'DROP, COVER and HOLD'.

Planning: The Bureau of Indian Standardshas published building codes and guidelinesfor safe construction of buildings againstearthquakes. Before the buildings areconstructed the building plans have to bechecked by the Municipality, according tothe laid down bylaws . Many existing lifelinebuildings such as hospitals, schools and firestations may not be built with earthquakesafety measures. Their earthquake safetyneeds to be upgraded by retrofittingtechniques.

Public education is educating the publicon causes and characteristics of an

Effect of Soil type on ground shaking Essential requirements in a Masonry building

earthquake and preparedness measures. Itcan be created through sensitization andtraining programme for community,architects, engineers, builders, masons,teachers, government functionariesteachers and students.

Engineered structures: Buildings needto be designed and constructed as per thebuilding by laws to withstand groundshaking. Architectural and engineeringinputs need to be put together to improvebuilding design and construction practices.The soil type needs to be analyzed beforeconstruction. Building structures on softsoil should be avoided. Buildings on softsoil are more likely to get damaged evenif the magnitude of the earthquake is notstrong as shown in Figure 2.1.7. Similarproblems persist in the bui ldingsconstructed on the river banks which havealluvial soil.

Fig: 2.1.7


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Web Resources:

§ www.nicee.org: Website of The NationalInformation Center of EarthquakeEngineering (NICEE) hosted at IndianInstitute of Technology Kanpur (IITK) isintended to collect and maintain informationresources on Earthquake Engineer-ing andmake these available to the interestedprofessionals, researche-rs, academiciansand others with a view to mitigateearthquake disasters in India. The host alsogives IITK-BMTPC Earthquake Tips.

§ www.imd.ernet.in/section/seismo/static/welcome.htm Earthquake Information –India Meteorological Department, India. IMDdetects and locates earthquakes andevaluates seismicity in different parts of thecountry.

§ www.bmtpc.org In order to bridge the gapbetween research and development andlarge scale application of new buildingmaterial technologies, the erstwhile Ministryof Urban Development, Government ofIndia, had established the Building MaterialsAnd Technology Promotion Council in July1990.

§ www.earthquake.usgs.gov Source forscience about the Earth, its natural and livingresources, natural hazards, and theenvironment.

Exercise:

1. What are earthquakes ? List out thecauses of an earthquake.

2. Differentiate between magnitude andintensity of an earthquake. How arethey measured ?

3. Identify three major mitigationmeasures to reduce earthquake risk.

2.2 Tsunami

The term Tsunami has been derived froma Japanese term Tsu meaning 'harbor' andnami meaning 'waves'. Tsunamis arepopularly called tidal waves but theyactually have nothing to do with the tides.These waves which often affect distantshores, originate by rapid displacement ofwater from the lake or the sea either byseismic activity, landslides, volcaniceruptions or large meteoroid impacts.What ever the cause may be sea water isdisplaced with a violent motion and swellsup, ultimately surging over land with greatdestructive power. The effects of atsunami can be unnoticeable or evendestructive.

Causes of a Tsunami

The geological movements that causetsunamis are produced in three majorways. The most common of these are faultmovements on the sea floor, accom-panied by an earth-quake. They releasehuge amount of energy and have thecapacity to cross oceans. The degree ofmovement depends on how fast theearthquake occurs and how much wateris displaced. Fig 3.1 shows how anearthquake causes tsunami.

The second most common cause of thetsunami is a landslide either occurring underwater or originating above the sea and thenplunging into the water. The largest tsunamiever produced by a landslide was in Lituya


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Fig 2.2.2 Picture of a Tsunami

Fig 3.1 An Earthquake causing Tsunami

Bay, Alaska 1958. The massive rock slideproduced a wave that reached a high watermark of 50 - 150 meters above the shoreline.

The third major cause of tsunami is volcanicactivity. The flank of a volcano located nearthe shore or under water may be uplifted ordepressed similar to the action of a fault, or,the volcano may actually explode. In 1883,the violent explosion of the famous volcano,Krakotoa in Indonesia, produced tsunamimeasuring 40 meters which crushed uponJava and Sumatra. Over 36,000 people losttheir lives in this tyrant waves.

General Characteristics:

Tsunami differs from ordinary ocean waves,which are produced by wind blowing overwater. The tsunamis travel much faster thanordinary waves. Compared to normal wavespeed of 100 kilometers per hour, tsunamiin the deep water of the ocean may travelthe speed of a jet airplane - 800 kilometersper hour! And yet, in spite of their speed,tsunami increases the water height only30-45cm and often passes unnoticed byships at sea.

Contrary to the popular belief, the tsunamiis not a single giant wave. It is possible for atsunami to consist of ten or more waveswhich is then termed as 'tsunami wave train'.The waves follow each other 5 to 90 minutesapart. Tsunami normally causes flooding asa huge wall of water enters the main land.

Predictability:There are two distinct types of tsunamiwarning:

a) International tsunami warning systemsand

b) Regional warning systems.


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Fig 2.2.3 Flooding caused by the 2004 Tsunami inTamil Nadu

Tsunamis have occurred in all the oceansand in the Mediterranean Sea, but the greatmajority of them have occurred in the PacificOcean. Since scientists cannot exactlypredict earthquakes, they also cannotexactly predict when a tsunami will begenerated.

a) International Tsunami WarningSystems: Shortly after the HiloTsunami (1946), the Pacific TsunamiWarning System (PTWS) wasdeveloped with its operational centerat the Pacific Tsunami Warning Center(PTWC) near Honolulu, Hawaii. ThePTWC is able to alert countries severalhours before the tsunami strikes. Thewarning includes predicted arrival timeat selected coastal communities wherethe tsunami could travel in few hours.A tsunami watch is issued withsubsequent arrival time to othergeographic areas.

b) Regional Warning Systems usuallyuse seismic data about nearbyearthquakes to determine if there is apossible local threat of a tsunami. Suchsystems are capable enough toprovide warnings to the general publicin less than 15 minutes.

In 1995 the US National Oceanic andAtmospheric Administration (NOAA)began developing the Deep OceanAssessment and Reporting of Tsunami(DART) system. By 2001 six stations hadbeen deployed in the Pacific Ocean. Eachstation consists of a sea bed bottompressure recorder (at a depth of about6000 m) which detects the passage of atsunami and transmits the data to asurface buoy. The surface buoy thenradios the information to the PTWC.

In India, the Survey of India maintains atide gauge network along the coast of India.The gauges are located in major ports asshown in the figure 2.2.4. The day-to-daymaintenance of the gauge is carried with theassistance from authorities of the ports.

Fig. 2.2.4 : Tide gauge network in India

Apart from the tide gauge, tsunami can bedetected with the help of radars. The 2004Indian Ocean tsunami, recorded data fromfour radars and recorded the height oftsunami waves two hours after theearthquake. It should be noted that thesatellites observations of the Indian Oceantsunami would not have been of any use in


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delivering warnings, as the data took fivehours to process and it was pure chancethat the satellites were overhead at that time.However, in future it is possible that thespace-based observation might play a directrole in tsunami warning.

Typical adverse effects:

Local tsunami events or those less than 30minutes from the source cause the majorityof damage. The force of the water can razeeverything in its path. It is normally theflooding affect of the tsunami that causesmajor destruction to the human settlements,roads and infrastructure thereby disruptingthe normal functioning of the society.

Withdrawal of the tsunami causes majordamage. As the waves withdraw towardsthe ocean they sweep out the foundationsof the buildings, the beaches get destroyedand the houses carried out to sea. Damageto ports and airports may preventimportation of needed food and medicalsupplies. Apart from the physical damage,there is a huge impact on the public healthsystem. Deaths mainly occur because ofdrowning as water inundates homes. Manypeople get washed away or crushed by thegiant waves and some are crushed by thedebris, causes.

There are very few evidences which showthat tsunami flooding has caused large scalehealth problem.

Availability of drinking water has alwaysbeen a major problem in areas affected bya disaster. Sewage pipes may be damagedcausing major sewage disposal problems.Open wells and other ground water may becontaminated by salt water and debris andsewage. Flooding in the locality may leadto crop loss, loss of livelihood like boats andnets, environmental degradation etc.

Tsunami - A Terror

The year 2004 has come to an end.A memorable year it has been.Ups and downs and highs and lows

in the past year we have seen.The year went by smoothlybut came to a crashing end.Nature's fury shattered the life of so manyBroken pieces we are still to mend.Tsunami - a huge tidal wave

swept over the life of all.Nature's wrath spared noneMankind suffered a great fall.Thousands of homes were destroyedThousands of lives were taken.We have taken nature for granted

and a heavy price we have forsaken.

The aftershocks of the disasterWe are still enduring.The ones alive are being given helpTheir pains we are curing.In the history of mankind

This blemish will remain forever.When reminded of this grave calamityThe world will always shiver.The wounds will take time to healThis disaster will always remain in ourmind.But we will stand up with a smile

And walk ahead leaving this terrorbehind.

Ashwathi ThampiJ.K. Singhania School(Standard VIII), Thane


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Date Location Impact1524 Near Dabhol, Maharashtra Sufficient data not available02 April 1762 Arakan Coast, Myanmar Sufficient data not available16 June 1819 Rann of Kachchh, Gujarat Sufficient data not available31 October 1847 Great Nicobar Island Sufficient data not available31 December 1881 An earthquake of 7.9 in the Entire east coast of India and

Richter scale in Car Nicobar Andaman & Nicobar Islands;Island 1m tsunamis were recorded at

Chennai.26 August 1883 Explosion of the Krakatoa volcano East coast of India was affected;

in Indonesian. 2m tsunamis were recorded atChennai.

26 June 1941 An 8.1 Richter scale earthquake in East coast of India was affectedthe Andaman archipelago. but no estimates of height of the

tsunami is available27 November 1945 An 8.5 Richter scale earthquake at West coast of India from north to

a distance of about 100km south Karwar was affected; 12m tsunamiof Karachi was felt at Kandla.

26 December 2004 Banda Aceh, Indonesia; Tamil Nadu, The East cost of India was affected.Kerala, Andhra Pradesh, Andaman The waves measured around 10 mand Nicobar Islands, India; Sri Lanka; high killing more than 10,000 preciousThailand; Malaysia; Kenya; Tanzania lives.

Table 2.2.1: History of tsunami’s in India

Distribution pattern of Tsunami inIndia:

Even though India has not faced frequentTsunamis but there is a need to identify theareas that are generally affected by Tsunamis.The whole of the Indian coastal belt is proneto Tsunami. Table 2.2.1 shows incidents oftsunamis that have affected our country.


While it is of course not possible to preventa tsunami, in certain tsunami pronecountries some measures have been takento reduce the damage caused on shore.Japan has implemented an extensiveprogramme of building tsunami walls of upto 4.5m (13.5 ft) high in front of populatedcoastal areas. Other localities have builtflood gates and channels to redirect thewater from incoming tsunamis. However,

their effectiveness has been questioned, astsunamis are often higher than the barriers.For instance, the tsunami which hit the islandof Hokkaido on July 12, 1993 created wavesas much as 30m (100 ft) tall - as high as a10-story building. The port town of Aonaeon Hokkaido was completely surrounded bya tsunami wall, but the waves washed rightover the wall and destroyed all the wood-

Fig 2.2.5 Tsunami walls in populated coastalareas of Japan


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framed structures in the area. The wall mayhave succeeded in slowing down andmoderating the height of the tsunami but itdid not prevent major destruction and lossof life.

Some other systematic measures to protectcoastlines against tsunamis include:

Site Planning and Land Management -Within the broader framework of acomprehensive plan, site planningdetermines the location, configuration, anddensity of development on particular sitesand is, therefore, an important tool inreducing tsunami risk.

Fig 2.2.6 Damaged houses constructed on the seacoast in Chennai

- The designation and zoning of tsunamihazard areas for such open-spaceuses as agriculture, parks andrecreation, or natural hazard areas isrecommended as the first land useplanning strategy. This strategy isdesigned to keep development at aminimum in hazard areas.

- In areas where it is not feasible torestrict land to open-space uses, otherland use planning measures can beused. These include strategicallycontrolling the type of developmentand uses allowed in hazard areas, andavoiding high-value and high-occupancy uses to the greatest degreepossible.

Engineering structures – Most of thehabitation of the fishing community is seenin the coastal areas. The housesconstructed by them are mainly of lightweight materials without any engineeringinputs. Therefore there is an urgent need toeducate the community about the goodconstruction practices that they should adoptsuch as:

Fig 2.2.7 Design solution to tsunami effect

• Site selection – Avoid building or livingin buildings within several hundred feetof the coastline as these areas aremore likely to experience damage fromtsunamis.

• Construct the structure on a higherground level with respect to mean sealevel.


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• Elevate coastal homes: Most tsunamiwaves are less than 3 meters in height.Elevating house will help reducedamage to property from mosttsunamis.

• Construction of water breakers toreduce the velocity of waves.

• Use of water and corrosion resistantmaterials for construction.

• Construction of community halls athigher locations, which can act asshelters at the time of a disaster.

Flood management - Flooding will resultfrom a tsunami. Tsunami waves will floodthe coastal areas. Flood mitigationmeasures could be incorporated.

Web Resources:

§ http://ioc.unesco.org/itsu/ IOC/UNESCOInternational Coordination group for theTsunami Warning System in the Pacific (ICG/ITSU), Paris, France

§ http://quake.usgs.gov/tsunami/ Tsunamis andEarthquakes, USGS, USA

§ www.asc-india.org Amateur Seismic Centreis a comprehensive website carrying detailsof state wise seismicity for the country. Thisalso has extensive reports on various pastEarthquakes/Tsunamis.

§ http://www.prh.noaa.gov/pr/itic/ InternationalTsunami Information Center, Honolulu, Hawaii

§ http://www.tsunami.org/ Pacific TsunamiMuseum site. Includes answers to frequentlyasked questions, links, and informationrelated to Pacific Ocean tsunamis.

Exercise:

1. What is Tsunami? Identify threecauses, consequences and impact oftsunami waves.

2. How can we predict Tsunami?

3. Suggest five risk reduction measuresthat can be taken up to prevent severedamage.

2.3 CYCLONE

What is a Cyclone?Cyclone is a region of low atmosphericpressure surrounded by high atmosphericpressure resulting in swirling atmosphericdisturbance accompanied by powerful windsblowing in anticlockwise direction in theNorthern Hemisphere and in the clockwisedirection in the Southern Hemisphere. Theyoccur mainly in the tropical and temperateregions of the world. Cyclones are calledby various names in different parts of theworld as mentioned in box on the next page.


Cyclones in India are moderate in nature.Some of the general characteristics of acyclone are:

1. Strong winds

2. Exceptional rain

3. Storm surge

Cyclones are generally accompanied by


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Cyclones are known by different namesin different parts of the world:

♦ Typhoons in the Northwest PacificOcean west of the dateline

♦ Hurricanes in the North AtlanticOcean, the Northeast Pacific Oceaneast of the dateline, or the SouthPacific Ocean.

♦ Tropical cyclones - the SouthwestPacific Ocean and Southeast IndianOcean.

♦ Severe cyclonic storm” (the NorthIndian Ocean)

♦ Tropical cyclone (the SouthwestIndian Ocean)

♦ Willie-Willie in Australia

♦ Tornado in South America

strong winds which cause a lot ofdestruction. In some cases it isaccompanied by heavy downpour and alsothe rise in the sea which intrudes inlandthere by causing floods.

Fig 2.3.1 Orissa Super Cyclone

29th October 1999, Super-cyclone with windspeed of 260-300 km/hour hit the 140kilometer coast of Orissa with a storm surgecreated in the Bay-of-Bengal with water level9 metres higher than normal. The super

Fig 2.3.2 Stages of cyclone formation

storm travelled more than 250 km inland andwithin a period of 36 hrs ravaged more than200 lakh hectares of land, devouring treesand vegetation, leaving behind a huge trailof destruction. The violent cyclone wasmerciless and broke the backbone ofOrissa’s economy and killed thousands anddevastated millions.

The development of a cyclone covers threestages namely

a) Formation and initial developmentstate: Four atmospheric/ oceanicconditions are necessary for theformation of a cyclone namely:

♦ A warm sea temperature inexcess of 26 degree centigrade,to a depth of 60 meters, whichprovides abundant water vapourin the air by evaporation.

♦ High relative humidity (degree towhich the air is saturated by


25

water vapor) of the atmosphereto a height of about 7000 meters,facilitates condensation of watervapor into droplets and clouds,releases heat energy andinduces drop in pressure.

♦ Atmospheric instability (an aboveaverage decrease of tempera-ture with altitude) encouragesconsiderable vertical cumuluscloud convection when conden-sation of rising air occurs.

♦ A location of at least 4-5 latitudedegrees from the Equator allowthe influence of the force due tothe earth’s rotation (Coriolisforce) to take effect in inducingcyclonic wind circulation aroundlow pressure centers.

Fig 2.3.3 Cyclone formation

b) Fully matured: The main feature of afully mature tropical cyclone is a spiralpattern of highly turbulent giant

cumulus thundercloud bands. Thesebands spiral inwards and form a densehighly active central cloud core whichraps around a relatively calm zone.This is called the “eye” of a cyclone.The eye looks like a black hole or adot surrounded by thick clouds. Theouter circumference of the thick cloudis called the ‘eye wall’.

c) Weakening or decay: A tropicalcyclone begins to weaken as soon asits source of warm moist air is abruptlycut off. This is possible when thecyclone hits the land, on the cyclonemoves to a higher altitude or whenthere is the interference of another lowpressure.

Depending on their track on the warmtropical sea and proximity to land a cyclonemay last for less than 24 hours to more than3 weeks. On an average the life cycle of acyclone (a cyclone to complete these threestages mentioned above) takes six days.The longest cyclone is typhoon John whichlasted for 31 days (August to September,1994 in the north east and north west pacificbasins).

Indian Cyclones

Cyclones vary in frequency in various partsof the world. The 7516.6 kilometers longIndian coastline is the earth’s most cyclonebattered stretch of the world. Around 8 percent of the total land area in India is proneto cyclones. About two-third of the cyclonesthat occur in the Indian coastline occur inthe Bay of Bengal. The states which aregenerally affected in the east coast areWest-Bengal, Orissa, Andhra Pradesh;Tamil Nadu and on the west coast Gujarat,Maharashtra, Goa, Karnataka and Kerala.


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Distributional Pattern:

The map of India (Fig 2.3.4) shows the areasthat are generally affected by strong winds/cyclones. Some of the major cyclones thathave affected the country in the past are asmentioned in table 2.3.1

Fig 2.3.4 Wind and Cyclone map of India

Table 2.3.1: Death associate with noteworthy Tropical Cyclones (1970 – 2005)

Sl No Year Area Death toll

1 1971 Eastern Coast 9658

2 1972 Andhra Pradesh and Orissa 100

3 1977 Chennai, kerala & Andhra Pradesh 14,204

4 1979 Andhra Pradesh 594

5 1981 Gujarat 470

6 1982 Gujarat & Maharashtra 500

7 1984 Tamil Nadu & Andhra Pradesh 512



10 1990 Orissa 250

11 1999 Orissa 8913

(Source: Office of the US Foreign Disaster Assistance)

damage. The satellites track the movementof these cyclones based on which the peopleare evacuated from areas lively to beaffected. It is difficult to predict the accuracy.Accurate landfall predictions can give onlya few hours’ notice to threatened population.

India has one of the best cyclone warningsystems in the world. The IndiaMeteorological Department (IMD) is thenodal department for wind detection,tracking and forecasting cyclones. Cyclonetracking is done through INSAT satellite.Cyclone warning is disseminated by severalmeans such as satellite based disasterwarning systems, radio, television,telephone, fax, high priority telegram, publicannouncements and bulletins in press.These warnings are disseminated to thegeneral public, the fishing community

Warning:Low pressure and the development can bedetected hours or days before it causes

especially those in the sea, port authorities,commercial aviation and the governmentmachinery.


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Elements at Risk: Strong winds, torrentialrains and flooding cause a huge loss to lifeand property. The 1999 Super Cyclone ofOrissa killed more than 10,000 preciouslives with women and children greatlyaffected. Apart from loss to life there is ahuge loss to infrastructures like houses builtof mud, older buildings with weak walls,bridges, settlements in low lying areas.

Typical Adverse effect:

First, in a sudden, brief onslaught, highwinds cause major damage to infrastructureand housing, in particular fragileconstructions. They are generally followedby heavy rains and floods and, in flat coastalareas by storm surge riding on tidal wavesand inundating the land over long distancesof even upto 15 kilometer inland.

Physical damage – structures will bedamaged or destroyed by the wind force,flooding and storm surge. Light pitched roofsof most structures especially the ones fittedon to industrial buildings will suffer severedamage.

Casualties and public heath – caused byflooding and flying elements, contaminationof water supplies may lead to viraloutbreaks, diarrhea, and malaria.

Water supplies – Ground and pipe watersupply may get contaminated by floodwaters.

Crops and food supplies – high winds andrains ruin the standing crop and food stocklying in low lying areas. Plantation type cropssuch as banana and coconut are extremelyvulnerable. Salt from the sea water may getdeposited on the agricultural land andincrease the salinity. The loss of the cropmay lead to acute food shortage.

Communication – severe disruption in thecommunication links as the wind may bringdown the electricity and communicationtowers, telephone poles, telephone lines,antennas and satellite disk and broadcastingservices. Transport lines (road and rail) maybe curtailed, Lack of proper communicationaffects effective distribution of reliefmaterials.

Possible Risk Reduction Meas-ures:

Coastal belt plantation - green beltplantation along the coastal line in a scientificinterweaving pattern can reduce the effect ofthe hazard. Providing a cover through greenbelt sustains less damage. Forests act as awide buffer zone against strong winds andflash floods. Without the forest the cyclonetravel freely inland. The lack of protective forestcover allows water to inundate large areas andcause destruction. With the loss of the forestcover each consecutive cyclone can penetratefurther inland.

Hazard mapping – Meteorological recordsof the wind speed and the directions givethe probability of the winds in the region.Cyclones can be predicted several days inadvance. The onset is extensive and often

2.3.5 Mangrove plantation on the coastal belt


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very destructive. Past records and paths cangive the pattern of occurrence for particularwind speeds. A hazard map will illustratethe areas vulnerable to cyclone in any givenyear. It will be useful to estimate the severityof the cyclone and various damageintensities in the region. The map isprepared with data inputs of pastclimatological records, history of windspeed, frequency of flooding etc. Fig.2.3.6shows the wind and cyclone zone map ofAndhra Pradesh.

Fig. 2.3.6 Andhra Pradesh state wind andcyclone zone map

Fig 2.3.7 A shelter with special feature to withstandcyclones and floods. Traditional homes can beimproved by building in disaster resistant features.Such homes could withstand cyclones with moderatespeeds.

plains is at utmost risk. Siting of key facilitiesmust be marked in the land use. Policiesshould be in place to regulate land use andbuilding codes should be enforced.

Engineered structures – structures needto be built to withstand wind forces. Goodsite selection is also important. Majority ofthe buildings in coastal areas are built withlocally available materials and have noengineering inputs. Good constructionpractice should be adopted such as:

- Cyclonic wind storms inundate thecoastal areas. It is advised to constructon stilts or on earth mound.

- Houses can be strengthened to resistwind and flood damage. All elementsholding the structures need to beproperly anchored to resist the upliftor flying off of the objects. For example,avoid large overhangs of roofs, and theprojections should be tied down.

- A row of planted trees will act as ashield. It reduces the energy.

- Buildings should be wind and waterresistant.

- Buildings storing food supplies mustbe protected against the winds andwater.

- Protect river embankments.Communication lines should beinstalled underground.

- Provide strong halls for communityshelter in vulnerable locations.

Land use control designed so that leastcritical activities are placed in vulnerableareas. Location of settlements in the flood


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Construction at ground level –risk of inundationIf natural elevation is not available construction on

stilts or on artificially raised earth mounds

Large overhangs get lifted and broken. For large overhangs, use ties.Fig. 2.3.8 Safe Construction Practices

Flood management – Torrential rains,strong wind and storm range leads toflooding in the cyclone affected areas. Thereare possibilities of landslides too. Floodmitigation measures could be incorporated(see section on floods for additionalinformation).

Improving vegetation cover – The rootsof the plants and trees keep the soil intactand prevent erosion and slow runoff to

Fig 2.3.9 Coastal belt plantation

prevent or lessen flooding. The use of treeplanted in rows will act as a windbreak.Coastal shelterbelt plantations can bedeveloped to break severe wind speeds. Itminimizes devastating effects. The Orissacalamity has also highlighted the need forurgent measures like shelterbelt plantationalong cyclone-prone coastal areas. Specieschosen for this purpose should not only beable to withstand the impact of strongcyclonic winds, but also check soil erosion.

Web Resources:§ www.imd.ernet.in Indian Meteorologi-cal

Department (IMD) provides all India weatherreport, end of monsoon season report,weather charts, satellite images, rainfall maps,earthquake reports and severe weatherwarnings. IMD provides cyclone warnings fromthe Area Cyclone Warning Centres (ACWCs)It has developed the necessary infrastructureto originate and disseminate the cyclonewarnings at appropriate levels. It has madeoperational a satellite based communication


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2.4 FLOOD

Flood is a state of high water level along ariver channel or on the coast that leads toinundation of land, which is not usuallysubmerged. Floods may happen graduallyand also may take hours or even happensuddenly without any warning due to breachin the embankment, spill over, heavy rainsetc.

There are different types of floods namely:flash flood, riverine flood, urban flood, etc.Flash floods can be defined as floods whichoccur within six hours of the beginning ofheavy rainfall, and are usually associatedwith cloud bursts, storms and cyclonesrequiring rapid localized warnings andimmediate response to reduce damage.Wireless network and telephoneconnections are used to monitor floodconditions. In case of flash floods, warningsfor timely evacuation may not always bepossible.

Causes:

There are several causes of floods and differfrom region to region. The causes may vary

system called Cyclone Warning DisseminationSystem for direct dissemination of cyclonewarnings to the cyclone prone coastal areas.

§ www.ndmindia.nic.in Natural DisasterManagement India. Provides current news onFlood, Drought and Cyclones, Weather Linksfrom NIC and weather conditions/temperatures on Indian Ocean(www.weather.nic.in).

§ www.bmtpc.org/disaster.htm In order to bridgethe gap between research and developmentand large scale application of new buildingmaterial technologies, the erstwhile Ministryof Urban Development, Government of India,had established the Building Materials AndTechnology Promotion Council in July 1990.

§ www.gsdma.org/cycpre.htm Link to Cyclonepreparedness on the Gujarat State DisasterManagement Authority website. TheGovernment of Gujarat (GOG) established theGujarat State Disaster Management Authorityto co-ordinate the comprehensive earthquakerecovery program.

§ www.osdma.org website of Orissa StateDisaster Mitigation Authority. The Governmentof Orissa established the Orissa State DisasterManagement Authority to co-ordinate thecomprehensive Orissa Super Cyclonerecovery program. Visit the section ‘SafetyTips’ for cyclones and other hazards.

§ www.tropmet.res.in The IITM functions as anational centre for basic and applied researchin monsoon meteorology of the tropics ingeneral with special reference to monsoonmeteorology of India and neighborhood. Itsprimary functions are to promote, guide andconduct research in the field of meteorologyin all its aspects.

§ www.colorado.edu/hazards is an excellent sitehaving a comprehensive coverage of disaster-related information organized in an easy toread way.

Exercise1. Explain the characteristics of a

cyclone.

2. Explain in detail the conditionsnecessary for the development of acyclone.

3. Identify risk reduction measures forcyclones.


31

from a rural area to an urban area. Some ofthe major causes are:

a. Heavy rainfall

b. Heavy siltation of the river bed reducesthe water carrying capacity of therivers/stream.

c. Blockage in the drains lead to floodingof the area.

d. Landslides blocking the flow of thestream.

e. Construction of dams and reservoirs

f. In areas prone to cyclone, strong windsaccompanied by heavy down pouralong with storm surge leads toflooding.

Typical Adverse Effects:

The most important consequence of floodsis the loss of life and property. Structureslike houses, bridges; roads etc. getdamaged by the gushing water, landslidestriggered on account of water gettingsaturated, boats and fishing nets getdamaged. There is huge loss to life andlivestock caused by drowning. Lack ofproper drinking water facilities,contamination of water (well, ground water,piped water supply) leads to outbreak ofepidemics, diarrhoea, viral infection, malariaand many other infectious diseases.

Flooding also leads to a large area ofagricultural land getting inundated as a resultthere is a huge crop loss. This results inshortage of food, and animal fodder. Floodsmay also affect the soil characteristics. Theland may be rendered infertile due to erosionof top layer or may turn saline if sea waterfloods the area.

Distributional Pattern of floods inIndia

Floods occur in almost all the river basinsof the country. The Vulnerability Atlas ofIndia shows pictorially the areas liable tofloods. Around 12 per cent (40 millionhectare) of land in India is prone to floods.

Fig 2.4.1 Map showing Flood Zones in India

Most of the flood affected areas lie in theGanga basin, Brahmaputra basin(comprising of Barak, Tista, Torsa,Subansiri, Sankosh, Dihang and Luhit), thenorthwestern river basin (comprisingJhelum, Chenab, Ravi, Sutlej, Beas and theGhagra), peninsular river basin (Tapti,Narmada, Mahanadi, Baitarani, Godavari,krishna, Pennar and the Kaveri) and thecoastal regions of Andhra Pradesh,Tamilnadu, orissa and Kerela. Assam, UttarPradesh, Bihar and Orissa are some of thestates who have been severely prone tofloods. Our country receives an annual


32

rainfall of 1200 mm, 85% of which isconcentrated in 3-4 months i.e June toSeptember. Due to the intense and periodicrain, most of the rivers of the country arefed with huge quantity of water, muchbeyond their carrying capacity.

Table 2.4.1 below shows some of the majorfloods that have affected the country.

Table 2.4.1 Death Toll in major floods of India

Year Number of Locationpeople killed

1961 2,000 North1968 4,892 (1) Rajasthan, Gujarat - (2) North-East, West Bengal, Assam1971 1,023 North India1978 3,800 North, Northeast1980 1,600 Uttar Pradesh, Bihar, Gujarat, Kerala, Haryana1989 1,591 Maharashtra, Andhra Pradesh, Gujarat1994 2,001 Assam, Arunachal Pradesh, Jammu and Kashmir, Himachal,

Punjab, Uttar Pradesh, Goa, Kerala, Gujarat states1995 1,479 Bihar, Haryana, Jammu & Kashmir, Punjab, Uttar Pradesh,

West Bengal, Maharashtra1997 1,442 Andhra Pradesh, Arunachal Pradesh, Assam, Bihar, Gujarat,

Himachal Pradesh, Jammu and Kashmir, Karnataka, Kerala,Maharashtra, Madhya Pradesh, Orissa, Punjab, Rajasthan,Sikkim, Uttar Pradesh, West Bengal states

1998 1,811 Assam, Arunachal, Bihar, Kerala, Meghalaya, Punjab, Sikkim,Uttar Pradesh, West Bengal states

2000 1,290 Gujarat, Andhra Pradesh, Assam, Arunachal Pradesh, Bihar,Himachal Pradesh, Kerala, Madhya Pradesh, Punjab, Uttar

Pradesh, West Bengal

level rises. Except for flash floods there isusually a reasonable warning period. Heavyprecipitation will give sufficient warning ofthe coming river flood. High tides with highwinds may indicate flooding in the coastalareas. Evacuation is possible with suitablemonitoring and warning. Warning is issuedby the Central Water Commission (CWC),Irrigation & Flood Control Department,

Warning:

Flood forecasting and warning has beenhighly developed in the past two decades.With the advancement of technology suchas satellite and remote-sensing equipmentsflood waves can be tracked as the water

and Water Resources Department.CWC maintains close liaison with theadministrative and state engineeringagencies, local civil authorities tocommunicate advance warning forappropriate mitigation and preparednessmeasures.


33


Mapping of the flood prone areas is aprimary step involved in reducing the risk ofthe region. Historical records give theindication of the flood inundation areas andthe period of occurrence and the extent ofthe coverage. Warning can be issuedlooking into the earlier marked heights of thewater levels in case of potential threat. Inthe coastal areas the tide levels and the landcharacteristics will determine thesubmergence areas. Flood hazard mappingwill give the proper indication of water flowduring floods.

Land use control will reduce danger of lifeand property when waters inundate thefloodplains and the coastal areas. Thenumber of casualties is related to thepopulation in the area at risk. In areaswhere people already have built theirsettlements, measures should be taken torelocate to better sites so as to reducevulnerability. No major development shouldbe permitted in the areas which aresubjected to high flooding. Importantfacilities like hospitals, schools should bebuilt in safe areas. In urban areas, waterholding areas can be created like ponds,lakes or low-lying areas.

Fig 2.4.3 Khash Dhalai Flood Shelter.Flood shelters like this are just one example of howcommunities can protect themselves from the worstof the floods. Banks of earth are raised by up to 5metres and cover an area of several kilometres. Thepeople dig a huge pond in the middle and use thisearth to raise the ground. Whenever the floods come,people can bring their livestock, possessions – eventheir homes – to safety. The pond in the middlebecomes an important source of food, as it is usedto farm fish.

Fig 2.4.2 Houses constructed on stilts in slum areas

Construction of engineered structures inthe flood plains and strengthening ofstructures to withstand flood forces andseepage. The buildings should beconstructed on an elevated area. Ifnecessary build on stilts or platform.

Flood Control aims to reduce flooddamage. This can be done by decreasingthe amount of runoff with the help ofreforestation (to increase absorption couldbe a mitigation strategy in certain areas),protection of vegetation, clearing of debrisfrom streams and other water holding areas,conservation of ponds and lakes etc. FloodDiversion include levees, embankments,dams and channel improvement. Dams canstore water and can release water at amanageable rate. But failure of dams inearthquakes and operation of releasing thewater can cause floods in the lower areas.Flood Proofing reduces the risk of damage.Measures include use of sand bags to keepflood water away, blocking or sealing ofdoors and windows of houses etc. Houses


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2.5 DROUGHT

What is Drought?

Drought is either absence or deficiency ofrainfall from its normal pattern in a regionfor an extended period of time leading togeneral suffering in the society. It is interplaybetween demand that people place onnatural supply of water and natural eventthat provides the water in a givengeographical region. The state of Keralawhich receives more than 3000 mm ofrainfall every year is declared droughtaffected as it is insufficient to have twogood crops. The more the imbalance insupply the higher is the drought. Thefollowing will help explaining this generaldefinition of the drought further.

♦ It is a slow on-set disaster and it isdifficult to demarcate the time of itsonset and the end.

♦ Any unusual dry period which resultsin a shortage of useful water.

may be elevated by building on raised land.Buildings should be constructed away fromwater bodies.

Flood Management In India, systematicplanning for flood management commencedwith the Five Year Plans, particularly withthe launching of National Programme ofFlood Management in 1954. During the last48 years, different methods of floodprotection structural as well as non-structural have been adopted in differentstates depending upon the nature of theproblem and local conditions. Structuralmeasures include storage reservoirs, floodembankments, drainage channels, anti-erosion works, channel improvement works,detention basins etc. and non-structuralmeasures include flood forecasting, floodplain zoning, flood proofing, disasterpreparedness etc. The flood managementmeasures undertaken so far have providedreasonable degree of protection to an areaof 15.81 million hectares through out thecountry.

Web Resources:

§ www.cwc.nic.in website of the Central WaterCommission of India, (CWC) of India.

§ http://wrmin.nic.in website of the Ministry ofWater Resources, GoI.

§ www.imd.ernet.in Indian MeteorologicalDepartment (IMD) provides all India weatherreport, end of monsoon season report,weather charts, satellite images, rainfall maps,earthquake reports and severe weatherwarnings.

§ www.ndmindia.nic.in Natural DisasterManagement India. Provides current news onFlood, Drought and Cyclones, Weather Linksfrom NIC and weather conditionstemperatures on Indian Ocean(www.weather.nic.in).

§ www.nih.ernet.in India National Institute ofHydrology perform tasks such as Groundwater zone mapping, Flood plain mapping,land use, salinity, sedimentation, Soil erosion,water-logging etc.

Exercise

1. Define Flood. List out some of thecauses and adverse effects of floods.

2. Name two basins in India that arefrequently affected by flood and explainthe warning dissemination system ofIndia in the flood affected areas.

3. Explain in detail atleast five possiblerisk reduction measures for floods.


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What on earth do you know aboutwater?

••••• Approximately 80 per cent ofearth’s surface is covered withwater but only 1% of it is freshwater that we can use.

••••• About 2.7 per cent of the totalwater available on the earth isfresh water of which about 75.2per cent lies frozen in PolarRegions and another 22.6 percent is present as ground water.The rest is available in lakes,rivers, atmosphere, moisture, soiland vegetation. This 1% of wateris now threatened by pollution!

••••• Today, we have approximately thesame amount of water as whenthe Earth was formed. Earth willnot get/generate any more water!

••••• We are using up the fresh waterfaster than we are recharging ourgroundwater

♦ Drought is a normal, recurrent featureof climate. Climate is expected to showsome aberrations and drought is justa part of it.

♦ Drought can occur by improperdistribution of rain in time and space,and not just by its amount.

♦ Drought is negative balance betweenprecipitation and water use (throughevaporation, transpiration by plants,domestic and industrial uses etc) in ageographical region.

The effects of drought accumulate slowlyover a considerable period of time.

Causes of Drought

Can you think of what causes drought?

Though drought is basically caused bydeficit rainfall, which is a meteorologicalphenomenon, it manifests into differentspheres because of various vulnerabilityfactors associated with them (see the box).Some of these factors are human induced.Though drought is a natural disaster, itseffects are made worst in developingcountries by over population, over grazing,deforestation, soil erosion, excessive useof ground and surface water for growingcrops, loss of biodiversity.


– Types of droughts

Drought proceeds in sequentialmanner. Its impacts are spread acrossdifferent domains as listed below.

– Meteorological drought

Meteorological drought is simpleabsence/deficit of rainfall from thenormal. It is the least severe form ofdrought and is often identified by sunnydays and hot weather.

– Hydrological drought

Hydrological drought often leads toreduction of natural stream flows orground water levels, plus stored watersupplies. The main impact is on waterresource systems.


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– Agricultural drought

This form of drought occurs whenmoisture level in soil is insufficient tomaintain average crop yields. Initialconsequences are in the reducedseasonal output of crops and otherrelated production. An extremeagricultural drought can lead to afamine, which is a prolonged shortageof food in a restricted region causingwidespread disease and death fromstarvation.

Socio-economic drought

Socio-economic drought correlates thesupply and demand of goods and serviceswith the three above-mentioned types ofdrought. When the supply of some goodsor services such as water and electricity areweather dependant then drought may causeshortages in supply of these economicgoods.

Measuring Drought :

Elements at Risk

In general, all those elements that areprimarily dependent on water are mostaffected. It affects the rainfed crops and thenslowly creeps into the irrigated crops. Peoplewho are dependent on agriculture and areaswhere the other livelihood opportunities areleast developed are greatly affected. Theherdsman, landless labourer, subsistencefarmers, women, children and farm animalsare the most vulnerable groups.

Can you think of some more vulnerabilityfactors to drought?

♦ Low soil moisture holding capacity♦ Absence of irrigation facilities♦ Livestock without adequate fodder

storage facilities♦ Poor water management♦ Deforestation♦ Over grazing♦ Water consuming cropping patterns♦ Excessive ground water draft♦ Soil erosion♦ Population growth and urbanization♦ Industrialization♦ Global warming

Can you believe it!!!

Cherapunji in Meghalaya, which was saidto receive highest rainfall in the world, isnow reeling under acute drinking waterproblem. This is because of water runoff,denudation and no storage facilities.

Fig 2.5.1

Meteorological Drought

Hydrological Drought

Agricultural Drought

Socio-economic Drought


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Drought Mathematics

The following criteria have been set bythe Indian Meteorological Division (IMD)for identifying the drought.

• Onset of drought: Deficiency of aparticular year’s rainfall exceeding25 per cent of normal.

• Moderate drought: Deficit of rainfallbetween 26-50 per cent of normal.

• Severe drought: Deficit of rainfallmore than 50 per cent of normal.

Fig 2.5.2 Map showing drought prone states in India.

Typical adverse effects

Drought, different from any other naturaldisaster, does not cause any structuraldamages. As the meteorological droughtturns into hydrological drought, the impactsstart appearing first in agriculture which ismost dependant on the soil moisture.Irrigated areas are affected much later thanthe rainfed areas. However, regionssurrounding perennial rivers tend tocontinue normal life even when droughtconditions are prevailing around. Theimpacts slowly spread into social fabric asthe availability of drinking water diminishes,reduction in energy production, groundwater depletion, food shortage, healthreduction and loss of life, increasedpoverty, reduced quality of life and socialunrest leading to migration.

Distribution PatternØ Around 68 per cent of India’s total area

is drought prone to drought.Ø 315 out of a total of 725 Talukas in 99

districts are drought prone.Ø 50 million people are annually affected

by drought.Ø In 2001 more than eight states suffered

the impact of severe drought.Ø In 2003 most parts of Rajasthan

experienced the fourth consecutiveyear of drought.


There are various mitigation strategies tocope up with drought.

1. Public Awareness and education: Ifthe community is aware of the do’s anddon’ts, then half of the problem issolved. This includes awareness on


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the availability of safe drinking water,water conservation techniques,agricultural drought managementstrategies like crop contingency plans,construction of rain water harvestingstructure. Awareness can begenerated by the print, electronic andfolk media.

2. Drought Monitoring: It is continuousobservation of the rainfall situation,availability of water in the reservoirs,lakes, rivers etc and comparing withthe existing water needs in varioussectors of the society.

3. Water supply augmentation andconservation through rainwaterharvesting in houses and farmers’fields increases the content of wateravailable. Water harvesting by eitherallowing the runoff water from all thefields to a common point (e.g. Farmponds, see the picture) or allowing itto infiltrate into the soil where it hasfallen (in situ) (e.g. contour bunds,contour cultivation, raised bed plantingetc) helps increase water availabilityfor sustained agricultural production.

4. Expansion of irrigation facilitiesreduces the drought vulnerability. Landuse based on its capability helps inoptimum use of land and water andcan avoid the undue demand createddue to their misuse.

5. Livelihood planning identifies thoselivelihoods which are least affected bythe drought. Some of such livelihoodsinclude increased off-farm employmentopportunities, collection of non-timberforest produce from the communityforests, raising goats, carpentry etc.

Fig. 2.5.3 Rain Water harvesting

Fig 2.5.4 A watershed showing collection of waterto common point.

6. Drought planning: the basic goal ofdrought planning is to improve theeffectiveness of preparedness andresponse efforts by enhancingmonitoring, mitigation and responsemeasures.

7. Planning would help in effectivecoordination among state and nationalagencies in dealing with the drought.Components of drought plan includeestablishing drought taskforce whichis a team of specialists who can advise


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the government in taking decision todeal with drought situation,establishing coordination mechanismamong various agencies which dealwith the droughts, providing cropinsurance schemes to the farmers tocope with the drought related croplosses, and public awarenessgeneration.

Ralegan, before drought mitigation efforts

Ralegan, after drought mitigation efforts

What a mitigation approach cando? A success story

The people of Ralegan Siddhi inMaharashtra transformed the dire straitsto prosperity. Twenty years ago thevillage showed all traits of abject poverty.It practically had no trees, the topsoil hadblown off, there was no agriculture andpeople were jobless. Anna Hazare, oneof the India’s most noted social activists,

Fig 2.5.5

Web Resources:

http://dmc.kar.nic.in/default.htmwww. watershedindia.netwww.rainwaterharvesting.orgwww.drought.unl. edu

Exercise

1. Why is drought a slow onset disaster?Identify five factors that cause drought.

2. Explain the four different types ofdrought

3. Identify the elements that are at risk inareas that are prone to drought andidentify five risk reduction measuresto combat drought.

started his movement concentrating ontrapping every drop of rain, which isbasically a drought mitigation practice.So the villagers built check dams andtanks. To conserve soil they planted trees.The result: from 80 acres of irrigated areatwo decades ago, Ralegan Siddhi has amassive area of 1300 acres underirrigation. The migration for jobs hasstopped and the per capita income hasincreased ten times from Rs.225 to 2250in this span of time.The entire effort was only people’senterprise and involved no funds orsupport from the Government.

2.6 LANDSLIDE

What is a landslide?

The term’ landslide’ includes all varieties ofmass movements of hill slopes and can bedefined as the downward and outwardmovement of slope forming materialscomposed of rocks, soils, artificial fills or


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Table 1 : DefinitionsLandslide Hazard refers to the potential of occurrence of a damaging landslide withina given area; such damage could include loss of life or injury, property damage, socialand economic disruption, or environmental degradation.Landslide Vulnerability reflects the extent of potential loss to given elements (or setof elements) within the area affected by the hazard, expressed on a scale of 0 (noloss) to 1 (total loss); vulnerability is shaped by physical, social, economic andenvironmental conditions.Landslide Risk refers to the probability of harmful consequences-the expected numberof lives lost, persons injured, extent of damage to property or ecological systems, ordisruption of economic activity –within a landslide prone area. The risk may be individualor societal in scope, resulting from an interaction between the hazard and individualor societal vulnerability.Landslide Risk Evaluation is the application of analyses and judgments(encompassing physical, social, and economic dimensions of landslide vulnerability)to determine risk management alternatives, which may include determination that thelandslide risk is acceptable or tolerable.

Fig 2.6.1 Landslide in hilly terrain of India

combination of all these materials alongsurfaces of separation by falling, sliding andflowing, either slowly or quickly from oneplace to another. Although the landslides areprimarily associated with mountainousterrains, these can also occur in areas wherean activity such as surface excavations forhighways, buildings and open pit minestakes place. They often take place inconjunction with earthquakes, floods andvolcanoes. At times, prolonged rainfallcausing landslide may block the flow of riverfor quite some time. The formation of riverblocks can cause havoc to the settlementsdownstream on its bursting. Some of thecommon definitions are below in table 1.

Causes of Landslide

There are several causes of landslide. Someof the major causes are as follows:

1. Geological Weak material: Weaknessin the composition and structure ofrock or soil may also cause landslides.

2. Erosion: Erosion of slope toe due tocutting down of vegetation,construction of roads might increasethe vulnerability of the terrain to slidedown.

3. Intense rainfall: Storms that produceintense rainfall for periods as short asseveral hours or have a moremoderate intensity lasting several dayshave triggered abundant landslides.Heavy melting of snow in the hillyterrains also results in landslide.

4. Human Excavation of slope and its toe,loading of slope/toe, draw down inreservoir, mining, deforestation,irrigation, vibration/blast, Waterleakage from services.


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Fig 2.6.2 Bhachau Landslide - The land slippedduring the 26th January 2001 earthquake event inBhachau. Note that people are still camped beneath.Monsoon rains could possibly wash the soil downslope.

5. Earthquake shaking has triggeredlandslides in many differenttopographic and geologic settings.Rock falls, soil slides and rockslidesfrom steep slopes involving relativelythin or shallow dis-aggregated soils orrock, or both have been the mostabundant types of landslides triggeredby historical earthquakes.

6. Volcanic eruption Deposition of loosevolcanic ash on hillsides commonly isfollowed by accelerated erosion andfrequent mud or debris flows triggeredby intense rainfall.

Type of Landslides:

The common types of landslides aredescribed below. These definitions arebased mainly on the work of Varnes(Varnes, D.J., 1978).

• Falls: Abrupt movements of materialsthat become detached from steepslopes or cliffs, moving by free-fall,bouncing, and rolling.

• Flows: General term including manytypes of mass movement, such asdebris flow, debris avalanche, lahar,and mudflow.

• Creep: Slow, steady downslopemovement of soil or rock, oftenindicated by curved tree trunks, bentfences or retaining walls, tilted polesor fences.

• Debris flow Rapid mass movementin which loose soils, rocks, and organicmatter combine with entrained air andwater to form slurry that then flowsdown slope, usually associated withsteep gullies.

• Debris avalanche A variety of veryrapid to extremely rapid debris flow.


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• Lahar Mudflow or debris flow thatoriginates on the slope of a volcano,usually triggered by heavy rainfalleroding volcanic deposits, suddenmelting of snow and ice due to heatfrom volcanic vents, or the breakoutof water from glaciers, crater lakesor lakes dammed by volcaniceruptions

• Mudflow Rapidly flowing mass of wetmaterial that contains at least 50 percent sand, silt, and clay-sizedparticles.

• Lateral spreads Often occur on verygentle slopes and result in nearlyhorizontal movement of earthmaterials. Lateral spreads usually arecaused by liquefaction, wheresaturated sediments (usually sandsand silts) are transformed from a solidinto a liquefied state, usually triggeredby an earthquake.

• Slides Many types of mass movementare included in the general term“landslide.” The two major types oflandslides are rotational slides andtranslational landslides.

• Topple A block of rock that tilts orrotates forward and falls, bounces, orrolls down the slope.

Adverse Effects:

The most common elements at risk are thesettlements built on the steep slopes, builtat the toe and those built at the mouth ofthe streams emerging from the mountainvalley. All those buildings constructedwithout appropriate foundation for a given

Fig 2.6.4 adverse effects of landslide

Distributional Pattern:

Landslides constitute a major natural hazardin our country, which accounts forconsiderable loss of life and damage tocommunication routes, human settlements,agricultural fields and forest lands. TheIndian subcontinent, with diversephysiographic, seismic, tectonic andclimatological conditions is subjected tovarying degree of landslide hazards; theHimalayas including Northeasternmountains ranges being the worst affected,followed by a section of Western Ghats andthe Vindhyas. Removal of vegetation andtoe erosion have also triggered slides.Torrential rainfall on the deforested slopesis the main factor in the Peninsular Indianamely in Western Ghat and Nilgiris. Humanintervention by way of slope modificationhas added to this effect.

soil and in sloppy areas are also at risk.Roads, communication lines are vulnerable.


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One of the worst tragedies took place atMalpa Uttarkhand (UP) on 11th and 17thAugust 1998 when nearly 380 people werekilled when massive landslides washedaway the entire village. This included 60pilgrims going to Lake Mansarovar in Tibet.Consequently various land management

Fig 2.6.5 Spots showing major landslides in India

measures have been initiated as mitigationmeasures. Fig. 2.6.6 shows landslidehazard zonation map of India with red beingareas more susceptible to landslides thanareas depicted in light yellow.

Table 2.6.2 : Some of the major Landslides in the last one decade

October 1990 Nilgris 36 people killed and several injured. Severalbuildings and communication network damaged

July 1991 Assam 300 people killed, road and buildings damagedNovember 1992 Nilgiris Road network and buildings damaged,

Rs.5 million damage estimateJuly 1993 Itanagar 25 people buried alive 2 km road damagedAugust 1993 Kalimpong, 40 people killed, heavy loss of

West Bengal propertyAugust 1993 Kohima, 200 houses destroyed, 500 people died, about 5 km

Nagaland road stretch was damagedNovember 1993 Nilgris 40 people killed, property worth several lakhs

damaged


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Source: http://www.geoengineer.org/photos/reearth1.jpg

Fig. 2.6.7 Retaining wall - Reinforced wall constructedas a mitigation measure.


Hazard mapping locates areas prone toslope failures. This will help to avoid buildingsettlements in such areas. These maps willalso serve as a tool for mitigation planning.

Land use practices such as:

§ Areas covered by degraded naturalvegetation in upper slopes are to beafforested with suitable species.Existing patches of natural vegetation(forest and natural grass land) in goodcondition, should be preserved

§ Any developmental activity initiated inthe area should be taken up only aftera detailed study of the region has beencarried out.

§ In construction of roads, irrigationcanals etc. proper care is to be takento avoid blockage of natural drainage

§ Total avoidance of settlement in therisk zone should be made mandatory.

§ Relocate settlements and infrastruc-ture that fall in the possible path of thelandslide

January 1994 Kashmir National Highway 1A severely damagedJune 1994 Varundh ghat, 20 people killed, breaching of ghat road

Konkan Coast damaged to the extent of 1km at severalplaces

May 1995 Aizwal 25 people killed. Road severely damagedMizoram

September 1995 Kullu, HP 22 persons killed and several injured. About 1 kmroad destroyed

14,August 1998 Okhimath 69 people killed18,August 1998 Malpa, 205 people killed. Road network to Mansarovar

Kali river disruptedAugust 2003 Uttarkashi Heavy loss of infrastructure

§ No construction of buildings in areasbeyond a certain degree of slope

Retaining Walls can be built to stop landfrom slipping (these walls are commonlyseen along roads in hill stations). These areconstructed to prevent smaller sized andsecondary landslides that often occur alongthe toe portion of the larger landslides.

Surface Drainage Control Works Thesurface drainage control works areimplemented to control the movement oflandslides accompanied by infiltration of rainwater and spring flows.


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Engineered structures with strongfoundations can withstand or take theground movement forces. Undergroundinstallations (pipes, cables, etc.) should bemade flexible to move in order to withstandforces caused by the landslide

Increasing vegetation cover is thecheapest and most effective way of arrestinglandslides. This helps to bind the top layerof the soil with layers below, while preventingexcessive run-off and soil erosion.

Insurance will assist individuals whosehomes are likely to be damaged bylandslides or by any other natural hazards.

References for further reading:§ http://www.csre.iitb.ac.in/rn/resume/landslide/

lsl.htm Landslide Information System - Centerof Studies in Resource Engineering IITMumbai.

§ http://landslides.usgs.gov USGS NationalLandslide Hazards Program (NLHP)

§ http://www.fema.gov/hazards/landslides/landslif.shtm Federal EmergencyManagement Agency FEMA, USA is taskedwith responding to, planning for, recoveringfrom and mitigating against disasters.

§ http://ilrg.gndci.pg.cnr.it/ The InternationalLandslide Research Group (ILRG) is aninformal group of individuals concerned aboutmass earth movement and interested insharing information on landslide research.

Exercise1. What are landslides ? List out five

major causes of landslides in India.

2. Identify major type of landslides.

3. Suggest risk reduction measures forlandslide mitigation.

Natural hazards & disaster management

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