eChapters

6.1 Introduction

Stratigraphy is the branch of geology which deals with the study of rock layers (strata) and layering (stratification) in their chronological order. It is primarily used in the study of sedimentary and layered volcanic rocks in order to interpret geological history and age. The term historical geology is also used as a synonym of stratigraphy but in a wider sense, it deals with the whole sequence of events that make up the history of the earth from its origin and age relations of rock strata, evolution through its life form, and structures. The scope of stratigraphy is very wide; it involves description and classification of layered sedimentary rocks and also of igneous & metamorphic rocks. The study involves correlation between different areas like lithological characters, fossil content, geophysical and geochemical properties including absolute radiometric dating.

6.2 Principles of Stratigraphy

Stratigraphy is based on the following few principles:

6.2.1 Law of superposition

In a sequence of horizontal sedimentary rock layers, the younger layers are on the top and the older layers are at the bottom. To put it another way, in a normal sequence, each bed is younger than the bed beneath it. Geologists today use it as the basis for a bed-by-bed analysis of geological history in a given area. This is important to stratigraphic dating, which assumes that an object cannot be older than the materials of which it is composed. This law known as "Law of Superposition" was first proposed by the scientist Nicolas Steno in the 17th century.

The remains of animals and plants of past ages preserved in the rocks are known as fossils, the study of which forms the subject of Palaeontology. The conditions for an animal or plant to become a fossil are firstly it must possess skeleton of some kind or some hard parts, since the soft parts are decomposed rapidly, secondly the organism must be covered up by sedimentary layer, otherwise it will soon crumble to pieces.

5.1 Modes of Preservation of Fossils

The conditions in which fossils occur depends, on their original composition and on the material in which they are embedded. The chief types are as follow:

5.1.1 The entire organism preserved

Occasionally the soft parts of the organism are preserved as well as the skeleton, the whole having suffered very little change. Instances of this are the woolly rhinoceros and mammoth found frozen in the mud and ice in Northern Siberia. Insects encased in fossil resin, known as amber, are found in the Oligocene beds in the Baltic shores of Persia, but the soft part of organisms are rarely preserved.

5.1.2 The skeleton preserved almost unchanged

Sometimes where the skeleton alone is preserved, it remains almost in its original condition, except that it has lost its organic matter. Thus the shells in the Pliocene beds of England differ from living ones only in being lighter, more porous and generally colourless. In some instances a certain amount of mineral matter, such as carbonate of lime, has been added to the skeleton, making it heavier and more compact.

The earth's crust is made up of minerals and rocks. Minerals are inorganic substances with a definite chemical composition, whereas rocks are mixture or aggregates of minerals. Each mineral is composed of certain elements present in fixed proportion. For example, mineral quartz, SiO₂ is a compound of the elements silicon (Si) and oxygen (O) combined in the proportion of 1:2, so its chemical formula is SiO₂, whereas rock granite is a mixture of several minerals like quartz, feldspar etc. Nature has provided unique physical properties to different minerals that can be used to identify them.

4.1 Physical Properties of Minerals

Majority of minerals contain following properties that can be used to identify them in field and in laboratory: crystal habit, cleavage, hardness, density, luster, streak, color, tenacity, magnetism, and taste.

4.1.1 Crystal habit

The faces that develop on a crystal depend on the space available for the crystals to grow. If crystals grow into one another or in a restricted environment, it is possible that no well-formed crystal faces will be developed. However, crystals sometimes develop certain forms more commonly than others, although the symmetry may not be readily apparent from these common forms. The term used to describe general shape of a crystal is habit.

Some common crystal habits are as follows:

3.1 Introduction

Crystallography is the science of crystals. The term crystal is derived from the Greek word “Crystallos” which means “ice”. The term was used for colorless quartz which was believed to be “fossilized” ice. Crystals are bodies bounded by flat surface, arranged on a definite plan which is an expression of the internal arrangement of the atoms. They are formed by consolidation of magma which is also considered as crystallization.

3.2 Terms in Use to Describe a "Crystal"

3.2.1 Faces

Faces are the plane surface in a crystal. The common faces are usually parallel to net planes containing the greatest number of lattice points or ions. Wide spacing between the net planes leads to development of faces in these planes. Faces are two types like and unlike faces.

2.1 Introduction

Topographic expression is the replica of geological structures present within the earths surface. When various types of rocks of an area are displayed on a map (sheet of paper), it is known as Geological Map. Normally geological maps prepared on topographic maps. Surface topography is best presented by contour lines on a plain paper.

The importance of geological maps is to understand the nature of structure and distribution of surface outcrops with their relation to contour lines. Horizontal and dipping beds are easily identified on map because, horizontal beds runs parallel to contour lines while inclined beds cut through different contours. The angle and direction of dip can be calculated from geological maps. Geological maps are of great importance to civil engineers, after studying geological maps and consultation with geologists, civil engineers can advice for construction of engineering structures like excavation of road cuttings and construction of canal, bridges, dams and tunnels etc. Geologists get vital clues about the geological history of an area, and can draw a cross section of an area and know the structure present underground.

1.1 Geomorphology

Geomorphology is the scientific study of the origin and evolution of topographic and bathymetric features created by physical or chemical processes operating at or near the earth's surface.

The surface of the earth is unstable and affected by a combination of surface and geologic processes that cause tectonic uplift and subsidence. Surface processes are mainly physical and chemical action of water, wind, ice, igneous activity and activities of living organisms on the surface of the earth. Upliftment of mountain ranges, the growth of volcanoes, isostatic changes in surface elevation and formation of deep sedimentary basins are categorized under Geological processes.

Main geomorphological processes occurring in nature are as follows:

1.1.1 Aeolian processes

Aeolian processes include activities of the winds, its ability to shape the surface of the earth. Wind acts as an effective agent of erosion, transportation and deposition materials, and large supply of fine, unconsolidated sediments. Aeolian processes are important in desert (arid) environments.

1.1.2 Fluvial processes

Moving water in a river channel, is able to mobilize sediment and transport it downstream. The rate of sediment transport depends on the availability of sediment itself and the discharge by river.

River originates from mountain with V shaped valley, which later increases in size, merging with other rivers. The network of rivers thus formed is known as drainage system. These systems show four general patterns viz. dendritic, radial, rectangular, and trellis etc. In the mature stage, the river form alluvial flood plains, meanders and ox-bow lakes. Finally when it merges to ocean, forms delta.

reach out their fingers it is gone” - Chinese Philosopher Lao Tzu Tao Te Ching. True to his verses, geohazards are phenomena regulated by the law of natureand it is beyond the human intellect to understand thoroughly and capability to conquer. This is the lesson learnt by us from so many incidences that geohazards cause greatest havoc wherein natural processes are going on and are inhabited by humans. Greed for natural resources and population pressures on the earth’s resources are the causes of many a catastrophic event. Examples in this regard are galore including, damning river courses and location of urban centers along rivers and coasts – flooding, cyclonic storms, tsunami hazards; alteration and deforestation hill slopes for agricultural and construction activities – landslides; unscrupulous utilization of ground water resources – drought, etc. This chapter is an attempt to draw the attention of human communityasa whole toturn towards learning to live with the nature without alterning the natural processes to get rid of impacts of geohazards as a best ever mitigation measure. In other words, this chapter attempts to emphasize the need to change our attitude to escape from natural hazards instead of attempting to tinker around natural processes only to get battered at the end.

INTRODUCTION

Oxford English dictionary states that the word ‘disaster’ is derived from the 16^th century French word ‘disastre’, which is a combination of two terms namely, ‘Des’ meaning bad or evil and ‘astre’ means star. Thus “desastre” signifies a ‘bad star’ or ‘evil star’. Disaster, therefore, implies loss or damage occurring due to some unfavorable star. However, in terms of modern knowledge, the word ‘disaster’ denotes any odd event, whether natural or man made, which can bring about sudden and great miseries to humanity in the form of loss of life or/ and property.

impacts other speheres and that too on a distal place! This chapter explains how global warming affects remote places like highlands of Bhutan. Severe hot summers during the year 1994 led to excessive melting of glaciers in the higher Himalayas. The exceptional melting contributed enormous amount of melt water to the lake basins, which caused breach of the morainic dam and consequent enlargement of the outlet of the Luggye Tsho and the Tshopda Tsho, Bhutan. Floods followed the breach on October 7, 1994. These floods destabilized the slopes on either bank of the Pho Chhu near Tshopda Tsho outlet making them prone to landslides. The flash floods also eroded the left lateral moraine of the Raphstreng Tsho, which had disturbed the original angle of repose. The Raphstrcng area is also prone to ice avalanches, rock glaciers, surge of which can damage the rim and also cause spillover of water. Examination of geological, geomorphological, geotechnical, microclimatic and hydrographic information in and around the glacial lakes led to improved understanding of breach characteristics based on which mitigation measures were suggested and implemented in the years 1996-97. Since then the lakes have remained intact. From this case study and satisfactory performanceof mitigationmeasures suggest that similar integrated studies have to be conducted for thorough understanding of hazard prone areas based on which mitigation measures have to be implemented for successful reduction of impacts.

INTRODUCTION

The Lunana area, situated in the northern district of Gasa, is one of the most extensively glaciated terrains of Bhutan (Fig. 1). In response to the general global warming, these glaciers like those of other parts of the Himalaya are in a state of steady retreat, often leaving behind a chain of lakes. Though the glacial lakes endow scenic beauty, they also pose environmental hazards, due to frequent bursting of their morainic dams and consequent flash floods. The last lake-burst occurred on 7^th October 1994, leading to floods in the Pho Chhu River. Following floods, the Geological Survey of India in collaboration with the Royal Government of Bhutan, investigated the Lunana area to identify the causes and effects of the floods and suggest remedial measures. More than a decade had passed since the implementation of mitigation measures and there has been no such breach and flood despite continued Glacial Vetreat during to Global Warming. This chapter describes the characteristics of these glacial lakes, nature and results of the study and mitigation efforts.

This chapter sheds light on a geohazard namely quicksand. Unlike other geohazards, it waits for its victims to cause hazard. Though discounted as a myth and also as a monster problem in Hollywood film stories, phenomenon of quicksand is real and could inflict life threatening dangers. Analyses of genetic causes, associated properties and locales of its occurrences indicate that more deaths might have resulted due to panic and drowning in waters than by quicksand itself. Based on these inferences, potential mitigation measures are presented in this chapter.

INTRODUCTION

Quicksand, referred as “pudhai manal” in Tamil, is one of the lesser known dangerous natural phenomena that cause death of human and other unsuspecting animals. It is a geohazard of different sort. It is different in a sense that it never “goes” anywhere like tsunami or causes hazard like flood or landslide or any other geohazard; but it waits for hapless victims; that is., it is harmless until human beings or other fauna step into the region of quicksand. It is commonly prevalent in many river beds and other locales near water bodies located amidst dense forests. Many a deaths occur due to quicksand but go unnoticed owing to its “non catastrophic” nature. It is also a geohazard less understood pertaining to causes of formation, potential to cause damage and occurrence (www.mythbuster.com). This chapter is an attempt to review the existing literature on this geohazard for better understanding.

This chapter documents shoreline changes of the Dakshina Kannada and Udupi districts of Karnataka State for the period between 1967 and 2005 studied by comparing the SOI topographic maps with IRS-1C/1D LISS-III satellite imageries through GIS techniques. Examination of coastal geomorphology, sediment flux and effectiveness of seawalls had indicated that the 130km long coastline of Dakshina Kannada and Udupi districts is essentially stable, but for seasonal variations. It has been estimated that, out of 130km, about 55km long coast is vulnerable to sea erosion, of which, 25km is covered byseawalls and covering another 10km length underway. It is revealed through field examination that protection of coastline through these measures is satisfactory only along few patches while other stretches of seawalls simply shift the zone of erosion to adjacent coastline owing to many reasons including quality of construction, unscientific positioning of seawalls, etc. It is also inferred that same is the case of many other coastlines elsewhere including Kerala coast. These experiences warrant scientific design and implementation of coastline protection measures.

INTRODUCTION

The 130km long coastal zone of Dakshina Kannada and Udupi districts is one of the densely populated coastal zones of India. The coastline is almost straight, regular and oriented towards N22°W, N12°W and N6°W directions at south of Mangalore, north of Mangalore and north of Malpe respectively. Barrier beaches and spits, ancient beach ridges, marshes, swamps and tidal flats characterize this zone. Natural features and man-made structures interrupt the shoreline. The natural features include estuarine mouths of Netravati-Gurpur rivers near Mangalore, Mulki-Pavanje rivers near Mulki, Udyavara river near Malpe, Sita-Swarna rivers near Barkur, Kollur-Chakra-Haladi rivers near Kundapur and rock exposures near Someshwar, Surathkal, Mulur, Kapu and north of Malpe (Fig. 1). The man-made structures include one major and four minor ports; breakwaters at the Netravati-Gurpur estuary, New Mangalore Port and Malpe harbor and a number of seawalls placed at various places along the coastline (Fig. 2). All these structures/features bring about local irregularity and contribute to erosion and accretion along the shoreline to some extent. Apart from these, source of beach material, coastal processes like wave refraction, longshore current, littoral drift etc.

Many types of geological hazards namely, tsunami, earthquakes, tsunami, floods and drought affect coastal areas like any other place on the Earth. As coastal regions are thickly populated and have abundant urban, industrial and recreational establishments, impacts of geohazards are always severe along coastal regions. Compliance to coastal zone regulations, with protection of sanddunesandmangroveswillbe the best mechanism to minimizethe damages from such hazards. In future, climate change may result in more hazards such as erratic rainfall and increase the frequency of droughts, floods and storm surges, etc. In this context, proposed coastal management zone for the coastal protection, disaster mitigation and management tools in coastal areas are examined in this chapter. It is suggested that extensive use of GIS and development of Geodatabase for the risk prone areas will serve as efficient tool for planners and policy makers to deal with geological hazards. In addition, it is felt that more efforts are needed in legal and institutional framework for integrated disaster management planning on local as well as national level.

INTRODUCTION

Geologic hazards are natural geological processes that inflict severe damage in areas of their operation if the area is utilized by anthropogenic activity in terms of habitation, industrial, recreational or commercial establishments. Many a times, natural geological processes that operated uninhibited for millions of years turn into geological hazards due to human intervention. These losses – lives and economic are not evenly distributed and are more prevalent in the developing countries due to higher population concentration and low level of economic growth. United Nations had realized the need of reducing these losses due to natural disasters and declared the last decade (1991-2000) as the International Decade for Natural Disaster Reduction. Objective of this proclamation was to reduce, through concerted efforts, the loss of life, property damage and socio-economic disruption caused by the natural disasters particularly in the developing countries (Tewar, 2000).

This chapter portrays flooding as a geohazard that can be managed with ease through simple and effective measures. Flooding is a recurrent geohazard that affects vast lands in India and elsewhere. Unlike many other geohazards, flooding event and probable area to be affected could be predicted with fairly accurate levels and hence, proper safety measures could be taken easily. However, as flash floods could not be predicted and the nature of flooding hazard that it brings in added danger of health hazard, crop damage and cutting off of supply and communication networks, flooding is as serious threat as any other geohazard. Scientifically designed urbanization and flood control measures are suggested for minimizing the potential impacts of flooding.

INTRODUCTION

Flooding is defined as a temporary submergence of a large area (that normally remains dry) under water by overflowing rivers and reservoirs as a result of heavy rains, high winds, cyclones, storm surges, tsunami, melting of snow or dam burst (Arya et al. 2005). The term “temporary submergence” denotes a time period ranging from few hours to about few months depending on type and location of flooding. Although flooding is a natural phenomenon that plays a major role in replenishing wetlands, recharging groundwater and supports agriculture, extreme demands on natural resources due to population growth, people and their property move closer to water bodies

This chapter explains how natural disasters are major catastrophic events, which are often aggravated by human intervention, resulting in adverse conditions affecting both natural resources and human habitats. Though drought is as disastrous as any other geohazard, it differs from other geohazards such that it is a ‘creeping phenomenon’, making its onset and end difficult to determine. Only a continuous monitoring of critical parameters ranging from crop failure to joblessness and shifting population, etc, could indicate drought in an area. In this chapter, we demonstrate a GIS based drought forecasting and monitoring model taking Gubbi Taluk of Karnataka as a case study. The approach includes creation of a spatial database of 17 critical parameters and their integration in GIS environment by developing a suitable rating and ranking scheme for the generation of drought severity map. The results have shown that drought could be monitored with the studied parameters and if suitable remedial measures are implemented, their effectiveness could also be monitored with this GIS model.

INTRODUCTION

India is a large country in terms of geographical area, exhibiting greater agro-climatic variation. The country is susceptible to several natural disasters, which are a major constraint to developmental activities. 

Despite widespread occurrence and its potency to inflict heavy causalities and damage to economy, generalizations could not be made to define “drought” – leave alone characterization, development of predictive model and common mitigation measures. Regional variation, be it definition or symptoms or causative factors or consequences and mitigation measures is the hallmark of drought. This chapter is an attempt to present a review on characteristics of drought for the benefit of devising mitigation and reclamation measures.

INTRODUCTION

“Drought” denotes the meteorological, agricultural, environmental, climatic, social, economic and political consequences of a gap between the water availability and demands for the needs of domestic, irrigational, industrial, commercial and recreational consumption in an area over extended period of time. As these demands vary from region to region and depend on too many parameters such as quantum of rainfall, geological and soil characteristics, land use, population, economic activity, climatic conditions, population and culture, drought conditions of an area may not have characteristics of some other region.

This chapter provides an introduction to cyclogenesis, nature of cyclone disaster and historic events. The mechanism that is in practice in cyclone mitigation, information dissemination and relief and rescue operations are detailed. As the state of Orissa is being battered more frequently by cyclones than any other state of India, special emphasis on cyclone disaster management system of Orissa is also discussed.

INTRODUCTION

Orissa state with immense natural resources is located between 17⁰27’N and 22⁰34’N latitudes and meridians of 81⁰27’E and 87⁰29’E longitudes. Orissa lies on the eastern coast of India with the waters of the Bay of Bengal swirling along its eastern and southeastern boundaries. It shares its boundaries with West Bengal and Jharkhand on the north, Chattisgarh on the west and Andhra Pradesh on the south. Out of the Indian mainland coastline of 7500 km, it constitutes a coastline of about 480 km. It extends for about 155,707 sq.km accounting about 4.74% of the total area of India. According to the 2001 census, it has 3.57 percent of the total population of India. Administratively, it has 30 districts, 3 Revenue Divisions, 58 Sub- Divisions, 51,061 villages and 127 Urban Centers.

Based on physiography, Orissa can be divided into three broad regions - the coastal plains, the middle mountainous region and the plateaus, and rolling up lands. The coastal plains extend from the River Subarnarekha in the north to the River Rushikulya in the south. The coastal zone covers nine districts namely Ganjam, Puri, Jagatsinghpur, Kendrapara, Jajpur, Khurda, Cuttack, Bhadrak and Balasore. It is narrow in the north, widest in the middle, narrowest in the Chilika coast and broad in the south. The coastal belt of Orissa lacks hills excepting few hillocks and mounds in the northern and southern parts. It has extensive low lands adjacent to the sea, sloping gently towards the shoreline of the Bay of Bengal. The coastline consists of the lakes, lagoons, marshes, bays and islands and natural harbors. The lakes in Orissa are natural and artificial. One of the blazing example of the natural lake is the Chilika lake.There is only one bay in Orissa which is the Hukitola bay. Eventually there are only two islands in Orissa - the Short’s Islands and the Wheeler Islands. Among the natural harbor, there is only one of its type in Orissa i.e. Paradeep which holds its recognition as the deepest natural port in the whole of India. The main drainage system of this area is represented by several rivers at their old stages flowing sluggishly towards the sea, which form topographic features like peneplains, natural levees, deltas, etc. (Fig.1). The major rivers flowing in the coastal belts are the Subarnarekha, the Budhabalanga, the Baitarani, the Brahmani, the Mahanadi and the Rushikulya. This region is the combination of several deltas of varied sizes and shapes formed by these rivers. The coastal belt has an area of 40,166 sq. km with a population of 68,79,379, which is 45 percent of the population of 9 coastal districts of Orissa.

Readers are introduced through this chapter to a geohazard (Landslide) that is most frequently publicized in mainstream media. Systematic examination of landslides and associated structural, tectonic, geological, geomorphological, meteorological, hydrogeological characteristics and land use pattern of Nilgiri hill area had indicated that steep slope, dipping of rockstowards slope, presence of clay layering in weathered rock types, events of continuous heavy rains, flooding on the slopes and improper land use practices play a major role in the genesis of landslides. Inaddition, ongoing seismotectonic activities in Southern Granulite Terrain of South India and reactivation of hidden blind shear zones were identified to be causative factors of recent increase of landslide occurrences.

INTRODUCTION

The downward movement of consolidated and unconsolidated soils and rock en masse from any geomorphic feature due to natural or manmade causes under the influence of gravity is termed as landslide (GSI, 1982). Nevertheless, presence of water, clay material, weak joints, favorable slope and many other characteristics also act as catalysis for this event. Landslides are one of the common geological hazards that affect countless population in India, especially in hilly terrains. Different reasons have been ascribed to different landslides of various terrains. Among them, reactivation of Bhavani shear zone (Prasannakumar and Llyod, 2007), high anthropo-geomorphic intervention (Basu, 2005), local geology, precipitation and slope (Bhattacharjee, 2005), presence of local vertical faults, triangular facets, abrupt deflection of streams and neotectonism

This chapter introduces the readers about volcanoes and associated features and hazards. Volcanic disasters are like any other geohazards in causing dangerous impacts. However, volcanic explosions are preceded by many surficial expressions that can be detected through satellite imageries, thermal sensors, change in magnetic and gravity anomalies, disappearances of vegetation, sudden appearances of anomalous water vapor, thermal springs and abnormal behavior of animals. Hence, unlike other geohazards, volcanic hazards could be forecast with fairly accurate time limits that may allow evacuation and precautionary safety measures. While avoidance is the best mitigation measure, proper land use planning, provision of scientifically designed damming and diversion methods could save lives and infrastructure from lava flows. Though, atmospheric contamination by volcanic gases, ash cloud and pyroclastic materials could not be thwarted and controlled and thus they could cause havoc.

INTRODUCTION

The term “Volcano” is derived from the name of Roman mythical God of fire “Vulcan”. A volcano is an opening of different shapes, through which, molten rock and gas get ejected either violently or simply flow over earth’s surface. The molten rock and gaseous materials are drawn from deep inside of crust or mantle of the Earth. Repeated ejection of molten materials through vent, fissures or plate margins forms volcanic mountains on earth’s continental or submarine regions.

Volcanism is a threat not only to the lives and infrastructure, but it also drastically alters landscape, impacts atmospheric quality and renders forests, cities and villages and cultivation lands useless. In addition, volcanic eruptions are capable of causing changes in global atmospheric cycles. For example, the eruptions of El Chicho’n in Mexico in 1982, Laki volcano in Iceland and Asama Volcano in Japan in the year 1783 and Krakatau volcano of Japan in the year 1883 have all impacted global climate and atmorpheric dynamics.

This chapter presents a case of Jind region of Haryana State, Northern India which had experienced mild tremors of ~ 3 on Richter scale magnitudes in the recent past with a gap of 1 to 2 years. Rejuvenation of the lineament controlled volcanoseismic process is identified as the probable cause of these tremors. This chapter describes seismotectonic characters, micro and mega seismicity of the area and few mitigation measures.

INTRODUCTION

The Haryana state consists of Delhi Super Group (DSG), Indo- Gangetic alluvial plain in the form of alluvial fan, sand dune, alluvium of Ambala, Yamuna and Ghagghar rivers and Siwalik Super Group (SSG) in the southern, central and northern parts respectively (Fig.1). The study area Jind is located in the central part of Haryana and comprises 200 – 600 m thick Indo-Gangetic alluvium. The alluvium is of Quaternary Period and composes alternating layers of clay, silt, sand and kankar. The Bhiwani and Tosham areas, located south of Jind, show the occurrence of Neoproterozoic granite and rhyolite of Malani Igneous Suite (MIS). The rocks occur in the form of ring structure/ring dyke on the hillocks amidst the alluvium. The metasediments (mica schist and quartzite) of Delhi Super Group are underling MIS at Tosham (located at 70 km southwest of Jind). As Jind region experiences mild tremors and there is no previous published work pertaining to the geology, tectonics and seismicity of the area the chapter records these aspects for better understanding and mitigation of earthquake hazard.

This chapter is an attempt to introduce basic facts about earthquake generation and the role of earthquakes in triggering secondary geohazards. Earthquake, unlike manyother geohazards is yet to be fully understood towards occurrence and magnitude for better mitigation measures. Though unpredictibility of this hazard makes it dangerous, earthquakes seldom kill lives. Instead, poor ability of man-made structures against ground-shaking waves has been the real cause of life loss and damage to property in most of the earthquake incidences. Furthermore, earthquakes generate secondary geohazards such as landslide, failure of dams and reservoirs, etc. Thus, earthquake, as a natural hazard has its own characteristic way of potential impactand hence classifying vulnerability of different regions and creating awareness on potential impact among common public is essential.

INTRODUCTION

The term “earthquake” denotes “shaking/vibration/trembling/ quivering/shuddering/ wobbling of Earth”. Earthquake is the quickest and most unpredictable natural hazard. It is nothing but a series of suddenly generated elastic waves occurring in the Earth due to internal and/or external causes from shallow (few kilometers) to about 700 kilometers depth. It is a form of motion of wave energy transmitted through the surface layer (crust) of the Earth. One generalization that can be made out of scientific and mainstream media information about earthquakes is that, “earthquakes seldom kill; but the associated phenomena such as landslides, flooding, volcanic eruptions and collapse of natural and man-made structures cause the real damage to lives and property”. This chapter is an attempt to describe the basic elements of earthquakes and few mitigation measures.

Need for systematic mapping and hazard zonation is emphasized in this chapter. Though prevention of natural disaster is not possible, its destruction could be minimized through implementation of effective hazard management system. With this motive, the coastal region between Tangapatnam and Ovari, Tamilnadu State has been classified into various categories of vulnerability based on its response to the 26th December 2004 tsunami. Based on the extent of seawater inundation and coastal geomorphic features, we have assessed the tsunami impact and estimated the behavior of the beaches in case of similar havoc in future. This study had shown that the maximum seawater inundation recorded in the study area is 750m in Colachel and the minimum is 100m in Kadiapatanam, Mandakadu and Vaniakudy areas. Chinnamuttom, Kanyakumari, Manakudy, Pallam and Colachel areas are under high risk.

INTRODUCTION

On 26^th December 2004, tectonic disturbances happened near Sumatra Island with an intensity of 9.3 in the Richter scale wrecked havoc on southwest part of India. In addition to inflicting life and infrastructure loss, the resultant tsunami event had also eroded severely the coastal region and modified topography of beach and shallow coastal regions. It did raise the concern of scientists and emergency planners about the impact of larger earthquake and consequent tsunami should there be any recurrence of such event. Despite becoming aware of tsunami hazard, there has been confusion about areas at risk and areas of safety. This chapter is an attempt to assess the vulnerability of part of Tamilnadu coast based on its geomorphological conditions and the impact of recent tsunami. The hazard maps have been generated and are intended for educational purposes, to improve awareness of tsunami hazards and to encourage responsible emergency planning efforts by illustrating the range of possible tsunami events.