eChapters

Abstract

Visualisation of geological process raises special issues for scientists and animators. The degree of physical movement of a rising arch or along a fault line may be very small compared to the normal terrain variation. Over a long time period the major changes in the environment may come from the more substantial surface manifestations of changing draining regimes. In Tamil Nadu State in South-Eastern India there are continuing tectonic movements arising from the collision of the subcontinent with the greater Asian land mass. Over comparatively recent times (7000 years) these movements have had a major impact on drainage and other hydrological outcomes. The Cauvery River in particular has migrated several hundred kilometers over this period. A mosaic was made from recent satellite imagery and then manipulated to create surface textures for dates between -7000 years and +1000 years. Changes in the terrain surface, such as rising arch structures and descending grabens, have been modelled and animated. The combination of terrain movement and surface change provides a visual history of the period.

Introduction

The continued northward movement (5±6 mm per year) of the subcontinental land mass of India induces substantial tectonic pressures all over India. In the southeast, primarily within Tamil Nadu, there is significant differential movement, both vertical and horizontal, of portions of the existing land mass. This is producing a number of effects:

Abstract

Drainages have characteristic pattern and life histories with youthful stage in hilly areas, mature stage in plains and old stage in the coastal zones. The deviations from their normal life histories, especially aberrations in their flow pattern in the form of various drainage anomalies have been inferred to be the indications of dominantly the Eustatic and Isostatic changes. This, especially after the advent of Earth Observing Satellites, has attracted the geoscientists from all over the world, for studying such drainage anomalies. In this connection, a study has been undertaken in parts of South India falling south of 14° south latitude to comprehensively map some drainage anomalies like deflected drainages, eyed drainages and compressed meanders and to evolve the tectonic scenario therefrom. The mapping of such mega drainage anomalies and the related lineaments/faults from the satellite digital data and the integration of such lineaments/faults with the overall lineament map of South India showed that the study area is marked by active N–S block faults and NE–SW sinistral and NW–SE dextral strike slip faults. Such an architecture of active tectonic grains indicates that the northerly directed compressive force which has originally drifted the Indian plate towards northerly is still active and deforming the Indian plate.

Introduction

Rivers have characteristic pattern and life histories with (1) short and straight drainages performing only erosion in the hilly catchments, (2) meandering and sinuous paths doing both erosion and deposition in the plains and (3) Brownian pattern of movement doing only dumping of sediments and building up of deltas in the coastal zones. Such characteristic life history of the rivers with youthful stage in the hills, mature stage in the plains and the old stage in the coastal zones in general are controlled by the base level of erosion or Mean Sea Level (Thornbury, 1985). But, the rock types and the geological structures of the terrain related to palaeo, time transgressive and ongoing tectonism too significantly control the drainage pattern and the related river flow dynamics in all these three stages. Hence, geoscientists from all over the world have all along been showing greater interest in understanding the drainage architecture in general and their anomalies in particular. That too, after the advent of Earth Observing Satellite technology, mapping of drainage pattern and their anomalies like dentritic, semi dentritic, trellis, parallel, annular, radial, deflected, pirated, avulted, eyed, compressed, preferentially migrated and other drainage anomalies have gained greater momentum, since, besides lithology, tectonics and sea level changes, these drainage anomalies have the credibility of providing information on the flood histories, seismic vulnerability, past climates and anthropogenic phenomenon too (Chitale, 1970; Chen and Stanley, 1995; Lillesand, 1989; Matmon et al., 1999; Miller, 1937; Reid, 1992; Saintot et al., 1999; Smith et al., 1997; Twidale, 2004; Thornbury, 1985 and many others). In different parts of the Indian sub-continent too, studies have been carried out on the drainage anomalies using topographic sheets, black and white panchromatic aerial photographs and orbital multimode and multispectral satellite data, to elucidate the structural fabric, tectonic processes, climatological and other phenomenon of especially the Quaternary period (Amalkar, 1988; Babu, 1975; Bakliwal and Sharma, 1980; Barooah and Bhattacharya, 1989; Mitra et al., 2005; Murty and Mishra, 1981; Narasimhan, 1990; Oldham et al., 1901; Philip et al., 1989; Rajaguru and Kale, 1985; Ramasamy, 1991, 2006; Ramasamy and Kumanan, 2000; Ramasamy et al., 1987, 1991, 2006; Singh et al., 1996; Sood et al., 1982; Thirunaranan, 1938; Vaidyanadhan, 1971; Yashpal et al., 1980).

Abstract

Overall geological histories of the Quaternary deltas of all over the world have been studied considerably, to understand the evolution, eustatic – isostatic changes, land – ocean interactive phenomenon, resources, environment etc. But tectonic signatures of these deltas have been less studied, though these have significance in understanding the natural resources, environment and evaluation of natural disasters. In this context, as the state of Tamil Nadu is a low easterly gradient plain, all the easterly flowing rivers have developed well evolved geomorphic features related to youthful, mature and old stages. Such old stages of the rivers are marked by the spectacular development of deltas. These deltas of Tamil Nadu have been studied in detail for understanding the tectonics with the help of visibly seen tectonic and geomorphic features in satellite based remote sensing and ground based data sets. The study has revealed that the upper age limit / ages of these deltas are probably of Middle to Late Holocene and the various tectonic and geomorphic anomalies observed in these deltas obviously indicate the tectonic processes/ phenomena that prevailed during Middle Holocene - till date. The Proto Cauvery delta of Chennai region is witnessing ongoing NE–SW sinistral, NW–SE dextral and E–W vertical tectonic activities. The streams in Ponnaiyar delta are showing persistent southerly migration due to the probable ongoing land subsidence along NE–SW faults in the southern part of the delta. The Cauvery river which has originally developed a broad bird-foot shaped – arcuate delta, has undergone a phase of anticlockwise rotational migration and stabilized in the northern rim of the delta as Coleroon river during 2300–750 Y.B.P. due to the ongoing tectonic emergence in the south of the delta almost since the last 6000 years or so. The Vellar river, in deltaic regime, shows northerly migration due to E–W grabening in the northern part of the delta. Vaigai and Manimuttar rivers are again migrating northerly in their deltaic regions due to the probable land arching to the south of their present day flow. Thus, the paper discusses the post deltaic / Middle -Late Holocene geological processes of Tamil Nadu deltas which are predominated by tectonic activities.

Abstract

The Cauvery delta is a major bird-foot shaped delta with its apex located east of Tiruchirappalli with the mother channel Cauvery flowing along Thanjavur– Kumbakonam – Kaveripoompattinam. The distributary drainages are radiating over an arc towards east from its apex with a fan shape and finally debouch into the sea from south of Tiruthuraipoondi in the south to Kaveripoompattinam in the north. All these distributary drainages are now seen as palaeochannels including the mother channel Cauvery, which is now called as “Palam Cauvery”. The present day flow of Cauvery river is confined to the northernmost rim of the delta as river Coleroon. On the basis of the archaeological, epigraphic and historical data analysed earlier and the14C dating carried out recently, the present authors infer that the age of the delta may vary from 2300 Y.B.P. ( Years Before Present) to 750 Y.B.P. and the age of the palaeochannels are also younging from 2300 Y.B.P. in the south to 750 Y.B.P. in the north. In the southern part of the Cauvery delta, the Mio-Pliocene Sandstone of Pattukottai-Mannargudi area is undergoing upliftment along N-S faults. On the basis of the rapid land progradation during 6085±233 Y.B.P. - 1020±80 Y.B.P. in Vedaranniyam coast, it is visualized that the Mio-Pliocene Sandstone must be undergoing upliftment significantly since 6100 Y.B.P. onwards. On the basis of the occurrence of older palaeochannels in the south, the gradual younging palaeochannels towards the north and the land emergence in the south of the Cauvery delta in Pattukottai – Mannargudi area, it is concluded that the distributary drainages of river Cauvery would have become sequentially defunct / shifted from south to north and finally the mother channel Cauvery also would have been pushed towards north to reach the present tract of Coleroon river. The thinner palaeochannels in the south and the gradual wider palaeochannels in the north of the delta further indicate that as the land was already undergoing emergence in the south even before river Cauvery has entered into Thanjavur plains, the river could not comfortably spread its distributaries in the south. Hence, the southern distributaries, after a brief flow, would have started drying sequentially from south to north during 2300–750 Y.B.P. thereby the floodwater of each of the southern distributary channel would have been pushed to its successive northern counterpart, i.e. the southern distributary (say 1), pushing its water to its immediate northern counterpart (say 2), then the combined flow of 1 and 2 pushing the water to 3 and so on. The anomalous eyed drainage and its modifications during the last 50–60 years and compressed meanders in Coleroon river, deflected drainages in Palam Cauvery, truncation and punctuation of beach ridges by the E – W faults along the N – S coast and such faults acting as pathways for the sub parallel creeks indicate vibrant Late Holocene geological history predominated by the tectonic movements in Cauvery delta.

Abstract

The drainage pattern and the architecture are the reflections of not only the tectono fabric of a region, but also the active tectonic processes. From amongst many drainage patterns and anomalies, the eyed drainages, deflected drainages and the compressed meanders interpreted from satellite images for Pudukkottai region of Southern Tamil Nadu infer to reflect the active N-S block faults and NE-SW sinistral and NW-SE dextral faults related to post collision tectonic phenomena.

Introduction

The Geoscientists have long back recognized that the drainages are the reflections of the surface and subsurface lithology, structure and tectano fabric and also the active tectonic movements especially of the Quaternary period (Thornbury, 1985). Hence, the Geoscientists have all along been showing greater interest in mapping the drainage patterns. However, the mapping of the drainage patterns and detection of tectonic features there from have gained greater momentum only after the advent of modern Remote Sensing technology. Since the airborne and satellite borne spectral images have the credentials of showing the drainage pattern, the drainage anomalies and the tectonic features related to them all of which were studied in conjunction to bring out information on the geological history of the Quaternary period by many workers (Vaidyanadhan, 1971; Murthy and Sastri, 1981; Agarwal and Mitra, 1991; Ramasamy, 1991; Saravanavel and Ramasamy, 2014).

Abstract

Being the junction between the continental and the oceanic plates, the coastal zones are always tectonically alert and hence vested with number of aults. The study of LANDSAT ETM FCC imagery revealed one such a major fault along NNE-SSW aligned Tamil Nadu coast from Chennai in the North northeast to Cape Comorin in the South southwest. This Precambrian boundary fault shows signs of repetitive reactivation during Gondwana, Tertiary and Late Holocene periods. While in former two periods it shows indications of faulting, in the latter period, it is manifested in the form of drainage deflections indicating sinistral movements of beds. While such sinistral morphology of the fault seems to be related to the Post collision compression, the seismicities in and in its close proximities indicate the seismic significance of this fault. In the context of natural resources and disasters viz: geothermal springs, flooding and seismicities, this fault demands deeper studies.

Introduction

The coastal regions in general form the junction between the continental and oceanic plates. Hence, the coastal regions are always tectonically active and thus vested with coast parallel, tangential and conjugate faults depending upon the tectonic history of the area. In the Indian subcontinent too, all along the 9000 km long east and west coast margins, number of major faults were mapped by the earlier workers. Significantly, Vardarajan and Ganju (1989) have brought out a comprehensive picture on the lineaments of the entire coastal zone of India using Landsat images. Vemban et al. (1977) earlier inferred faults along certain segments of east coast of Tamil Nadu and observed them to be lithological contacts and also seismogenic in nature. Raiverman et al. (1966) have again inferred earlier a N-S curvilinear fault in Thanjavur deltaic region and attributed it to post drift kinematics of the Indian plate. Ramasamy (1989) has brought out the morphotectonic and morphodynamic model of the east and west coasts of India on the basis of tectonic and geomorphic signatures using Landsat satellite images. Ramasamy (2006) developed a first time comprehensive model on the active tectonics of the Indian Peninsular and in which he brought out detailed information on the varied geomorphic, tectonic and hydrological anomalies and inferred them to be related to the whirling and fracturing of the Indian plate due to the still prevailing N–S to NNE – SSw compressive force which originally drifted the Indian plate to the present position after the breakup of the Gondwana land.

Abstract

The frequently recurring earth tremors / Seismicities in parts of Tamil Nadu & Kerala and the earthquakes of higher magnitude in Central India in the recent years have gradually dissolved the concept of shield area stability for the South India and the concept of mid-plate seismicity has emerged in the minds of geoscientists, Hence, the geoscientists have embarked into a number of studies to bringout seismotectonic maps for South India. In this context, a detailed studies have been carried out by the authors in parts of westernghats (Kodaikkanal and Varushanad hills) in Tamil Nadu. In the said study lineaments were interpreted using high resolution IRS satellite data and from the lineament pattern, isofracture, lineament density and lineament interaction intensity the strain maxima axes were drawn. Such strain maximas were observed to fall in N- S, E – W and NE –SW directions. These strain maximas were found to coincide with various drainage anomalies, like radial, compressed meandering and eyed drainages indicating that these lineaments are prone for seismicity/ earth tremors.

Abstract

The coastal regions are always tectonically active since these form the junction between the continental and oceanic plates. These tectonic activities and the resultantly tutored fluvial and marine geomorphic processes and the independent fluvial and marine geomorphic processes carve out the coastal morphology. And if these coastal geomorphic features are studied, it will lead to the understanding of the morphotechtonics. One such a study carried out for a part of Ganjam coast, revealed various geomorphic anomalies viz: presence of high order hill ranges only in the north eastern and south western parts of the area with the central plain, northerly migrating Ganjam river, development of wide beach ridges only along the central plain, all indicating the Late Quaternary upliftment of the central plain.

Introduction

The Indian subcontinent is vested with nearly 9,000km long coastline both in its eastern and the western continental margins. These coasts provide unique configuration with convexities (land protruding into the coast), concavities (vice-versa), deltas of different morphologies, beach ridges and swales, bay mouth bars, peaks, serrations and projections in the shorelines, all indicating the vibrant tectonic, fluvial, marine and aeolian processes. As the coastal zones in general, form the boundaries between the continental and oceanic plate margins, these are inherent weak zones prone to tectonic activities, which in conjunction with other geomorphic processes, provide unique architecture to the coasts with above varied geomorphic features. That too, the Indian coasts were inferred to stand as testimony to the vibrant tectonic activities and other related geodynamic processes of the Quaternary period (Ramasamy, 1989; Ramasamy, 1999).

Abstract

Indian Peninsular shield has been thought as tectonically inert and aseismic for many years by the Geoscientists. But, subsequent to the disastrous earthquakes in Killari, Jabalpur and Kutch, studies have been initiated in multiple directions on various aspects of seismicities. The present study is aimed at bringing out a possible picture on the seismic vulnerability of parts of Westernghats of Tamil Nadu using various tectano geomorphic anomalies like unifrequency lineaments and different levels of dissection of plateaus, denudational geomorphic anomalies like anomalous talus materials and fluvial geomorphic anomalies like radial drainages, compressed meanders, eyed drainages and wider flood plains interpreted from the raw and digitally processed Landsat TM and IRS P6 LISS-III satellite datasets. The subsequent generation of individual GIS layers on these anomalies and their integration revealed that the N-S faults are tectonically active and the NE-SW and NNE-SSW faults are active faults. Many earthquake epicenters were also found to fall along these lineaments / faults.

Introduction

The Indian peninsular shield, exposing the Archaeozoie - Proterozoic piles of rocks, is known for its tectonic inertness and the related land stability. Owing to such shield area character, the geoscientists were also having strong convictions for a long time that seismically the area is safe.

Abstract

Landslides have become a recurring phenomenon in most of the mountainous regions of the world. In Indian peninsular, the landslides which were mostly confined to the tectonically active Himalayan Mountains once, have started spreading over to the other mountain belts of the Peninsula. The Tirumala – Tirupati hills, which is drawing millions of pilgrims from all over the world is facing landslides especially along the newly built southern uphill Ghat Road. The geology of the area, studied using geomatics tools like Remote Sensing, SRTM based Digital Elevation Models, GPS Survey, etc., showed that Tirumala hills is under the grip of upward tectonic movement as evidenced from the N-S and E–W oriented Pleistocene faults, intensely dissected Plateau top Cuddapah Quartzites, retreating escarpments, exhaustive debris slopes, extensive valley fills along the slopes, colluvial fills in lower slopes, palaeo debris flows along the southern and western obsequent slopes of the Tirumala hills etc. All these indicate the inherent landslide vulnerability of the slopes. The E-W trending dykes which are piercing the slopes and standing as ridges add further landslide vulnerability to such fragile slopes. So, the new ghat road laid along such southern slope is obviously facing landslides. However, the detailed geomatics based studies show that the dykes, valley fills and steep slopes are particularly more vulnerable to landslides. Though remedial measures have been broadly evolved, abandoning the southern uphill new ghat road and widening the older northern downhill ghat road seems to be the better and long term feasible alternative to prevent Landslides.

Abstract

Landslides have become a fast spreading epidemic in the mountain belts around the world. As both the natural geosystem and the triggering parameters this phenomenon, the scientists & technocrats from all over the world have started studying it using varying parameters and multivariate advanced scientific tools. In this connection the present study lays an emphasis on the need for giving deserving importance to one of the important geosystem parameters, namely the geomorphology in Landslide Vulnerability Mapping. The same has been accomplished by taking the Nilgiri Mountains of Western Ghats, South India as the test site.

Introduction

Landslides are the most commonly witnessed geohazards in mountainous systems of all over the world causing greater and recurring loss to Man, his properties and to his various developmental programmes. As these landslides mostly occur after heavy rainfalls, it was considered as the most important triggering parameter for the landslides. In indian subcontinent, the landslides of Himalayan region while were inferred to be predominately due to Active tectonics (1,2,3,4,5,6,7,8,9,10) landslides of Westernghats of Maharastra were explained to be the effect of extensive weathering and the rock falls from the cliff and the summit zone (11,12) but in contrast, the landslides of Nilgiri mountains have been attributed to deforestation, direct entry of rain water into the soil system and the resultant pore pressure increase (13,14,15,16,17,18,19,20,21) but the studies carried out (22) in the Nilgiri Mountains indicated that various geosystem parameters viz: Lithology, Structure, Geomorphology, Slope etc., occur in various permutations and combinations and assign different landslide vulnerability grades to the land systems and when such vulnerable zones are interfered by the triggering parameters, the landslides occur.

Abstract

The recent disastrous tsunami of December 26, 2004 has not only alarmed the administrative and the planning machinery to have tsunami mitigation strategies for India. But also signalled the geoscientists to have a deeper look on the phenomenon of tsunami and the vulnerabilities of the Indian coasts. In this context, the authors have conducted a study primarily to evaluate the responses of the coastal Geosystems to the tsunami inundation, as it is a very vital component in f raming strategies for mitigating the effect of tsunami. The study has revealed that the central coastal parts of Tamil Nadu, namely Cuddalore – Nagapattinam districts, which were worst affected by the recent tsunami, expose a combination of landforms of tectonic, fluvial, fluvio – marine and marine processes. These different landforms have responded differently to the recent tsunami viz: as facilitators, carriers, accommodators, absorbers, barriers etc. on the basis of the same, different eco – friendly, cost effective and result oriented methods are suggested to mitigate the effects of tsunamis.

Introduction

Tsunami is an unfamiliar term and also a scantily referred term in the dictionaries in India till December 26, 2004. Even the students of geosciences were all along been taught about the origin and impact of tsunamis by citing examples from the Pacific Ocean. But the term tsunami has now become a widely known and a commonly deliberated phenomenon in India amongst various cross sections of the society irrespective of age and literacy. However, the historical tsunami data (USGS & GSI websites)

Abstract

The article briefly narrates the initiatives taken by the Department of Science and Technology, Govt. of India, New Delhi in providing solutions to rapidly growing Landslide Disasters in India. Duly considering the importance of the issue, the DST has embarked on a National Landslide Programme more than two decades ago and brought voluminous information on Landslide Vulnerability Mapping, Site Specific Landslide Investigations, Landslide Kinematics, Instrument Based Forewarning etc. by funding large number of research projects to various Academic/Research institutions in the country. In addition, the bilateral collaborative programme launched on Geohazards between India & Norway, resulted in bilateral flow of knowledge and capacity building amongst various tiers of the Academic, Research and the Planning Hierarchy, yielding tangible benefits.

Keywords: Landslides in India, DST’s Initiatives.

INTRODUCTION

Landslides cause extensive damages to roads, bridges, human dwellings, agricultural lands, forests and other establishments year after year resulting in immense losses of life and properties. The entire Himalayan region has been the target of intense development activities for the last few decades. Hence the instabilities along the natural slopes are accentuated by the human activities since the development schemes are often not properly planned and implemented (Valdiya 1980; Thakur 2001). This has become the case in most of the mountains in India. Keeping in view of the stability of the slopes, the need of the hour is to achieve sustainable development of the hilly regions while implementing various developmental schemes. So there has to be a major S&T role to play to minimize the landslide problems. This should include all possible corrective and preventive measures to minimize the losses due to this disaster.

Abstract

Landslides have become a recurring phenomenon in most of the mountainous regions of the world. In Indian peninsular, the landslides which were mostly confined to the tectonically active Himalayan Mountains once, have started spreading over to the other mountain belts of the Peninsula. The Tirumala – Tirupati hills, which is drawing millions of pilgrims from all over the world is facing landslides especially along the newly built southern uphill ghat road. The geology of the area, studied using Geomatics tools like Remote Sensing, SRTM based Digital Elevation Models, GPS Survey, etc., showed that Tirumala hills is under the grip of upward tectonic movements as evidenced from the N-S and E-W oriented Pleistocene faults, intensely dissected Plateau top Cuddapah Quartzites, retreating escarpments, exhaustive debris slope, extensive valley fills along the slopes, colluvial fills in lower slopes, palaeo debris flows along the southern and western obsequent slopes of the Tirumala hills etc. All these indicate the inherent landslide vulnerability of the slopes. The E-W trending dykes which are piercing the slopes and protruding as ridges add further landslide vulnerability to such fragile slopes. So, the new ghat road laid along such southern slope is obviously facing landslides. However, the detailed Geomatics based studies show that the dykes, valley fills and steep slopes are particularly more vulnerable to landslides. Though remedial measures have been broadly evolved, abandoning the southern uphill new ghat road and widening the older northern downhill ghat road seems to be the better and long term feasible alternative to prevent Landslides in the area.

Abstract

Northeastern part of the Indian subcontinent is seismically an active region, and is further prone to excessive rainfall and frequent landslides, which cause disruption of the road networks during the monsoonic months every year. The region owns a typical morphotectonic setup where many active thrusts and faults have carved out the landforms and physiography of the major part of the region. The creeping phenomenon of the N-S trending prominent strike-slip fault, namely the Churachandpur - Mao Fault (CMF), is one of the triggering factors for the frequent landslides and low magnitude earthquakes. The life line of Manipur, the national high way NH39, traverses along and in close proximity to this fault in Manipur, and hence the life is paralysed in the area during the monsoonic months. From the GPS campaign mode studies on the western and eastern sides of the CMF, it is observed that there is a change in the crustal velocities from 16 - 22 mm/yr in the east to 33 - 42 mm/yr in the west. Micro-deformations are also observed in the form of displacements respectively with the vertical, N-S and E-W components of–0.111 mm/yr (downward), 0.03 mm/yr (northward) and –0.011 mm/yr (westward). The net displacement is 0.126 mm/yr with an azimuth of N 85° and dipping of 13° towards west. Neotectonic movements along the CMF, as per the GPS measurements, suggest an aseismic nature of the fault with dextral component. Fault plane solutions of the earthquakes show northerly directed principal P-axis indicating the extension (T-axis) along east-west. The resultant creeping of micro-deformation towards the western slopes of the terrain is aligned with the principal T-axis. The creeping triggers the micro seismicity as well as the landslides along the CMF.

Abstract

The Sonapur landslide located in the south eastern fringe of Shillong Plateau falls in NH44 connecting Shillong with Agartala. The slide is repeatedly active and massive debris flows occur during every monsoonic season since 1999. The studies carried out under the NRDMS funded project shows that the slide falls in the tectonically active E-W Dauki fault system, which not only forms the southern boundary of the Shillong plateau but also the near vertical plane along which the Shillong plateau has been uplifted due to the northerly compressive force and the collision of Indian plate with Eurasian plate. Such post collision tectonic uplift and the southerly tilt of the Shillong plateau in its southern part, monoclinal southerly dipping sediments south of Dauki fault, Sylhet trough, occurrence of NE-SW sinistral (shears) and NW-SE dextral faults in Sonapur area, high seismic activity and rainfall are responsible for the Sonapur Landslide.

Abstract

The landslides have become the fast spreading disaster all over the Indian sub-continent. As such landslides were mostly occurring in the Mighty Himalayan Mountains, it was all along attributed to active tectonics. But when it started occurring in most of the mountain belts of India, various geological parameters, the anthropogenic phenomenon and rain fall were inferred to be the main causes for the landslides. Hence when this concept emerged, and again the Remote Sensing and the GIS technologies have phenomenally evolved, different types of variables, again on different resolutions and different methodologies have been adopted to prepare landslide vulnerability maps and this has started yielding varying types of outputs. As the landslide vulnerability zonation mapping (LVZ) is the first step in landslide studies it is essential to evolve a suitable methodology for the same. So the present study was carried out in a test site of around 300 sq.km in between Coonoor and Otacamund, Nilgiri mountains, Western Ghats, South India. In the said study, a set of 12 Earth System Parameters/Variables which could contribute to landslide vulnerability were prepared as GIS raster databases from the data interpreted from satellite MSS data and field geological and geophysical data sets. Similar GIS database was generated on 144 landslides. These landslides were superposed over such 12 Earth system parameters data and landslide vulnerability weightages were assigned to each subvariables of these Earth system parameters. In assigning weightages using such landslide incidence data various methods viz; slope, integrated terrain, information value, weight of evidence, index overlay and BIS methods were used and landslide vulnerability zonation maps were prepared adding all the 12 weightages assigned Earth system variables. In this, all the 12 earth system parameters were having same resolutions. Then the outputs were compared which revealed that the information value method is the best suited method for LVZ mapping followed by weight of evidence method.

Abstract

Prediction of the occurrences of Landslides requires a set of complex analyses, involving multitude of factors which are to be studied systematically in order to evaluate the landslide vulnerability. The increasing availability of computer-based tools and data storage capabilities are found to be useful in landslide vulnerability mapping. One such significant tool in landslide studies is Geographic Information System (GIS). In this article some approaches were made to model the land slide hazard for Sirumalai Hills, Dindigul District, Tamil Nadu, India using Geographical Information Systems and the same is presented in this paper.

Abstract

Landslides are the most common hazards in hilly regions. Rapid development and the resultant uncontrolled interactions with ecosystems are the major reasons for the landslides, besides the rainfall. So, the assessment of landslides hazard vulnerability is a prerequisite before making any developments related to settlements, hill resorts, hydropower projects and the related network of Ghat roads. The present study deals with the assessment of landslides in two different sites; Site-1 located in the Ghat section of Yercaud hills between 10/4 and 29/6 km stones in the southwestern slopes of Shevroy hills, Salem, and the Site-2 located in the Ghat road between Lower camp and Kumuli in Theni districts, Tamil Nadu. The Theni ghat road in the National Highway-220 is connecting Tamil Nadu with Kerala and is the lifeline for Sabarimala, Tekkadi and Munnar. Besides, a series of pan stacks conveying water from Periyar reservoir in Kerala to the power house located at Lower camp in Tamil Nadu also lie in this stretch of hills. Landslide vulnerability mapping was carried out in an area of 130sq.km in Site-1 and 6.7 sq.km in Site-2 by assigning numerical values to the causative factors of slope instability such as lithology, structure, slope morphometery, relative relief, land use and land cover, and ground water conditions following the BIS code No. 14496 (1998) for preparing landslide hazard zonation maps. The study in Yercaud hills revealed that out of 12 slope facets, facet 1 to 6, 9 and 12 fall under moderate landslide hazard zone whereas facets 7, 8, 10, and 11 fall under high hazard zone. The area falling in facets 3, 4 and 5 of Kumuli ghat section fall under high landslide hazard zone, the slope facets 1, 2, 9 and 10 fall in the moderate hazardous zone and other facets in low hazardous zone.

Abstract

Similar to other north eastern states of India, the state of Manipur is also prone to recurring landslides. The National Highway 150 and the state Highway in Ukhrul, Nunghar and Paorei sectors often witness landslides due to geological complexities, rainfall and anthropogenic activities. So a study was conducted to prepare the landslide hazard zonation map for the region using the method developed by Bureau of Indian Standards, which indicates that 67.32 km² (nearly 56%) fall under high hazard zone. The RMR and SMR studies carried out in five test sites in such high hazard zone show that four sites fall under highly unstable category (class IV) and one under partially unstable category (class III). The kinematic analysis indicates dominant wedge failure. The improper landuse, lack of adequate drainage and toe removal for road widening are the major causative factors for the recurring landslides.