landforms - a development and environment magazine

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Expert PanelB MeenakumariFormer Chairperson,National Biodiversity Authority, Chennai.

Rasik RavindraGeologist and Secretary General, 36 IGC, New Delhi.

Sachidanand SinhaProfessor, CSRD,Jawaharlal NehruUniversity, New Delhi.

Ajit TyagiAir Vice Marshal (Retd) Former DG, IMD,New Delhi.

Saraswati RajuFormer Professor, CSRD,Jawaharlal NehruUniversity, New Delhi.

D MukhopadhyayChief ExecutiveACRA,Noida, U. P.

Prithvish NagFormer Vice Chancellor,MG Kashi Vidyapeeth,Varanasi.

B SenguptaFormer Member Secretary, Central Pollution Control Board, New Delhi.

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Landforms in india4 Fluvial Geomorphology: An Indian Perspective

Dhruv sen singh There are 22 major river basins in India. Among them three main

basins have their origin in Himalaya.

10 Cachar Valley: A Cauldron of Adverse Natural PhenomenonKuldeep Kachroo

The Cachar valley has a very fragile environmental setting where neo-tectonic activity is still underway.

18 Narmada’s Distinctive Litho-tectonic Features anulekha Prasad The Narmada flows in a general ENE-WSW direction over a length of

1,312 km, draining into the Gulf of Khambhat in the Arabian Sea.

20 Lake Lonar ratish Kumar jha The Lonar is one of the best preserved impact structures

and the only one to have been formed on volcanic rocks.

22 Desert Landforms sudesh Kumar Wadhawan Landforms in deserts have evolved through a long period of time

through the interplay between fluvial and aeolian processes.

in Brief1 Letters; 2 Editor’s Note;9 The Karst Caves of India; 17 Columnar Basalt;30 The Atolls of Lakshadweep; 31 Badland Topography;32 Barren Island; 33 India’s Tombolo;34 Hot Springs; 35 Human Induced Land Subsidence; 48 Books & Websites.

GeoGraphy and youVol. 19 Issue 17 No. 128 March 1-15, 2019

G’nY SINCE 2001GEoGraphYaNdYou.Com

a dEvElopmENt aNd ENvIroNmENt fortNIGhtlY

28 Coastal Geomorphology sulagna chattopadhyay The coastal landforms are erosional or depositional

depending upon the process of their genesis.

36 Ice as an Agent of Sculpting Land rasik ravindra The major part of ice and glaciers are found as ice caps and ice sheets

in Arctic, Antarctic and Greenland, apart from the Himalaya, Andes and Europe.

arctic-antarctic42 Polar Regions from the Sky alvarinho j Luis Sea ice is frozen seawater that floats on the ocean surface.

It increases in winter and melts away in summer.

the clarity of the water in river Dawki, cherrapunjee, meghalaya makes the boat look like it’s suspended in mid-air.

This journo-mag is incomparable with the other popular magazines available in the market since it provides unparalleled content. Recently I have read the National Centre for Antarctic and Ocean Research special Issue, India’s Polar Endeavours, Vol 19, Issue 16, No. 127. It has showcased India’s role in the polar regions highlighting the geopolitics and its present scenario towards the resources in the Arctic. Such articles are very informative and represent India’s growing significance globally. —ShIVANShu SAxENA viacustomer feedback.

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2 March 1-15 2019 GeoGraphy and you vol 19, issue 17

February, 1-15, 2019. vol 19. issue 15, no. 126: I was absolutely absorbed reading the special Biodiversity Issue, India’s Ecological Diversity Vol 19, Issue 15, No. 126. The articles were so captivating that I got excited and found myself reading all of it at a go. I recall reading some trending articles covering substantial perspective on coastal regulation policy and on access and benefit sharing—the discourses were brought out with nuances which many newspapers fail to publish. G’nY is a must have for all the people who like to be well read and updated. —PRAVEEN via Customer Feedback

GeoGraphy and you March 1-15 2019 3

Sulagna ChattopadhyayFounder-Editor, Geography and You,New Delhi

Editor’s noteI am delighted to bring before you the first ever G’nY issue on geomorphology showcasing India’s myriad landforms. I had often wondered as a young student of geography why we so often quoted examples of faraway lands when describing fantastic landforms that were so painstakingly shaped over millions of years. Today, we have greater access to a lot more information. We have scholars who have brilliantly described features that we all readily identify in text, but are unable see on our land. This issue would break the barrier and help transport you to the real life instances of what you have only seen in texts till date. You will also read about how neo-tectonic movement can create landforms, such as the Barak River in the Cachar valley. The article presents an interesting insight about how a zero gradient river changes its course over the decades. You will also notice a brief section on Arctic and Antarctic. Considering the tireless effort of our scientists and geologists working in these inhospitable terrains, we felt it was pertinent to bring to you the features and landforms that have been identified by them in the Polar realms. However, we do understand that there is a lot more that needs to be covered. We would in the future focus on more terrain related content with treatises on mountains, hills, plateaus, and plains in India—the four major types of landforms.

Happy reading!

Rasik RavindraThe author is Geologist and Secretary General, 36th International Geological Congress, New Delhi

The earth is a unique planet—the only one known to sustain life. Enveloped by mighty oceans, clothed by soil, lofty mountains and dense forests, fed by rivers and nourished by rains–it has been held in awe and even worshiped over centuries. The natural wonders of the earth are sculpted by nature over geological times. It is these architectural wonders or landforms, its evolution and the processes of formation that constitute geomorphology. A subject common to physical geography, geology and natural sciences—geomorphology is a fascinating subject in the sense that it answers questions of natural curiosity and encourages us to understand our surroundings. The processes that play a role in formation of landforms, their evolution and disappearance holds the key to sustenance of life and the preservation of biodiversity. In fact, some of the processes such as the three stages in development of a fluvial regime draw a close analogy from the life cycle of humans —young, mature and old.

An attempt has been made to cover the four major domains of physical geomorphology—fluvial, desert, glacial and coastal geomorphology and highlight the essential landforms and structures associated with these processes in the current volume. Some of the key morphological features exposed in different parts of India such as karsts caves, columnar basalts, the Ram Setu, subsidence of land in West Bengal, badlands etc have also been briefly touched.

Guest Editor


By Dhruv Sen Singh

The author is Professor at the Department of Geology, University of Lucknow, Lucknow, India. The article should be cited as Singh D.S., 2019. Fluvial Geomorphology An Indian Perspective, Geography and You, 19(17): 4-8

Fluvial GeomorpholoGy AN INdIAN PersPectIverivers are a life-sustaining resource for plants, animals and humans.

During its arduous journey rivers carve out several erosional and depositional features that define the geomorphology of a river basin.

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a view of Burhi Gandak, Champaran, Bihar.

Rivers constitute water that flows in a definite direction through a channelised way, transporting sediments and water from the source to the sink. Rivers are a

renewable natural resource and a veritable lifeline for society. All ancient civilisations of the world evolved on the banks of rivers—the Harappan civilisation at Indus, Egypt at Nile, Babylon at Tigris, and Mesopotamia between Euphrates and Tigris. However, rapidly growing population, urbanisation and industrialisation are adversely affecting the rivers and their environment. The encroachment by man within the natural cycle of rivers has polluted the water, increased their sediment load, changed their capacity to transport and disturbed the ecosystem, which in turn has changed river dynamics, resulting in amplified floods causing loss of life and property. The rivers which served as life line for millions of years for the survival of mankind are now looking towards humans for their own survival (Singh, 2018).

classification of indian riversThe rivers of India can be classified into three groups:a. The Himalayan rivers such as the Ganga, the

Ghaghara, Great Gandak and the Kosi etc., which originate in the higher Himalaya and are generally snow fed (Fig. 1).

b. The Ganga plain rivers such as the Gomati, the Sai, the Chhoti Gandak etc., which originate in this region and are generally fed by groundwater (Fig. 2).

c. Peninsular rivers, which originate in peninsular India and are rain fed, often forming waterfalls for example the Godavari, the Krishna, the Narmada etc. (Fig.3).

river basins of indiaAs per the Central Water Commission of India, there are 22 major river basins in the nation. Among them the three main basins that drain the northern and eastern India and have their origin in Himalaya are the Ganga, the Indus and the Brahmaputra river basins. The Ganga and the Brahmaputra river basins have an area of 861,452 sq km and 194,413 sq km respectively (Misra, 2014), and drain into Bay of Bengal. The Indus on the other hand, drains into the Arabian Sea and is


the longest river in South Asia with a basin area of 321,289 sq km (Jain et. al., 2018).

Among the others basins, mention may be made of peninsular river basins such as that of Godavari (312,812 sq km), Krishna (258,948 sq km), Mahanadi (141,589 sq km) (Jha, 2013) and river basins of east flowing rivers between Pennar and Kanyakumari and between Mahanadi and Pennar. Between them, these river basins drain 100,139 sq km and 86,643 sq km of the area respectively (MoSPI, 2018).

The river basins of west flowing rivers of Kutch and Saurashtra including the Luni basin drain 321,851 sq km area of western India (Jha, 2013). The Narmada River basin of central India drains 98,796 sq km (ibid).

life cycle and fluvial featuresThe life cycle or journey of a river, from its origin to its merger with the sea, is divided into three stages—the youth, mature and old stage quite akin to the life cycle of humans. The morphology and its depositional and/or erosional landforms are accordingly different in each of these stages. A term ‘channel’ (Fig. 1 and 2) is often used to define the body of a river or conduit that contains moving water. In its prime (youth), the river is full of energy. It gushes with full force from its source, gathers momentum and has a deep, down cutting power due to the high gradient. It therefore cuts deep gorges giving a ‘V’ shaped cross section to its valleys (Fig. 1). The river valleys are negative landforms and are carved by rivers under direct control of climate and tectonics. The two margins of the river channel are called banks, which may be left or right, as viewed in the direction the flow of river (Fig. 2).

In the mature stage, a river has more water due to several tributaries joining it. The river has a moderate gradient now, less than that it had in its youthful stage, but more than that it would have in its old stage. It has a broader ‘U’ shape channel and still has erosional powers, to not only cut down vertically but also cut laterally to give rise to eroded banks or cliffs (Fig. 4). Lateral-fluvial erosion is a natural hazard as it eats up fertile banks of a river. The banks that consist of sand, silt and clay in different proportions are prone to such erosion as these are non-cohesive and unconsolidated so can undergo weathering, slumping and sliding (Fig. 5).

Fig. 1. ‘V’ shaped valley, Ganga river, rishikesh, Uttarakhand; 2. a river channel - groundwater fed with both banks visible - Chhoti Gandak river, deorea, UP; 3. Narrow Narmada channel, cutting through rocks near Jabalpur, MP; 4. a cliff section, Yamuna river, Kalpi, UP; 5. Lateral erosion, Ghaghara river, deoria , UP.

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Fig. 6. three river terraces - t0, t1 and t2 deposited by Chhoti Gandak, deoria, UP; 7. Point bar deposits, Chhoti Gandak, UP; 8. Braided bar and lateral bar deposits, Ganga, rishikesh, Uttarakhand; 9. a natural levee, Chhoti Gandak, deoria, UP; 10. Confluence of the Ganga (shown in upper part) with Burhi Gandak, Gogri-Jamalpur, Bihar.

A river accumulates a good deal of sediment load along its way and may deposit some of it along the banks as fluvial terraces or flood plain deposits when the water rises and overflows its banks during floods. A river may deposit several levels of terraces which are older at the top and youngest at the level closest to the river.

Floods occur when the discharge exceeds the capacity of the channel in a way that the water level crosses the danger mark at a particular site and inundates low-lying areas. The magnitude of the flood depends upon the intensity of the rainfall, its duration, ground conditions such as the breaking of levee due to rise of water level and/or blocking of the natural drainage.

River terraces are former river valley floor surfaces. These are made up of sand, silt and clay. The different levels of river terraces are largely the products of river rejuvenation due to sea level changes under direct control of climate and tectonics. It represents the remnants of a river channel or flood plain when the river was flowing at a higher level. Due to the process of rejuvenation (upliftment of an area or lowering of sea level), the same river renews vertical erosion and down cuts its earlier floodplain. The older channel or floodplain stands as a terrace above the present day level of the river. In the Ganga Plain mainly three such river terraces has been identified T2, T1 and T0 (Fig. 6). The rocks and boulders transported by the river are broken into rounded to sub-rounded pebbles and deposited in order of their fineness—larger sized pebbles at the base and gradually finer ones upwards.

Point bars, braid bars and natural levee deposits are among some of the depositional landforms of a river. The point bar is a crescent shape deposition of sand and gravel present in the inner side of the bend of a meandering river (Fig. 7). Deposition on point bar results from lateral migration of a meandering river during flooding and may be as thick as the depth of the river. The bedload of sand and gravel deposited within the channel of braided river are known as braided bar deposits while the lateral bar deposits are channel bars deposited at one side of a braided river(Fig. 8).

During the time of floods, river water overtops its bank and enters into the flood plain and deposits the sediments. The coarser sediments are deposited along the river bank and the finer sediments are carried further onto the flood plain. Repeated

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deposition of sediments raises the river bank and results in a natural levee, which dips away from the channel at a very low angle (Fig. 9). Several tributaries join a major river, called the trunk river to give rise to a drainage pattern. Very often, two or more major rivers join together at a point termed confluence—the confluence of the Ganga and the Yamuna at Sangam (Prayag raj). Figure 10 shows the confluence of the Ganga (shown in upper part of the photograph) with the Burhi Gandak river at Gogri-Jamalpur in Bihar. One can note the contrast in colour between the waters of the two rivers—Ganga carrying a larger sediment load while Burhi Gandak comparatively pristine.

During the last stages the river joins the sea to end its journey. It may form an estuary—a small and narrow channel or place where it meets the ocean and a mixing of oceanic and river water takes place. A delta is formed at a place where flowing water body joins a stagnant water body. The river at such stages drops its entire load and takes whatever path it finds to meet the base level. The term evolved from the fourth letter of the Greek alphabet—delta. The letter resembles the

shape created at the mouth of Nile where it joins the ocean. The deltas of the river Ganga in Bengal and Indus in the Arabian Sea have formed large fan deposits known as the Bengal fan (Fig. 11a & b) and the Indus fan respectively.

referencesJha A.K., 2013. Water availability, scarcity and climate

change in India: A review. Asian Journal of Water Environment, 1(1): 50-66.

Jain S.K., P.K. Agarwal and V.P. Singh, 2018. Hydrology and Water Resources of India. Water Science and Technology Library, 57. Springer, Dordrecht.

Ministry of Statistics and Programme Implementa-tion (MosPI), 2018. EnviStats India 2018 (Environmental Accounts) : Social Statistics Divi-sion, Government of India, New Delhi.

Misra H.N. (ed.), 2014. Managing Natural Resources: Focus on Land and Water. PHI Learning Pvt. Ltd.

Singh D.S., (2018). Concept of Rivers: An Intro-duction for Scientific and Socioeconomic Aspects. In The Indian Rivers, pp.1-23, Springer, Singapore.

Fig 11a. the western-most part of the Ganga delta where the hoogli branches off from the Ganga 300 km to the north, and flows by the city of Kolkata before flowing into the Bay of Bengal. high sediment load is evident in the satellite image by the light brown colour of the water. the deep green colour depicts mangrove swamps.Fig 11b. Ganga fan.

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The article should be cited as GnY staff, 2019. Karst topography, Geography and You, 19(17): 9

also the deepest direct shaft in the nation—Krem Shrieh, 8.9 km through a maze of fossil passages. Meghalaya also has the highest cave passage density in India with a labyrinth of paths underground, especially true of the Nongkhlieh Ridge (125 km of cave passages in an area of 30 sq km) (Prokop, 2014). The stalagmite in the Mawmluh cave located 2.3 km from Sohra (Cherrapunji) was recently in news as it aided the discovery of an anomaly at the 4.2 ka interval. This marked the beginning of the Meghalayan age—also called upper Holocene (G’nY, 2018). Each of the stalagamite layers of Mawmluh had different levels of oxygen isotopes which revealed 20-30 per cent decrease in monsoon rainfall over the ages.

referencesGnY Staff., 2018. Meghalayan age, Geography and You,

18(3): 114.Laitphlang D., 2018. Meghalaya: At over 24,000

metres in length, world’s longest sandstone cave found, Hindustan Times. Available at: https://bit.ly/2Hispfa

ProkopP.,2014. The Meghalaya Plateau: Landscapes in the Abode of the Clouds’, in Kale V.S. (ed.) Landscapes and Landforms of India,World Geomorphological Landscapes, Springer, pp. 173-180, doi: 10.1007/978-94-017-8029-2_17.

I N B r I e f

By Staff Reporter

The labyrinthian caves within the Meghalaya plateau present a fine example of a karst landform.

Karst landform is produced through the action of water causing chemical weathering of soluble carbonate rocks such as magnesium and calcium carbonates. Caves,

sinkholes, underground rivers, barren and rocky ground and lack of surface water bodies are results of such chemical processes in a karst region.

Stalagmite, halectite, stalactite pillars are some of the main features of karst caves. Stalagmites and stalactites are formed by the deposition of calcium rich material brought by the water percolating into caves or any other sheltered environment. The layers represent each cycle of deposition that can be dated by isotopic methods. The cone shaped deposit that grows from the ground upward is called a stalagmite while the deposit hanging from the roof is known as a stalactite.

In India one can find karst regions in Andhra Pradesh (Borra cave) and extensively in Meghalaya. With an average annual rainfall of 1150 cm, Meghalaya abounds in karst features. More than 1,650 caves and cave locations are found in Meghalaya, out of which over 1,000 have been explored or partially explored. About 491 km of karst caves have been surveyed so far (Laitphlang, 2018). The State hosts the longest natural cave in India—Krem Liat Prah, 30 km, as

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The Cachar valley records a number of neo-tectonic activities. A photo from NIT Campus in Silchar, the main town of this area, overlooking the river Barak.



By Kuldeep Kachroo

The author is Director (Retd.) at Geological Survey of India, Faridabad, Haryana. The article should be cited as Kachroo K., 2019. Cachar valley: A cauldron of adverse natural phenomenon. Geography and You,19(17): 10-16

A CAuldroN of AdverSe NATurAl pheNomeNoNThe Cachar Valley is a small, narrow sub basin of the Barak river. This area is

subjected to continuous tectonic activity, morphological changes and flooding. Human activities have aggravated the situation.

CaCHar Valley


The Cachar valley, a sub basin of the Barak river basin in Assam, frequently witnesses catastrophic events of floods, landslides and subsidence due to a combination of

tectonic, geomorphologic, geological and climatic conditions. In 1781 a sudden rise of the river wiped out nearly one-third of the population; an earthquake in 1869 changed the topography creating several depressions while the 1891 earthquake led to the subsidence of a number of tea gardens in the area.

The Cachar valley is small and narrow, with a width varying from 1 to 8 km and a length of approximately 50 km. Silchar, the main town of this area is one of the biggest in the northeastern part of India. The valley in the north is bounded by precipitous slopes of the Barail Range and is limited in the south by north-south trending low ridges with intervening valleys. The narrow Cachar valley has a very fragile environmental setting where mountain building activity is currently taking place resulting in continuous

morphological changes. A number of neo-tectonic activities are recorded in the area which range in age from 40,000 years to a few decades before present (BP).

The Barak River, which is in a deltaic state with a gradient ratio of 1:21,500 in the Cachar valley, has neither the gradient nor the flood plain to accommodate the vast amount of water that a number of tributaries bring to it. These tributaries drain 60 per cent of the total water from the 27,000 sq km area of the Barak valley into the small and narrow Cachar valley, resulting in frequent floods. That the Barak River is controlled by tectonic activity is evidenced by the river flowing 12 m below mean sea level (m s l) and displaying drainage reversals despite being in deltaic condition.

The Cachar basin, a part of the larger basin of the Barak River that is the second largest river of northeastern India, is part of the Ganga -Brahmaputra-Meghna drainage system. Of the total catchment area of 41,723 sq km of the Barak basin in India, the Cachar basin has a catchment

Location of Cachar sub-basin. River Barak may be seen flowing through the centre of the valley. The largest town of this area- Silchar is marked along the river.Source: Kachroo et al, 1992

Fig. 1: Location of Cachar Valley, Assam

Krishnanagar

Chunchura

AlipurKolkata

Howrah

Barddhaman

BaharampurSiuri

Ingrajbazar

Bangladesh

Balurghat

Tura

GuwahatiDispur

Purnia

Jalpaiguri Cooch Behar

Tezpur

Nowgong

Jorhat

Phek

KarongUkhru

Diphu

Kohima

Tamenglong

JowaiHaflong

Imphal

Churachandpur

Barak River

Cachar Valley

Agartala Aizawl

Lunglei

Saiha Area of study

Darjeeling

Silchar


of around 25,086 sq km. The river originates from the hilly areas of the Myanmar-Nagaland border. It traverses through parts of Nagaland, Manipur, Mizoram and the hills of Assam for about 403 km before entering the plains of the Cachar sub-basin at Lakhipur (Fig. 1).

At Lakhipur where the river enters into the plains, the catchment of Barak is 14,450 sq km while the total catchment at Bhanga is 25,086 sq km. This implies that in the short distance of about 50 km, a catchment of about 10, 636 sq km of very high rainfall area is added to the river. The water yield from the catchment area, after it emerges from the hills, far outstretches the annual water yield when it leaves Bhanga. At Lakhipur the average annual yield is 14,077 million cubic meters (M cu m) while at Badarpurghat the yield more than doubles to an average of 29,600 M cu m. The monsoon and non-monsoon yield at Lakhipur is 12,073 and 2,004 M cu m, respectively. At Badarpurghat, the yield in the two seasonal extremes is 24,368 and 5,232 M cu m, respectively. This means that the

river has to accommodate the huge water yield in a very short distance and in a narrow valley which leads to immense problems of drainage (Brahmaputra Board, 1988).

The area falls along the monsoon trough and also receives heavy rainfall in the pre-monsoon period from frequent storms rising in the Bay of Bengal followed by the monsoon which brings heavy rains in the catchment area, exacerbating the problems of flooding.

GeomorphologyThe Cachar valley is juxtaposed with a contrasting tectonic setting where the available data suggests that the area is subjected to continuous tectonic activity. It is bounded by the active Dauki fault. In fact the Haflong-Disang Cachar basin has a contrasting geomorphic set up from north to south, as it lies at the confluence of a mature and an immature topography. The Barak River separates the geomorphic setup of the north and the south. Major geomorphic units include coalescing

2a. hanging bils/ cut-off meanders; 2b. Straight course of Barak beyond Badarpur; 2c. Barak river course in recent times.Source: Kachroo et al, 1992

Fig. 2: Barak River morphology in different sections

a

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Changes in the Barak from 1920 to 2019

Badarpur

Salchapara Silchar

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Badarpur

Salchapara Silchar

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Badarpur

Salchapara Silchar

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channel characteristicsThe Barak at Lakhipur is 150 m wide and 15 m deep. It maintains a straight course up to Narayanpur from where it starts meandering. The low mounds (hills) around Kashipur tea garden restricts the river towards the south, thus influencing the free meandering of the channel in its flood plain. Near Silchar the course is restricted to the north part of the flood plain under the influence of the hills in the south. Beyond Silchar, the river, instead of flowing through the centre of the valley, flows hugging the southern bank up to Badarpur. From here up to Bhanga, the river runs straight and is highly entrenched (Fig. 2b). It is a very abnormal state for a river, especially when it is in the deltaic state. On both sides of the river, all along its course, there are a number of cut-off meanders some of which are of very recent origin (Fig. 2a).

The cut-off meanders are left hanging along the flood plain of the river and at places are more than 8-10 m above the river level. These cut-off meanders give rise to the depression—bils. The formation of the cut-off meanders indicate straightening of the course which is anomalous as the river has a very low gradient, which is a deltaic state for any river. The channels at places coalesce into a complex of bil and hoars (Fig. 2d).

ridges and valleys in the south, narrow flood plains of Barak with general elevation varying from 15 to 25 m above the m s l, which are almost flat except the depressions of the older channel and oxbow lakes. In the north the major geomorphic units are the terraces that occur as a tableland 4-5 m above the adjoining flood plains and high structural hills which form the northern limit of the basin.

drainageThe Barak River drains the whole of the Barak valley and is joined by four major tributaries. The rivers which join the Barak along the left bank (south) in the Cachar valley follow long and highly meandering routes with lots of water bodies like bils and haors (Fig. 2), while those which join from right bank have short and a high gradient path. The Barak River meanders along a highly entrenched course until it reaches Bhanga where the river acquires a complete deltaic state with very low bank and trough distributaries.

In the Cachar valley the river bank height varies between 10 and 15 m. Within the valley, between Lakhipur and Bhanga, the river is traversed by two NNE-SSW trending ridges. These ridges divide the river in three different blocks (Kachroo et al., 1992).

The rivers which join the Barak along left bank follow long and highly meandering routes, while the ones which join from the right bank have a short and high gradient path.Source: Kachroo et al., 1992

2d. Bils and haors (dark spots) in valley


The tributaries of the left bank drain 33 per cent of the Barak valley and bring in a water yield of 40 per cent into the narrow valley, while the tributaries of the right bank drain 5 per cent and bring in a water yield of 15 per cent into the Barak valley, thus loading the river with large volume of water. This unprecedented input of water creates anomalies in the drainage system of the Cachar valley.

The complete transformation of an irrigation canal (Kata khal) into a sinuous meandering river and duplication of the pattern of the parent river (Dhaleshwari) in less than a century (Fig. 3a) is indication of the ferocity of the tectonic activity of the Cachar valley. The Barak River profile is perhaps one of the clearest indications that the mountain building activity is taking place in the area. There is no other explanation for the river to erode below m s l (Fig. 3b) at regular intervals particularly when the river has a very low gradient.

The flow of river below m s l only indicates that the river is flowing over a continuously sinking area along the synclinal axis (Fig. 3b), a sign of continuous tectonic activity constantly changing the morphology.

neo-tectonismThere are numerous evidences of ongoing neo-

tectonic activity in the area:Presence of buried tree trunks in Chandipur

tea estate on the banks of Barak dated 1570±90 years (Kar, 1990).

Presence of buried vertical trees along the river section near Ganigram.

Presence of hanging bil (oxbow lakes and cut-off meanders) all along the flood plain of Barak River.

Straightening of the Barak despite being in a deltaic state.

Entrenched nature of the Barak River.Sinking of part of a tea garden in the north bank

of the Barak River.Transformation of the Kata khal canal into a

meandering river in just a century.Flowing of river below m s l at different places

along the synclinal axis of folds.

changes induced byanthropogenic activityThe Barak basin has been a scene of intense anthropogenic activity since the nineteenth century. The change in the demography of the area and the increase in population has led to encroachment of low lying areas which earlier used to serve as flood cushions. Thus the rivers were denied their flood plains thereby leading to

Fig. 3a: Showing Transformation of Katakhal

Fig. 3b: Showing profile of Barak River in Cachar valley and the mean sea level.

An irrigation canal, the Katakhal changed into a sinuous meandering river duplicating the pattern of the parent Dhaleshwari in less than a century points towards intense tectonic activity in the Cachar valley.Source: Kachroo et al., 1992; Section: Bramhaputra Board, 1988.

Bhanga

Dhaleswari

Dhaleshwari

Katakhal

Katakhal

Ghagra

-6.46-7.29

-11.41-8.76

-4.46-4.18

-10.27-4.21 -5.23 9.60

-12.31

JatingaMadura

Badri

Average water level

Sonai

0 m s l

Chiri

Index

-12.31 Bed level

Anticlinal axis

Section line

Bara

k


the problem of siltation of the river channel and consequent floods. The roads and railway lines built to cater to the need of the day have cut across the drainage lines and do not leave sufficient free way to allow uninterrupted flow of peak discharge resulting in water logging.

Embankment (Fig. 2d) and road construction has been on going in the valley since India’s independence and so far embankments of more than 750 km in length have been constructed very close to the river banks resulting in greater duration of the back flow into the tributaries and lack of space for the surface run off to flow into channels. The construction of embankment has converted a part of the area into low intensity flood zone of long duration from high intensity flood zone of short duration.

Way forwardClear evidences posit that the area is undergoing rapid tectonic changes which are discernible. The profile of the Barak, which indicates the river flowing alternately above and below the m s l can only be explained by constant down-warping/

subsidence taking place along synclinal axis and uprising along anticline axis. This is in sync with the young orogeny, east to west along the Indian plate.

Anthropogenic activities have further aggravated the situation. The root cause lies in the engineering solutions that have not taken into consideration the intensity of the tectonic changes taking place. In order to provide a solution to the problem it is important to identify the exact nature of activity that constantly changes the physiography of the area and scientifically quantify the changes taking place within the Cachar valley.

referencesBrahmaputra Board, 1988. Master Plan Barak Sub

basin, 1-3: 1-26. Available at https://bit.ly/2HCwlZtKachroo K., N. Rajendran and S.K. Kar, 1992.

Geoenvironmental appraisal of Barak basin.Unpublished report of Geological Survey of India.

Kar S.K., 1990. Report on drilling at Alipur (Silchar) as a part of Environmental studies of Barak valley, Cachar district, Assam (Interim Report).

A view of Sadarghat bridge over the Barak river in Silchar, Assam from a Boeing 737-200 aircraft.

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The article should be cited as GnY staff, 2019. Columnar basalt, Geography and You, 19(17): 17

ColumnarBasalt

Interestingly, the basalts found in the wall of a pristine, 16 km diameter impact crater at Marte Valles, Mars, as also in the nearby volcanic plains of Elysium Planitia–Amazonis Planitia and northeast Hellas, have been found to exhibit similar columnar jointing as observed in terrestrial columnar basalts (Milazzo et al., 2009).

referencesDegraff J.M. and A. Aydin, 1987. Surface morphology of columnar joints and its significance to mechanics and direction of joint

growth. Geology Society Australia Bulletin, 99 (5): 605-617. Available at: https://bit.ly/2G3fjmE

Goehring L. and S.W. Morris, 2008. Scaling of columnar joints in basalt. Journal of Geophysical Research: Atmospheres, 113(B10203): 1-18, doi:10.1029/2007JB005018

Milazzo M.P, L.P. Keszthelyi, W.L. Jaeger, M. Rosiek, S. Mattson, C. Verba, R.A. Beyer, P.E. Geissler and A.S. McEwen, 2009. Discovery of columnar jointing on Mars. Geology, 37 (2): 171-174. Available at: https://bit.ly/2G4MKVX

Spry A., 1962. The origin of columnar jointing, particularly in basalt flows. Journal of the Geological Society of Australia, 8(2): 191-216. Available at: https://bit.ly/2uYg2jI

By Staff Reporter

Hexagonal structures of basaltic rocks comprises columns and are separated by vertical or horizontal fractures.

Hexagonal columns of basalt standing tall and pillar like,

look aesthetically pleasing in the natural environment. These structures form in basaltic rocks and consist of columns that are separated by vertical joints and/or horizontal fractures in the rocks. Such features are extensively found in the volcanic terrain of central parts of India especially in the Deccan traps. Formed during the cooling of magma, these rocks are fractured into columnar prisms by thermal stresses. Spry (1962) recognised a ‘threefold structural division with a lower colonnade, central entablature and upper colonnade. Joints in many flows form in a definite sequence with master joints first, mega-columns next, then normal columns and finally cross-fractures’.

Goehring and Morris (2008) have shown by experimental modelling that the column radius and striation size are proportional to each other and inversely proportional to the cooling rate of the lava. Further studies by Degraff and Aydin (1987) indicate that columnar joints grow incrementally from exterior to interior regions of solidifying magma bodies.

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Narmada flows in a general ENE-WSW direction over a length of 1,312 km. A view of the Narmada rift valley, Bheraghat, near Jabalpur.



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The role of geology, particularly of the structure and tectonics as also of lithology of a region in controlling its drainage path

is conspicuously displayed in some cases. Both the structure and lithology offer weak planes for water to cut through the rocks and follow a course of least resistance. The Narmada River offers an excellent example of this. It flows in a general ENE-WSW direction over a length of 1,312 km, draining finally in the Gulf of Khambhat in the Arabian Sea. A remarkably straight course can be seen in the topographic map (Fig. 1). It follows the Narmada-Son Lineament, which is a part of Central Indian Suture (CIS) zone that separates two Precambrian crustal blocks to its north and south with distinctive litho-tectonic features. The CIS extends from the Delhi-Aravalli thrust- contact in the northwest to the Singhbhum shear zone in the southeast (Jain et al., 1995).

The Narmada has cut deep gorges through marble rocks near Jabalpur, Madhya Pradesh. It displays several palaeochannels near Bheraghat, where older channels may be seen to occur towards north at a higher elevation. Because of the upliftment of the northern block due to ongoing neo-tectonic activities, the river channel has gradually shifted towards the south in the Holocene/recent period. The path of the Narmada-Son Lineament is also referred to as a rift valley.

The flow of Narmada is constricted by rocky gorges, rapids and wide alluvial reaches that also display meandering paths of the river. The study of its channel forms in the alluvium reach by Rajguru et al., (1995) has shown that channel size, shape and bed forms in the Narmada are related to very large recent floods that have built discontinuous floodplains between the cliffs, creating a channel in channel topography. Narmada valley,

1. satellite view of the course of the Narmada; 2. lineament controlled drainage path of the river

1

2

The article should be cited as Prasad A., 2019. Narmada’s distinctive litho-tectonic features, Geography and You 19(17): 18-19

By Anulekha Prasad

Distinctive Litho-tectonic FeaturesNarmada offers an excellent example of geological control over river

morphology where the waters follow a course of least resistance.

NarmaDa’s

geologically a graben or a sunken block, has been a palaeontological treasure. A number of rare dinosaur fossils and fossil skull of early man (Sonakia et al., 1985) have been discovered here.

referenceJain S.C., K.K. Nair and D. Yedekar, 1995. Geoscientific

studies of the Son-Narmada-Tapti lineament zone. Geological Survey of India, Special Publication, 10 : 333-371.

Rajguru S.N., A. Gupta, S.N. Kale and R.K. Ganjoo, 1995. Geomorphology of a selected reach of the Narmada River, India: A study in channel form and behavior. Earth Surface Processes and landforms, 20: 407-421.

Sonakia, A. and K. A. Kennedy, 1985. Skull cap of an early man from the Narmada valley alluvium (Pleistocene) of central India, American Anthropologist, 87(3): 612-616.

20 MARCH 1-15 2019 GeoGRApHy And you vol 19, issue 17

By Ratish Kumar Jha

LAKELAKEL NARL NARL NARL NAR

Lonar crater is one of India’s spectacular landforms that is a well known example of a best preserved meteorite impact structure on the volcanic

rocks of the Buldhana district of Maharashtra.

The article should be cited as Jha R.K., 2019. Lake Lonar, Geography and You, 19 (17): 20-21

l a nd f or m s I n I nd I a

GeoGRApHy And you MARCH 1-15 2019 21

Apart from common geomorphic landforms—mountain chains, volcanoes, rivers etc, formed by the dynamic processes of the earth system, there are some rare

features that owe their origin to extraterrestrial sources such as meteorites. The Lonar crater of Maharashtra is a feature that is well known world over as one of the best preserved impact structure and the only one to have been formed on the volcanic rocks on the earth. Situated in the Buldhana district of Maharashtra, the circular crater is 1.88 sq km in diameter with a maximum depth of 150 m. It was formed by the hyper velocity large impact of a huge meteorite fall that pushed rocks into the earth and consequently pushed out the host rocks to form a 20 m high rim from the ground level. The crater is significant as its geological setting is similar to craters commonly found on the surface of moon and other inner solar system planetary bodies.

The Lonar crater was formed about 570,000 years ago in the 65 million year old basalt of the Deccan Traps. The evidence of lake’s extraterrestrial origin comes from raised rim and the ‘ejecta blanket’—the material ejected out during the impact and spread over a distance of 1 km all around the crater. The ejected material comprises fallen debris, shatter cones, impact breccia, maskelynite, and micro breccia. The glass spherules and micro breccia are closely associated with the craters found in moon.

The studies carried out by Chakrabarti and Basu (2006) have revealed that the impact breccia of the crater is enriched in rubidium (Rb), barium (Ba) and lead (Pb), and to some extent in thorium (Th )and uranium (U). These rocks also show more radiogenic strontium (Sr), higher Rb/Sr ratio and lower radiogenic neodymium (Nd) and samarium (Sm)/Nd ratios.

Being a deep closed inland brackish water lake, the Lonar supports a fascinating micro ecosystem and varied biodiversity (Musaddiq et al., 2001). The water shows high salinity and alkalinity (1460-2230mg/l) with 11 phytoplankton species. The lake also houses rare microbial, plant and wildlife. The string of old temples all around the periphery of the lake, though in dilapidated condition, gives an ancient look to the environment.

There is a small lake adjacent to Lonar—Amber lake, which appears to have been formed by a fragment of the same meteorite or a smaller meteorite, accompanying the main one.

ReferencesChakrabarti R. and A. Basu, 2006. Trace element and

isotopic evidence for Archean basement in the Lonar crater impact breccia, Deccan Volcanic Province. Earth and Planetary Science Letters, 247(3-4): 197–211, doi:10.1016/j.epsl.2006.05.003.

Gupta R.D., A. Banerjee, S. Goderis, P. Claeys, F. Vanhaecke and R. Chakrabarti, 2017. Evidence for a chondritic impactor, evaporation-condensation effects and melting of the Precambrian basement beneath the ‘target’ Deccan basalts at Lonar crater, India. Geochimica et Cosmochimica Acta, 215: 51-75.

Maloof A.C., S.T. Stewart, B.P. Weiss, S.A. Soule, N.L. Swanson-Hysell, K.L. Louzada, I. Garrick-Bethell and P.M. Poussart, 2010. Geology of Lonar Crater, India .Geological Society of America Bulletin 122(1-2): 109–126, doi: 10.1130/B26474.1

Musaddiq M., A.K. Fokmale and R. Khan, 2001. Microbial diversity and ecology of Lonar Lake, Maharashtra, India. Journal Aquatic Biology, 16(2): 1-4.

Satyanarayana S., P.R. Chaudhari and S. Dhadse, 2008. Limnological study on Lonar Lake : A unique brackish crater lake in India, in Sengupta M. and Dalwani R. (eds.) Proceeding of Taal 2007. The 12th world Lake Conference, pp. 2061-2066. Ph

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Desert landforms are result of various factors including tectonic activities. A view of Sam sand dunes, Jaisalmer.

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The author is Director General (Retd.,), Geological Survey of India. [email protected]. The article should be cited as Wadhawan S.K., 2019. Desert landforms, Geography and You; 19(17): 22-27

Deserts are diverse in nature and found on almost all latitudes.

Landforms in desert have evolved through long periods of time and

have been created by erosional and depositional processes of the

present as well as the past climatic domains.

desertLANDFORMS


Deserts are barren, inhospitable dry lands with an abundance of searing sunlight. These are characterised by having a mean annual precipitation of less than

250 mm to a maximum of 500 mm and very high evaporation rates. Nearly 30 per cent of the land surface in the world bears an arid and a semi-arid environment (Cook and Warren, 1973). The surface water drainage is ephemeral and mostly ends up in inland basins—or drains seasonally into depressions, thus forming a shallow and saline lake or playa. These water stressed regions are prone to frequent droughts and support xerophytic vegetation that grows deep roots to tap scarce groundwater that is generally brackish due to impeded movement. Desert plants in many instances cannot access freshwater for years, prompting them to grow long roots to reach into the deep groundwater (Dhir, 2018).

The four fundamental types of deserts are the hot and dry (or subtropical) desert, the semi-arid (or cold winter) desert, the coastal desert and the cold (or polar) desert. Polar deserts are covered with ice that cannot be absorbed by plants. Antarctica is the world’s largest cold desert. Mid-latitude deserts occur mostly deep inside the continents and lie in the topographical shadow zones—Takla Makan, Gobi, Nevada and Patagonia deserts on the east of Andes. However, the most widespread are the low latitude deserts or the subtropical deserts located between 20o and 35o north and south of the equator, experiencing high pressure atmospheric circulation patterns. These include the Sahara, Arabia, Mexican Arizona, Mojave, Atacama, Kalahari-Namib and the Great Australian desert (Kar, 2014). The Thar desert of India is also one among the above mentioned deserts.

Landforms in any desert have evolved through a long period of interplay between fluvial and aeolian processes operative during wet and dry climatic regimes, especially during the Quaternary period. However, periodic tectonic activities have also influenced desert landscape evolution. Desert landforms have been created by erosional and depositional processes of the present as well as the past climatic domains (Wadhawan, 1996).

rocky uplandsSharply defined rocky uplands or residual hills are

developed in arid environments and are erosional landforms where vegetation is sparse and overland seasonal water flow is effective in creation of cliffs on bare resistant rocks such as monadnocks over granites and gneissic rocks or plateau over horizontally disposed sedimentary rocks (Fig. 1 and 2).

Retreating cliffs produce a tabletop mesa or a smaller steep-sided isolated hill called a butte. High speed winds in the deserts perform two kinds of erosional work—abrasion and deflation. Loose sand particles lying on the ground surface may be lifted and rolled over thus carving striations and wearing out edges or polishing thereby forming sand blasted faceted ventifacts. A similar act of abrasion against the resistant granitic outcrops would create curved up excavation pits, hollowed grooves and sculpt what are called as the tafonis. Cavernous weathering that produces tafoni and alveolar relief along joints is dominantly developed in many granite residual hills and some ferruginous sandstone hills (Fig. 3 and 4).

Wind transported and blowing away of sand is called deflation, that can result in carving depressions or shallow blow-outs and blasting off of the dune sands. Desert pavements are formed when winds deflate the finer sand grains and the residual lag deposits of coarser clastics are left behind that may range in size from pebbles to small boulders (Fig. 5). These gravel spreads are called reg (Arabic for stone) or serir and form a protective armour layer of closely packed resistant clasts.

ephemeral river coursesOwing to scanty rainfall, the deserts are generally devoid of any integrated surface water drainage courses. However, some channels incise their intermittent drainage routes particularly along the desert margins, through the aggraded sandy sheets that end up in inland basins (Fig. 6). Remote sensing and aerial photo-interpretation have aided in deciphering several palaeo-channels that are indicative of dominance of past wetter climatic regimes when well defined river courses were traversing through lowlands in the deserts.

lakes and playasClosed lake basins in the deserts form an important landform. Lakes and playas have existed in arid regions episodically throughout the Cenozoic. Studies of lakes have become an


1: Jabel hill in oman; 2: residual hill of sandstone forming butte with bare cliffs in thar Desert, Jodhpur, rajasthan; Fig.3: tafonis carved by abrading winds in Sendra Granite at the margin of thar Desert,Pali, rajasthan; Fig.4: tafonis sculpted in granite hill at thar Desert margin, Mt Abu, rajasthan; 5: Desert Pavement at Bhojka in Western thar Desert; 6: Ephemeral channel incised in thar Desert; 7: Sambhar Salt Lake, thar Desert; 8: Didwana Salt Lake, thar Desert; 9. Active Barchan Dune Fields at Sam, Jaisalmer; 10: Active Barchan Dune Fields at Sam, Jaisalmer; 11: rake-Like Clustered Parabolic Dunes in Central thar Desert; 12: Superimposed/ multi-storied complex dunes in central thar Desert,Shergarh, Jodhpur, rajasthan.

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important tool for reconstructing palaeo-climatic changes at a regional level. These saline lakes are the repositories of geological, geochemical, bio-geochemical information of Late Quaternary –Holocene period. A number of inland ranns (ephemeral playa lakes), with a flat salt-encrusted surface that get inundated during the monsoon are found within the desert. Study of lakes incorporates geomorphological, geological, bio-stratigraphic and multi-proxy approaches to reconstruct palaeo-hydrological and palaeo-climatic changes in the deserts (Singhvi and Kar, 2004). The Sambhar and Didwana saline lakes in Thar desert, India have been an important source for production of common salt (Fig. 7 and 8). Several playas in the deserts are also a rich source of gypsum and calcareous mud.

sand dunesFive basic dune types are recognised in the deserts—crescent, linear, star, dome and parabolic (Wadhawan, 1996). Dune covered areas may occur in three forms—simple (isolated dunes of basic type); compound (larger dunes on which smaller dunes of same type form); and, complex dunes (combinations of different types) (Fig. 13).

Fig. 13: Diagrammatic representation of various types of dunes

Barchan dunesBarchans are the crescent-shaped mounds which are generally wider than long. The leeside slipfaces are on the concave sides of the dunes (Fig. 9 and 10). These dunes form when winds blow consistently from one direction (unimodal winds). They form separate crescents when the sand supply is comparatively small. When the sand supply is greater, they may merge into barchanoid ridges and then prograde into thick transverse dunes. Characteristically abundant barchan dunes may merge into barchanoid ridges, which then grade into linear (or slightly sinuous) transverse dunes, so called because they lie transverse, or across, the wind direction, with the wind blowing perpendicular to the ridge crest.

Longitudinal or Seif DunesLongitudinal or the seif dunes are linear (or slightly sinuous) dunes with two slip faces. They are called seif dunes after the Arabic word for ‘sword’ as the two slip faces make them sharp-crested. Longitudinal dunes are associated with bidirectional winds. The long axes and ridges of these dunes extend along the resultant direction of sand movement. Some linear dunes

Barchan dune

Transverse dune

Sleep slip face

Sleep slip faceGentle windward slopeWind direction

Wind direction

Gentle windward slope

Blowout duneVariable wind direction

Longitudinal dune Equal slopes

Wind direction

Gentle windward slope

Sleep slip face


merge to form Y-shaped compound dunes. The longitudinal dunes are found confined mostly to the western and south-western parts of the Thar desert where they show their grading boundaries with the parabolic dunes on the west and the large transverse dunes on the east and northwest.

Parabolic DunesU-shaped mounds of sand with convex noses trailed by elongated arms are parabolic dunes. These dunes are formed from blowout dunes where the erosion of vegetated sand leads to a U-shaped depression. The elongated arms are held in place by vegetation; the largest arm is recorded in the Thar desert to be upto 8 km. These dunes occur as U-shaped, or hairpin dunes, and in the Thar desert they occur mostly as compound parabolic dunes or coalesce typically forming clustered and rake-like parabolic dunes that laterally share their longitudinal arms (Wadhawan, 1996; Fig. 11). Parabolic dunes occur in areas where very strong winds are mostly unidirectional and fairly consistent as is the case with the parabolic dune fields in the central and south-western Thar desert.

Although these dunes are found in areas now characterised by variable wind speeds, the effective winds associated with the growth and migration of both the parabolic and crescent dunes probably are the most consistent in wind direction. The grain size for these well-sorted, very fine to medium sands is about 0.06 to 0.5 mm. Parabolic dunes have loose sand and steep slopes only on their outer flanks. Presently reactivated crestal parts of the older stable parabolic dunes support superimposed aeolian sands in the form of linear dunes as obstacle extensions or climbing and falling barchans thus forming complex multi-storied aeolian deposits (Fig. 12).

soils and hard pans in desertsSoils that form in arid climates are predominantly mineral rich with low organic content, mostly rich in calcium carbonate. The repeated accumulation of water and evaporation in some soils causes distinct salt layers to form. Calcium carbonate precipitated from solution may cement sand and gravel into hard layers called ‘calcrete’ that form layers up to 50 m thick. Calcretes in deserts can occur in a variety of geological and geomorphic settings, including as regolith over hard bedrock, within sheet-wash aggraded plains, colluvio-

aeolian sequences and older stabilised dunes (Dhir et al., 2004). Caliche is a reddish-brown to white layer found in many desert soils. Caliche or clayey kankar deposits commonly occur as nodules or as coatings on mineral grains formed by the complicated interaction between water and carbon dioxide released by plant roots or by decaying organic material.

Way forward Although deserts are water scarce regions and are prone to droughts, yet they are a rich source of common salt, gypsum and various other minerals. The various landforms of deserts form an interesting landscape that is specially sculpted by arid conditions. The indepth study of these phenomena has allowed modern engineering to work out solutions that can help build infrastructure and allow human habitation in these regions.

referenceCook R.U. and W. Andrew, 1973. Geomorphology in Deserts:

Los Angeles, California University Press,pp. 374. Dhir R.P., D.C. Joshi and S. Kathju, 2018. Thar Desert in

retrospect and prospect. Scientific Publishers.Dhir R.P., S.K. Tandon, B.K. Sareen, R. Ramesh, T.K.G.

Rao, A.J. Kailath and N. Sharma, 2004. Calcretes in the Thar desert: genesis, chronology and palaeoenvironment. Journal of Earth System Science, 113(3): 473-515.

Hess D. and D. Tasa, 2012. Physical Geography: A Landscape Appreciation. PHI Learning Pvt. Ltd. New Delhi. pp. 561.

Kar A., 2014. The Thar or the Great Indian Sand Desert, in Kale V.S. (ed.) Landscapes and Landforms of India, World Geomorphological Landscapes, Dordrecht, Springer, pp. 79-90.

McKee E.D., 1979. In A study of global sand seas: U.S. Government Printing Office,Professional Paper, doi: 10.3133/pp1052.

Singhvi A.K. and A. Kar, 1992. Thar Desert-In Rajasthan: Land, Man & Environment. Geological Society of India Publications, 9(1): 191.

Singhvi A.K. and A. Kar, 2004. The Thar desert in Rajasthan since last interglacial-evidences from dunes and lakes-a review. Quaternary International. 105:75-87.

Wadhawan S.K., 1996. Textural attributes of recent aeolian deposits in different sub-basins of the Thar Desert, India. Journal of Arid Enviornments, 32 (1): 59-74. Available at :doi:10.1006/jare.1996.0006


By Sulagna Chattopadhyay

The article should be cited as Chattopadhyay S., 2019. Coastal geomorphology, Geography and You, 19 (17): 28-29

Coastal landforms constitute erosional or depositional features. Sea cliff, sea caves, sea arches etc., are erosional landforms whereas landforms such as beach, bar, barrier are depositional in nature.

India has a coastline approximately 7,500 km long that bounds its land from three sides—western, southern and eastern. A coastline may be defined as a ‘coastline of emergence’ or a ‘coastline

of submergence’ depending on whether it is formed by the upliftment of land (or by the lowering of the sea level) or by an opposite phenomenon—subsidence or sea level rise, respectively. The Tamil Nadu coast, for example, represents a coast of emergence. The northern part of the western coast of India is ‘submergent’, as a result of faulting, while the southern part (Kerala) represents an ‘emergent’ coast (Khullar, 2018). The landforms occurring in the coastal regions are carved out by marine processes as a result of the dynamic physical processes in time and space (Pethick, 2000). The common coastal geomorphic features that can be observed as different components of the coastal oceans are straits, channels, continental submarine margins and continental shelves etc., (Nag, 2010). The tidal and the coastal

waves along with sediment flux are responsible for shaping these landforms. The coastal landforms also undergo changes due to climate variations (glacial/interglacial periods) that cause a rise or fall in the sea level. A coastline may exhibit a straight or an irregular coast (Fig. 1), deltaic coast (Fig. 2), mud flats (Fig. 3), coastal dunes (Fig. 4), sandy beaches, tidal flats, etc. The coastal landforms may be defined as erosional landforms or depositional landforms depending upon the process of their genesis. Among the former are—chasms, wave-cut platforms, sea cliffs, sea caves, sea arches, chimney rocks etc., while the latter category of landforms comprise—beach, bar, barrier, spit, hook etc.

The erosional landforms rise due to the dynamic processes of onshore and offshore waves coupled with the sediment flux that are brought in by the weathering of the coastal rocks or the finer sediment from the offshore part of the sea itself. The coastal erosion often eats up the highland adjoining the sea, as in

CoaStal GeomorpholoGy

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Coastal landforms and shorelines and the changes imposed on them due to cyclones, transgression of sea and tidal action, tsunamis etc., are best monitored by remote sensing methods that repetitively use modern satellite images taken over different time spans (Nayak, 2017). Such studies have also been used to prepare coastal vulnerability maps showing likely areas that may be inundated by waves of different magnitude.

referencesKhullar D.R., 2018. India a Comprehensive Geography,

New Delhi, Kalyani Publishers.Pethick J., 2000. An introduction to coastal

geomorphology. Oxford University Press Inc,pp., 260.

Hegde A.V., 2010. Coastal erosion and mitigation methods-global state of art. Indian Journal of Geo-Marine Sciences, 39(4): 521-530.

Nag P., 2010. Coastal Geomorphic features around Indian Ocean. Indian Journal of Geo-Marine Sciences, 39(4): 557-561.

Nayak S., 2017. Coastal zone management in India -present status and future needs, JournalGeo-spatial Information Science, 20(2):15-19.

Maravanthe beach in Karnataka (Fig. 5). When the strong sea waves strike continuously against a rocky coast, cliffs are formed. The energy of striking waves is increased manifold by the accompanying fine sediments. At times the wave action erodes softer or more vulnerable part of the rocks along the coast carving a cave. Sea arches are formed when the waves cut through the cliff making a hole that leaves a bridge like structure in the rock. Part of the bridge along with a supporting column may yield to intensive wave action, leaving only the other column—thus giving rise to what is called a chimney rock. Marine transgression on the region adjoining the sea may result in a relatively plain area that is referred to as a marine plain.

The beach is a depositional landform, which is formed as a result of deposition of reworked sediments along the coastal slopes merging with sea. The deposition of sand or rock debris at a distance from the shore gives rise to sand bars. These may get submerged by the tidal currents. If one end of this feature is joined with the land while the other half is in the sea, it is called as a spit or a hook if the end towards the land is curved.

1. Satellite picture of parts of gujarat coast showing straight and irregular coastline; 2. a deltaic coast of West bengal. note the deposition of sediments in the bay of bengal form the ‘bengal Fan’; 3. Satellite image of inner gulf of Kutch showing extensive mudflats; 4. Coastal dunes at Pingleshwar beach, Kutch; 5. Coastal erosion at Maravanthe beach, Karnataka.

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The article should be cited as GnY staff, 2019. The Atolls of Lakshadweep, Geography and You, 19(17): 30

The ATolls of Lakshadweep

large territory (Hoon, 2012). Lakshadweep is the only atoll formation in

India. The atolls vary in shape from circular, sub circular to elliptical—some enclosed with lagoons, while others partly inundated (Mallik, 2017). The islands are flat and scarcely rise more than 2 m. The soils are structureless, formed by coral detritus and as such the soil fertility and water holding capacity are extremely poor. Apart from coconut, little else can be grown here. Freshwater resources are contained in a lens shaped aquifer 1.5 m below the surface. Freshwater is limited and the hydrological system is extremely fragile—the water being periodically renewed by rainfall. Eleven out of the 36 islands of Lakshadweep are inhabited—Agatti, Andrott, Amini, Bangaram, Bitra, Chetlat, Kadmat, Kavaratti, Kalpeni, Kiltan and Minicoy. An old dialect of Malayalam is spoken on all the islands except Minicoy, where they speak Mahl and are culturally similar to the people of Maldives.

referencesHoon V., 2012. Livelihood and changing social values

in Lakshadweep, Geography and You, 12(75): 12-18.

Mallik, T.K., 2017. Coral atolls of Lakshadweep, Arabian Sea, Indian ocean. MOJ Ecology & Environmental Sciences, 2(2): 68-83, doi: 10.15406/mojes.2017.02.00021.

Census of India, 2011. Lakshadweep provisional population data sheet basic figures at a glance, Government of India. Available at https://bit.ly/2WnlFrg

By Staff Reporter

With 36 low lying coralline islands, the Lakshadweep presents a unique landform that barely rises 2 m above the sea level.

The Lakshadweep islands are situated on the northern part of Laccadive-Maldive-Chagos ridge, lying off the west coast of India. It comprises coral atolls, reefs and submerged

banks, which surround 36 low lying coralline islands. With a population of 64,429 in 2011 (Census, 2011) and a land area of 32 sq km, the island group is densely inhabited. The land area accounts for less than 1 per cent of the total area of the Union Territory of Lakshadweep. Taken in totality, with the lagoons and the exclusive economic zone—the coral atolls (Fig. 1) occupy a

Fig 1: Atoll formation

Single sand bar island

30 mShallow lagoon

Old Coral/Lime StonePlatform

Reef

Reef

Subsidedvolcanic island

part of Chagos Ridge

Source: Hoon, 2012

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The article should be cited as Bhusan S., 2019. Badland topography, Geography and You, 19 (17): 31

BadLandTopogrAphy

Ravines or badland topography is developed when the horizontal or slightly tilted alluvial deposits, are acted upon by gully and/or wind erosion giving rise to a dissected

terrain. The upliftment of land due to neo-tectonic activity results in rejuvenation of rivers. These rivers or channels, equipped with the newly gained energy, attempt to reach base level of erosion, thus producing a dense system of interconnected gullies and ridges that constitute badlands.

One of the best examples is perhaps offered by the Indo-Gangetic plains of northern India which represent one of the most extensive deposits of alluvial in the world. These alluvial sediments were deposited in the Himalayan foreland basin between Siwaliks in the north and Bundelkhand-Vindhyan Plateau in the south. The middle alluvial Ganga plains, part of the larger Himalayan foreland basin, exhibit development of an intricate

By Sweta Bhusan

Badlands are a dense system of interconnected gullies and ridges. The Indo-Gangetic plains offer one of the best examples of such an area.

network of gullies, ravines and extensive dissected landscape (badlands) carved out in the plains of Chambal, Betwa and Yamuna rivers and their tributaries in central India (Joshi, 2014). The strengthening of southwest monsoon in the Holocene is believed to be the reason for increased headward erosion (Ranga et al., 2015). The present day ravines consist of steep slopes and channels separated by ridges, which gained notoriety as the refuge for ‘dacoits of Chambal’ since centuries.

referencesJoshi V. U., 2014. The Chambal Badlands, Landscapes and

Landforms of India, Dordrecht: Springer, pp.143–149, doi:10.1007/978-94-017-8029-2_13

Ranga V., S.N. Mohapatra and P. Pani, 2015. Geomorphological evolution of badlands based on the dynamics of palaeo-channels and their Implications. Journal of Earth System Science, 124(5): 909-920.

the ravines consist of a deeply dissected landscape with an intricate network of gullies. a view of Chambal

region, Madhya Pradesh.

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The article should be cited as Ghosh R., 2019. Volcanoes, Geography and You 19(17): 32

Barren Island

If one could slice the earth from one end to the other, the earth’s interior would

be seen to comprise an outer solid crust (0-35 km), a highly viscous mantle (35-2890 km), a liquid outer core (2890-5150 km) that is much less viscous than the mantle, and a solid inner core (5150-6360 km). The mantle has molten magma which finds its way through cracks or weak structural openings to rise to the surface of the earth in the form of hot lava, gases and/or ash in the form of volcanic eruption, as the pressure inside builds up to a critical limit. A volcanic eruption may be silent and compose of only gases if the magma is thin. On the other hand, if the magma is thick and sticky, the gas cannot escape, so it explodes with a loud thundering noise and explosion. The magma pours out from fissures or cone like features flowing down the sides.

Volcanic eruptions are known to have changed the weather, bring devastation to the area and wiping out life—human, animal and plant—from the area. The Mount St Helens’ eruption in 1980 killed thousands of animals and birds while the eruption of Tambora, Indonesia, in 1815, killed around 92,000 people and threw ash and gas

into the atmosphere that cooled the world climate for more than a year. The evidences of Tambora eruption are available in most of the ice cores drilled across the world as volcanic ash. The world has several hundreds of active

volcanoes where lava is intermittently thrown out.

In India, the Barren Island, located in the union territory

of Andaman and Nicobar is the only active volcano. Some volcanic activity in the past has been reported from the nearby island of Narcondum. Geologically, the site of volcano lies in the midst of a volcanic belt on the edge of the Indian and Burmese tectonic plates. The volcano attains a height of 354 m with a 2 km wide caldera. Since 1787, when the first eruption is recorded, the volcano is known to have erupted more than six times notably in 1789, 1795, 1803, 1852, 1991 (lasting 6 months),1994 and 2005. The most recent eruption took place in 2017 (Koshy, 2017).

referencesKoshy J., 2017. Why the Barren island volcano

erupt again, The Hindu. Available at: https://bit.ly/2M3HiJ7.

By Rajoli Ghosh

Located in the Andaman and Nicobar, Barren island is the only active volcano in India.


The article should be cited as GnY staff, 2019. India’s tombolo, Geography and You, 19(17): 33

IndIa’s Tombolo

formed at this time. Udhayana Pillai added during the proceedings that the bridge belonged to the Miocene era (ibid).

The region is highly dynamic because of the confluence of the Indian Ocean and Bay of Bengal and is subject to constant modification. Changes in the region are evident from multi-temporal satellite imagery. Strong sea currents continually reshape the coastal landforms, as do cyclones and associated storm surges.

referencesKVNS R., 2013. Ram Sethu (The Adam’s Bridge)

Figures& Facts. Jawaharlal Nehru Technological University, Kakinada (OCTAVIA).

Mitra D., 2014. Dhanushkodi-a disaster that wiped out India’s geography, Geography and You, 14(83): 44-47.

PavlopoulosK., Evelpidou N., and Vassilopoulos A., 2009. Mapping Geomorphological Environments, Springer-Verlag Berlin Heidelberg, doi:10.1007/978-3-642-01950-0.

Rao M. V., Chidambaram L., Bharktya D., and Janardhanan M., 2010. Integrated Analysis of Late Albian to Middle Miocene Sediments in Gulf of Mannar Shallow Waters of the Cauvery Basin, India: A Sequence Stratigraphic Approach. In Proceedings of 8th biennial international conference and exposition on petroleum geophysics, pp. 1-9. Hyderabad, Springer.

India

Sri Lanka

By Staff ReporterAdam’s Bridge or the Ram Setu is an interesting geological formation that holds mythical significance for the subcontinent.

A tombolo is formed when a cuspate foreland connects another coastline, usually of an island, with a rocky or sandy spit (Pavlopoulos, 2009). India’s tombolo, the Adam’s Bridge-

Ram Setu, is a 30 km long chain of limestone shoals between Rameswaram and Mannar island (KVNS, 2013). It separates the Gulf of Mannar in south-west from the Palk Strait in north-east.

The sub-basin of the Gulf of Mannar is understood to constitute the south-eastern offshore section of the Cauvery basin, the southern most of the mesozoic rift basins along the east coast of India (Rao et al. 2010). The late Jurassic fragmentation of eastern Gondwanaland into India, Antarctica, and Australia initiated the formation of mesozoic rift basins on the eastern continental margin of India including the Cauvery basin. Numerous deep extensional faults developed in the NE-SW direction during rifting which initiated active subsidence that resulted in the formation of graben and horst blocks, subdividing the Cauvery basin into many sub-basins including the Gulf of Mannar.

A group of professors from Madurai Kamaraj University asserted in 2007 that the Adam’s Bridge was ‘a geological formation, which took place around 17 million years ago when India and SriLanka were detached in a drift’ (Mitra, 2014). It had been geologically proven that sand bars were

A

Tombolo

tombolo is formed when a cuspate foreland connects another coastline,

formed at this time. Udhayana Pillai added during the proceedings that the bridge belonged to the Miocene era (ibid).

Adam’s Bridge or the Ram Setu is an interesting geological formation that holds interesting geological formation that holds mythical significance for the subcontinent.

formed at this time. Udhayana Pillai added during the proceedings that the bridge belonged to the

interesting geological formation that holds mythical significance for the subcontinent.

DhanushkodiFerry

Pemban I.

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Adam’s bridge

Talaimannar

mannar

mannar island

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The article should be cited as Prasad N., 2019. Hot springs, Geography and You, 19(17): 34

HotSPRINGS

Ganga spring Akhara Bazar, Kullu; Tattapani on the bank of river Satluj; and Manikaran Sahib-all in Himachal Pradesh ; Reshi located on the bank of river Rangeet in Sikkim; Kah-do Sang Phu and Yumthang with water temperature close to 500C (Tourism and Civil Aviation Department, Govt. of Sikkim, 2017) also in Sikkim. Most of these springs are known for their medicinal and therapeutic values as the water carries many minerals dissolved in solution, especially sulphur. The sites of these springs and others such as at Badrinath, Hemkund sahib, Gauri Kund (on way to Kedanath shrine) and the one near Yamunotri temple in Uttarakhand are famous pilgrimage locations.

Mention may also be made of hot water springs of Bakreshwar in West Bengal; Taptapa and Atri in Odisha; Vajreshwari, Maharashtra ; and Sohna in Haryana.

referencesPlanning Commission of India , 2005. Himachal Pradesh

development report. Government of India. Available at : https://bit.ly/2HQdevk

Tourism and Civil Aviation Department, 2017. Hot springs, Government of Sikkim. Available at : https://bit.ly/2M8rZil. Accessed on: May 24, 2019.

By N Prasad

High temperatures beneath the earth surface heat up water in aquifers which emerge as hot springs.

Hot water springs, as the term implies, are the springs that bring up heated groundwater on to the surface of the earth. As compared to cool water springs

that abound the earth, especially hilly terrains, hot water springs are less common and emerge only at favourable geological locales. As is well known, the temperatures at the deeper levels in our earth are much higher due to the existence of molten rocks at depths. These higher temperatures are transferred to the rocks in upper layers of the crust, which in turn heat up the water present in the pore spaces of the rocks. As the water heats up its density decreases, resulting in its rising towards the surface and finally emerging as a geothermal spring at sites of geological weaknesses such as cracks, faults etc. A term geyser is used for hot water springs when the water intermittently gushes out fountain-like from the surface and is on many occasions accompanied by steam.

Though hot water springs are spread all over in India, some of the well known hot water springs are-springs of Panamik in Nubra valley, Ladakh (Jammu and Kashmir); the Vashisht hot springs with temperature 590C (Planning Commission, 2005), located near Manali; Kheer

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a view of Manikaran hot spring, himachal Pradesh

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The article should be cited as GnY staff, 2019. Human induced land subsidence, Geography and You. 19(17): 35

LANDSubSidence

Lowering of the land surface can occur due to natural causes such as earthquake, faulting, landslide, creep etc. However, humans can also cause land to subside due to excessive

pumping of groundwater, extraction of oil and gas from underground reservoirs, subsurface mining etc. These anthropogenic causes resulting in inland subsidence holds serious repercussions, especially for urban areas. There are several such examples from south western United States (Leake, 2016), Jakarta (Abidin et al., 2011) and West Bengal (Ganguly, 2011).

The groundwater that is trapped in the pore spaces of sediments such as sand or gravel present in the aquifers is under pressure due to overlying sedimentary and alluvial sequence. When the water is withdrawn in excessive quantities surpassing aquifer recharge, the aquifer suffers a reduced water pressure. This reduces the support to the overlying unconsolidated clay and silt layers, resulting in compaction of sediments which leads to visible reduction in the elevation of the land surface.

A study conducted by Ganguly (2011) in Singur block, Hooghly, West Bengal has shown that the rate of decline of static water table, the depth of total aquifer system and the hydro-geological characteristics of the aquifer control the rate of subsidence in an area. While the average rate of subsidence was 0.92 mm/year during 1998-2002, it increased to 8.7 mm/year during 2002-2006. The estimated average rate of land subsidence was 6.13 mm/year for 1 m drop of static water table.

referencesAbidin H.Z., H. Andreas, I. Gumilar et al., 2011. Land

subsidence of Jakarta (Indonesia) and its relation

with urban development. Natural Hazards, 59(3): 1753–1771. Available at: https://doi.org/10.1007/s11069-011-9866-9

Ganguly M., 2011. Groundwater withdrawal and land subsidence: A study of Singur Block, West Bengal, India. International Journal of Geomatics and Geosciences 2(2): 465.

Leake S.A., 2016. Land subsidence from ground-water pumping. U.S. Geological Survey. Available at: https://geochange.er.usgs.gov/sw/changes/anthropogenic/subside/

By Staff Reporter

Excessive withdrawal of groundwater leads to reduced water pressure in aquifers resulting in reduced support of the overlying unconsolidated clay or silt.

Human induced

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Water table

Before extensive pumping of well

Well

Sand and gravel

Clayey silt

Lowered land surfaceWater table

After pumping

Confining bedArtesian squire

Artesian squire

Artesian squire

Artesian squire


The glaciers cover 10 per cent of the land surface on earth and sculpt various landforms. A view from the road on the way to Hattu peak, Shimla.

L a nd f or m s I n I nd I a


By Rasik Ravindra

Iceas an agent agent aof sculptIng

land

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The glaciers have sculpted various landforms transforming the geomorphology of earth. These landforms are the result of processes of weathering, erosion and deposition under harsh climatic regimes.

The author is Secretary General, 36 I G C. [email protected]. The article should be cited as Ravindra R., 2019. Ice as an agent of sculpturing land, Geography and You; (19)17: 36-41


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1. Snout of dakshin Gangotri glacier, Schirmacher oasis, east Antarctic; 2. Snout of Bara Shigri glacier, chandra basin, Himachal Pradesh; 3. Aerial view of mountain / valley glacier / cirque glacier of higher Himalaya, Himachal Pradesh; 4. Tidal glacier, ny Alesund, Svalbard, Arctic; 5. continental ice sheet, east Antarctic. Schirmacher oasis in the forefront and Wohlthat mountains in the far north. The distance between the two is nearly 100 km; 6a. Jagged hills of discontinuous disposition in the Wohlthat mountains, central dronning maud Land, east Antarctic.

Glaciers are formed when snow, compressed into large thickness of crystalline ice mass, develops an ability to move due to sheer mass. These glaciers together

with snow and ice constitute the cryosphere which covers nearly 10 per cent of the surface of the earth (NSIDC, undated). The major part of ice and glaciers is found as ice caps and ice sheets in Arctic, Antarctic and Greenland, apart from the Himalaya, Andes and Europe. The glacierised area of the earth is spread over nearly 15 million sq km of the land surface and account for approximately 75 per cent of the freshwater resources of the world (ibid). During the Quaternary period that lasted for 2.6 million years, the earth saw many changes in its climate, forcing repeated glacial and interglacial cycles, caused by the earth’s orbital changes including the tilt of its axis (Milankovitch cycles). As evidenced by the ice cores drilled from various locations of Antarctica, such as Vostok and Dome C, the earth witnessed eight cycles of ice ages each separated by an interglacial period in its history of past 750,000 years (EPICA, 2004). During the immediate past ice maxima period (~20,000 years

before present), the glaciers covered 32 per cent of the land surface and sculpted various landforms transforming the geomorphology of earth into a shape that we see today. Not far back, between 17th and late 19th century—during the period called ‘Little Ice Age’—the world saw consistently cooler temperatures that helped the glaciers advance. The advance or retreat of a glacier is seen at its snout, which may be defined as the terminus, toe, or the end of a glacier at any given point in time (Figs. 1 and 2).

There are several types of glaciers, such as mountain or valley glaciers which originate in higher altitudes of mountains and slide down the slopes occupying valleys over large distances for example the Himalayan or Alpine glaciers (Fig. 3). A tributary glacier may look like a hanging glacier if its link with the main trunk glacier is broken and it is left alone at the higher reaches of the mountains. Tide water glacier (Fig. 4) on the other hand extends up to sea and may give rise to icebergs as its tongues calve into the ocean. Large concentration of continental masses of glacial ice spread over land in the form of ice sheets are found in Antarctica (Ravindra and Chaturvedi, 2011) and Greenland, the former being the largest

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6b. Sharp peaks, arêtes, horns etc. in Ladakh Himalaya; 7. chandra Tal, a melt water glacial lake at 4,500m (above mean sea level), Lahaul Spiti, Himachal Pradesh; 8a. Glacial striations and grooves, Schirmacher oasis, east Antarctic; 8b. Glacial polishing and varnishing on rocks underlying glacier, Schirmacher oasis, east Antarctic; 9. Perched boulder, Schirmacher oasis, east Antarctic; 10. roche-moutonees observed in periglacial environment, Schirmacher oasis, east Antarctic.

accumulation of ice on this planet (Fig. 5).

Landform developmentThe landscape in glacial and periglacial environments is sculpted by the processes of weathering, erosion and deposition under harsh climatic regimes—caused by the agents of weathering and deposition such as strong winds, intense solar radiation, extreme cold surface temperatures and the movement of glaciers. The diurnal variation causes freezing and thawing in the rocks, resulting in their shattering, producing fields of broken rocks strewn in the form of block fields. On the higher reaches of the mountain, the glacial regime exhibit alpine topography that comprise serrated ridge tops, jagged peaks, arêtes, tors and/or horns (Fig. 6 a and b). The chemical leaching due to capillary action and salt formation imprint their marks on the landscape. The glacial and fluvio-glacial action of the ice (with melt water) together with the scouring action of the ice act upon comparatively weaker lithology to give rise to a number of depressions that gradually become the loci of accumulation of melt water, giving rise to melt water lakes (Fig. 7).

The advancing and retreating glaciers are powerful agents of erosion and deposition. The more prominent landforms under the influence of these factors are described below:Glacial Striation and Polishing: As the glaciers move over the hard rocks, they carve out groves and striations on the rocks below caused by the boulders or fragments of the rocks carried by it on the under side. The accompanying polishing gives a look of varnishing to the rocks that can be seen when the glaciers retreat and rocks become exposed (Fig. 8 a and b). The presence of coarse sand and pebbles on the top surfaces of the outcrops as well as the spread of boulders on the hill tops speak of an extensive coverage of glaciers over a terrain. The boulders, up to 2 m×1.5 m size, of completely different composition than the rocks of the hills on which they are found, occur as glacial erratic or perched boulders on the hill tops vacated by glacier in Schirmacher hills of east Antarctica (Fig. 9) indicating long distance transportation.

Roche-Moutonees: These are glaciated bedrock surfaces, usually in the form of rounded knobs,


the upstream side of which has been subjected to glacial scouring that has produced a gentle, polished and striated slope. The downstream side is subjected to glacial plucking that result in a steep and irregular slope. The ridges dividing the upstream and downstream slopes are therefore perpendicular to the general flow direction of the former ice mass. The modified roche-moutonees structures (Fig. 10), typical of a periglacial environment, are displayed along the northern margin of Schirmacher hills, Antractica, where one side of the hill is striated, rounded or flat with minor gradient towards the upstream direction, while the other side (lee side) has steeper gradient in the opposite direction.Glacial valleys: Glacial landscapes show ‘U’ shaped glacial valleys as against ‘V’ shaped valleys in a fluvial domain (Fig. 11). This is so because a glacier cuts through the sides of the valley with equal force as it cuts downwards while making its way down the slope. A combined or post glacial fluvial action on the valleys may exhibit downward cutting of valley base, modifying the ‘U’ shape. Patterned Ground: These micro-relief structures are found near flat or moderately sloping ground in a glacial environment and are formed due to sorting of soil material under the influence of the frost action in the upper layer

of active zone of the permafrost (Ravindra, 2001). The response of the moisture present in the soil and freezing and thawing causes heaving of the soil resulting in the sorting of debris in the forms of strips, polygons, circles etc. The sorted polygons (Fig. 12) display a core area, comprising medium to coarse sand with cobbles and pebbles, while the outer rim shows concentration of larger sized boulders.Moraines: These are depositional landforms that are seen as ridges, mounds or irregular mass of unstratified drift left behind by a retreating glacier. It comprises chiefly boulders, gravel, sand and clay material. Moraines are the most dominant landforms in a glaciated terrain that also play an important role in unearthing the movement pattern of the glaciers. Various parameters such as different levels and morphology of the moraines, degree of surface weathering, wind polishing, growth of lichens, development of cryogenic and honey comb-structures, etc., have been used to establish the chronology of moraines (Bardin, 1971).

Moraines are defined as terminal, push, medial or ablation moraines depending upon their location and mode of deposition. While the end moraine constitutes the debris dumped at the terminus of retreating glacier, lateral moraines are deposited on sides and often

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14

12

15

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11. u Shaped glacial valley in Schirmacher oasis; 12. Patterned ground, Schirmacher oasis; 13. Two levels of lateral moraines of a glacier in chandra basin; 14. medial moraine, chota Shigri glacier; 15. crevasses in the accumulation area of Sutri dhaka Glacier, chandra basin Himacha Pradesh; 16. moulin, Sutri dhaka Glacier.


occur as long, flat or low gradient high ridges of boulders of diverse size and composition, loosely held together by sand and clay (Fig. 13). Medial moraines are present on the central part of the trunk glacier especially where two tributary glaciers coalesce to enact the union of two lateral moraines (Fig. 14). Ablation moraines are mainly concentrated along the margin of the continental ice, especially at locations where the gradient of ice sheet is moderate to low. The areas southwest of the Indian Antarctic station, Maitri shows many such trails at different altitudes. There is marked parallelism between the curvature of these moraines and that of the margin of the continental ice.

Two other structures associated with glaciers are crevasses and moulins. A crevasse is a fissure or deep, wedge-shaped cleft or an opening in a moving mass of ice such as a glacier or an ice sheet (Fig. 15). Crevasses usually form in the top 50 m of a glacier, where the ice is brittle and the strain is accumulated due to differential movement. A moulin, on the other hand, is a near circular, vertical to near vertical well-like opening within a glacier or an ice sheet, into which the melt water enters from the surface and may lubricate the base of the glacier accelerating the speed of the movement of the glacier, as shown in figure 16 (NASA, 2006).

Way forwardIce plays a critical role and is an active agent in sculpting landforms such as block fields, melt water lakes, roche-moutonees, glacial valleys, patterned ground, moraines etc. With rising temperatures, many such landforms will transform again, with a greater fluvial influence.

referencesAugustine L. et al., 2004. Eight Glacial cycles from

an Antarctic Ice core, Nature, 429: 623-628, doi. 10.1038/nature02599

Bardin V.J., 1971. Moraines of Antarctica, in Adie R.J. (ed.) Antarctic Geology and Geophysics. Oslo, Universitetesforlaget, pp. 663-667.

NASA, 2006. Moulin ‘Blanc’: NASA Expedition Probes Deep Within a Greenland Glacier: NASA, Available at : https://go.nasa.gov/2HvyR3B

Ravindra R. and A. Chaturvedi, 2011. Antarctic Ice sheet, in Singh V.P., Singh P. and Haritashya U.K. (eds.) Encyclopaedia of Snow, Ice and Glaciers, Springer, pp. 44-54. Available at: https://nsidc.org/cryosphere/glaciers.

Ravindra R., 2001. Geomorphology of Schirmacher Oasis, East Antarctica. Proceedings of Symposium. Snow, Ice and Glaciers, March 1999. Geological Survey of India, Special Publication, 53: 379-390.

An erosional land surface in a glacial area in the Himalayan region.

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By Alvarinho J Luis

The author is a senior scientist at the National Centre For Polar And Ocean Research, Goa. [email protected]. The article should be cited as Luis Alvarinho J, 2019. Arctic and Antarctic from the Sky, Geography and You, 19(17): 42-47

Remote sensing is a space-based satellite technique preferred for its repetitive coverage of inaccessible and rugged terrain for surface

characterisation. This paper showcases climate change in the vulnerable polar realms by adapting different algorithms to the satellite

technology to infer surface signatures.

Polar regionsfrom the

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sea ice is frozen seawater that floats on the ocean surface.

a bird’s eye view of cold daylight of sea ice.


Remote sensing (RS) is a tool for data acquisition through two primary techniques-active and passive. Active RS is employed during consistent cloud cover and

darkness, where the sensor in orbit (eg., LIDAR and RADAR) sends its own signal and records the backscatter signal. During cloud free conditions however, the passive RS measures the radiation reflected from the surface, eliminating the need to send its own signals. Researchers working on polar areas use this data to study temporal sea ice concentration (SIC) changes, estimate glacier surface velocity, map blue ice areas, detect crevices and surface melt on the ice sheet etc.

polar sea ice variabilitySea ice is frozen seawater that floats on the ocean surface. It forms in winter and melts in summer and has a high albedo (>90 per cent) which alters the atmospheric heat budget. In the polar winter, high convective heat loss in dark conditions freezes the fresh water leaving dense brine, which sinks down to the abyssal depth. Through

thermohaline circulation this dense brine plume eventually makes its way to the global oceans, as the Antarctic bottom water. Measurements from NASA’s Scanning Multichannel Microwave Radiometer (SMMR) during 1978, and the Special Sensor Microwave/Imager (SSM/I) sensors from 1987 onwards, provide a time series of sea ice concentration spanning 38 years, which helps

Fig. 2. Trend in satellite-derived sea ice concentration

Summer Autumn

Indian Ocean

Amundsen Sea ASL

Belling-shausen

Sea

Weddell Sea

Spring

SIC trend

-0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6

Winter

Western Pacific OceanROSS Sea

Mapped over a period of 1979 to 2015 sea ice concentration shows large variations during summer (Dec-Feb), autumn (Mar-May), winter (June-Aug), and spring (Sept-Nov). Black contours envelope areas with significance p<0.05. Positive values indicate increasing trend.

Fig. 1. Interannual variability of Antarctic sea ice extent from satellite observations

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illion

sq km

)

Sea i

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illion

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Summer

1980 1986 1990 1995 2001 2005 2007 2013

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1514

Trend: 2.05 per cent per decadeTrend: 1.48 per cent per decadeTrend: 3.68 per cent per decade


Fig. 3. Geolocation of Polar Record Glacier, East Antarctic (top) and Landsat-8 imagery depicting the position and extent of the glacier (bottom)

Antarctic

72o 38'E

68o 4

4'S

68o 4

4'S

69o 4

2'S

69o 4

2'S

70o 4

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70o 4

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75o 1'E 77o 24'E

72o 38'E 75o 1'E 77o 24'E

climate scientists to monitor the interannual variations and trends.

The satellite-observed sea ice concentration data was used to derive sea ice extent by summing up only those pixels with sea ice content greater than 15 per cent. The sea ice covers an area of about 14-16 million sq km in late February/March (winter) in the Arctic and 17-20 sq km in the Southern Ocean in September (austral winter). On an average, seasonal decrease is much larger in the Southern Ocean, with only about 5-6 million sq km remaining at the end of summer. In terms of overall trend, the Antarctic sea ice extent exhibits a positive trend of about 2 per cent per decade during 1979-2015. In winter (summer) the trend is weaker at 1.48 (3.68) per cent per decade. However, some regions such as Bellingshausen-Amundsen Sea show a decrease of 3700 sq km per year which is due to high melting during December to May. Likewise, Weddell Sea shows a decrease by 1500 sq km per year from June to November. Nevertheless, the Antarctic sea ice extent exhibits

high interannual variability which is enhanced post 2000 (Fig. 1). There is also large seasonal variability in the trend depicted in Fig. 2 for all the sectors. For example, after a record-high in September (20 million sq km) during 2012 to 2014, the Antarctic sea ice has decreased by 6.82 million sq km during September to November, 2016. This amounts to 18 per cent more loss than in any previous September-November months during the satellite era (Turner et al., 2017). Though this increase is statistically not significant, what causes it is ambiguous.

This small increasing trend in Antarctic is contrary to results from coupled climate models as well. The positive sea ice trend is attributed in part to the stratospheric ozone depletion over Antarctica that promotes a dip in the mean sea level pressure in the Amundsen Sea (Amundsen Sea Low, ASL), west Antarctica (Sigmond and Fyfe, 2010). The small overall Antarctic increase in sea ice extent appears to be the residual of a coherent pattern of a much larger regional increase and decrease that almost compensates each other (Fig.1). These large local areal changes can also be viewed as changes in the length of the ice season (Stammerjohn et al., 2012).

The seasonal variability in sea ice concentration results from a combination of winds and ocean circulation. The ASL primarily controls the atmospheric conditions between the Antarctic Peninsula and the Ross Sea and promotes northward-blowing winds over the region (Fig. 2). The interannual sea ice extent variability in the Ross Sea sector is significantly correlated with the strength of these winds and the depth of ASL. Stronger cold winds facilitate coastal polynya formation along the Ross ice shelf boundary and increase the sea ice production (Holland and Kwok, 2012). Other researchers attributed the positive trend to changes in atmospheric circulation induced by Southern Annular Mode (SAM) and El Niño-Southern Oscillation (ENSO), with more La Niña events since the late 1990 (Zhang, 2007). Our understanding of the increase in sea ice extent is fragmentary, as the climate models are unable to replicate the observed scenario.

SAM, which is the index of pressure difference between subtropics and coastal Antarctic, has switched to positive since 2000. This is responsible for a shift in the strong wind region called west


facilitated by northward Ekman transport. The availability of cold water during summer preconditions the surface for formation of more sea ice in winter.

Monitoring changes in Glaciervelocity in antarcticObservations of ice motion in glaciers are critical to understand mass balance and its contribution to sea level rise, apart from predicting future changes. Most of the studies use Synthetic Aperture Radar (SAR) and optical data with the methodologies for velocity study through SAR including Interferometeric SAR (InSAR), Digital Elevation SAR (DInSAR), offset tracking, and feature tracking which have reasonable results. Feature tracking is one of the most effective ways to study glacier as it allows the estimation of displacement between two images-a reference image and a search image. Since the 1980s, image matching technique has been used by manually inspecting the images and identifying the same objects in the images from two different time periods. Scambos et al. (1992) was the first to perform image matching based on normalized cross-correlation. Image matching methods can be either area-based or feature-based. Area based methods operate directly on image quantities

Fig. 5: Resultant surface velocity field for Polar Record glacier located on the East Antarctica using optical satellite data

73o40'E 73o50'E 74o00'E 74o10'E

Flow directionHigh (9.81 M/Day)

Low (0 M/Day)

76o00'E 76o10'E 76o20'E

69o 2

0'S

70o 0

'S

69o 1

5'S

69o 5

5'S

Fig. 4. Methodology adopted for estimation of the glacier surface velocity

Correlation

SNR Result

Displacement Map

Vector Field

North-South Result

COSI-Corr

Pre-Event Image Post-Event Image

Orthorectification

East-West Result

wind drift in the Southern Ocean towards Antarctica. The surface water cools rapidly by larger net surface heat loss and through upwelling,


in particular, where basal melt is accelerated. Continuous monitoring of calving events along the coast of Antarctica is required to detect breakaway of icebergs from glaciers and ice sheets to the oceans, since they are the major contributor to current sea-level change. With a new satellite NISAR, by NASA and ISRO, geospatial applications to cryosphere will receive a fillip.

referencesCavalieri D.J. and C.L. Parkinson, 2012. Arctic sea ice

variability and trends, 1979–2010, The Cryosphere, 6: 88–889.

Holland P.R., and R. Kwok, 2012. Wind-driven trends in Antarctic sea-ice drift. Nature Geosciences, 5: 872–875, doi:10.1038/ngeo1627.

Liu T., M. Niu, Y. Yang, 2017. Ice Velocity Variations of the Polar Record Glacier (East Antarctica) Using a Rotation-Invariant Feature-Tracking Approach. Remote Sensing, 10: 42.

Scambos T.A., M.J. Dutkiewicz, J.C. Wilson and R.A. Bindschadler, 1992. Application of image cross-correlation to the measurement of glacier velocity using satellite image data, Remote Sensing Environment, 42(3): 177–186.

Sigmond M. and J.C. Fyfe, 2010. Has the ozone hole contributed to increased Antarctic sea ice extent?, Geophysical Research Letters, 37, L18502, doi:10.1029/2010GL044301.

Stammerjohn S., R. Massom, D. Rind, and D. Martinson, 2012. Regions of rapid sea ice change: An inter-hemispheric seasonal comparison, Geophysical Research Letters, 39, L06501, doi:10.1029/2012GL050874

Turner J., J.C. Comiso, G.J. Marshall, T.A. Lachlan-Cope, T. Bracegirdle, T. Maksym, M.P. Meredith, Z. Wang, and A. Orr, 2009. Non-annular atmospheric circulation change induced by stratospheric ozone depletion and its role in the recent increase of Antarctic sea ice extent, Geophysical Research Letters, 36, L08502, doi:10.1029/2009GL037524.

Turner J., T. Phillips, G.J. Marshall, J.S. Hosking, J.O. Pope, T.J. Bracegirdle, and P. Deb, 2017. Unprecedented springtime retreat of Antarctic sea ice in 2016, Geophysical Research Letters, 44: 6868–6875, doi:10.1002/2017GL073656.

Zhang J.L., 2007. Increasing Antarctic sea ice under warming atmospheric and oceanic conditions, Journal of Climate, 20(11): 2515–2529.

like brightness or phase. Feature-based methods match features that are extracted from the images in a pre-processing step. Such features can be crevasses, rocks or other differences in digital numbers. The window size to be correlated has to be large enough to ensure that texture and not noise is matched.

A study was conducted on the Polar Record Glacier, east Antarctic located on the eastern side of the Amery Ice Shelf (Fig. 3). It is the largest outlet glacier along the Ingrid Christensen Coast, bounded by Meknattane Nunataks and Dodd Island.

The study used Landsat 8 OLI images (panchromatic band) for the estimation of velocity. The study for the estimation of glacier velocity was first conducted on a single image pair using four different tools-Image GeoRectification and Feature Tracking (ImGRAFT), Normalized Cross-Correlation (CIAS), COSI-Corr and image-to-image cross-correlation (IMCORR). The statistical evaluation COSI-Corr method yielded pixel-level velocity with both magnitude and directions. The pre-event and post-event images were selected and ortho-rectified. The images were then correlated with each other with a search window size of 256 x 256 pixels (max value) to 8 x 8 pixels (min value) with the step size of 8 pixels and mask threshold of 0.9 using the frequency correlator option. The procedure is summarized in figure 4.

The velocity of the Polar Record Glacier is observed to be 1-2 m per day. The velocity and the direction presented in figure 5 agree with previous studies (Liu et al., 2017).

Way forwardFuture studies should focus on bipolar sea ice variations using a record of satellite-based sea ice concentration over 38 years. This will also help decipher teleconnections between the poles. Sea ice volume estimates are crucial for evaluating interannual changes in sea ice and the contributing factors like freshwater released from ice sheet melt etc. The changes in the ice sheet elevation due to basalt and surface melting by constructing digital elevation models using Sentenal 1 & 2, ALOS –PALSAR sensors will provide a wealth of information about the health of the glaciers and ice sheet over the west Antarctic


aeolian Geomorphology: a new introductionBy: ian livingstone and a. Warrencover: hardcover

publisher: Wiley-Blackwellpublished: 2019price: USD 73pages: 336

Geology and Geomorphology of alluvial and Fluvial FansBy: d ventra and l e clarkecover: Hardcoverpublisher:

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Fundamentals of GeomorphologyBy: richard John huggettcover: Hardcoverpublished: 2018

publisher: Taylor&FrancisisBn-10: 0815350899isBn-13: 978-0815350897price: USD 41.6pages: 578

urban Geomorphology: landforms and processes in citiesBy: Mary J Thornbush and

casey d allencover: Paperbookpublisher: Elsevierpublished: 2018price: USD 130pages: 362

Quaternary Geomorphology in india: case studies from thelower Ganga BasinBy: Balai chandra das, sandipan Ghosh & aznarul islamcover: Hardcoverpublisher: Springerpublished: 2019isBn-10: 3319904264isBn-13: 978-3319904269price: USD 149pages: 224

This book is a unique collection of field based

studies on the micro basins of river Ganga. The papers discuss the various geomorphological facets of lower Ganga basin and its subsidiary river basins. The primary focus of the book is on laterites, palaeoenvironment and palaeogeomorphology, palaeo-coastal landforms, neo-tectonism, tidal-fluvial dynamics,

extra-channel geomorphology and channel-pattern adjustment. Some of the river basins, that the book covers are westernmost fringe of lower Ganga–Brahmaputra delta, laterites in Rajmahal Basalt Traps and Rarh Bengal, Ajay-Damodar interfluve etc. Published in 2019, the book is likely to be helpful for researchers and post graduate students engaged in fluvial studies.

Website

British society of Geomorphologywww.geomorphology.org.uk/The content is unique and defines geomorphology in detail. It also provides information about the researches, grants, awards and educational resources for geologists and geographers engaged in the area of work. Various journals and publications are also available on the website. It also provides access to photos of geomorphological features submitted by its members.

national Geophysical research institutewww.ngri.org.in/The website provides information on research themes—earthquake hazard, geodynamics and natural resources. One can also find concise facts and analysis about earth process modelling, electric geophysics, electromagnetic geophysics, geochemistry, geochronology, geodesy, rock mechanics etc.

Geological survey of indiawww.gsi.gov.inThe website provides insights about geological activities carried out in India. Annual reports from various years and a gamut of publications are available on the website. Information about training institutes that are helpful for geological research is also listed.

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