A Development AnD environment fortnightly 60 ` Price ou y and ssue No. 128 17, i hy Vol. 19, P

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geomorphology SpeCIAl Landforms IN IN d I a

Coastal GeomorpholoGGyy Desert lanDforms ICe as an aGent of sCulptInG lanD fluvIal GeomorpholoGy CaChar valley PARI Strengthening Democracy NEW DELHI, LONDON, The U. K. Joint International Course (New Delhi + London) on “Public Policy Management in Parliamentary Democracy” For officers of Ministries/Departments/Autonomous Organisations/Institutions and PSUs under Government of India, State Assemblies and States Governments PARI CAlendAR 24th June - 3rd July, 2019; 15th – 24th July, 2019; 19th – 28th August, 2019; 9th – 18th September, 2019; 14th – 23rd October, 2019; 11th – 20th November, 2019; 9th – 18th December, 2019; 13th – 22nd January, 2020; 10th – 19th February, 2020; 16th – 25th March, 2020

Officers from 80 Central Ministries/Autonomous Bodies/PSUs and State Assemblies have received training so far Ministry of Tribal Affairs, Ministry of Sciences, Ministry of Electronics and Information Technology, Ministry of Development of North Eastern , Department of Space, National Aluminium Company (NALCO), National Buildings Construction Corporation (NBCC), Bharat Heavy Electricals Limited(BHEL), Hindustan Aeronautics Limited (HAL), Central Coalfields Limited (CCL), South Eastern Coalfields Limited (SECL), Central Board of Excise and Customs (CBEC), Coalfields Limited (MCL), Western Coalfields Limited (WCL), Deptt. of Scientific and Industrial Research (DSIR), Indian Bank, RITES Limited, Telecommunications Consultants India Limited (TCIL), ONGC, UM-DAE Centre for Excellence in Basic Sciences, CSIR - Central Electrochemical Research Institute , Securities and Exchange Board of India (SEBI), Integrated Coastal and Marine Area Management (ICMAM), India Meteorological Department (IMD), Indira Gandhi Centre for Atomic Research, Lokopriya Gopinath Bordoloi Regional Institute of Mental Health, Institute of Nano Science and Technology (INST), National Biodiversity Authority (Ministry of Environment, Forest and Climate Change), All India Institute of Medical Sciences, AIIMS (New Delhi), Jawaharlal Institute of Post Graduate Medical Education & Research (JIPMER), Ircon International Limited, Central Mine Planning & Design Institute Limited (CMPDI), National Highways Authority of India (NHAI), Institute for Plasma Research, Office of the Controller General of Defence Accounts, National Institute of Tuberculosis and Respiratory Diseases, National Council for Promotion of Sindhi Language (NCPSL), Ministry of Road Transport & Highways, NPC, IIFT, NSDC, IOCL, Ministry of Communication (Department of Posts), National Institute of Rural Development and Panchayati Raj, Meghalaya Legislative Assembly Secretariat, Punjab Vidhan Sabha Secretariat, Central Institute of Himalayan Culture Studies (CIHCS), Chittaranjan National Cancer Institute (CNCI), Sikkim Legislative Assembly Secretariat, Government of National Capital Territory of Delhi; National Council of Science Museums, Kolkata, West Bengal; Physical Research Laboratory, Ahmedabad, ; Central Council For Research in Unani Medicine, New Delhi, Bharat Petroleum, , ; Children’s Film Society India, Mumbai, Maharashtra; Hindustan Petroleum Corporation Limited, Mumbai, Maharashtra; National Institute for Micro, Small and Medium Enterprises (ni-msme), Hyderabad, Telangana; National Institute of Rock Mechanics, Bangalore, Karnataka; Mizoram Legislative Assembly Secretariat, Aizwal, Mizoram; Ministry of Personnel P.G. and Pensions, Department of Pension & Pensioners Welfare, New Delhi; All India Institute of Medical Sciences (AIIMS), Jodhpur, Rajasthan; Ministry of Personnel P.G. and Pensions, Department of Personnel & Training, New Delhi ; National Technical Research Organisation (NTRO), New Delhi; Ministry of Health & Family Welfare, N.D.; Ministry of Shipping, New Delhi; Ministry of Commerce & Industry, Department of Industrial Policy & Promotion, New Delhi PARLIAMENTARY & ADMINISTRATIVE RESEARCH INSTITUTE LIGHTS, Research Foundation An Educational Not-for-Profit organisation 604, Bhikaji Cama Bhawan, Bhikaji Cama Place, New Delhi -110066 Tel: +91-11-40159058, 46014233, Please contact: Amit Kumar, Mobile: 7678491255 Website: www.pariparliament.org | E-mail : [email protected], [email protected] G’nY SINCE 2001 a dEvElopmENt aNd GEoGraphYaNdYou.Com GeoGraphy and you ENvIroNmENt fortNIGhtlY Vol. 19  Issue 17 No. 128  March 1-15, 2019 Photo courtesy: amit jain the clarity of the water in river Dawki, cherrapunjee, meghalaya makes the boat look like it’s suspended in mid-air.

Landforms in india 28 Coastal Geomorphology 4 Fluvial Geomorphology: An Indian Perspective sulagna chattopadhyay Dhruv sen singh The coastal landforms are erosional or depositional There are 22 major river basins in India. Among them three main depending upon the process of their genesis. basins have their origin in Himalaya. 36 Ice as an Agent of Sculpting Land 10 Cachar Valley: A Cauldron of Adverse Natural rasik ravindra Phenomenon The major part of ice and glaciers are found as ice caps and ice sheets Kuldeep Kachroo in , Antarctic and Greenland, apart from the Himalaya, The Cachar valley has a very fragile environmental setting and . where neo-tectonic activity is still underway. arctic-antarctic 18 Narmada’s Distinctive Litho-tectonic Features 42 Polar from the Sky anulekha Prasad alvarinho j Luis The Narmada flows in a general ENE-WSW direction over a length of ice is frozen seawater that floats on the surface. 1,312 km, draining into the Gulf of in the . It increases in winter and melts away in summer.

20 Lake Lonar ratish Kumar jha The Lonar is one of the best preserved impact structures in Brief and the only one to have been formed on volcanic rocks. 1 Letters; 2 Editor’s Note; 9 The Karst Caves of India; 17 Columnar Basalt; 30 The Atolls of Lakshadweep; 22 Desert Landforms 31 Badland Topography; sudesh Kumar Wadhawan 32 Barren Island; 33 India’s Tombolo; Landforms in deserts have evolved through a long period of time 34 Hot Springs; 35 Human Induced Land Subsidence; through the interplay between fluvial and aeolian processes. 48 Books & Websites.

Expert Panel B Meenakumari Ajit Tyagi Rasik Ravindra Saraswati Raju Former Chairperson, Air Vice Marshal (Retd) Geologist and Former Professor, CSRD, National Biodiversity Former DG, IMD, Secretary General, Jawaharlal Nehru Authority, Chennai. New Delhi. 36 IGC, New Delhi. University, New Delhi.

Prithvish Nag B Sengupta Sachidanand Sinha D Mukhopadhyay Former Vice Chancellor, Former Member Secretary, Professor, CSRD, Chief Executive MG Kashi Vidyapeeth, Central Pollution Control Jawaharlal Nehru ACRA, Varanasi. Board, New Delhi. University, New Delhi. Noida, U. P. 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 GeoGraphy and you articles covering substantial perspective on coastal regulation policy and editor on access and benefit sharing—the discourses were brought out with SuLagNa CHaTTOPaDHyay nuances which many newspapers fail to publish. G’nY is a must have for Guest editor all the people who like to be well read and updated. Rasik RavindRa —PRAVEEN via Customer Feedback

senior advisors For more details log on to our website www.geographyandyou.com ajit tyagi Rasik RavindRa saRaswati Raju This journo-mag is incomparable with I discovered G’nY while I was visiting the the other popular magazines available in Delhi Book Fair, 2019. It is a gold mine leGal advisor KRISHNENDu DaTTa the market since it provides unparalleled in all sense because of the astounding content. Recently I have read the National content and its presentation provided research bY liGhts Centre for Antarctic and Ocean Research at such a nominal price. The National cover Photo special Issue, India’s Polar Endeavours, Centre for Antarctic and Ocean Research THE LITTLE RaNgEET IN SIKKIm Vol 19, Issue 16, No. 127. It has showcased special issue was phenomenal. I loved By PRaSaD India’s role in the polar regions highlighting learning about India’s research in the corresPondence/ the geopolitics and its present scenario Polar Regions and in the himalaya. Such editorial oFFice towards the resources in the Arctic. Such exquisite information are not generally 707, BHIKajI Cama BHawaN, RK PuRam, articles are very informative and represent available in the local media and I am NEw DELHI - 110066 India’s growing significance globally. thankful to G’nY for publishing it. PHONE: +91-11-46014233; +91-11-26186350 —ShIVANShu SAxENA via —PRIYAm ShANkAR via FOR NEw SuBSCRIPTIONS, customer feedback. customer feedback. RENEwaLS, ENquIRIES PLEaSE CONTaCT CIRCuLaTION maNagER The issues published in the recent months Reading G’nY has always given me an E-maIL: info@ geographyandyou.com have covered pertinent themes such as enthralling experience. Amongst my PLEaSE vISIT OuR SITE aT farming and agriculture. The content of this other favourite G’nY issues, I found www.geographyandyou.com FOR FuRTHER INFORmaTION. particular issue titled ‘On the Farm Front, myself fascinated by the Aravalli issue Vol 18, No. 123’ shared the present scenario (Vanishing Profiles, Vol 19, Issue 9, No. ©GeoGraPhY and You aLL RIgHTS RESERvED of farmer suicides and rainfed agriculture 120). This issue was quite different from THROugHOuT THE wORLD. in India and also featured the importance of the other G’nY issues. It was region REPRODuCTION IN aNy maNNER, PaRT OR wHOLE, IS an unconventional agricultural produce like specific and gave a true picture of the PROHIBITED. millets and its prospect in India amongst the ramifications that were happening in others.—GOwThAm via and around this area. The articles in this Printed, Published and oWned bY sulaGna customer feedback. issue not only highlighted the problems chattoPadhYaY. but also gave practical applicable Printed at The G’nY journo-mag has been producing solutions. I wish to read more of such INDIa gRaPHIC SySTEmS significant articles. The images and the region specific issues touching upon PvT. LTD. F-23, OKHLa INDuSTRIaL aREa, PHaSE-1, content of the articles captivate the eyes and several important dynamics.—DOllY via NEw DELHI - 110020. mind of the reader. I believe this is one of the customer feedback. Published From best magazine which attracts a large number IRIS PuBLICaTION PvT. LTD. of students who are interested in various I have been reading G’nY for a very long 111/9 KISHaNgaRH, aRuNa aSaF aLI maRg, vaSaNT exam preparation. Relevant articles reduce time and it has been producing good KuNj, NEw DELHI-70. pressure on the students and keep them well content with remarkable quality. Issue gEOgRaPHy aND yOu informed—muzAmmIl via related to timing needs to be solved. DOES NOT TaKE aNy customer feedback. — ABhIShEk via customer feedback. RESPONSIBILITy FOR RETuRNINg uNSOLICITED PuBLICaTION maTERIaL.

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2 March 1-15 2019 . GeoGraphy and you vol 19, issue 17 Guest Editor The earth is a unique planet—the only one known to sustain life. Enveloped by mighty , 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 Rasik Ravindra curiosity and encourages us to understand our surroundings. The The author is Geologist processes that play a role in formation of landforms, their evolution and and Secretary General, disappearance holds the key to sustenance of life and the preservation 36th International Geological Congress, of biodiversity. In fact, some of the processes such as the three stages New Delhi 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.

Editor’s note I 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 Sulagna Chattopadhyay texts till date. You will also read about how neo-tectonic movement Founder-Editor, can create landforms, such as the Barak River in the Cachar valley. Geography and You, The article presents an interesting insight about how a zero gradient New Delhi 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!

GeoGraphy and you . March 1-15 2019 3 Landforms in india

By Dhruv Sen Singh Fluvial GeomorpholoGy AN INdIAN PersPectIve rivers 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.

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

4 March 1-15 2019 . GeoGraphy and you vol 19, issue 17 ivers 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 forR 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 rivers The rivers of India can be classified into three groups: a. The Himalayan rivers such as the Ganga, the , 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 india As 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 basins. The Ganga and the Brahmaputra river basins have an area of 861,452 a view of Burhi Gandak, sq km and 194,413 sq km respectively (Misra, Champaran, Bihar. 2014), and drain into . The Indus on

Photo: PrasadPhoto: the other hand, drains into the Arabian Sea and is

GeoGraphy and you . March 1-15 2019 5 1 the longest river in South 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 2 100,139 sq km and 86,643 sq km of the area respectively (MoSPI, 2018). The river basins of west flowing rivers of Kutch and including the Luni basin drain 321,851 sq km area of (Jha, 2013). The basin of drains 98,796 sq km (ibid).

life cycle and fluvial features 3 The 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 4 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). 5 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 Fig. 1. ‘V’ shaped valley, Ganga river, rishikesh, erosion is a natural hazard as it eats up fertile Uttarakhand; 2. a river channel - groundwater fed with banks of a river. The banks that consist of sand, both banks visible - Chhoti Gandak river, deorea, UP; silt and clay in different proportions are prone 3. Narrow Narmada channel, cutting through rocks near Jabalpur, MP; 4. a cliff section, river, to such erosion as these are non-cohesive and Kalpi, UP; 5. Lateral erosion, Ghaghara river, unconsolidated so can undergo weathering, deoria , UP. slumping and sliding (Fig. 5).

6 March 1-15 2019 . GeoGraphy and you vol 19, issue 17 A river accumulates a good deal of sediment 6 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 T0 terraces which are older at the top and youngest at Active flood plain the level closest to the river. T1 Floods occur when the discharge exceeds the T1 T2 capacity of the channel in a way that the water level crosses the danger mark at a particular site and 7 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 8 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 Little bar (upliftment of an area or lowering of sea level), the same river renews vertical erosion and down Braided bar 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 9 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 10 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). Fig. 6. three river terraces - t0, t1 and t2 deposited During the time of floods, river water overtops by Chhoti Gandak, deoria, UP; 7. Point bar deposits, Chhoti Gandak, UP; 8. Braided bar and lateral bar its bank and enters into the flood plain and deposits deposits, Ganga, rishikesh, Uttarakhand; 9. a natural the sediments. The coarser sediments are deposited levee, Chhoti Gandak, deoria, UP; 10. Confluence of along the river bank and the finer sediments are the Ganga (shown in upper part) with Burhi Gandak, carried further onto the flood plain. Repeated Gogri-Jamalpur, Bihar.

GeoGraphy and you . March 1-15 2019 7 11 a

11 b

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.

deposition of sediments raises the river bank and shape created at the mouth of Nile where it joins results in a natural levee, which dips away from the ocean. The deltas of the river Ganga in Bengal the channel at a very low angle (Fig. 9). Several and Indus in the Arabian Sea have formed large tributaries join a major river, called the trunk river fan deposits known as the (Fig. 11a & b) to give rise to a drainage pattern. Very often, two or and the Indus fan respectively. more major rivers join together at a point termed confluence—the confluence of the Ganga and the references Yamuna at Sangam (Prayag raj). Figure 10 shows Jha A.K., 2013. Water availability, scarcity and climate the confluence of the Ganga (shown in upper part change in India: A review. Asian Journal of Water of the photograph) with the Burhi Gandak river Environment, 1(1): 50-66. at Gogri-Jamalpur in Bihar. One can note the Jain S.K., P.K. Agarwal and V.P. Singh, 2018. contrast in colour between the waters of the two Hydrology and Water Resources of India. Water rivers—Ganga carrying a larger sediment load Science and Technology Library, 57. Springer, while Burhi Gandak comparatively pristine. Dordrecht. During the last stages the river joins the sea to Ministry of Statistics and Programme Implementa- end its journey. It may form an estuary—a small tion (MosPI), 2018. EnviStats India 2018 and narrow channel or place where it meets the (Environmental Accounts) : Social Statistics Divi- ocean and a mixing of oceanic and river water sion, Government of India, New Delhi. takes place. A delta is formed at a place where Misra H.N. (ed.), 2014. Managing Natural Resources: asa flowing water body joins a stagnant water body. Focus on Land and Water. PHI Learning Pvt. Ltd. N : JPL/

The river at such stages drops its entire load and Singh D.S., (2018). Concept of Rivers: An Intro- Y

takes whatever path it finds to meet the base level. duction for Scientific and Socioeconomic rtes U The term evolved from the fourth letter of the Aspects. In The Indian Rivers, pp.1-23,

Greek alphabet—delta. The letter resembles the Springer, Singapore. Co Photo

8 March 1-15 2019 . GeoGraphy and you vol 19, issue 17 IN BrIef By Staff Reporter The Karst CaVEs OF INDIA The labyrinthian caves within the Meghalaya plateau present a fine example of a karst landform.

arst landform is produced through also the deepest direct shaft in the nation—Krem the action of water causing chemical Shrieh, 8.9 km through a maze of fossil passages. weathering of soluble carbonate Meghalaya also has the highest cave passage density rocks such as magnesium and in India with a labyrinth of paths underground, calcium carbonates. Caves, especially true of the Nongkhlieh Ridge (125 km sinkholes, underground rivers, barren and rocky of cave passages in an area of 30 sq km) (Prokop, Kground and lack of surface water bodies are results 2014). The stalagmite in the Mawmluh cave located of such chemical processes in a karst region. 2.3 km from Sohra (Cherrapunji) was recently in Stalagmite, halectite, stalactite pillars are some news as it aided the discovery of an anomaly at of the main features of karst caves. Stalagmites and the 4.2 ka interval. This marked the beginning of stalactites are formed by the deposition of calcium the Meghalayan age—also called upper Holocene rich material brought by the water percolating into (G’nY, 2018). Each of the stalagamite layers of caves or any other sheltered environment. The Mawmluh had different levels of oxygen isotopes layers represent each cycle of deposition that can which revealed 20-30 per cent decrease in monsoon be dated by isotopic methods. The cone shaped rainfall over the ages. deposit that grows from the ground upward is called a stalagmite while the deposit hanging from references the roof is known as a stalactite. GnY Staff., 2018. Meghalayan age, Geography and You, In India one can find karst regions in Andhra 18(3): 114. Pradesh (Borra cave) and extensively in Laitphlang D., 2018. Meghalaya: At over 24,000 Meghalaya. With an average annual rainfall of metres in length, world’s longest sandstone cave o) 1150 cm, Meghalaya abounds in karst features. found, Hindustan Times. Available at: https://bit. More than 1,650 caves and cave locations are ly/2Hispfa found in Meghalaya, out of which over 1,000 ProkopP.,2014. The Meghalaya Plateau: Landscapes erimentor (CC P have been explored or partially explored. About in the Abode of the Clouds’, in Kale V.S. (ed.) 491 km of karst caves have been surveyed so far Landscapes and Landforms of India,World rishi the ex h (Laitphlang, 2018). The State hosts the longest Geomorphological Landscapes, Springer, pp. 173- natural cave in India—Krem Liat Prah, 30 km, as 180, doi: 10.1007/978-94-017-8029-2_17.

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

GeoGraphy and you . March 1-15 2019 9 Landforms in india

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.

10 March 1-15 2019 . GeoGraphy and you vol 19, issue 17 By Kuldeep Kachroo CaCHar Valley A CAuldroN of AdverSe NATurAl pheNomeNoN The 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.

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

GeoGraphy and you . March 1-15 2019 11 he Cachar valley, a sub basin of morphological changes. A number of neo-tectonic the Barak river basin in Assam, activities are recorded in the area which range frequently witnesses catastrophic in age from 40,000 years to a few decades before events of floods, landslides and present (BP). subsidence due to a combination of The Barak River, which is in a deltaic state with tectonic, geomorphologic, geological and climatic a gradient ratio of 1:21,500 in the Cachar valley, conditions.T In 1781 a sudden rise of the river has neither the gradient nor the flood plain to wiped out nearly one-third of the population; accommodate the vast amount of water that a an earthquake in 1869 changed the topography number of tributaries bring to it. These tributaries creating several depressions while the 1891 drain 60 per cent of the total water from the 27,000 earthquake led to the subsidence of a number of sq km area of the Barak valley into the small tea gardens in the area. and narrow Cachar valley, resulting in frequent The Cachar valley is small and narrow, with floods. That the Barak River is controlled by a width varying from 1 to 8 km and a length of tectonic activity is evidenced by the river flowing approximately 50 km. Silchar, the main town of 12 m below mean sea level (m s l) and displaying this area is one of the biggest in the northeastern drainage reversals despite being in deltaic part of India. The valley in the north is bounded condition. by precipitous slopes of the Barail Range and is The Cachar basin, a part of the larger basin limited in the south by north-south trending of the Barak River that is the second largest low ridges with intervening valleys. The narrow river of northeastern India, is part of the Ganga Cachar valley has a very fragile environmental -Brahmaputra-Meghna drainage system. Of the setting where mountain building activity is total catchment area of 41,723 sq km of the Barak currently taking place resulting in continuous basin in India, the Cachar basin has a catchment

Fig. 1: Location of Cachar Valley, Assam Darjeeling Jorhat Tezpur Jalpaiguri Cooch Behar Nowgong Dispur Guwahati Diphu Phek Purnia Kohima Tura Jowai Karong Haflong Ukhru Balurghat Tamenglong Imphal Ingrajbazar Cachar Valley Silchar Bangladesh Churachandpur Barak River Baharampur Agartala Aizawl Siuri

Krishnanagar Barddhaman Lunglei Chunchura Saiha Area of study Howrah Alipur Kolkata

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

12 March 1-15 2019 . GeoGraphy and you vol 19, issue 17 of around 25,086 sq km. The river originates from river has to accommodate the huge water yield the hilly areas of the Myanmar-Nagaland border. in a very short distance and in a narrow valley It traverses through parts of Nagaland, Manipur, which leads to immense problems of drainage Mizoram and the hills of Assam for about 403 km (Brahmaputra Board, 1988). before entering the plains of the Cachar sub-basin The area falls along the monsoon trough and at Lakhipur (Fig. 1). also receives heavy rainfall in the pre-monsoon At Lakhipur where the river enters into the period from frequent storms rising in the Bay of plains, the catchment of Barak is 14,450 sq km Bengal followed by the monsoon which brings while the total catchment at Bhanga is 25,086 heavy rains in the catchment area, exacerbating sq km. This implies that in the short distance the problems of flooding. of about 50 km, a catchment of about 10, 636 sq km of very high rainfall area is added to the Geomorphology river. The water yield from the catchment area, The Cachar valley is juxtaposed with a after it emerges from the hills, far outstretches contrasting tectonic setting where the available the annual water yield when it leaves Bhanga. data suggests that the area is subjected to At Lakhipur the average annual yield is continuous tectonic activity. It is bounded by the 14,077 million cubic meters (M cu m) while at active Dauki fault. In fact the Haflong-Disang Badarpurghat the yield more than doubles to Cachar basin has a contrasting geomorphic an average of 29,600 M cu m. The monsoon and set up from north to south, as it lies at the non-monsoon yield at Lakhipur is 12,073 and confluence of a mature and an immature 2,004 M cu m, respectively. At Badarpurghat, the topography. The Barak River separates the yield in the two seasonal extremes is 24,368 and geomorphic setup of the north and the south. 5,232 M cu m, respectively. This means that the Major geomorphic units include coalescing

Fig. 2: Barak River morphology in different sections

a c Changes in the Barak from 1920 to 2019 Cut-off meander 1920

Badarpur Salchapara Silchar

1930

Badarpur

Salchapara Silchar

b 1977

Badarpur

Salchapara Silchar

2019

Badarpur

Silchar

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

GeoGraphy and you . March 1-15 2019 13 2d. Bils and haors (dark spots) in valley

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

ridges and valleys in the south, narrow flood channel characteristics plains of Barak with general elevation varying The Barak at Lakhipur is 150 m wide and 15 from 15 to 25 m above the m s l, which are almost m deep. It maintains a straight course up to flat except the depressions of the older channel and Narayanpur from where it starts meandering. oxbow lakes. In the north the major geomorphic The low mounds (hills) around Kashipur tea units are the terraces that occur as a tableland garden restricts the river towards the south, thus 4-5 m above the adjoining flood plains and high influencing the free meandering of the channel in structural hills which form the northern limit of its flood plain. Near Silchar the course is restricted the basin. to the north part of the flood plain under the influence of the hills in the south. Beyond Silchar, drainage the river, instead of flowing through the centre of The Barak River drains the whole of the Barak the valley, flows hugging the southern bank up to valley and is joined by four major tributaries. The Badarpur. From here up to Bhanga, the river runs rivers which join the Barak along the left bank straight and is highly entrenched (Fig. 2b). It is a (south) in the Cachar valley follow long and highly very abnormal state for a river, especially when meandering routes with lots of water bodies like it is in the deltaic state. On both sides of the river, bils and haors (Fig. 2), while those which join all along its course, there are a number of cut-off from right bank have short and a high gradient meanders some of which are of very recent path. The Barak River meanders along a highly origin (Fig. 2a). entrenched course until it reaches Bhanga where The cut-off meanders are left hanging along the river acquires a complete deltaic state with very the flood plain of the river and at places are more low bank and trough distributaries. than 8-10 m above the river level. These cut-off In the Cachar valley the river bank height varies meanders give rise to the depression—bils. between 10 and 15 m. Within the valley, between The formation of the cut-off meanders indicate Lakhipur and Bhanga, the river is traversed by two straightening of the course which is anomalous as NNE-SSW trending ridges. These ridges divide the river has a very low gradient, which is a deltaic the river in three different blocks (Kachroo state for any river. The channels at places coalesce et al., 1992). into a complex of bil and hoars (Fig. 2d).

14 March 1-15 2019 . GeoGraphy and you vol 19, issue 17 Fig. 3a: Showing Transformation Fig. 3b: Showing profile of Barak River in Cachar of Katakhal valley and the mean sea level.

Dhaleshwari

Katakhal Dhaleswari Jatinga Sonai Katakhal Madura Chiri Bhanga Badri Ghagra Barak Average water level Index 0 m s l Anticlinal axis -4.18 -4.21 -7.29 -5.23 9.60 -4.46 -10.27 Section line -6.46 -8.76 -11.41 -12.31 -12.31 Bed 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.

The tributaries of the left bank drain 33 per tectonic activity in the area: cent of the Barak valley and bring in a water yield  Presence of buried tree trunks in Chandipur of 40 per cent into the narrow valley, while the tea estate on the banks of Barak dated 1570±90 tributaries of the right bank drain 5 per cent and years (Kar, 1990). bring in a water yield of 15 per cent into the Barak  Presence of buried vertical trees along the river valley, thus loading the river with large volume of section near Ganigram. water. This unprecedented input of water creates  Presence of hanging bil (oxbow lakes and cut-off anomalies in the drainage system of the Cachar meanders) all along the flood plain of Barak valley. River. The complete transformation of an irrigation  Straightening of the Barak despite being in a canal (Kata khal) into a sinuous meandering river deltaic state. and duplication of the pattern of the parent river  Entrenched nature of the Barak River. (Dhaleshwari) in less than a century (Fig. 3a) is  Sinking of part of a tea garden in the north bank indication of the ferocity of the tectonic activity of the Barak River. of the Cachar valley. The Barak River profile is  Transformation of the Kata khal canal into a perhaps one of the clearest indications that the meandering river in just a century. mountain building activity is taking place in the  Flowing of river below m s l at different places area. There is no other explanation for the river along the synclinal axis of folds. to erode below m s l (Fig. 3b) at regular intervals particularly when the river has a very low gradient. changes induced by The flow of river below m s l only indicates that anthropogenic activity the river is flowing over a continuously sinking The Barak basin has been a scene of intense area along the synclinal axis (Fig. 3b), a sign of anthropogenic activity since the nineteenth continuous tectonic activity constantly changing century. The change in the demography of the the morphology. area and the increase in population has led to encroachment of low lying areas which earlier neo-tectonism used to serve as flood cushions. Thus the rivers There are numerous evidences of ongoing neo- were denied their flood plains thereby leading to

GeoGraphy and you . March 1-15 2019 15 IA med IkI W NS y: Commo y: TeS o Cour T ho p A view of Sadarghat bridge over the Barak river in Silchar, Assam from a Boeing 737-200 aircraft.

the problem of siltation of the river channel and subsidence taking place along synclinal axis and consequent floods. The roads and railway lines uprising along anticline axis. This is in sync with built to cater to the need of the day have cut across the young orogeny, east to west along the the drainage lines and do not leave sufficient free . way to allow uninterrupted flow of peak discharge Anthropogenic activities have further resulting in water logging. aggravated the situation. The root cause lies in Embankment (Fig. 2d) and road construction the engineering solutions that have not taken has been on going in the valley since India’s into consideration the intensity of the tectonic independence and so far embankments of more changes taking place. In order to provide a than 750 km in length have been constructed solution to the problem it is important to identify very close to the river banks resulting in greater the exact nature of activity that constantly changes duration of the back flow into the tributaries and the physiography of the area and scientifically lack of space for the surface run off to flow into quantify the changes taking place within the channels. The construction of embankment has Cachar valley. converted a part of the area into low intensity flood zone of long duration from high intensity flood references zone of short duration. Brahmaputra Board, 1988. Master Plan Barak Sub basin, 1-3: 1-26. Available at https://bit.ly/2HCwlZt Way forward Kachroo K., N. Rajendran and S.K. Kar, 1992. Clear evidences posit that the area is undergoing Geoenvironmental appraisal of Barak basin. rapid tectonic changes which are discernible. Unpublished report of Geological Survey of India. The profile of the Barak, which indicates the river Kar S.K., 1990. Report on drilling at Alipur (Silchar) flowing alternately above and below the m s l can as a part of Environmental studies of Barak valley, only be explained by constant down-warping/ Cachar district, Assam (Interim Report).

16 March 1-15 2019 . GeoGraphy and you vol 19, issue 17 In BrIef

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

exagonal Interestingly, the basalts columns found in the wall of a of basalt pristine, 16 km diameter standing tall impact crater at Marte and pillar like, Valles, Mars, as also in the look aesthetically pleasing nearby volcanic plains of Hin the natural environment. Elysium Planitia–Amazonis These structures form in Planitia and northeast basaltic rocks and consist of Hellas, have been found to columns that are separated exhibit similar columnar by vertical joints and/or jointing as observed in horizontal fractures in the terrestrial columnar basalts rocks. Such features are (Milazzo et al., 2009). extensively found in the volcanic terrain of central references parts of India especially in Degraff J.M. and A. Aydin, 1987. the Deccan traps. Formed Surface morphology of columnar during the cooling of magma, joints and its significance to these rocks are fractured into mechanics and direction of joint columnar prisms by thermal stresses. Spry (1962) growth. Geology Society Bulletin, 99 (5): recognised a ‘threefold structural division with a 605-617. Available at: https://bit.ly/2G3fjmE lower colonnade, central entablature and upper Goehring L. and S.W. Morris, 2008. Scaling of colonnade. Joints in many flows form in a definite columnar joints in basalt. Journal of Geophysical sequence with master joints first, mega-columns Research: Atmospheres, 113(B10203): 1-18, next, then normal columns and finally cross- doi:10.1029/2007JB005018 fractures’. Milazzo M.P, L.P. Keszthelyi, W.L. Jaeger, M. Rosiek, Goehring and Morris (2008) have shown S. Mattson, C. Verba, R.A. Beyer, P.E. Geissler by experimental modelling that the column and A.S. McEwen, 2009. Discovery of columnar radius and striation size are proportional to each jointing on Mars. Geology, 37 (2): 171-174. other and inversely proportional to the cooling Available at: https://bit.ly/2G4MKVX rate of the lava. Further studies by Degraff and Spry A., 1962. The origin of columnar jointing, Aydin (1987) indicate that columnar joints grow particularly in basalt flows. Journal of the incrementally from exterior to interior regions of Geological Society of Australia, 8(2): 191-216. solidifying magma bodies. Available at: https://bit.ly/2uYg2jI Pul

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

GeoGraphy and you . March 1-15 2019 17 Landforms in india

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.

18 March 1-15 2019 . GeoGraphy and you vol 19, issue 17 By Anulekha Prasad NarmaDa’s Distinctive Litho-tectonic Features Narmada offers an excellent example of geological control over river morphology where the waters follow a course of least resistance.

he role of geology, particularly of the 1 structure and tectonics as also of lithology of a region in controlling its drainage path isT 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 2 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 1. satellite view of the course of the Narmada; 2. lineament zone in the southeast (Jain et al., 1995). controlled drainage path of the river The Narmada has cut deep gorges through near Jabalpur, . It geologically a graben or a sunken block, has displays several palaeochannels near Bheraghat, been a palaeontological treasure. A number of where older channels may be seen to occur rare dinosaur fossils and fossil skull of early man towards north at a higher elevation. Because (Sonakia et al., 1985) have been discovered here. of the upliftment of the northern block due to ongoing neo-tectonic activities, the river reference channel has gradually shifted towards the south Jain S.C., K.K. Nair and D. Yedekar, 1995. Geoscientific in the Holocene/recent period. The path of the studies of the Son-Narmada-Tapti lineament zone. Narmada-Son Lineament is also referred to as a Geological Survey of India, Special Publication, 10 : 333-371.

(Bottom) rift valley. si The flow of Narmada is constricted by rocky Rajguru S.N., A. Gupta, S.N. Kale and R.K. Ganjoo, gorges, rapids and wide alluvial reaches that also 1995. Geomorphology of a selected reach of haturvedi, G c display meandering paths of the river. The study of the Narmada River, India: A study in channel K r ); its channel forms in the alluvium reach by Rajguru form and behavior. Earth Surface Processes and toP et al., (1995) has shown that channel size, shape landforms, 20: 407-421. arth ( e Sonakia, A. and K. A. Kennedy, 1985. Skull cap of an le and bed forms in the Narmada are related to very G large recent floods that have built discontinuous early man from the Narmada valley alluvium he Goo t floodplains between the cliffs, creating a channel (Pleistocene) of central India, American in channel topography. Narmada valley, Anthropologist, 87(3): 612-616.

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

GeoGraphy and you . March 1-15 2019 19 landforms In IndIa

By Ratish Kumar Jha LAKE L 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

20 MARCH 1-15 2019 . GeoGRApHy And you vol 19, issue 17 part from common geomorphic Being a deep closed inland brackish water lake, the landforms—mountain chains, Lonar supports a fascinating micro ecosystem and volcanoes, rivers etc, formed by varied biodiversity (Musaddiq et al., 2001). The water the dynamic processes of the shows high salinity and alkalinity (1460-2230mg/l) earth system, there are some rare with 11 phytoplankton species. The lake also houses features that owe their origin to extraterrestrial rare microbial, plant and wildlife. The string of old sourcesA such as meteorites. The Lonar crater temples all around the periphery of the lake, though of Maharashtra is a feature that is well known in dilapidated condition, gives an ancient look to the world over as one of the best preserved impact environment. structure and the only one to have been formed There is a small lake adjacent to Lonar—Amber on the volcanic rocks on the earth. Situated lake, which appears to have been formed by a in the Buldhana district of Maharashtra, the fragment of the same meteorite or a smaller circular crater is 1.88 sq km in diameter with meteorite, accompanying the main one. a maximum depth of 150 m. It was formed by the hyper velocity large impact of a huge References meteorite fall that pushed rocks into the earth Chakrabarti R. and A. Basu, 2006. Trace element and and consequently pushed out the host rocks to isotopic evidence for Archean basement in the Lonar form a 20 m high rim from the ground level. crater impact breccia, Deccan Volcanic Province. The crater is significant as its geological setting Earth and Planetary Science Letters, 247(3-4): is similar to craters commonly found on the 197–211, doi:10.1016/j.epsl.2006.05.003. surface of moon and other inner solar system Gupta R.D., A. Banerjee, S. Goderis, P. Claeys, F. planetary bodies. Vanhaecke and R. Chakrabarti, 2017. Evidence for The Lonar crater was formed about 570,000 a chondritic impactor, evaporation-condensation years ago in the 65 million year old basalt effects and melting of the Precambrian basement of the Deccan Traps. The evidence of lake’s beneath the ‘target’ Deccan basalts at Lonar crater, extraterrestrial origin comes from raised rim India. Geochimica et Cosmochimica Acta, 215: and the ‘ejecta blanket’—the material ejected out 51-75. during the impact and spread over a distance of Maloof A.C., S.T. Stewart, B.P. Weiss, S.A. Soule, N.L. 1 km all around the crater. The ejected material Swanson-Hysell, K.L. Louzada, I. Garrick-Bethell comprises fallen debris, shatter cones, impact and P.M. Poussart, 2010. Geology of Lonar Crater, breccia, maskelynite, and micro breccia. The India .Geological Society of America Bulletin 122(1-2): glass spherules and micro breccia are closely 109–126, doi: 10.1130/B26474.1 associated with the craters found in moon. Musaddiq M., A.K. Fokmale and R. Khan, 2001. The studies carried out by Chakrabarti and Microbial diversity and ecology of , Basu (2006) have revealed that the impact breccia Maharashtra, India. Journal Aquatic Biology, 16(2): of the crater is enriched in rubidium (Rb), barium 1-4. (Ba) and lead (Pb), and to some extent in thorium Satyanarayana S., P.R. Chaudhari and S. Dhadse, 2008. sA (Th )and uranium (U). These rocks also show Limnological study on Lonar Lake : A unique more radiogenic strontium (Sr), higher Rb/Sr brackish crater lake in India, in Sengupta M. and ratio and lower radiogenic neodymium (Nd) and Dalwani R. (eds.) Proceeding of Taal 2007. The 12th

Photo Courtesy: NA Courtesy: Photo samarium (Sm)/Nd ratios. world Lake Conference, pp. 2061-2066.

GeoGRApHy And you . MARCH 1-15 2019 21 Landforms of IndIa

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

22 March 1-15 2019 . GeoGraphy and you vol 19, issue 17 By Sudesh Kumar Wadhawan desertLANDFORMS 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.

ASAD 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 Photo: Pr Photo:

GeoGraphy and you . March 1-15 2019 23 eserts are barren, inhospitable developed in arid environments and are erosional dry lands with an abundance landforms where vegetation is sparse and overland of searing sunlight. These are seasonal water flow is effective in creation of characterised by having a mean cliffs on bare resistant rocks such as monadnocks annual precipitation of less than over granites and gneissic rocks or plateau over 250 mm to a maximum of 500 mm and very high horizontally disposed sedimentary rocks Devaporation rates. Nearly 30 per cent of the land (Fig. 1 and 2). surface in the world bears an arid and a semi-arid Retreating cliffs produce a tabletop mesa environment (Cook and Warren, 1973). The or a smaller steep-sided isolated hill called a surface water drainage is ephemeral and mostly butte. High speed winds in the deserts perform ends up in inland basins—or drains seasonally two kinds of erosional work—abrasion and into depressions, thus forming a shallow and deflation. Loose sand particles lying on the saline lake or playa. These water stressed regions ground surface may be lifted and rolled over are prone to frequent droughts and support thus carving striations and wearing out edges or xerophytic vegetation that grows deep roots to polishing thereby forming sand blasted faceted tap scarce groundwater that is generally brackish ventifacts. A similar act of abrasion against the due to impeded movement. Desert plants in many resistant granitic outcrops would create curved up instances cannot access freshwater for years, excavation pits, hollowed grooves and sculpt what prompting them to grow long roots to reach into are called as the tafonis. Cavernous weathering the deep groundwater (Dhir, 2018). that produces tafoni and alveolar relief along joints The four fundamental types of deserts are is dominantly developed in many granite residual the hot and dry (or subtropical) desert, the hills and some ferruginous sandstone hills (Fig. 3 semi-arid (or cold winter) desert, the coastal and 4). desert and the cold (or polar) desert. Polar deserts Wind transported and blowing away of sand are covered with ice that cannot be absorbed is called deflation, that can result in carving by plants. Antarctica is the world’s largest cold depressions or shallow blow-outs and blasting off desert. Mid-latitude deserts occur mostly deep of the dune sands. Desert pavements are formed inside the and lie in the topographical when winds deflate the finer sand grains and the shadow zones—Takla Makan, Gobi, Nevada residual lag deposits of coarser clastics are left and deserts on the east of Andes. behind that may range in size from pebbles to small However, the most widespread are the low boulders (Fig. 5). These gravel spreads are called latitude deserts or the subtropical deserts located reg (Arabic for stone) or serir and form a protective between 20o and 35o north and south of the armour layer of closely packed resistant clasts. equator, experiencing high pressure atmospheric circulation patterns. These include the Sahara, ephemeral river courses Arabia, Mexican Arizona, Mojave, Atacama, Owing to scanty rainfall, the deserts are generally Kalahari-Namib and the Great Australian desert devoid of any integrated surface water drainage (Kar, 2014). The of India is also one courses. However, some channels incise their among the above mentioned deserts. intermittent drainage routes particularly along Landforms in any desert have evolved through the desert margins, through the aggraded sandy a long period of interplay between fluvial and sheets that end up in inland basins (Fig. 6). Remote aeolian processes operative during wet and sensing and aerial photo-interpretation have aided dry climatic regimes, especially during the in deciphering several palaeo-channels that are Quaternary period. However, periodic tectonic indicative of dominance of past wetter climatic activities have also influenced desert landscape regimes when well defined river courses were evolution. Desert landforms have been created traversing through lowlands in the deserts. by erosional and depositional processes of the present as well as the past climatic domains lakes and playas (Wadhawan, 1996). Closed lake basins in the deserts form an important landform. Lakes and playas have rocky uplands existed in arid regions episodically throughout Sharply defined rocky uplands or residual hills are the Cenozoic. Studies of lakes have become an

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

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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 9 10 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 11 12 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.

GeoGraphy and you . March 1-15 2019 25 important tool for reconstructing palaeo-climatic Barchan dunes changes at a regional level. These saline lakes Barchans are the crescent-shaped mounds are the repositories of geological, geochemical, which are generally wider than long. The leeside bio-geochemical information of Late Quaternary slipfaces are on the concave sides of the dunes (Fig. –Holocene period. A number of inland ranns 9 and 10). These dunes form when winds blow (ephemeral playa lakes), with a flat salt-encrusted consistently from one direction (unimodal winds). surface that get inundated during the monsoon They form separate crescents when the sand are found within the desert. Study of lakes supply is comparatively small. When the sand incorporates geomorphological, geological, supply is greater, they may merge into barchanoid bio-stratigraphic and multi-proxy approaches ridges and then prograde into thick transverse to reconstruct palaeo-hydrological and palaeo- dunes. Characteristically abundant barchan dunes climatic changes in the deserts (Singhvi and Kar, may merge into barchanoid ridges, which then 2004). The Sambhar and Didwana saline lakes in grade into linear (or slightly sinuous) transverse Thar desert, India have been an important source dunes, so called because they lie transverse, or for production of common salt (Fig. 7 and 8). across, the wind direction, with the wind blowing Several playas in the deserts are also a rich source perpendicular to the ridge crest. of gypsum and calcareous mud. Longitudinal or Seif Dunes sand dunes Longitudinal or the seif dunes are linear (or Five basic dune types are recognised in the slightly sinuous) dunes with two slip faces. deserts—crescent, linear, star, dome and parabolic They are called seif dunes after the Arabic word (Wadhawan, 1996). Dune covered areas may for ‘sword’ as the two slip faces make them occur in three forms—simple (isolated dunes of sharp-crested. Longitudinal dunes are associated basic type); compound (larger dunes on which with bidirectional winds. The long axes and smaller dunes of same type form); and, complex ridges of these dunes extend along the resultant dunes (combinations of different types) (Fig. 13). direction of sand movement. Some linear dunes

Fig. 13: Diagrammatic representation of various types of dunes

Barchan dune Sleep slip face

Gentle windward slope Sleep slip face Wind direction Gentle windward slope Transverse dune

Wind direction

Longitudinal dune Equal slopes Gentle windward slope

Sleep slip face

Variable wind direction Wind direction Blowout dune

26 March 1-15 2019 . GeoGraphy and you vol 19, issue 17 merge to form Y-shaped compound dunes. The aeolian sequences and older stabilised dunes longitudinal dunes are found confined mostly to (Dhir et al., 2004). Caliche is a reddish-brown to the western and south-western parts of the Thar white layer found in many desert soils. Caliche desert where they show their grading boundaries or clayey kankar deposits commonly occur as with the parabolic dunes on the west and the large nodules or as coatings on mineral grains formed transverse dunes on the east and northwest. by the complicated interaction between water and carbon dioxide released by plant roots or by Parabolic Dunes decaying organic material. U-shaped mounds of sand with convex noses trailed by elongated arms are parabolic dunes. Way forward These dunes are formed from blowout dunes Although deserts are water scarce regions and where the erosion of vegetated sand leads to a are prone to droughts, yet they are a rich source U-shaped depression. The elongated arms are of common salt, gypsum and various other held in place by vegetation; the largest arm is minerals. The various landforms of deserts form recorded in the Thar desert to be upto 8 km. an interesting landscape that is specially sculpted These dunes occur as U-shaped, or hairpin dunes, by arid conditions. The indepth study of these and in the Thar desert they occur mostly as phenomena has allowed modern engineering compound parabolic dunes or coalesce typically to work out solutions that can help build forming clustered and rake-like parabolic dunes infrastructure and allow human habitation in that laterally share their longitudinal arms these regions. (Wadhawan, 1996; Fig. 11). Parabolic dunes occur in areas where very strong winds are mostly reference unidirectional and fairly consistent as is the case Cook R.U. and W. Andrew, 1973. Geomorphology in Deserts: with the parabolic dune fields in the central and Los Angeles, California University Press,pp. 374. south-western Thar desert. Dhir R.P., D.C. Joshi and S. Kathju, 2018. Thar Desert in Although these dunes are found in areas retrospect and prospect. Scientific Publishers. now characterised by variable wind speeds, the Dhir R.P., S.K. Tandon, B.K. Sareen, R. Ramesh, T.K.G. effective winds associated with the growth and Rao, A.J. Kailath and N. Sharma, 2004. Calcretes migration of both the parabolic and crescent in the Thar desert: genesis, chronology and dunes probably are the most consistent in wind palaeoenvironment. Journal of Earth System Science, direction. The grain size for these well-sorted, very 113(3): 473-515. fine to medium sands is about 0.06 to 0.5 mm. Hess D. and D. Tasa, 2012. Physical Geography: A Parabolic dunes have loose sand and steep slopes Landscape Appreciation. PHI Learning Pvt. Ltd. New only on their outer flanks. Presently reactivated Delhi. pp. 561. crestal parts of the older stable parabolic dunes Kar A., 2014. The Thar or the Great Indian Sand Desert, support superimposed aeolian sands in the form in Kale V.S. (ed.) Landscapes and Landforms of India, of linear dunes as obstacle extensions or climbing World Geomorphological Landscapes, Dordrecht, and falling barchans thus forming complex multi- Springer, pp. 79-90. storied aeolian deposits (Fig. 12). McKee E.D., 1979. In A study of global sand : U.S. Government Printing Office,Professional Paper, doi: soils and hard pans in deserts 10.3133/pp1052. Soils that form in arid climates are predominantly Singhvi A.K. and A. Kar, 1992. Thar Desert-In Rajasthan: mineral rich with low organic content, mostly rich Land, Man & Environment. Geological Society of in calcium carbonate. The repeated accumulation India Publications, 9(1): 191. of water and evaporation in some soils causes Singhvi A.K. and A. Kar, 2004. The Thar desert in distinct salt layers to form. Calcium carbonate Rajasthan since last interglacial-evidences from precipitated from solution may cement sand and dunes and lakes-a review. Quaternary International. gravel into hard layers called ‘calcrete’ that form 105:75-87. layers up to 50 m thick. Calcretes in deserts can Wadhawan S.K., 1996. Textural attributes of recent occur in a variety of geological and geomorphic aeolian deposits in different sub-basins of the Thar settings, including as regolith over hard bedrock, Desert, India. Journal of Arid Enviornments, 32 (1): within sheet-wash aggraded plains, colluvio- 59-74. Available at :doi:10.1006/jare.1996.0006

GeoGraphy and you . March 1-15 2019 27 Landforms in india

By Sulagna Chattopadhyay CoaStal GeomorpholoGy 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.

ndia has a coastline approximately waves along with sediment flux are responsible 7,500 km long that bounds its land from for shaping these landforms. The coastal three sides—western, southern and landforms also undergo changes due to climate eastern. A coastline may be defined as a variations (glacial/interglacial periods) that ‘coastline of emergence’ or a ‘coastline cause a rise or fall in the sea level. A coastline of submergence’ depending on whether it is may exhibit a straight or an irregular coast formedI by the upliftment of land (or by the (Fig. 1), deltaic coast (Fig. 2), mud flats (Fig. 3), lowering of the sea level) or by an opposite coastal dunes (Fig. 4), sandy beaches, tidal flats, phenomenon—subsidence or sea level rise, etc. The coastal landforms may be defined as respectively. The Tamil Nadu coast, for erosional landforms or depositional landforms example, represents a coast of emergence. The depending upon the process of their genesis. northern part of the western coast of India is Among the former are—chasms, wave-cut ‘submergent’, as a result of faulting, while the platforms, sea cliffs, sea caves, sea arches, southern part (Kerala) represents an ‘emergent’ chimney rocks etc., while the latter category of

coast (Khullar, 2018). The landforms occurring landforms comprise—beach, bar, barrier, spit, Rala

in the coastal regions are carved out by marine hook etc. Ke hin, processes as a result of the dynamic physical The erosional landforms rise due to the C processes in time and space (Pethick, 2000). dynamic processes of onshore and offshore

The common coastal geomorphic features that waves coupled with the sediment flux that are abian Sea Co at can be observed as different components of the brought in by the weathering of the coastal aR coastal oceans are straits, channels, continental rocks or the finer sediment from the offshore submarine margins and continental shelves part of the sea itself. The coastal erosion often etc., (Nag, 2010). The tidal and the coastal eats up the highland adjoining the sea, as in

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

28 March 1-15 2019 . GeoGraphy and you vol 19, issue 17 1 4

2 5

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 showing extensive mudflats; 4. Coastal dunes at Pingleshwar beach, Kutch; 5. Coastal erosion at Maravanthe beach, Karnataka.

3

Maravanthe beach in Karnataka (Fig. 5). When Coastal landforms and shorelines and the the strong sea waves strike continuously against changes imposed on them due to cyclones, a rocky coast, cliffs are formed. The energy of transgression of sea and tidal action, tsunamis etc., striking waves is increased manifold by the are best monitored by remote sensing methods accompanying fine sediments. At times the wave that repetitively use modern satellite images taken action erodes softer or more vulnerable part over different time spans (Nayak, 2017). Such of the rocks along the coast carving a cave. Sea studies have also been used to prepare coastal arches are formed when the waves cut through vulnerability maps showing likely areas that may the cliff making a hole that leaves a bridge like be inundated by waves of different magnitude. structure in the rock. Part of the bridge along with a supporting column may yield to intensive references wave action, leaving only the other column—thus Khullar D.R., 2018. India a Comprehensive Geography, giving rise to what is called a chimney rock. New Delhi, Kalyani Publishers. Marine transgression on the region adjoining Pethick J., 2000. An introduction to coastal the sea may result in a relatively plain area that is geomorphology. Oxford University Press Inc, referred to as a marine plain. pp., 260. The beach is a depositional landform, which Hegde A.V., 2010. Coastal erosion and mitigation is formed as a result of deposition of reworked methods-global state of art. Indian Journal of Geo- sediments along the coastal slopes merging with Marine Sciences, 39(4): 521-530. sea. The deposition of sand or rock debris at a Nag P., 2010. Coastal Geomorphic features around distance from the shore gives rise to sand bars. . Indian Journal of Geo-Marine These may get submerged by the tidal currents. If Sciences, 39(4): 557-561. one end of this feature is joined with the land while Nayak S., 2017. Coastal zone management in India the other half is in the sea, it is called as a spit or a -present status and future needs, Journal hook if the end towards the land is curved. Geo-spatial Information Science, 20(2):15-19.

GeoGraphy and you . March 1-15 2019 29 In BrIef

By Staff Reporter The ATolls of Lakshadweep With 36 low lying coralline islands, the Lakshadweep presents a unique landform that barely rises 2 m above the sea level.

he Lakshadweep islands are situated large territory (Hoon, 2012). on the northern part of Laccadive- Lakshadweep is the only atoll formation in Maldive-Chagos ridge, lying off India. The atolls vary in shape from circular, the west coast of India. It comprises sub circular to elliptical—some enclosed with coral atolls, reefs and submerged lagoons, while others partly inundated (Mallik, banks, which surround 36 low lying coralline 2017). The islands are flat and scarcely rise more islands.T With a population of 64,429 in 2011 than 2 m. The soils are structureless, formed (Census, 2011) and a land area of 32 sq km, the by coral detritus and as such the soil fertility island group is densely inhabited. The land area and water holding capacity are extremely poor. accounts for less than 1 per cent of the total area Apart from coconut, little else can be grown of the Union Territory of Lakshadweep. Taken here. Freshwater resources are contained in a in totality, with the lagoons and the exclusive lens shaped aquifer 1.5 m below the surface. economic zone—the coral atolls (Fig. 1) occupy a Freshwater is limited and the hydrological

Fig 1: Atoll formation system is extremely fragile—the water being periodically renewed by rainfall. Eleven out of Single sand bar island the 36 islands of Lakshadweep are inhabited— Reef Agatti, Andrott, Amini, Bangaram, Bitra, Chetlat, Kadmat, Kavaratti, Kalpeni, Kiltan and Shallow lagoon Minicoy. An old dialect of Malayalam is spoken 30 m on all the islands except Minicoy, where they Reef speak Mahl and are culturally similar to the Old Coral/ people of Maldives. Lime Stone Platform references Hoon 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 & Subsided Environmental Sciences, 2(2): 68-83, doi: volcanic island 10.15406/mojes.2017.02.00021. part of Chagos Ridge Census of India, 2011. Lakshadweep provisional population data sheet basic figures at a glance, Government of India. Available at https://bit.

Source: Hoon, 2012 ly/2WnlFrg

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

30 March 1-15 2019 . GeoGraphy and you vol 19, issue 17 In BrIef

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

avines or badland topography is network of gullies, ravines and extensive dissected developed when the horizontal or landscape (badlands) carved out in the plains of slightly tilted alluvial deposits, are Chambal, Betwa and Yamuna rivers and their acted upon by gully and/or wind tributaries in central India (Joshi, 2014). The erosion giving rise to a dissected strengthening of southwest monsoon in the terrain. The upliftment of land due to neo-tectonic Holocene is believed to be the reason for increased Ractivity results in rejuvenation of rivers. These headward erosion (Ranga et al., 2015). The present rivers or channels, equipped with the newly gained day ravines consist of steep slopes and channels energy, attempt to reach base level of erosion, thus separated by ridges, which gained notoriety as the producing a dense system of interconnected gullies refuge for ‘dacoits of Chambal’ since centuries. and ridges that constitute badlands. One of the best examples is perhaps offered by references the Indo-Gangetic plains of northern India which Joshi V. U., 2014. The Chambal Badlands, Landscapes and represent one of the most extensive deposits of Landforms of India, Dordrecht: Springer, pp.143– alluvial in the world. These alluvial sediments 149, doi:10.1007/978-94-017-8029-2_13 were deposited in the Himalayan foreland basin Ranga V., S.N. Mohapatra and P. Pani, 2015. between Siwaliks in the north and Bundelkhand- Geomorphological evolution of badlands based Vindhyan Plateau in the south. The middle on the dynamics of palaeo-channels and their alluvial Ganga plains, part of the larger Himalayan Implications. Journal of Earth System Science, 124(5): foreland basin, exhibit development of an intricate 909-920.

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

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

GeoGraphy and you . March 1-15 2019 31 In BrIef

By Rajoli Ghosh Barren Island Located in the Andaman and Nicobar, Barren island is the only active volcano in India.

f one could slice into the atmosphere the earth from that cooled the world one end to the climate for more than a other, the earth’s year. The evidences of interior would Tambora eruption are be seen to comprise an available in most of the Iouter solid crust (0-35 ice cores drilled across km), a highly viscous the world as volcanic mantle (35-2890 km), a ash. The world has liquid outer core (2890- several hundreds of active 5150 km) that is much less volcanoes where lava is viscous than the mantle, and a intermittently thrown out. solid inner core (5150-6360 km). In India, the Barren Island, The mantle has molten magma which located in the union territory finds its way through cracks or weak structural of Andaman and Nicobar is the only active openings to rise to the surface of the earth in the volcano. Some volcanic activity in the past form of hot lava, gases and/or ash in the form of has been reported from the nearby island of volcanic eruption, as the pressure inside builds Narcondum. Geologically, the site of volcano up to a critical limit. A volcanic eruption may be lies in the midst of a volcanic belt on the edge silent and compose of only gases if the magma is of the Indian and Burmese tectonic plates. The thin. On the other hand, if the magma is thick and volcano attains a height of 354 m with a 2 km sticky, the gas cannot escape, so it explodes with a wide caldera. Since 1787, when the first eruption loud thundering noise and explosion. The magma is recorded, the volcano is known to have pours out from fissures or cone like features erupted more than six times notably in 1789, flowing down the sides. 1795, 1803, 1852, 1991 (lasting 6 months),1994 Volcanic eruptions are known to have changed and 2005. The most recent eruption took place in the weather, bring devastation to the area and 2017 (Koshy, 2017). wiping out life—human, animal and plant—from the area. The Mount St Helens’ eruption in 1980 references killed thousands of animals and birds while the Koshy J., 2017. Why the Barren island volcano eruption of Tambora, Indonesia, in 1815, killed erupt again, The Hindu. Available at: https://bit. around 92,000 people and threw ash and gas ly/2M3HiJ7. sA

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

32 March 1-15 2019 . GeoGraphy and you vol 19, issue 17 In BrIef

By Staff Reporter Adam’s Bridge or the Ram Setu is an IndIa’s Tombolo interesting geological formation that holds

India mythical significance for the subcontinent.

Rameshwaram

Pemban I. Ferry Dhanushkodi Talaimannar

Adam’s bridge Sri Lanka mannar island mannar

tombolo is formed when a cuspate formed at this time. Udhayana Pillai added during foreland connects another coastline, the proceedings that the bridge belonged to the usually of an island, with a rocky Miocene era (ibid). or sandy spit (Pavlopoulos, 2009). The region is highly dynamic because of the India’s tombolo, the Adam’s Bridge- confluence of the Indian Ocean and Bay of Bengal Ram Setu, is a 30 km long chain of limestone shoals and is subject to constant modification. Changes Abetween Rameswaram and Mannar island (KVNS, in the region are evident from multi-temporal 2013). It separates the in south-west satellite imagery. Strong sea currents continually from the in north-east. reshape the coastal landforms, as do cyclones and The sub-basin of the Gulf of Mannar is associated storm surges. understood to constitute the south-eastern offshore section of the Cauvery basin, the southern references most of the mesozoic rift basins along the east KVNS R., 2013. Ram Sethu (The Adam’s Bridge) coast of India (Rao et al. 2010). The late Jurassic Figures& Facts. Jawaharlal Nehru Technological fragmentation of eastern Gondwanaland into University, Kakinada (OCTAVIA). India, Antarctica, and Australia initiated the Mitra D., 2014. Dhanushkodi-a disaster that wiped formation of mesozoic rift basins on the eastern out India’s geography, Geography and You, 14(83): continental margin of India including the 44-47. Cauvery basin. Numerous deep extensional faults PavlopoulosK., Evelpidou N., and Vassilopoulos developed in the NE-SW direction during rifting A., 2009. Mapping Geomorphological which initiated active subsidence that resulted Environments, Springer-Verlag Berlin Heidelberg, in the formation of graben and horst blocks, doi:10.1007/978-3-642-01950-0. subdividing the Cauvery basin into many sub- Rao M. V., Chidambaram L., Bharktya D., and basins including the Gulf of Mannar. Janardhanan M., 2010. Integrated Analysis of Late A group of professors from Madurai Kamaraj Albian to Middle Miocene Sediments in Gulf of University asserted in 2007 that the Adam’s Mannar Shallow Waters of the Cauvery Basin, Bridge was ‘a geological formation, which took India: A Sequence Stratigraphic Approach. In place around 17 million years ago when India and Proceedings of 8th biennial international conference SriLanka were detached in a drift’ (Mitra, 2014). It and exposition on petroleum geophysics, pp. 1-9. had been geologically proven that sand bars were Hyderabad, Springer.

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

GeoGraphy and you . March 1-15 2019 33 In BrIef By N Prasad HotSPRINGS High temperatures beneath the earth surface heat up water in aquifers which emerge as hot springs.

a view of Manikaran hot spring, himachal Pradesh

ot water springs, as the term Ganga spring Akhara Bazar, Kullu; Tattapani on implies, are the springs that the bank of river Satluj; and Manikaran Sahib- bring up heated groundwater all in Himachal Pradesh ; Reshi located on the on to the surface of the earth. As bank of river Rangeet in Sikkim; Kah-do Sang compared to cool water springs Phu and Yumthang with water temperature that abound the earth, especially hilly terrains, close to 500C (Tourism and Civil Aviation Hhot water springs are less common and emerge Department, Govt. of Sikkim, 2017) also in only at favourable geological locales. As is well Sikkim. Most of these springs are known for their known, the temperatures at the deeper levels in medicinal and therapeutic values as the water our earth are much higher due to the existence of carries many minerals dissolved in solution, molten rocks at depths. These higher temperatures especially sulphur. The sites of these springs and are transferred to the rocks in upper layers of the others such as at Badrinath, Hemkund sahib, crust, which in turn heat up the water present in Gauri Kund (on way to Kedanath shrine) and the the pore spaces of the rocks. As the water heats up one near Yamunotri temple in Uttarakhand are its density decreases, resulting in its rising towards famous pilgrimage locations. the surface and finally emerging as a geothermal Mention may also be made of hot water springs spring at sites of geological weaknesses such as of Bakreshwar in West Bengal; Taptapa and Atri cracks, faults etc. A term geyser is used for hot in Odisha; Vajreshwari, Maharashtra ; and Sohna water springs when the water intermittently in Haryana. gushes out fountain-like from the surface and is on many occasions accompanied by steam. references Though hot water springs are spread all over in Planning Commission of India , 2005. Himachal Pradesh India, some of the well known hot water springs development report. Government of India. Available are-springs of Panamik in Nubra valley, at : https://bit.ly/2HQdevk Ladakh (Jammu and Kashmir); the Vashisht Tourism and Civil Aviation Department, 2017. Hot hot springs with temperature 590C (Planning springs, Government of Sikkim. Available at : https:// Commission, 2005), located near Manali; Kheer bit.ly/2M8rZil. Accessed on: May 24, 2019.

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

34 March 1-15 2019 . GeoGraphy and you vol 19, issue 17 In BrIef By Staff Reporter Human induced LANDSubSidence Excessive withdrawal of groundwater leads to reduced water pressure in aquifers resulting in reduced support of the overlying unconsolidated clay or silt.

owering of the land surface can Water table occur due to natural causes such Well as earthquake, faulting, landslide, creep etc. However, humans can also cause land to subside due to excessive pumping of groundwater, extraction of oil and Sand and gravel gasL from underground reservoirs, subsurface mining etc. These anthropogenic causes resulting Artesian squire in inland subsidence holds serious repercussions, Clayey silt especially for urban areas. There are several such Artesian squire examples from south Before extensive pumping of well (Leake, 2016), Jakarta (Abidin et al., 2011) and West Bengal (Ganguly, 2011). The groundwater that is trapped in the pore Lowered land surface spaces of sediments such as sand or gravel present Water table 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 Artesian squire unconsolidated clay and silt layers, resulting in Confining bed compaction of sediments which leads to visible Artesian squire reduction in the elevation of the land surface. After pumping 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 with urban development. Natural Hazards, 59(3): characteristics of the aquifer control the rate of 1753–1771. Available at: https://doi.org/10.1007/ subsidence in an area. While the average rate of s11069-011-9866-9 subsidence was 0.92 mm/year during 1998-2002, it Ganguly M., 2011. Groundwater withdrawal and increased to 8.7 mm/year during 2002-2006. The land subsidence: A study of Singur Block, West estimated average rate of land subsidence was 6.13 Bengal, India. International Journal of Geomatics mm/year for 1 m drop of static water table. and Geosciences 2(2): 465. Leake S.A., 2016. Land subsidence from ground- references water pumping. U.S. Geological Survey. Available Abidin H.Z., H. Andreas, I. Gumilar et al., 2011. Land at: https://geochange.er.usgs.gov/sw/changes/ subsidence of Jakarta (Indonesia) and its relation anthropogenic/subside/

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

GeoGraphy and you . March 1-15 2019 35 Landforms In IndIa

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.

36 March 1-15 2019 . GeoGraphy and you vol 19, issue 17 By Rasik Ravindra Ice as an agent of sculptIng land 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. d

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

GeoGraphy and you . March 1-15 2019 37 laciers are formed when snow, before present), the glaciers covered 32 per cent of compressed into large thickness the land surface and sculpted various landforms of crystalline ice mass, develops transforming the geomorphology of earth into a an ability to move due to sheer shape that we see today. Not far back, between 17th mass. These glaciers together and late 19th century—during the period called with snow and ice constitute the cryosphere ‘Little Ice Age’—the world saw consistently cooler whichG covers nearly 10 per cent of the surface temperatures that helped the glaciers advance. The of the earth (NSIDC, undated). The major advance or retreat of a glacier is seen at its snout, part of ice and glaciers is found as ice caps and which may be defined as the terminus, toe, or the ice sheets in Arctic, Antarctic and Greenland, end of a glacier at any given point in time apart from the Himalaya, Andes and Europe. (Figs. 1 and 2). The glacierised area of the earth is spread over There are several types of glaciers, such as nearly 15 million sq km of the land surface and mountain or valley glaciers which originate in account for approximately 75 per cent of the higher altitudes of mountains and slide down the freshwater resources of the world (ibid). During slopes occupying valleys over large distances for the Quaternary period that lasted for 2.6 million example the Himalayan or Alpine glaciers (Fig. years, the earth saw many changes in its climate, 3). A tributary glacier may look like a hanging forcing repeated glacial and interglacial cycles, glacier if its link with the main trunk glacier is caused by the earth’s orbital changes including the broken and it is left alone at the higher reaches of tilt of its axis (Milankovitch cycles). As evidenced the mountains. Tide water glacier (Fig. 4) on the by the ice cores drilled from various locations other hand extends up to sea and may give rise to of Antarctica, such as Vostok and Dome C, the icebergs as its tongues calve into the ocean. Large earth witnessed eight cycles of ice ages each concentration of continental masses of glacial separated by an interglacial period in its history ice spread over land in the form of ice sheets are of past 750,000 years (EPICA, 2004). During the found in Antarctica (Ravindra and Chaturvedi, immediate past ice maxima period (~20,000 years 2011) and Greenland, the former being the largest

1 2 3 eL AT P SH ku v A n, L

4 5 6 a ATHA mAn rA , A L A vindr rA ik rAS , A rm HA nd S AnA rm

1. Snout of dakshin Gangotri glacier, Schirmacher oasis, east Antarctic; 2. Snout of Bara Shigri glacier, chandra basin, Himachal A

Pradesh; 3. Aerial view of mountain / valley glacier / cirque glacier of higher Himalaya, Himachal Pradesh; 4. Tidal glacier, ny Alesund, y: P Svalbard, Arctic; 5. continental ice sheet, east Antarctic. Schirmacher oasis in the forefront and Wohlthat mountains in the far north. TeS

The distance between the two is nearly 100 km; 6a. Jagged hills of discontinuous disposition in the Wohlthat mountains, central o cour

dronning maud Land, east Antarctic. PHoT

38 March 1-15 2019 . GeoGraphy and you vol 19, issue 17 accumulation of ice on this planet (Fig. 5). The advancing and retreating glaciers are powerful agents of erosion and deposition. The Landform development more prominent landforms under the influence The landscape in glacial and periglacial of these factors are described below: environments is sculpted by the processes of Glacial Striation and Polishing: As the glaciers weathering, erosion and deposition under move over the hard rocks, they carve out groves harsh climatic regimes—caused by the agents of and striations on the rocks below caused by the weathering and deposition such as strong winds, boulders or fragments of the rocks carried by it intense solar radiation, extreme cold surface on the under side. The accompanying polishing temperatures and the movement of glaciers. The gives a look of varnishing to the rocks that can be diurnal variation causes freezing and thawing in seen when the glaciers retreat and rocks become the rocks, resulting in their shattering, producing exposed (Fig. 8 a and b). The presence of coarse fields of broken rocks strewn in the form of block sand and pebbles on the top surfaces of the fields. On the higher reaches of the mountain, outcrops as well as the spread of boulders on the the glacial regime exhibit alpine topography that hill tops speak of an extensive coverage of glaciers comprise serrated ridge tops, jagged peaks, arêtes, over a terrain. The boulders, up to 2 m×1.5 m tors and/or horns (Fig. 6 a and b). The chemical size, of completely different composition than the leaching due to capillary action and salt formation rocks of the hills on which they are found, occur imprint their marks on the landscape. The glacial as glacial erratic or perched boulders on the hill and fluvio-glacial action of the ice (with melt tops vacated by glacier in Schirmacher hills of water) together with the scouring action of the ice east Antarctica (Fig. 9) indicating long distance act upon comparatively weaker lithology to give transportation. rise to a number of depressions that gradually become the loci of accumulation of melt water, Roche-Moutonees: These are glaciated bedrock giving rise to melt water lakes (Fig. 7). surfaces, usually in the form of rounded knobs,

6 b 7 8 a

8 b 9 10

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.

GeoGraphy and you . March 1-15 2019 39 11 12 13

14 15 16

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. the upstream side of which has been subjected of active zone of the permafrost (Ravindra, to glacial scouring that has produced a gentle, 2001). The response of the moisture present polished and striated slope. The downstream side in the soil and freezing and thawing causes is subjected to glacial plucking that result in a heaving of the soil resulting in the sorting of steep and irregular slope. The ridges dividing the debris in the forms of strips, polygons, circles upstream and downstream slopes are therefore etc. The sorted polygons (Fig. 12) display a core perpendicular to the general flow direction of the area, comprising medium to coarse sand with former ice mass. The modified roche-moutonees cobbles and pebbles, while the outer rim shows structures (Fig. 10), typical of a periglacial concentration of larger sized boulders. environment, are displayed along the northern Moraines: These are depositional landforms that margin of Schirmacher hills, Antractica, where are seen as ridges, mounds or irregular mass of one side of the hill is striated, rounded or flat with unstratified drift left behind by a retreating glacier. minor gradient towards the upstream direction, It comprises chiefly boulders, gravel, sand and while the other side (lee side) has steeper gradient clay material. Moraines are the most dominant in the opposite direction. landforms in a glaciated terrain that also play an Glacial valleys: Glacial landscapes show ‘U’ shaped important role in unearthing the movement pattern glacial valleys as against ‘V’ shaped valleys in a of the glaciers. Various parameters such as different fluvial domain (Fig. 11). This is so because a glacier levels and morphology of the moraines, degree cuts through the sides of the valley with equal of surface weathering, wind polishing, growth force as it cuts downwards while making its way of lichens, development of cryogenic and honey down the slope. A combined or post glacial fluvial comb-structures, etc., have been used to establish action on the valleys may exhibit downward the chronology of moraines (Bardin, 1971). cutting of valley base, modifying the ‘U’ shape. Moraines are defined as terminal, push, Patterned Ground: These micro-relief structures medial or ablation moraines depending upon are found near flat or moderately sloping their location and mode of deposition. While ground in a glacial environment and are the end moraine constitutes the debris dumped formed due to sorting of soil material under the at the terminus of retreating glacier, lateral influence of the frost action in the upper layer moraines are deposited on sides and often

40 March 1-15 2019 . GeoGraphy and you vol 19, issue 17 S evenir de d y: TeS o cour PHoT An erosional land surface in a glacial area in the Himalayan region.

occur as long, flat or low gradient high ridges of Way forward boulders of diverse size and composition, loosely Ice plays a critical role and is an active agent in held together by sand and clay (Fig. 13). Medial sculpting landforms such as block fields, melt water moraines are present on the central part of the lakes, roche-moutonees, glacial valleys, patterned trunk glacier especially where two tributary ground, moraines etc. With rising temperatures, glaciers coalesce to enact the union of two many such landforms will transform again, with a lateral moraines (Fig. 14). Ablation moraines greater fluvial influence. are mainly concentrated along the margin of the continental ice, especially at locations where references the gradient of ice sheet is moderate to low. The Augustine L. et al., 2004. Eight Glacial cycles from areas southwest of the Indian Antarctic station, an Antarctic Ice core, Nature, 429: 623-628, doi. Maitri shows many such trails at different 10.1038/nature02599 altitudes. There is marked parallelism between Bardin V.J., 1971. Moraines of Antarctica, in Adie the curvature of these moraines and that of the R.J. (ed.) Antarctic Geology and Geophysics. Oslo, margin of the continental ice. Universitetesforlaget, pp. 663-667. Two other structures associated with glaciers are NASA, 2006. Moulin ‘Blanc’: NASA Expedition crevasses and moulins. A crevasse is a fissure or Probes Deep Within a Greenland Glacier: NASA, deep, wedge-shaped cleft or an opening in a moving Available at : https://go.nasa.gov/2HvyR3B mass of ice such as a glacier or an ice sheet (Fig. 15). Ravindra R. and A. Chaturvedi, 2011. Antarctic Ice Crevasses usually form in the top 50 m of a glacier, sheet, in Singh V.P., Singh P. and Haritashya where the ice is brittle and the strain is accumulated U.K. (eds.) Encyclopaedia of Snow, Ice and Glaciers, due to differential movement. A moulin, on the Springer, pp. 44-54. Available at: https://nsidc. other hand, is a near circular, vertical to near vertical org/cryosphere/glaciers. well-like opening within a glacier or an ice sheet, Ravindra R., 2001. Geomorphology of Schirmacher into which the melt water enters from the surface Oasis, East Antarctica. Proceedings of and may lubricate the base of the glacier accelerating Symposium. Snow, Ice and Glaciers, March the speed of the movement of the glacier, as shown in 1999. Geological Survey of India, Special figure 16 (NASA, 2006). Publication, 53: 379-390.

GeoGraphy and you . March 1-15 2019 41 Arctic-AntArctic

By Alvarinho J Luis Polar regions from the

RemoteSky 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.

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

42 March 1-15 2019 . GeoGraphy and you vol 19, issue 17 sea ice is frozen seawater that floats on the ocean surface. a bird’s eye view of cold daylight of sea ice. Photo Courtesy: Johannes Courtesy: Plenio Photo

GeoGraphy and you . March 1-15 2019 43 emote sensing (RS) is a tool for thermohaline circulation this dense brine plume data acquisition through two eventually makes its way to the global oceans, primary techniques-active and as the Antarctic bottom water. Measurements passive. Active RS is employed from NASA’s Scanning Multichannel Microwave during consistent cloud cover and Radiometer (SMMR) during 1978, and the Special darkness, where the sensor in orbit (eg., LIDAR Sensor Microwave/Imager (SSM/I) sensors from andR RADAR) sends its own signal and records the 1987 onwards, provide a time series of sea ice backscatter signal. During cloud free conditions concentration spanning 38 years, which helps 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 Fig. 1. Interannual variability of Antarctic sea ice extent from satellite observations ice concentration (SIC) changes, estimate glacier Annual mean surface velocity, map blue ice areas, detect crevices 12 and surface melt on the ice sheet etc. Winter 17 10 16 15 polar sea ice variability 8 Sea ice is frozen seawater that floats on the ocean 14 Summer surface. It forms in winter and melts in summer 6 and has a high albedo (>90 per cent) which alters Sea ice extent (million sq km) the atmospheric heat budget. In the polar winter, 1980 1986 1990 1995 2001 2005 2007 2013 Sea ice extent (million sq km) high convective heat loss in dark conditions Trend: 2.05 per cent per decade freezes the fresh water leaving dense brine, Trend: 1.48 per cent per decade which sinks down to the abyssal depth. Through Trend: 3.68 per cent per decade

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

Summer Autumn

Weddell Sea Indian Ocean

Belling-shausen Sea

ASL Mapped over a period Western of 1979 to 2015 sea ice concentration shows large Winter Spring 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.

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

44 March 1-15 2019 . GeoGraphy and you vol 19, issue 17 climate scientists to monitor the interannual high interannual variability which is enhanced variations and trends. post 2000 (Fig. 1). There is also large seasonal The satellite-observed sea ice concentration variability in the trend depicted in Fig. 2 for all data was used to derive sea ice extent by summing the sectors. For example, after a record-high in up only those pixels with sea ice content greater September (20 million sq km) during 2012 to 2014, than 15 per cent. The sea ice covers an area of the Antarctic sea ice has decreased by 6.82 million about 14-16 million sq km in late February/March sq km during September to November, 2016. (winter) in the Arctic and 17-20 sq km in the This amounts to 18 per cent more loss than in any in September (austral winter). On previous September-November months during an average, seasonal decrease is much larger in the the satellite era (Turner et al., 2017). Though this Southern Ocean, with only about 5-6 million sq increase is statistically not significant, what causes km remaining at the end of summer. In terms of it is ambiguous. overall trend, the Antarctic sea ice extent exhibits This small increasing trend in Antarctic is a positive trend of about 2 per cent per decade contrary to results from coupled climate models during 1979-2015. In winter (summer) the trend is as well. The positive sea ice trend is attributed in weaker at 1.48 (3.68) per cent per decade. However, part to the stratospheric ozone depletion over some regions such as Bellingshausen-Amundsen Antarctica that promotes a dip in the mean sea Sea show a decrease of 3700 sq km per year level pressure in the Amundsen Sea (Amundsen which is due to high melting during December Sea Low, ASL), west Antarctica (Sigmond and to May. Likewise, shows a decrease Fyfe, 2010). The small overall Antarctic increase by 1500 sq km per year from June to November. in sea ice extent appears to be the residual of a Nevertheless, the Antarctic sea ice extent exhibits 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 Fig. 3. Geolocation of Polar Record Glacier, East (Stammerjohn et al., 2012). Antarctic (top) and Landsat-8 imagery depicting the position and extent of the glacier (bottom) 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 Antarctic 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 72o 38'E 75o 1'E 77o 24'E production (Holland and Kwok, 2012). Other researchers attributed the positive trend to changes in atmospheric circulation induced by 44'S 44'S o o Southern Annular Mode (SAM) and El Niño- 68 68 Southern Oscillation (ENSO), with more La Niña events since the late 1990 (Zhang, 2007). Our understanding of the increase in sea ice extent is 42'S 42'S o o 69

69 fragmentary, as the climate models are unable to replicate the observed scenario. SAM, which is the index of pressure difference 40'S 40'S o

o between subtropics and coastal Antarctic, has 70 70 switched to positive since 2000. This is responsible o o 77o 24'E 72 38'E 75 1'E for a shift in the strong wind region called west

GeoGraphy and you . March 1-15 2019 45 Fig. 4. Methodology adopted for estimation of the glacier surface velocity

COSI-Corr

Pre-Event Image Post-Event Image

Orthorectification

Correlation

North-South Result East-West Result SNR Result

Displacement Map

Vector Field

Fig. 5: Resultant surface velocity field for Polar facilitated by northward Ekman transport. Record glacier located on the East Antarctica using The availability of cold water during summer optical satellite data preconditions the surface for formation of more 73o40'E 73o50'E 74o00'E 74o10'E sea ice in winter. Monitoring changes in Glacier velocity in antarctic 55'S

o Observations of ice motion in glaciers are critical 15'S o 69 to understand mass balance and its contribution 69 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 0'S o including Interferometeric SAR (InSAR), Digital 70 20'S o Elevation SAR (DInSAR), offset tracking, and 69 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 76o00'E 76o10'E 76o20'E matching technique has been used by manually High (9.81 M/Day) inspecting the images and identifying the same Flow direction Low (0 M/Day) objects in the images from two different time periods. Scambos et al. (1992) was the first to perform image matching based on normalized wind drift in the Southern Ocean towards cross-correlation. Image matching methods can Antarctica. The surface water cools rapidly by be either area-based or feature-based. Area based larger net surface heat loss and through upwelling, methods operate directly on image quantities

46 March 1-15 2019 . GeoGraphy and you vol 19, issue 17 like brightness or phase. Feature-based methods in particular, where basal melt is accelerated. match features that are extracted from the images Continuous monitoring of calving events along in a pre-processing step. Such features can be the coast of Antarctica is required to detect crevasses, rocks or other differences in digital breakaway of icebergs from glaciers and ice sheets numbers. The window size to be correlated has to the oceans, since they are the major contributor to be large enough to ensure that texture and not to current sea-level change. With a new satellite noise is matched. NISAR, by NASA and ISRO, geospatial A study was conducted on the Polar Record applications to cryosphere will receive a fillip. Glacier, east Antarctic located on the eastern side of the Amery Ice Shelf (Fig. 3). It is the largest references outlet glacier along the Ingrid Christensen Coast, Cavalieri D.J. and C.L. Parkinson, 2012. Arctic sea ice bounded by Meknattane Nunataks and variability and trends, 1979–2010, The Cryosphere, Dodd Island. 6: 88–889. The study used Landsat 8 OLI images Holland P.R., and R. Kwok, 2012. Wind-driven trends (panchromatic band) for the estimation of in Antarctic sea-ice drift. Nature Geosciences, 5: velocity. The study for the estimation of glacier 872–875, doi:10.1038/ngeo1627. velocity was first conducted on a single image pair Liu T., M. Niu, Y. Yang, 2017. Ice Velocity Variations of using four different tools-Image GeoRectification the Polar Record Glacier (East Antarctica) Using and Feature Tracking (ImGRAFT), Normalized a Rotation-Invariant Feature-Tracking Approach. Cross-Correlation (CIAS), COSI-Corr and image- Remote Sensing, 10: 42. to-image cross-correlation (IMCORR). The Scambos T.A., M.J. Dutkiewicz, J.C. Wilson and statistical evaluation COSI-Corr method yielded R.A. Bindschadler, 1992. Application of image pixel-level velocity with both magnitude and cross-correlation to the measurement of glacier directions. The pre-event and post-event images velocity using satellite image data, Remote Sensing were selected and ortho-rectified. The images Environment, 42(3): 177–186. were then correlated with each other with a search Sigmond M. and J.C. Fyfe, 2010. Has the ozone window size of 256 x 256 pixels (max value) to 8 hole contributed to increased Antarctic sea ice x 8 pixels (min value) with the step size of 8 pixels extent?, Geophysical Research Letters, 37, L18502, and mask threshold of 0.9 using the frequency doi:10.1029/2010GL044301. correlator option. The procedure is summarized Stammerjohn S., R. Massom, D. Rind, and D. in figure 4. Martinson, 2012. Regions of rapid sea ice change: The velocity of the Polar Record Glacier is An inter-hemispheric seasonal comparison, observed to be 1-2 m per day. The velocity and the Geophysical Research Letters, 39, L06501, direction presented in figure 5 agree with previous doi:10.1029/2012GL050874 studies (Liu et al., 2017). Turner J., J.C. Comiso, G.J. Marshall, T.A. Lachlan- Cope, T. Bracegirdle, T. Maksym, M.P. Meredith, Way forward Z. Wang, and A. Orr, 2009. Non-annular Future studies should focus on bipolar sea ice atmospheric circulation change induced by variations using a record of satellite-based sea stratospheric ozone depletion and its role in ice concentration over 38 years. This will also the recent increase of Antarctic sea ice extent, help decipher teleconnections between the Geophysical Research Letters, 36, L08502, poles. Sea ice volume estimates are crucial for doi:10.1029/2009GL037524. evaluating interannual changes in sea ice and Turner J., T. Phillips, G.J. Marshall, J.S. Hosking, the contributing factors like freshwater released J.O. Pope, T.J. Bracegirdle, and P. Deb, 2017. from ice sheet melt etc. The changes in the ice Unprecedented springtime retreat of Antarctic sheet elevation due to basalt and surface melting sea ice in 2016, Geophysical Research Letters, 44: by constructing digital elevation models using 6868–6875, doi:10.1002/2017GL073656. Sentenal 1 & 2, ALOS –PALSAR sensors will Zhang J.L., 2007. Increasing Antarctic sea ice under provide a wealth of information about the health warming atmospheric and oceanic conditions, of the glaciers and ice sheet over the west Antarctic Journal of Climate, 20(11): 2515–2529.

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