Relative Dating of Moraines by Lichenometric and Schmidt Hammer Techniques in the Gangotri Glacier Valley, Uttarkashi District, Uttaranchal

8/12/2019 Relative Dating of Moraines by Lichenometric and Schmidt Hammer Techniques in the Gangotri Glacier Valley, Utt

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Special Publication of the Palaeontological Society of India, No.2, 2005, pp. 201-206

RELATIVE DATING OF MORAINES BY LICHENOMETRIC AND SCHMIDT HAMMER TECHNIQUES INTHE GANGOTRI GLACIER VALLEY, UTTARKASHIDISTRICT, UTTARANCHAL

DIVYA DARSHAN A WASTHI, RAMESHWAR BALI and N. K. TEWARIDEPARTMENT OF GEOLOGY, UNlVERSITY OF LUCKNOW, LUCKNOW-226007

ABSTRACTLichenometric and Schmidt Hammer techniques have been used for relative dating of moraines in theGangotri Glacier Valley Uttaranchal. Five ground/recessional moraines have been studied in the area between

Gaumukh and Bhojbas. Based on the known ages of two moraines 1935 AD and 1900 AD), the relative agesof two moraines on the downstream side have been computed as 1897 AD and 1881 AD by lichenometrictechnique on the basis of the growth rate of lichen Dimelaena oreina. The re lative age of another moraine onthe upstream side devoid of the lichen D oreina has been established as 1970 AD by the Schmidt Hammertechnique.Key words: Gangotri Glacier, Moraine, Lichenometry, Schmidt Hammer, Dating techniques.

INTRODUCTIONThe Gangotri glacier in the Uttarkashidistrict, Uttaranchal, is one of the largest valley

glaciers in India and exhibits several geomorphicfeatures, viz. lateral, terminal, recessionalmoraines, fluvio-glacial terraces, debris cones,etc. Auden, 1935; Bali etat., 2 03). The morainicmaterial, on which l ichens generally grow, canbe dated using lichenometric techniques.Lichenometric techniques, initiated by Beschel1950), were further refined and applied by many

workers for dating rock surfaces in several partsof the world Beschel, 1961; Porter, 1981; Gordonand Sharp, 1983; Innes, 1986). In the glaciatedregions, the technique is based on theassumption that the morainic material is devoidof lichens at the time of deglaciation, and onlyafter a certain period of time the lichens beginto grow on the surfaces. The diameter of thethallus of the individual specimen increasesprogressively with the passage of time. Thus,the size of the thallus is proportional to theperiod of its growth.

Species having a nearly circular outlineare preferred, as the technique involvesmeasurement of the diameter of the thallus. Fora particular species, the maximum sizes of thethalli on different surfaces of known ages areused to obtain a growth rate . The age of anundated surface can be found by measuringthe diameter of the largest thallus of the samespecies on that surface, and correlating it withthe growth rate obtained earlier.

Since each li chen species has a time lagbefore it colonises the rocks, Lichenometry isinapplicable for the dating of young moraineson which the lichens have not appeared as yet.In these cases, the Schmidt Hammer techniquesmay be used Matthews and Shakesby, 1984;Evans et aI., 1999 .

Based on the assumption that the bouldersurfaces progressively weather with time, theSchmidt Hammer has been used by manyworkers to determ ine the age of the glacialdeposits. The Schmidt hammer, initially


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202 D. D AWASTHI, R BALI AND N K TEWARIdesigned for ll situ testing of surface hardnessof concrete and later adopted for determiningthe hardness/ strength of rocks in the field,measures the rebound distance for a controlledimpact on a rock surface. The rebound valueR) reflects the surface hardness/ strength of

the rock and is indicative of the relativeweathering of the rock material with time.

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PRESENT STU YIn India, Iichenometric studies were first

undertaken in the Gangotri area in 1976 seeSrivastava et ai. 2001). In the present study,investigations have been carried out in theGaumukh - Gangotri area fig. 1), andLichenometric / Sc hmidt Hammer datingtechniques have been atlempted on five of the

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Fig. 1 a Location of Gangotri glacier in India; b: Geomorphological map of the area between Gaumukh andGangotri; c: Location of the moraines A, B, C, D, and E in the study area .


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204 D. D. A WASTHI, R. BALI AND N K. TEWARIhave been found suitable for lichenometricstudies. In the present work, the lichenometricstudies are based on the growth rate of thelichen Dimelaena ore na.

The lichen imelaena ore ina has acrustose-effigurate thallus i.e. centrallycrustose and marginally lobate), pale greenishyellow, orbicular in outline, with radiatinglobules and black apothecia fig . 3) . Thediameters of the largest thalli of the lichenDimelaena oreina growing on the boulders inthe moraines A, B, C, D and E have beenmeasured and the maximum diameter of thethallus for each moraine is gi ven in Table - 1The moraine A is devoid of the speciesimelaena ore ina as the lichen has not

colonized these rocks as yet. The largestdiameters of the thalli of Dimelaena ore ina formoraines Band C are plotted against the knownages of the moraines, i.e. 1935 AD and 1900 ADrespectively fig. 4). On extrapolation of thegraph, the ages of moraines D and E, which aredownstream of the moraines Band C, arecalculated as 1897 AD and 1881 AD respectivelyon the basis of lichenometry.

A Schmidt Hammer Type -L) has been used to determine therebound or R-values for relativestrength of the rock materialconstituting the boulders in thedifferent moraines of the area.Precautions were taken tominimise the sources of errorwhile operating the instrument.Since measurements withdifferent instruments may vary,only one instrument was usedthroughout the study, and thedata has always been generatedwith the instrument being heldperpendicular to the rock surface.Since lithology has an important

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RELATIVE DATING OF MORAINES IN THE GANGOTRI GLACIER VALLEY 205moraines A, B, C, D, and E),with five blows per boulder,and the mean of these fiveblows is presented for the tenboulders of each moraine inTable - 2 The mean R- valuesso obtained for each moraineare plotted against theknown ages of the morainesa n d C and the

lichenometric dates formoraines D and E fig. 5). Thedate for the moraine A which

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206 D D A WASTHI, R BALI AND N K TEWARIHowever, since the growth rates of lichens, aswell as the degree of weathering of rocks areboth affected by climatic and other factors, thecorrelation data must be generated for eachlocality to match the studies.ACKNOWLEDGEMENTS

The authors are thankful to Prof. M. PSingh, Head, Department of Geology ,University of Luck now for providing laboratoryfacilities and to Prof. I B. Singh for his constantencouragement. Fieldwork for the present studywas carried out as part of a project funded bythe Department of Science and TechnologyNew Delhi (Project No. ESI91/021/97 . Thefinancial assistance received is thankfullyacknowledged.REFERENCESAuden, J.B. 1937; The Snout of Gangotri glacier,Tehri Garhwal. Rec. Geol. Surv.lndia 72: 135-140.Bali, R., Awasthi, D.D. and Tewari, N. K. 2003.Neotectonic Control on the Geomorphic Evolutionof the Gangotri Glacier Valley, Garhwal Himalaya.Gondwana Research 6 : 829-838.Beschel, R. E. 1961 . Dating rock surfaces by lichengrowth and its application to Glaciology andPhysiography (Lichenometry). In: Raasch, G.O.

(Ed.), Geology o he Arctic. 2 : 1044-62. Universityof Toronto press, Toronto.Evans, D J. A., Archer, S. and Wilson, D J. H1999. A comparison of the Iichenometric andSchmidt hammer dating techniques based on datafrom the proglacial areas of some Icelandic glaciers.Quaternary Science Reviews 18 : 13-41.Gordon, J. E and Sharp, M. 1983. Lichenometryin dating recent glacial landforms and deposits,southeast Iceland. Boreas 12 : p 191-200.Innes, John L 1986. Dating Exposed Surfaces inthe Arctic by Lichenometry: The Problem of ThallusCircularity and its Effect on Measurement Errors.Arctic 39(3) : pp. 253-259.Matthews, T A. and Shakesby, R. A. 1984. Thestatus of the Little Ice Age in southern Norway:relative-age dating of Neoglacial moraines withSchmidt hammer and lichenometry. Boreas13 : 333-346.OrombeIli, G. and Porter, S. C. 1983. Lichengrowth curves for the southern flank of the MontBlanc Massif, western Italian Alps. Arctic andAlpineResearch. 15(2) : 193-200.Porter, S. C. 1981. Lichenometric studies in theCascade range of Washington: Establishment ofRhizocarpon geographicum growth curves at MountRainier. Arctic alld Alpille Research 13( I) : 1/-23.Srivastava, D., Bhattacharya, D. N., Shukla, S.P. and Kaul, M. K 200 I. Lichenometry studies onHimalayan glacier. Geol Surv India Spl. Pub 53 :151-155.

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Relative Dating of Moraines by Lichenometric and Schmidt Hammer Techniques in the Gangotri Glacier Valley, Uttarkashi District, Uttaranchal