Radiometric Chronology of Neh–nar Glacier, Kashmir

Abstract

Surface and core samples of Neh–nar Glacier in the Kashmir Valley have been analysed for the radionuclides 32Si. 210Pb, 40K, and 137Cs. The lateral and vertical profiles (at an altitude of about 4 140 m) reveal: (1)32Si activity decreasing slowly from the accumulation zone to 4 050 m altitude and then abruptly towards the snout. (2)Five zones of alternating high and low 210Pb activity in the surface samples. (3)An horizon at between 2 and 3 m depth containing 210Pb activity above natural levels. This horizon is also associated with 137Cs and a maximum in total ß activity. The ice samples have been dated on the basis of a simplified two–component model, the “fresh“contribution determined by 2l0Pb and the old component by 32Si. The following conclusions can be drawn from these observations: (1)The model age of the snout ice is c. 850 years. (2)The average rate of ice movement in the lower glacier is about 2 m/year, which compares well with the annual movement rate of 2.65 m/year observed since 1974.

Basal flow rate of Changme-Khangpu glacier, Sikkim Himalaya based on32Si and210Pb chronology

“…Dating of snow, firn and glacier ice by radioisotopes requires proper knowledge of their half-life values and average fallout values in the precipitation. Based on various considerations, discussed in detail by Nijampurkar et al (1982), the apparent ages of the surface and deep ice samples have been calculated using appropriate half-lives for cosmogenic 32Si (105 yr) and radiogenic 2~°pb (22-3 yr). Mean weighted fallout values in precipitation of 0.7 dpm/ton for 32Si and 8 dpm/L for 2:°pb are adopted in the present work for calculation of age (Nijampurkar et al 1982).…”

“…Based on various considerations, discussed in detail by Nijampurkar et al (1982), the apparent ages of the surface and deep ice samples have been calculated using appropriate half-lives for cosmogenic 32Si (105 yr) and radiogenic 2~°pb (22-3 yr). Mean weighted fallout values in precipitation of 0.7 dpm/ton for 32Si and 8 dpm/L for 2:°pb are adopted in the present work for calculation of age (Nijampurkar et al 1982). The 32Si and 2 ~0pb activities in one year's fallout of fresh snow samples (cK-1, cK-3) were found to be 0-88 + if09 dpm/ton and 8"5 dpm/L respectively which are a little higher than the values adopted for age calculations and those reported in the literature (Bhandari et al 1982;Clausen et al 1967;Nijampurkar et al 1982Nijampurkar et al , 1984.…”

“…Mean weighted fallout values in precipitation of 0.7 dpm/ton for 32Si and 8 dpm/L for 2:°pb are adopted in the present work for calculation of age (Nijampurkar et al 1982). The 32Si and 2 ~0pb activities in one year's fallout of fresh snow samples (cK-1, cK-3) were found to be 0-88 + if09 dpm/ton and 8"5 dpm/L respectively which are a little higher than the values adopted for age calculations and those reported in the literature (Bhandari et al 1982;Clausen et al 1967;Nijampurkar et al 1982Nijampurkar et al , 1984. The ages of these samples are, therefore, assumed to be zero for calculation of ice flow rates.…”

“…Estimation of ice movement by conventional methods at depths is usually cumbersome and gives information only about short term flow rates. The modern radioisotopic techniques, however, provide a unique approach to investigate flow rates over a period of a few centuries (Bhandari et ai 1982;Nijampurkar et al 1982Nijampurkar et al , 1984). An attempt is made in this paper to estimate the past average basal flow rate of the Changme-Khangpu glacier using natural radioisotopes like cosmogenic silicon-32 (half-life = 105 years; Kutschera et al 1980) and radiogenic lead-210.…”

Oxygen isotopic ratios of some Himalayan glaciers

“…Nehnar, located in the Kashmir Valley (34O09'N,75O3 I'E) in the western Himalayas is a small (3.4 km long and 0.35 km wide at the maximum) valley glacier extending over the altitude range of 3900-4700 m. Changme-Khangpu (CK) is another young and small valley type glacier located in the Sikkim valley (27O58'N, 88O42'E) in the altitude range of 4800-5500 m. It is 5.8 km long and drains into Tista river. The chronology and ice dynamics of these glaciers have been studied earlier (Bhandari et al, 1983;Nijampurkar et al, 1982).…”