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Late Pleistocene and Holocene Glaciations in the Nepal Himalayas and Their Implications for Reconstruction of Paleoclimate

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Title: Late Pleistocene and Holocene Glaciations in the Nepal Himalayas and Their Implications for Reconstruction of Paleoclimate
Other Titles: ネパール・ヒマラヤにおける更新世後期以降の氷河変動と古気候復元
Authors: Asahi, Katsuhiko Browse this author
Issue Date: 24-Sep-2004
Abstract: Glacial landforms indicate the existence of the past glaciation, and the limits of glacier extent may suggest paleoclimatic conditions. Nevertheless, the lack of the numerical dating has poorly defined the history of glaciations throughout the Himalayas. In the last decade, new dating techniques were developed and started to be applied to the glacial deposits in the Western Himalayas. The Nepal Himalayas are governed by the strong summer monsoon environments; hence, summer monsoon precipitation plays an important role in glacier nourishment. When the geographical extent of the Himalayas is considered, however, the amount of winter precipitation, which is delivered by the westerlies, should be considered on the glaciation in western Nepal. The region of the Nepal Himalayas is particularly important because it makes the junction between the westward summer monsoon and eastward winter westerlies along the southern flank of the great Himalaya. A comparative study on the glaciation limit between eastern and western Nepal, therefore, will lead to understanding the relative importance of the monsoon and westerlies during the Last Glacial. This study aims to show the framework of the history of glaciations in the Nepal Himalayas with the aid of numerical dating, and can imply the paleoclimate during the Last Glacial. Two study areas of the Kanchenjunga and Khumbu Himals were selected from eastern Nepal, and three areas of the Chandi, Api, and Sisne Himals were selected from western Nepal. This study first delineated detailed distribution maps of glacial landforms in the entire part of each study area by aerial photograph interpretation and field observation. The morphostratigraphy of the glacial landforms led to the classification into five moraine complexes, which were recognized in each study area. This configuration of glacial landforms could be recognized in each study area. This classification was confirmed by relative dating methods, mainly based on the weathering criteria of boulders on moraines. Absolute age, by optically stimulated luminescence (OSL) and radiocarbon datings, and relative dating constrained the history of glaciation. From younger to older order, the stages are the LIA (Little Ice Age), Holocene, Late Glacial (correlated with the Younger Dryas), LGM (Last Glacial Maximum), and the early substage of the Last Glacial iii which correlated with MIS 3. Even in the LGM, the terminal position of the glacier was somewhat enlarged compared with that of the present glaciers. This fact implies that the glaciation was restricted even during the LGM. Glacial equilibrium line altitude (ELA) is the elevation where the accumulation and ablation of a glacier are balanced. This is an appropriate indicator for the glaciation and local climate. A comparison of ELA between the LGM and the present can show that the relative climatic enhancement or weakness between the monsoon and westerlies controlled the style and timing of glaciations in the Nepal Himalayas. Distinguished higher altitudes of the maximum elevation of lateral moraines (MELM) were used to estimate the ELAs during the LGM. During the LGM period, the latitudinal profiles of ELA had the same inclination tendency toward the south as present. It suggests that monsoon precipitation is likely to have been a ruling resource over glacier accumulation. The inclination of ELAs had been enhanced southward during the LGM in eastern Nepal, whereas the gradient had been almost equal as today in western Nepal. This fact can imply that the decreased precipitation in summer restricted the glaciation throughout Nepal, and that the enhanced winter precipitation possibly maintained glaciers in western Nepal.
Conffering University: 北海道大学
Degree Report Number: 甲第7034号
Degree Level: 博士
Degree Discipline: 地球環境科学
Type: theses (doctoral)
Appears in Collections:学位論文 (Theses) > 博士 (地球環境科学)

Submitter: 朝日 克彦

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