書籍等出版物

国際共著
2005年12月

Uplift of the Himalaya-Tibet region and the Asian monsoon-geological, geomorphic and environmental consequences

  • ゴータム ピタンバル

担当区分
共編者(共編著者)
出版者・発行元
John Wiley & Sons, Inc.
DOI
10.1111/j.1440-1738.2005.00497.x
ISBN

This thematic section contains 11 contributions based on presentations given at a special session entitled ‘Uplift of Himalaya–Tibet Region and Asian Monsoon: Interactions among Tectonic Events, Climatic Changes and Biotic Responses during Late Tertiary to Recent Times’ of the This thematic section contains 11 contributions based on presentations given at a special session entitled ‘Uplift of Himalaya–Tibet Region and Asian Monsoon: Interactions among Tectonic Events, Climatic Changes and Biotic Responses during Late Tertiary to Recent Times’ of the 19th Himalaya–Karakoram–Tibet (HKT) Workshop in Niseko, Japan, in 2004. It is a cross-section of current multidisciplinary research in earth and environmental sciences dealing with the Himalayas and adjacent regions. A wide range of subjects is covered, including regional geology and paleontology, glaciology and geomorphology, environmental pollution and natural hazards, and climate. We hope that bringing these subjects together in one thematic issue will help readers understand a wide variety of natural phenomena and their records as manifestations of complex interactions between tectonic processes causing the uplift of the Himalayan region and climate, in particular the Asian monsoon. The special session was planned with collaboration and support from two Japanese 21st Century Center of Excellence (COE) Projects: ‘Neo-Science of Natural History – Origin and Evolution of Natural Diversity’ (leader: H. Okada) at Hokkaido University and ‘Dynamics of the Sun–Earth–Life Interactive System’ (leader: T. Yasunari) at Nagoya University.
The first three papers are devoted to traditional geological research across the central part of the Himalayas in various geotectonic settings: high Himalaya (the summit region of Mount Everest, Nepal), the Himalayan foothills (Karnali River Basin, Nepal) and the intermountain basin (Kathmandu Valley, Nepal). Sakai et al. precisely locate the Qomolangma detachment below the top of the world that separates the unmetamorphosed and fossiliferous summit limestone of Ordovician age from the metamorphic yellow band. The latter has chronological evidence of two phases of metamorphism (at 33.3 and 24.5 Ma) and rapid cooling (200°C/my) during the Middle Miocene (15.5–14.4 Ma). Huyghe et al. combine data on facies associations, clay minerals and isotopic abundances of the sedimentary fill of the Karnali River section, which contains the most continuous and magnetostratigraphically best-dated archive of sediments recording the post-Middle Miocene erosion of the Himalayas, and decipher the late Tertiary tectonic evolution of the Himalayan mountain range and associated climate changes. Paudayal presents pioneering work that uses scanning electron microscope observations of fossil pollen grains from the fluvio-lacustrine sediments of the Kathmandu Valley in an attempt to reconstruct past vegetation/climate conditions at ca 40 000 years bp. He suggests that the observed vegetation changes imply a decrease in altitude of at least 1000 m during the late Pleistocene. The fourth paper, by Matsuoka et al., compares the radiolarian fauna in the Xialu chert in Tibet with those from coeval formations in southwest Japan and the western Pacific and investigates their use in Mesozoic paleoceanographic reconstructions.
The subsequent two papers address the geomorphologic history of the region, with a focus on glacial deposits. Kuhle gives a summary of extensive, mostly descriptive research carried out during his numerous expeditions in a broad region that he terms ‘high Asia’ (Himalayas–Karakoram–Tibet and Hindukush, as well as east Zagros and Sayans). The observations in this paper will be a valuable framework to compare with more quantitative data that needs to be accumulated in the years ahead. In contrast, Waragai's paper deals with past climatic reconstruction based on calcrete in the lateral moraine of the Batura Glacier in the Karakoram mountain range. This compact study combines field observations with quantitative data obtained by employing a variety of analytic techniques (i.e. electron probe microanalysis, X-ray diffraction, ion chromatography) to determine the mineralogy and chemistry of calcrete, glacier ice and melt water. The age of calcrete formation is estimated to be approximately 7300 years bp using accelerator mass spectrometry 14C dating.
Abe et al. use the output of a numeric simulation based on the atmosphere–ocean coupled general circulation model (CGCM) and address the problem of sensitivity of the climate response in central Asia to the uplift of the Tibetan Plateau. The numeric experiments suggest that significant drying of central Asia corresponded to the period in which the Tibetan Plateau exceeded approximately half its present-day height. Quantitative data on climate change in the Himalayan region obtained through direct or indirect observations, or numeric modeling can still only provide insights into large-scale effects and further studies in this field are needed. The output of such studies will be invaluable for understanding the regional climate variability and future climate changes, as well as developing a better understanding of the interactions between tectonics and climate.
Results of studies on glacial and periglacial environments and aspects of natural hazards, such as the floods generated by lake outbursts and mass movements related to freezing–thawing cycles in mountainous regions, are discussed in the next two papers. Iturrizaga explores the history of the glacial lake outbursts since the mid-nineteenth century in the Karambar Valley in Hindukush, Pakistan, based on geomorphologic field observations, study of historical records, and interviews with the local inhabitants. The author points out that there seem to be no simple logistic and technical solutions to lessen the known danger and possible disastrous impacts of spontaneous glacial lake outbursts on the ever-expanding infrastructure in the flood-prone floors of the Karambar, Ishkoman and Gilgit Valleys. Likewise, Regmi and Watanabe attempt to quantify the rate and depth of displacement of solifluction lobes in the upper slopes (altitudes exceeding 5300 m) of the Kangchenjunga area, Nepal, based on field monitoring using glass fiber tubes as well as considering parameters such as precipitation and ground temperature vs depths and ground moisture. The movements described are rather slow (a maximum of 11 mm/year); however, further studies on the wider implications of these movements for mountain ecology are needed.
The last two papers address the problems of debris flows and urban environmental pollution, respectively. Adhikari and Koshimizu analyze the geological, geomorphologic, hydrologic and engineering geological data, as well as the perceptions of the local people to decipher the cause, initiation mechanism and deposition process related to the 1996 Larcha debris flow disaster caused by landslide damming of a mountain stream and its outbreak triggered by intensive rainfall. Gautam et al. demonstrate the effectiveness of combining the rock-magnetic properties (mainly the magnetic susceptibility and the saturation isothermal remanence) and the heavy metal composition of soils in the Kathmandu urban and suburban area, Nepal, for rapid quantitative and qualitative analysis of the status of environmental pollution caused by anthropogenic activities. Though described in the Nepalese context, these data have relevance to any mountain and urban settings.
We hope that these papers will stimulate interest in collaborative multidisciplinary research by adapting an integrated approach to understanding the earth and environmental processes in the HKT region, rather than being constrained by the boundaries of traditional disciplines.
We acknowledge the contributions and support of K. Arita, chief organizer of the HKT19 Workshop, and H. Okada (COE Leader) in holding the special session. We thank the reviewers for providing both critical reviews and constructive suggestions on the submitted manuscripts and the authors for their prompt and positive responses during their revisions. Including this multidisciplinary issue in The Island Arc would not have been possible without the close involvement of the Editor-In-Chief, S. Wallis, in both the organization and the final stages of editing.

リンク情報
DOI
https://doi.org/10.1111/j.1440-1738.2005.00497.x
URL
https://onlinelibrary.wiley.com/toc/14401738/14/4 本文へのリンクあり
ID情報
  • DOI : 10.1111/j.1440-1738.2005.00497.x