日本における1960–2010年の氷河地形研究

Abstract

Fifty years of studies on glacial landforms in Japan between 1960 and 2010 are reviewed from the personal perspective of a researcher who devoted a major part of his life to these studies. The 1960s was a period in which there was a paradigm shift in the history of glacial landform studies in Japan. This resulted from a series of studies by Tomoya Iozawa using aerial photograph interpretation. He was the first researcher to observe and identify all of the glacial landforms in Japan using aerial photographs, and divided them into two groups: the older and more widespread (Yokoo Stage) and the younger and much less widespread (Karasawa Stage). Following his methodology and staging, extensive research was done in the 1970s, and tephrochronological studies revealed that the older and younger stages correspond to MIS 4 and 2 respectively, although MIS 3 glaciation was recognized later in the Hidaka Range, Hokkaido. A researchers union of glacial and periglacial landforms called Kanrei-chikei Danwakai was established in 1972, Proposed and organized by Isozawa and other young students including the author, it stimulated research. In the 1980s, a reconstruction of the mass balance and flows of past glaciers from glacial landforms was attempted by the author and other researchers. This led to the estimation of the Equilibrium Line Altitude (ELA) of former glaciers in Japan. Inventory work and monitoring of perennial snow patches in the Japanese Alps were also begun in the 1980s, and they encouraged studies on the transformation from perennial snow patch to glacier. In addition, the discovery of an ice body at the bottom of Kuranosuke Cirque, Mt. Tateyama, Northern Japanese Alps gave an important hint to estimating the present (topographical) snowline altitude, which could be much lower than the former evaluation determined only from free air temperature. Both the study of perennial snow patches and mapping of the former ELA clarified the importance of precipitation when determining snowline altitude, and the present ELA was estimated at 2970 m just below the peak of Mt. Tateyama (3003 m). Since the 1990s, glacial landform studies became more closely related to global climatic change within the framework of IGBP-PAGES. Glacial fluctuations in Japan in the last glacial period were mainly controlled by monsoon changes and migration of westerlies, which caused a southern migration of the polar frontal zone. Although the glaciers in Japan were small, even in the glacial period, it is now believed that they are an important indicator of climatic changes because they are very sensitive to monsoon and westerly changes.