I love traveling and have been interested in landforms (ground surface features) that are often part of a scenic view. This is why I chose to specialize in geomorphology. This field investigates how various landforms were created and how they will change in the future.
Topographical changes can progress gradually over a long period of time or they can occur abruptly, triggered by some rare natural phenomenon. The latter case includes geomorphic changes caused by volcanic activity, crustal movement, and large-scale flooding that occur once in a hundred to thousand years. As such changes occur over a period of thousands to hundreds of thousands of years, landforms change drastically.
Historical documents recording topographical changes are rare, so understanding these changes requires analysis of the landforms themselves or the sediments that constitute them. Such analysis reveals past phenomena and thus enables us to make predictions about phenomena that may occur in the future.
As stated above, volcanic activity, crustal movement, and large-scale flooding can cause topographical changes. Research on the process of such changes can significantly contribute to human life by enabling prediction of natural disasters and suggesting the possibility of an unprecedented natural disaster.
Also, as the public better understands landforms, people become able to judge what kind of land is safe or dangerous when a natural disaster occurs.
In this context, the learning goal in the physical geography course offered by the Faculty of Education is that the students, who will become teachers in the future, become able to discuss the process of land formation in connection with disaster prevention.
Proving to the world the correctness of the prevailing view in Japan on alluvial fans that are discussed in textbooks used in the Japanese junior high schools.
The amount of available data on alluvial fans is small compared with other landforms that make up plains. Therefore, we did not conduct detailed investigations of individual alluvial fans, but instead considered alluvial fans located all over Japan and tried to get a general sense of where they are formed and how they will change.
Alluvial fans are fan-shaped landforms resulting from deposition of gravel carried by rivers. Six of the seven textbooks used at the junior high schools in Japan state that alluvial fans are formed by rivers. Relatively small alluvial cones that are composed of gravel and have a steep slope have conventionally been regarded as alluvial fans formed by rivers.
The alluvial fans are fan-shaped landforms formed by either debris flows or river flows. (They are mainly debris-flow alluvial fans, but river-flow alluvial fans are also included.)
Alluvial fans are formed by debris flows not river flows. (Denial of river-flow alluvial fans) (Blair and McPherson, 1994) Need for redefinition; prediction of rare sediment-related disaster and floods enabled by landform classification
Distinction between alluvial fans formed by rivers and those formed by debris flows is generally made by conducting field studies and making judgements based on observation of deposits. However, it is difficult to find outcrops containing such deposits.
The goal is to provide an answer to the question of where alluvial fans are formed and how they will change. Areas with an alluvial fan and areas without one differ in how floods occur. Also, alluvial fans formed by debris flows and those formed by rivers differ in how sediment-related disaster occur. Therefore, as a by-product of the research, we will be able to make predictions about future natural disasters and create hazard maps.
The riverbed (above) of the Matsukawa River (an upper stream of the Mogamigawa River) in the Yonezawa Basin in Yamagata Prefecture and deposits at an alluvial fan (below). It looks like a river-flow alluvial fan, but is actually a debris-flow alluvial fan.
Depositional slopes of 0.5-1.5° are not found. Alluvial fans are steep fan-shaped landforms with a slope of 1.5° or more (Blair and McPherson 1994).
Many gently sloped, fan-shaped landforms in Japan that were formed by rivers are not alluvial fans.
Leave some room for thinking
When asked a question by children, it is important to give an answer to only what is asked and leave some room for their thinking. It is also important to talk to them in a way to calm them and lead them to the next word.
As depositional slopes of 0.5-1.5° are found, alluvial fans with slopes less than 1.5° must be in humid climate regions (Japan, Taiwan, and the Philippines). Therefore, the basis for rejecting the fact that gently sloped, fan-shaped landforms created by rivers are alluvial fans was not correct.
Vice-President, Saitama University
Professor, Social Studies Education
Education and professional experienceEducation
Bachelor’s degree in Earth science (University of Tokyo, Faculty of Science, 1975)
Master’s degree in geography (University of Tokyo, Graduate School of Science, 1977)
Doctoral coursework in geography completed (University of Tokyo, Graduate School of Science, 1982)
Doctor of Science (University of Tokyo, 1985)
Lecturer, Hokkai-Gakuen University (1984)
Assistant Professor, Hokkai-Gakuen University (1985)
Professor, Hokkai-Gakuen University (1989)
Assistant Professor, Saitama University, Faculty of Education (1989)
Professor, Saitama University, Faculty of Education (1999 to 2014)
Councilor, Saitama University (2000-2004)
Dean, Saitama University, Faculty of Education (2012 to 2014)
Director, Association of Japanese Geographers (2006-2010)
Chief Editor, Association of Japanese Geographers (2008-2010)
Director, Tokyo Geographical Society (2009 to 2011)
Liaison, Tokyo Geographical Society (2009 to 2011)
Committee member, Japanese Geomorphological Union (1999 to 2015)
Chief Editor, Japanese Geomorphological Union (2009 to 2013)
*Alluvial Fans in Japan* (1988, Kokon Shoin, in Japanese, single author)
*Alluvial Fans in the World* (2006, Kokon Shoin, in Japanese, single author)
*The Topography of Japan, Part 1: An Overview* (2001, University of Tokyo Press, in Japanese, coauthor)
*The Geography of Japan: An Overview, Part 1 (Natural Features)* (2005, Asakura Publishing, in Japanese, coauthor)