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Vol.54-3 CONTENTS

Continuous Caldera Changes in Miyakejima Volcano after 2001

Hiroyuki HASEGAWA, Hiroshi P. SATO and Junko IWAHASHI

Abstract

This study investigated the evolvement of the caldera at Miyakejima volcano after February 2001. DEMs acquired with Light Detection and Ranging (LIDAR) surveys were used for analysis. Topographic changes for each surface category were examined and the change in shape was analysed. Results showed that the caldera floor had risen more than 10 m because of secondary sediment caused by collapse of the caldera wall. However, topographic changes on slope surfaces were limited to gullies. The caldera wall height was 450 m at its maximum; its slope was steep. Analysis of the shape change revealed that the volume of the caldera increased by 10.0 million m3 from February 2001 to September 2003. Lost substance in the new crater and around it reached 8.6 million m3, whereas volume expansion of other areas was only 1.7 million m3. These facts indicate that the main cause of caldera expansion was the formation of a new crater. Because of measurement errors, we could not determine whether or not the caldera floor has been subsiding. As a whole, the caldera volume has continued to increase. Additionally, the caldera wall slope is steeper than the angle of repose. These facts imply that enlargement of the caldera area will continue for the time being. Keywords: Miyakejima volcano, Caldera evolvement, LIDAR survey

Contents

1. Introduction
2. LIDAR data
3. Results
4. Discussion
5. Conclusions
References

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