Volcanic eruption causes pyroclastic flow, lava flow, volcanic bomb and ashfall disasters simultaneously, furthermore lahar disaster due to rain in the aftermath. In rare case it causes a lahar by crater lake outburst at the moment of eruption, damaging tremendously. This rare lahar disaster is not only terrible in damage but also difficult in countermeasure. The paper investigated existing drainage channels of countermeasures for this rare lahar through research papers and evaluated the effectiveness, resulting in a fact that excepting the Mt. Kelud case they aimed to confine an imminent outburst of crater lake formed after an eruption and are not effective for the next eruption. In the Mt. Kelud drainage tunnels were constructed to confine this rare lahar in 1928, and is functioning as of now by improving through several times of eruptions. The paper reviewed the construction and improvement history of the crater lake drainage tunnels in Mt. Kelud, and evaluated the function as a countermeasure for the lahar caused by crater lake outburst.

The Joganji River basin has experienced numerous severe sediment-related disasters due to the vast sediment deposits (approximately 0.1 billion m3) originating from a massive mountain collapse triggered by the Hietsu earthquake in 1858. Over the past century, numerous sabo facilities have been constructed, effectively reducing sediment runoff from this mountainous region. Monitoring of bedload and debris flow has been conducted since the 1960 s in this basin. In October 2012, a sabo dam with a movable shutter, i.e., an adjustable gate system designed to regulate sediment discharge during floods, was installed in the middle reaches of the river to control sediment transport. The effectiveness of sediment control operations has been monitored using sensor data collected around dams. Pilot operations have been conducted during flood events since July 2016 using five distinct operational patterns, most recently on 8 July 2020 and 1 July 2023. The performance of the movable shutter system was evaluated through these controlled flood operations. The present study introduces recent examples of applied sediment control using the movable shutter at the Myoju Sabo Dam. Active control of sediment runoff during floods was demonstrated using multiple sensors, including the Japanese pipe-hydrophone, photoelectric sensors (PE), and submerged load cell. Differences in the longitudinal distribution of bedload and wash load were observed depending on the shutter operation method, providing insights into effective flood-time sediment management strategies