Two volcaniclastic deposits-a debris-avalanche deposit (NgDA) and a lahar deposit (NgL) were discoverd alone the Nigorikawa River on the western slope of Aso central cones, southwestern Japan. The Nigorikawa debris-avalanche deposit, having a maximum thickness >3 m, contains numerous plastically deformed debris-avalanche blocks (<3.7 m) of volcanic ash and soil layers in a poorly-sorted silty to clay matrix. The Nigorikawa lahar deposit contains many subangular to subrounded lithic clasts (<0.7 m) and shows clast-supported and matrix-rich depositional structures. We obtained a ^14C age of 2,230±70 years BP from a wood remains (the Yayoi period: 300 BC-300 AD) underlying the debris-avalanche deposit. We obtained a ^14C age of 4,100±60 years BP (2880-2480 cal BC) from a wood fragment in NgL. These ^14C ages indicate that major volcaniclastic flows have inundated the Nigorikawa River multiple times in the past 4,000 years. Although the source and cause of the western part of Aso central cones.