Magnitude of the sediment transport event due to the Late Pleistocene sector collapse of Asama volcano, central Japan

A rapid, large-scale sediment transport event due to a catastrophic landslide plays an important role in changing drainage basin topography. However, volumetric evaluation of such events that occurred before the Holocene has been limited. This study quantitatively examines the volume of sediments derived from the Late Pleistocene (24 ka) sector collapse of Asama volcano, central Japan. A sequence of sediments supplied from the sector collapse was identified based on geological and geomorphological field surveys and literature search. The total volume of the sediments was estimated from borehole columns to be 4.9–5.4 km3. Reconstruction of the morphology of the volcanic edifice before and after the collapse provided an estimated volume of the lost sector of 4.0 km3. The greater estimated volume of the sediments released by the collapse is attributed to the entrainment of fluvial material during the flow of volcanic debris and to dilation of the original volcanic material.