Effects of Volcanic Ash on the Runoff Process in Sakurajima Volcano

摘要

We investigated the effects of volcanic ash covering on the runoff process and the areas contributing to the occurrence of Hortonian overland flow on a bare land slope by spreading Sakurajima volcanic ash over the experimental catchment. Results of analyses by a runoff model and field investigation showed that the ash-covering caused a decrease of rainfall loss and Manning's coefficient of roughness and an increase of the area contributing to the occurrence of Hortonian overland flow, surface runoff, and sediment discharge. However, the rainfall loss and Manning's coefficient of roughness increased over time through the armoring of the surface volcanic ash layer, and as a result, the area contributing to the occurrence of Hortonian overland flow, surface runoff, and sediment discharge also decreased.