Volcano eruption during the snow season may lead to a drastic snowmelt owing to eruption heat, resulting in a mudflow. This phenomenon is called “snowmelt-type volcanic mudflow.” A snowmelt-type volcanic mudflow has more water when compared with an ordinary mudflow caused by rainfall such that this type of mudflow can become larger and has the potential to reach more remote areas with greater speed. It triggers tremendous damage in lower reaches in some cases. Therefore, adequate measures should be taken against snowmelt-type volcanic mudflow, and monitoring should be conducted in a volcanic area with snow. However, a snowmelt-type volcanic mudflow rarely occurs and as only a few examples are available, this type of mudflow is less understood. Accordingly, this study examines the generation process of snowmelt-type volcanic mudflow using experiments. The following two types of experiments were conducted. (1) The speed of snow melting is determined by mixing snow and heated gravel. (2) The process in which gravel comes flying and penetrates the snow layer is examined. These experiments have clarified the following points. The speed of melting snow varies depending on the contact condition of snow and heated gravel; the speed of melting snow increases where there is a mixture of snow and heated gravel; under the same condition of the amount of gravel, the smaller the grain size is, the greater is the speed of snow melting; and there is a correlation between the kinetic energy of the gravel flying and the mass of the snow pushed aside by penetration of gravel into snow layer. The findings revealed that 5 cm diameter gravel can melt snow most effectively.

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