Volcanic Hazard Map of Hon-Shiranesan.

This map shows a phreatic eruption at Hon-Shiranesan.
In the 1939 eruption, 6 cm thick volcanic ash was deposited in the Kusatsu urban area. There is also a possibility of a magmatic eruption at Mt. In the event of a magmatic eruption, as shown in the "Kusatsu-Shiranesan Volcano Disaster Prevention Map," large cinders and pyroclastic flows could reach farther away, and during the snow season, pyroclastic flows with high temperatures could melt the snow at once and send large mudflows down.

This diagram does not show the "eruption alert level" announced by the Japan Meteorological Agency.

Kusatsu-Shiranesan Volcano Disaster Prevention Map

If an explosive eruption occurs at Yugama and the south wall of Yugama breaks, ejecta and hydrothermal fluids are released at once, and mud flows may flow down the valley. In the case of a snowy season, snow along the flow path would also be swept away, resulting in a large mud flow (a phenomenon that may occur once every 200 years or so). The figure above shows the area where mudflow could occur under this scenario. It is assumed to reach the confluence of the Agatsuma River in about 70 minutes.

Enlarged view of the crater perimeter of the diagram if Hon-Shiranesan were to erupt.

This diagram assumes a phreatic eruption that actually occurred suddenly in 2018. There is a possibility of a magmatic eruption at Hon-Shiranesan. When a magmatic eruption occurs, large cinder cones and pyroclastic flows can reach farther than shown in this figure, and during the snow season, hot pyroclastic flows can cause snow to melt in a big rush.
During the snow season, hot pyroclastic flows are expected to melt the snow and send large amounts of mudflows down the mountain.





For details, please refer to the following URL

1. https://www.town.kusatsu.gunma.jp/www/doc/KusatsuShirane_volcano_hazard_map.pdf
2. https://www.town.kusatsu.gunma.jp/www/doc/KusatsuShirane_volcano_hazard_map_Secondary_reader.pdf

Please note that it may take some time to open the file due to its large file size.