How Mt. Bandai Was Shaped
Mt. Bandai was originally a symmetrical stratovolcano, a volcano built up of layers of lava and ash. Volcanic activity 2,500 years ago caused the top of the mountain to collapse in on itself, creating the 1.2-kilometer wide 350-meter deep Numanodaira Caldera. Before the collapse, it had four peaks of between 1,430 meters and 1,816 meters in height: O Bandai, Kushigamine, Akahaniyama, and Ko Bandai.
A phreatic (steam-blast) eruption in 1888 destroyed the former summit of Ko Bandai or “Little Bandai.” The blast left the mountain with only three peaks, triggered a devastating landslide, and cast debris throughout the area. Hikers to this now inactive volcano can see where the collapse of Ko Bandai occurred and look out across the surrounding area with its many ponds and lakes (around 300) that were formed when the landslide blocked river valleys.
The mountain is carefully monitored for activity to predict and prepare for any future eruptions.