Mount Hachikubo is a volcanic mountain (altitude 674 meters) formed about 17,000 years ago. The erupted magma with dissolved gases produced volcanic rocks (called scoria) and accumulated to form this flat-top pyramid shaped mountain. The holes in the rock were created when the bubbly magma cooled down and solidified. The reddish color is due to the iron contents oxidized at a high temperature. The low viscosity magma flew into the valleys and formed the flat-top landscape. Over the edge of such a magma flow, occurred Joren Falls, a famous plunge waterfall in the Central Izu.