How Was Mount Fuji Formed?

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Mount Fuji, the tallest mountain in Japan, was formed by a series of volcanic eruptions that occurred over approximately the last 100,000 years. Geologists identified four major stages of volcanic eruption in Mount Fuji’s formation process. These stages deposited layers of basalt and andesite rock in the mountain. The volcano is still active, with the most recent eruption occurring in 1707.

The deepest layers of Mount Fuji were formed by several old volcanoes called Komitake and Ko-Fuji. These volcanoes were active until approximately 10,000 years ago. The shapes of the two underlying volcanoes contribute to the irregularity of the volcano’s present shape. Komitake and Ko-Fuji became inactive when large lava flows began to emerge from the presently active volcano. This volcano, known as New Fuji, deposited a large amount of basalt rock over the old volcanoes.

Most of the eruptions occurred between 3,000 and 4,500 years ago. Fuji’s last eruption in 1707 was the largest in history, and it took place at the volcano’s summit. More than 100 smaller cone volcanoes are found on the mountain’s flanks, but these are considerably less active. There was concern beginning in 2000 that the volcano at Mount Fuji was awakening and would erupt again, but a 21st century eruption has yet to occur.