Mount Azumaya is one of the 100 Famous Japanese Mountains. The 2,354 m (7,723 ft) high peak lies, on the border of Nagano Prefecture and Gunma Prefecture. There exist alternative spellings of the mountain's name.The mountain should not be confused with Mount Azumaya of which there are two, one in Nagano Prefecture and the other in Saitama Prefecture. Though the reading is the same, the name written in Kanji differs from the mountain in this article.Mount Azumaya was formed between 900,000 and 300,000 years ago by andesite lava flowing out of a Stratovolcano. An eruption 340,000 years ago formed a caldera of circa 3 kilometers in diameter.