How the Iwate Volcanic Group Formed
Mt. Iwate is just one of over 25 peaks in the vast Iwate Volcanic Mountain Range, which is about 13 kilometers long. The line of prominent peaks starts with Mt. Mitsuishiyama in the west, then moves eastward to Mt. Omatsukurayama, Mt. Inukurayama, and Mt. Ubakurayama.
The Mt. Iwate stratovolcano itself anchors the eastern section of the range, featuring a symmetrical peak called Mt. Yakushidake, the highest point in the range at 2,038 meters. The spectacular Yakehashiri Lava Flow, a formation created when the volcano erupted in 1732 that was later designated a Special Natural Monument, runs down the side of the mountain.
The peaks of the western side of the mountain range are arranged around the rim of an ancient oval-shaped caldera that stretches 2.5 kilometers from Mt. Kurokurayama to Mt. Yakushidake. The rugged southern ridge of the prominent western Nishi-Iwate caldera is distinguished by particularly dramatic rock formations that have earned it the name Onigajo, or “demon’s castle.”
The western part of the Mt. Iwate stratovolcano is thought to have formed through repeated eruptions and collapses over the past 700,000 years, while the eastern side is much younger.