Complex sentence: This mountain is the highest in the Chūgoku region, and the most important volcano on the Daisen volcanic belt: a part of Southwest Honshu volcanic arc, where the Philippine Sea Plate is subducting under the Amurian Plate.
Split into simpler sentences: This mountain is the highest in the Chūgoku region, and the most important volcano on the Daisen volcanic belt. The Daisen volcanic belt is a part of Southwest Honshu volcanic arc, where the Philippine Sea Plate is subducting under the Amurian Plate.