Mount Iwate
Geology. Mount Iwate consists of a younger eastern symmetrical stratovolcano (Higashi-Iwate, "East Iwate") overlapping an older western stratovolcano (Nishi-Iwate, "West Iwate") which has collapsed to form a caldera. Nishi-Iwate was formed approximately 700,000 years ago, and forms two-thirds of the mountain body. Higashi-Iwate was a later (300,000 years ago) parasitic volcano, which now forms the summit of the mountain. The oval-shaped, 1.8 x 3 km caldera of Nishi-Iwate has a 0.5 km wide crater, partially filled by a crater lake called Lake Onawashiro. Several somma including Yakushidake, the largest, surround the  more recent Higashi Iwate crater rim. During the historical period, Mount Iwate erupted in 1686-1687 with a pyroclastic surge; however, the eruption of 1732 was much larger and resulted in a substantial lava flow on the northeast slopes of the mountain. This four-kilometre long lava flow ("Yakebashiri Lava Flow") has been designated a Natural Monument by the Japanese government. Mount Iwate has largely been quiet since 1732, with a small emission of steam and ash in 1919 and a series of volcanic earthquakes from 1998 to 2003.