Iwate

Japan - Honshu

SUMMARY:

Type: composite
Activity: dormant
Last Eruption: 1919 AD
Rock Type: ?
Eruptive Volume: ? cu km
Location Map from Xerox PARC
Latitude: 39.85 N
Longitude: 141.00 E

GEOLOGIC HISTORY

Located on northern Honshu northwest of Morioka City, Iwate sits adjacent to an older cone. Viewed from the east, Iwate volcano has a symmetrical profile that invites comparison with Fuji, but on the west an older cone is visible containing an oval-shaped, 1.8 x 3 km caldera. After the growth of Nishi-Iwate volcano beginning about 700,000 years ago, activity migrated eastward to form Higashi-Iwate volcano. Iwate has collapsed seven times during the past 230,000 years, most recently between 739 and 1615 AD. The summit cone of Iwate volcano, Yakushi-dake, is truncated by a 500-m-wide crater. It rises well above and buries the eastern rim of the caldera, which is breached by a narrow gorge on the NW. A central cone containing a 500-m-wide crater partially filled by a lake is located in the center of the oval-shaped caldera. A young lava flow from Yakushi-dake descended into the caldera and a fresh-looking lava flow from the 1732 eruption traveled down the NE flank.

Historic Activity:

  • About 25 eruptions from 1597 to 1863.
  • The latest eruption took place in 1919 and was a small phreatic explosion.
  • Fumarolic activity was reported in 1934.

Recent Activity:

  • Sept. 15, 1995, seismometers registered intermittent small-amplitute volcanic tremors and low-frequency earthquakes. Again on Oct. 20, 1995.
  • Small-amplitude volcanic tremor occurred on Jan. 13, 24, and 29, 1996. Again on Mar. 4, May 12, June 10, 11, 12, and 17, . On Aug. 25, a M 1.9 earthquake was recorded 3 km beneath the top of Iwate. This was considered a remarkable event in this region. On Sept. 11, Oct. 2, Nov. 24 and 25 shallow volcanic microearthquakes were recorded. On Sept. 12 and Oct. 11 small-amplitude volcanic tremors occurred.
  • Tremor and earthquake swarm on Nov. 12, 1999.

Data Sources

  • Global Volcanism Network (V. 20, No. 9 to V. 25, No. 2).

ADDITIONAL INFORMATION

Last Update: 10/29/00