Anak Ranakah

Lesser Sunda Islands

SUMMARY:

Type: dome
Activity: active
Last Eruption: 1988 AD
Rock Type: ?
Eruptive Volume: ? cu km
Location Map from Xerox PARC
Latitude: 8.62 S
Longitude: 120.52 E

GEOLOGIC HISTORY

A new lava dome, named Anak Ranakah (Child of Ranakah) was formed in 1987 in an area without previous historical eruptions at the base of the large older lava dome of Gunung Ranakah. An arcuate group of lava domes extending westward from Gunung Ranakah occurs on the outer flanks of the poorly known Poco Leok caldera on western Flores Island.

The crater, of unknown age, is one of at least 13 that comprise a 12-km-long, 1-km-wide chain with a N65°E trend. The vent is ~ 8 km NE of Poco Leok caldera and solfatara field at about 2,100 m elevation. There has been no eruptive activity in the Poco Leok area for at least the past 400 years. An E-W ridge connects Gunung Ranakah (200 m SW of the vent) to Gunung Mandasowu in the E. A broad flat-floored valley with an average elevation of 2,000 m covers the 2 km between the two peaks. VSI volcanologists estimated that the crater had been approximately 50-70 m deep and 200 m in E-W dimension before lava extrusion began.

Historic Activity:

  • None

Recent Activity:

  • Explosions began at 2200 on December 28, 1987 from a pre-existing crater in an area without known historic eruptive activity. The crater, of unknown area, is 1 of at least 13 that comprise a 12 km-long, 1 km-wide chain with a N65°E trend. The vent is approximately 8 km NE of Poco Leok caldera and solfatara field. There has been no eruptive activity in the Poco Leok area for at least the past 400 years. From December 28 to January 2 numerous explosions sent columns 500-2000 meters above the vent. No evidence of new magmatic material as of January 1. Larger explosions began on January 3 with dark ash plumes to 4 to 6 km above the summit. A dome of lava has filled the crater and a flow 300-350 meters long, 200 meters wide, and 40 meters thick had formed in January 1988. Estimated rate of lava extrusion averages 500,000 cubic meters/day. By late February 1988 lava flow had extended north, east, and south from the dome and the rate of lava extrusion had dropped to 200,000 cubic meters/day. Continued dome growth through June 1988 and slowed in July and August 1988. Dome growth ended by late August 1988.

Data Sources

  • Smithsonian's SEAN Bulletin (V. 12, No. 12 to V. 14, No. 11)
  • Global Volcanism Network (V. 16, No. 3).

ADDITIONAL INFORMATION

Last Update: 2/29/00