Report on Bogoslof (United States) — 18 January-24 January 2017
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 18 January-24 January 2017
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2017. Report on Bogoslof (United States). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 18 January-24 January 2017. Smithsonian Institution and US Geological Survey.
53.93°N, 168.03°W; summit elev. 150 m
All times are local (unless otherwise noted)
AVO reported that an explosive event at Bogoslof began at about 1320 on 18 January, generating an ash plume that rose at least to an altitude of 9.4 km (31,000 ft) a.s.l. and drifted NE. The dark (ash-rich) plume was identified in satellite images and observed by a pilot, and produced lightning strikes and infrasound signals detected by sensors in Sand Point and Dillingham. Analysis of a satellite image suggested the presence of very hot material (lava) at the surface immediately surrounding the vent, which was the first such observation since the beginning of the eruption. AVO raised the Aviation Color Code (ACC) to Red and the Volcano Alert Level (VAL) to Warning. A second lower-altitude cloud was visible in satellite images around 1400, likely corresponding with an increase in seismic tremor that occurred from 1340-1355. The ACC was lowered to Orange and the VAL was lowered to Watch the next day.
Another explosion was detected at 1317 on 20 January, following an approximately 30-minute-long increase in seismic activity, based on seismic data and lightning detected from the World Wide Lightning Location Network. Pilots observed an ash plume rising to an altitude of 11 km (36,000 ft) a.s.l. and drifting SE. Satellite images indicated an ice-rich plume and lava present at the vent. The ACC was raised to Red and the VAL was raised to Warning, but were again lowered one level to Orange and Watch, respectively, the next day. Several lightning strikes north of Bogoslof indicated that an explosive event began at 1409 on 22 January. An ash plume identified in satellite images rose to an altitude of 9.1 km (30,000 ft) a.s.l. The ACC was raised to Red and the VAL was raised to Warning, and again lowered one level the next day. Following a period of increasing seismicity, an explosive event began at 0453 on 24 January, as indicated in seismic data and lightning detection, prompting AVO to raise the ACC to Red and the VAL to Warning. Seven minutes later an ice-rich plume which likely contained ash rose too altitudes of 7.6-10.7 km (25,000-35,000 ft) a.s.l. and drifted E.
Geologic Background. Bogoslof is the emergent summit of a submarine volcano that lies 40 km north of the main Aleutian arc. It rises 1500 m above the Bering Sea floor. Repeated construction and destruction of lava domes at different locations during historical time has greatly modified the appearance of this "Jack-in-the-Box" volcano and has introduced a confusing nomenclature applied during frequent visits of exploring expeditions. The present triangular-shaped, 0.75 x 2 km island consists of remnants of lava domes emplaced from 1796 to 1992. Castle Rock (Old Bogoslof) is a steep-sided pinnacle that is a remnant of a spine from the 1796 eruption. Fire Island (New Bogoslof), a small island located about 600 m NW of Bogoslof Island, is a remnant of a lava dome that was formed in 1883.