|Start:||September 17, 2006 ± 10 Minutes||Observed|
|Stop:||September 17, 2006 ± 30 Minutes||Observed|
|Lahar, debris-flow, or mudflow: ||
|Fumarolic or hydrothermal activity: ||
|Radial fissure: ||
|ColHeight: ||6100 m |
|MaxVEI: ||2 |
|Duration: ||About 10 hours |
On Sunday, September 17, AVO was notified of two distinct plumes rising from the vicinity of Fourpeaked and Douglas. The plumes originated from Fourpeaked Mountain, and represent phreatic explosions at the volcano, followed by new fumarolic activity. Estimates from photographs and NEXRAD radar indicate the plumes reached approximatly 20,000 ft asl (6000 m). AVO raised the level of concern color code from unassigned to YELLOW on Wednesday, September 20, 2006. Due to waning fumarolic activity and decreased seismicity, AVO lowered the level of concern color code to GREEN on June 8, 2007.
From the Smithsonian Institution (2007): "Until the eruption of Fourpeaked on 17 September, evidence for eruptive activity in the past 10,000 years was uncertain. The volcano is largely glacier covered with only isolated outcrops (see figure 1 in original text). This report discusses the initial observation of plumes and subsequent activity until the end of October 2006. Fourpeaked is in S Alaska ~ 320 km SW of Anchorage. It is SW of the mouth of Cook Inlet and within NE Katmai National Park (see figure 2 in original text).
"On the evening of 17 September, AVO received several reports of two discrete plumes rising from the Cape Douglas area. The plumes were photographed at an unstated time on 17 September from the town of Homer (see figure 3 in original text). At this stage, neither Douglas nor Fourpeaked had devoted seismic instruments.
"Retrospective analysis of data from the NEXRAD Doppler radar in King Salmon showed an unusual cloud starting at 1200 on 17 September. The maximum cloud height determined by radar during the first hour of the event was 6 km altitude. The radar return from the cloud continued until at least 2145 (see figure 4 in original text).
"A cloud of sulfur dioxide gas was observed by colleagues at the Volcanic Emissions Group at the University of Maryland Baltimore. They used data collected at 1500 by the Ozone Monitoring Instrument (OMI) on NASA's Aura satellite (see figure 5 in original text).
"On the basis of the suite of visual, radar, and satellite observations, all the 17 September clouds were inferred volcanic in origin. Although satellite data did not detect ash during this event, AVO received reports of a trace of ashfall at Nonvianuk Lake outlet (110 km WNW) and near Homer (150 km NE). Field observers saw deep scouring of a glacier flowing W from the summit, indicating flooding, probably from the 17 September event. In the caption to a 20 September AVO photo by K.L. Wallace there was noted a 'continuous layer of discolored snow and ice above [~1 km elevation,]~3,000 feet asl on the NE flank of Fourpeaked volcano (S of Douglas volcano). Could possibly be ash from the 9/17/06 event.'
"Both fixed-wing and helicopter overflights in the Cape Douglas area on 20 September confirmed the source of volcanic activity to be Fourpeaked volcano. AVO raised the Level of Concern Color Code from "Not Assigned" to YELLOW on 20 September.
"A 23 September observation flight conducted in relatively good weather permitted the first look at the summit since the event of 17 September. Observers saw a linear series of vents running N from the summit for about 1 km. Most of these vents vigorously emitted steam and other volcanic gases. Gas measurements indicated abundant quantities of sulfur dioxide, hydrogen sulfide, and carbon dioxide. Thermal measurements of up to 75°C were recorded at the vents, although steam was likely obscuring hotter areas. Adjacent glacial ice had been disrupted and showed signs of subsidence. Airborne gas measurements taken on 23, 24, and 30 September again documented high emission rates of sulfur dioxide, hydrogen sulfide, and carbon dioxide, and a distinct sulfur smell was evident up to 50 km from the summit. An AVO status report on 3 October noted that cloudy conditions had prevented visual or satellite observations, but limited seismic data being received did not indicate significant volcanic activity.
"The AVO reported that volcanic unrest continued at Fourpeaked during 30 September-24 October. A seismometer installed on 25 September indicated ongoing low-level seismicity. Due to the limited number of seismometers, earthquake epicenters were not located. Emission rates of sulfur dioxide were high during 4-10 October and on 27 October. Observations were hindered due to cloud cover, but on 12 October AVO staff reported that two prominent vents were emitting steam and gas. Figure 6 [in original text] shows several shots illustrating the enlarged opening in the ice on 15 October.
"On 20 October, field crews installed a web camera located 16 km (10 miles) N of Fourpeaked. Steam plumes originating from vents along the summit were visible via the web camera on 27 and 30 October. Steaming continued through at least 4 November (see figure 7 in original text)."
For detailed observations and photographs of this event, pelase see: Neal, C.A., McGimsey, R.G., Dixon, J.P., Manevich, Alexander, and Rybin, Alexander, 2009, 2006 Volcanic activity in Alaska, Kamchatka, and the Kurile Islands: Summary of events and response of the Alaska Volcano Observatory: U.S. Geological Survey Scientific Investigations Report 2008-5214, 102 p., available at http://pubs.usgs.gov/sir/2008/5214/
McGimsey and others (2011) report that throughout the first half of 2007, seismicity, steaming, and gas emissions decreased at Fourpeaked following the 2006 eruption.