Event Name : Veniaminof 2002/9
|Start:||September 28, 2002 ||Observed|
|Stop:||March 23, 2003 ± 1 Months||Observed|Description:
|MaxVEI: ||1 ||
From Neal and others (2005): "On the basis of several days of increasingly frequent, emergent seismic events on multiple stations of the new Veniaminof network (Dixon and others, 2002), AVO announced Level of Concern Color Code YELLOW on September 11, 2002. Following established protocols, the Anchorage Volcanic Ash Advisory Center (VAAC) issued a one-time volcanic ash advisory [see fig. 4 in original text].
"Over subsequent weeks, seismicity was characterized by periods of above-background activity alternating with quiet intervals. Telephone calls to Perryville and other nearby communities[see fig. 5 in original text] turned up no unequivocal observations of unrest until September 24 when AVO received phone reports and digital photographs from the Perryville Native Council. These images showed small, faint gray clouds rising just above the intracaldera cone that has been the source of all known historical eruptions at Veniaminof (Miller and others, 1998). One observer described 'puffs' of mixed dark and white clouds approximately every 5 minutes. Another observer described the 'puffs' as solid white and emanating from the top of the cone.
"Perryville residents next reported 'plumes of smoke' between 8 and 10 pm on October 1. Others reported 'rumbling' during the evening, however no clearly correlative signals were noted on seismograms. One and one half minutes of video taken on October 2 or 3, about 2 pm, from the vantage of the Sandy River (~45 km [28 mi] west of the active cone) showed several small, dilute, gray-brown clouds rising about 300-600 ft above the intracaldera cone and drifting a short distance to the north. In the 1.5 minutes of tape, two distinct 'puffs', about 1 minute apart, rise from the cone and drift downwind. The cone was not unusually snow free, however, a dark covering of ash was visible on the caldera ice field at the base of the cone and extending generally north. On October 6, Sandy River Lodge [see fig. 5 in original text] reported black ash and 'smoke' rising 400-500 ft above the cone, explosions, and ground shaking.
"Cloud-free satellite images of the Veniaminof caldera revealed nothing unusual until October 2 when AVO acquired a Moderate Resolution Imaging Spectroradiometer (MODIS) image that captured a localized, gray deposit on the caldera ice field [see fig. 6 in original text]. The image shows a faint, fan-shaped deposit extending generally east from the cone to the caldera boundary and perhaps just beyond. When viewed in light of reports from Perryville and the video from Sandy River, the dark fan likely represents ash fall from low-level phreatic activity on October 1. No thermal anomalies were detected in satellite imagery throughout this period and no incandescence was reported. A compilation of reports from residents and other observers through the end of the year is presented in table 3. Seismicity and reports of discolored clouds over the intracaldera cone gradually declined through the fall.
"A re-invigorated hydrothermal system beneath the intracaldera cone may account for these intermittent ejections of diffuse, ash-bearing clouds. It seems unlikely that this was prompted by a new magmatic intrusion at depth based on the lack of volcano-tectonic earthquakes. Increased hydrothermal activity may have been related to what was, according to some long time residents of the area, one of the rainiest autumns in memory. Although precipitation falling at the elevation of the intracaldera cone would have been in the form of snow (C. Searcy, NOAA, oral.commun., 2003), precipitation in Cold Bay [see fig. 1 in original text] was approximately 80% above normal for the month of October, according to long term climate records maintained by NWS (National Oceanic and Atmospheric Administration: http://www.arh.noaa.gov/climate.php). King.Salmon, the other nearby long-term weather station, recorded approximately 45% and 60% more precipitation than normal in the months of September and October, respectively."
The 2002 activity continued into 2003. From McGimsey and others (2005): "On January 3, 2003, AVO belatedly received a report from the caretaker of a lodge located northwest of the volcano describing his observations from about mid-December, 2002, during clear weather, of distinct puffs of steam coming from the intracaldera cone. AVO upgraded the Level of Concern Color Code to YELLOW on Monday, January 6, 2003. Several weeks of poor weather conditions followed before clear views revealed that intermittent episodes of steam and diffuse ash emissions from the active cone continued [see fig. 15 in original text]. AVO seismologists detected the onset of small, volcano-tectonic earthquakes on Veniaminof seismic stations beginning on the morning of January 29, 2003 and a commensurate decline in amplitudes and numbers of low-frequency events (S. Moran, written communication). Elevated seismicity continued, and on March 11, a 4-hour period of continuous seismic tremor was observed followed by 17 hours of discrete seismic events and 3-4-minute-long tremor bursts. This culminated with another 4-hour period of continuous tremor on March 12, which was followed by a distinct decline in seismicity over the next several days. The last report of emissions from the active cone was from Mark Battaion in Perryville on March 23, 2003 [see fig. 16 in original text].
From Neal and others (2005): "In the summer of 2003, AVO geologists visited the summit caldera of Veniaminof and examined the intracaldera cone for evidence of the 2002 activity (K. Wallace, written.commun., 2003). Within 50 m (160 ft) of the east side of the cone, the ice surface was dusted with fine wind blown debris derived from the cone. A crevasse at the base of the cone revealed a prominent, 1-cm-thick (0.4 in), black, scoriaceous deposit 1 m (3 ft) beneath the surface [see fig. 7a, b, in original text]. Scoria fragments ranged from fine ash to medium lapilli (with a maximum diameter of 5 mm [0.2 in]). The base of the crevasse was not visible, however no other debris layers were recognized over a thickness of at least 10 m (33 ft) suggesting that this type of depositional event was not common (e.g. wind reworking of cone debris). In hand sample, the tephra consists of abundant black iridescent, glassy scoria; hydrothermally altered scoria (with native sulfur and secondary minerals); and rare individual crystals. Microscopic investigation showed all glass fragments to be devitrified. Wallace and co-workers concluded that this deposit represented recycled cone material ejected during low-level phreatic explosions in October 2002.
"In response to the 2002 unrest at Veniaminof, AVO staff conducted outreach to communities in the vicinity of the volcano and compiled contact phone lists of observers and others who would be helpful in tracking activity on our behalf. We were in frequent telephone contact with people in Perryville, regional airlines, and our colleagues at U.S. Fish and Wildlife Service (USFWS) and the Alaska State Troopers who were often flying in the area. At least one private lodge near the volcano contacted AVO for information on potential hazards. AVO posted a 'Frequently-Asked-Questions' about Veniaminof on our web site, a first in the history of AVO.
"Interestingly, the change in Level of Concern Color Code to YELLOW for Veniaminof occurred on September 11, 2002, during a time when the Department of Homeland Security had recently established a Threat Level of ORANGE. It is therefore possible that reaction to our initial information release on September 11 may have been more pronounced than usual, and confusion over the two color designations may explain why some residents of the Peninsula thought AVO had declared an 'imminent' eruption.
"From September 11 to November 18, 2002, AVO issued three special information release notices on the increased seismicity and its eventual decline at Veniaminof. The volcano was mentioned in weekly updates from September 13 through November 22. AVO reverted to color code GREEN on November 18. During the time of heightened activity, the AVO seismology and remote sensing groups increased the frequency of analysis of Veniaminof seismicity and relevant satellite imagery."