Report on Atka Volcanic Complex (United States) — November 2014
Bulletin of the Global Volcanism Network, vol. 39, no. 11 (November 2014)
Managing Editor: Richard Wunderman.
Atka Volcanic Complex (United States) Summary of activity during 1998-2007
Please cite this report as:
Global Volcanism Program, 2014. Report on Atka Volcanic Complex (United States) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 39:11. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN201411-311160
Atka Volcanic Complex
52.331°N, 174.139°W; summit elev. 1518 m
All times are local (unless otherwise noted)
Korovin is a stratovolcano located on Atka Island in the central Aleutian Islands; its most recent reported activity ended in 2007. This report summarizes and contains new information on activity from 1998 to 2007 by drawing on information primarily from the Alaska Volcano Observatory (AVO) and their cited publications. Much of the summary takes the form of a table at the end of the report.
Atka volcanic complex. According to Myers and others (2002) Korovin is a part of the 360 km2 Atka volcanic complex, found on the northern part of Atka Island. It is the largest modern complex within the central Aleutians (Myers and others, 2002). The ancestral Atka volcano, in the complex, was described as a large shield volcano consisting of basaltic and basaltic andesite flows, which was subsequently surrounded by a series of satellite vents (Myers and others, 2002).
A caldera forming eruption at the Atka shield volcano occurred ~300,000-500,000 years ago, creating a 5-km-diameter caldera. Associated with that event was the eruption of a large dacitic flow, called Big Pink. Regarding the composition of Big Pink, Myers and others (2002) said, "It consists of pumiceous and glassy units but is not associated with any ash flows." After the caldera formation, the volcanic centers of Korovin, Kliuchef, Konia and Sarichef formed. Figure 4 is a topographic map showing the location of these four volcanic centers and the location of the Atka caldera. These structures all comprise the Atka volcanic complex.
Korovin volcano. Korovin is located 21 km NE from the town of Atka (figure 4). It is the largest and tallest volcano of the post-caldera volcanic centers within the Atka volcanic complex. According to Myers and others (2002), Korovin shows little evidence of glaciation, unlike Kliuchef, located ~5 km S of Korovin. Regarding Korovin' edifice and age, Myers and others (2002) say "Its uneroded form suggests the volcano is mostly Holocene in age."
Korovin has a basal diameter of ~7 km and two summit vents located 0.6 km apart (Myers and others, 2002). The NW summit vent has a small crater and is the lower of the two vents. The SE summit has a 1 km wide crater, with steep walls and a depth of several hundred meters (Myers and others, 2002). The SE summit crater sometimes contains a crater lake and is considered Korovin's active crater. Figure 5 is an aerial photo of Korovin, highlighting its two summit vents.
During the summer of 2004, AVO installed a network of seismic stations throughout the northern part of Atka Island. Data from the network was accessible in March 2005; however, it wasn't until December 2005 that Korovin was considered seismically monitored. On 2 December 2005, Korovin was also officially assigned the Level of Concern Color Code Green after "a sufficient period of background seismicity had been recorded" (McGimsey and others, 2007). Before, AVO had listed Korovin as UA (unassigned) during periods when no significant activity was noted. AVO assigns volcanoes UA when there is no real-time seismic network in the area that can be used to define background levels of seismicity.
In addition to being seismically monitored, Korovin is also monitored through ground-based, aerial, and satellite imagery and photographs. Korovin and its plumes are often photographed by residents of Atka village (figures 6 and 7), which are then sent to the AVO. Figure 8 provides examples of photos of Korovin taken from satellites. Images from figures 6-8 furnish various kinds of evidence, from steaming (i.e. non-eruptive cases, figure 7), ash-bearing plumes (figure 6), and the result of ash-bearing eruptions (ash on the snow surface seen in satellite views, figure 8). Evidence of these kinds is summarized in next section.
|Figure 7. Photograph of a steam column rising from Korovin on 27 July 2007. Steam was estimated to reach ~215-245 m above the crater. The photo was captured by Louis Nevzoroff from Atka village. Taken from McGimsey and others (2011).|
Activity during 1998-2007. During this interval (table 1), activity ranged from eruptive cases to those that were considered non eruptive.
Activity was often reported to AVO by Atka village residents and pilots in the area. Korovin was also monitored through satellite imagery, when weather conditions were favorable. During this interval, the highest plumes were observed on 30 June 1998 and reached an altitude of ~9.1 km. As activity varied, the Aviation Color Code (ACC), the Volcanic Activity Alert Level (VAAL), and the Level of Concern Color Code (LCCC) were changed to reflect Korovin's activity status.
AVO presented general information on reported activity from 1998-2007 on their website. For each of the events within this interval, AVO cited information from several sources, some of which included the following: McGimsey and others (2003), which discussed activity in 1998; McGimsey and others (2008), which discussed 2005 activity; Neal and others (2009) that looked at 2006 activity; and McGimsey and others (2011) that detailed 2007 activity. AVO also referenced several past Bulletin reports, which highlighted Korovin activity (BGVN 23:06, and 31:02).
Our summary in table 1 summarizes the following: (1) the basic information on Korovin's activity from the AVO website and (2) additional information from some of AVO's cited references. Greater detail can be found on AVO's website and in their cited references.
AVO: Eruption started, 30 June 1998 ±1 month. Eruption end, 30 June 1998 ± 7 days
McGimsey and others (2003):
Eruption start / stop dates: 30 June / 8 July
"…, the timing of this activity remains poorly constrained; intermittent ash may, in fact, have occurred weeks or prior to June 30."
10 May- Pilot observed ash on SE slope. Pilot had seen no ash the previous week and speculated the ash was deposited a few days prior to May 10
28 June-Individual reported a dark ash plume over Korovin
30 June-VPSO in Atka village reported two separate clouds, first at ~0730 and second at ~0830. Second cloud rose ~9.1 km and was tinted orange. VPSO said events "produced dustings of ash in Atka". AVO received 2 pilot reports: (1) at 1115, noted volcanic cloud reached ~4.9 km a.s.l., (2) at 1720, cloud to 9.1 km near Korovin
2 July- Resident reported a 'rusty' cloud, ~4.9 km a.s.l. moving SE
3 July- Pilot reported profuse steam from summit crater and ash on S, SE and E flanks. Thin trail of ash extended SW towards Atka village
8 July- AVO noted minor, weakly ash-bearing clouds over Korovin with satellite images
AVO: Eruption started, July 2002 ±1 month. Considered a questionable eruption
McGimsey and others (2008):
5 July- Satellite photo of ash deposits on upper E flank of Korovin (figure 8, top). "Intermittent, minor phreatic eruptions through a hot, roiling lake in the south summit crater of Korovin [is] the probable source."
AVO: Eruption started, June 2004 ±1 month. Considered a questionable eruption
McGimsey and others (2008):
4 July- Satellite photograph shows ash deposits on upper E flank of Korovin (figure 8, bottom). Same explanation as 5 July 2002
Neal and others (2009):
7 July- Korovin photographed with ash covering the snow on its E flank. According to the caption of the photograph, "The deposit may be the result of phreatic explosions or vigorous wind remobilization of ash from within the summit crater."
19 July- Aerial photograph of Korovin showing ash deposited around the crater vent. The caption for the photograph states, "At times, a shallow body of gray, turbid water partially fills the inner crater and, in 2004, was observed roiling. Phreatic explosions from this water-rich, high-temperature system may be responsible for the occasional localized ash-fall deposits seen on the upper flanks of Korovin."
AVO: Eruption started, 23 February. Eruption end, 7 May ± 14 days. Considered a questionable eruption.
McGimsey and others (2008):
23 February- Clear day. Residents noted minor steaming around 1200. Around 1900, residents observed dark cloud rising several thousand feet and drifting E (figure 6). Ash seen falling out near base of plume. Minutes later, three or four smaller gray puffs seen. No other activity seen that night. In satellite imagery, small steam plume with minor ash noticed. Height of plume estimated at ~3 km.
24 February- LCCC was raised from UA (unassigned) to Yellow
4 March- LCCC reduced from Yellow to UA
19 March- Pilot report noted steam rising several thousand feet above Korovin
Early May- Observational data showed roiling lake in SE crater emptied. Visible glow.
AVO: Seismicity without confirmed eruption, start / end: 13 September
McGimsey and others (2008):
13 September- Long sequence of strong seismicity. Sequence began with two small local events, then ~30 minutes of weak tremor, and then ~20 weak local events. Nothing unusual noted in satellite images from this time.
AVO: Non-eruptive activity started, 16 January 2006 and ended September 2007 ± 2 months.
Neal and others (2009):
16 January 2006- Background seismic activity increased
17-18, 21 Jan and 21-22 Feb- burst of tremor-like signals
22 February 2006- LCCC increased from Green to Yellow
Early March- Seismicity stabilized and then decreased
8 March- LCCC downgraded from Yellow to Green
July- Increased number of earthquakes in vicinity of Korovin
September and October- Increased tremor episodes
19 October- SE crater lake disappeared by this date and absent for rest of 2006. Lake present on 12 September (satellite data).
29 October- White vapor plumes rose several hundred meters above Korovin and coincided with ~5-min of strong tremor
5 November 2006- Strongest earthquake swarm recorded by seismic network
6 November- Yellow ACC and an Advisory VAAL declared
18 November- dark-gray ash on E flank of SE crater observed in ASTER satellite images. Ash was not present in image from 21 November. ASTER satellite imagery showed warm spots in Korovin crater
Late November 2006- Significant deformation in latter half of 2006. Circular pattern of uplift, as much as 5 cm noted through July and October InSAR data. November-December- Seismicity high; strong, short-lived signals. Low-frequency tremor bursts.
11, 21 and 24 December 2006- Residents photographed large, white-vapor plumes rising from Korovin. One resident noted that he saw ash falling below the plume he reported. Ash was not verified on the ground
End of 2006-No ash detected in atmosphere or on ground through satellite data. Rise in ground temperature also not detected
McGimsey and others (2011):
Beginning of 2007- ACC, Yellow, and VAAL, Advisory due to increased activity in 2006. High seismicity from 2006 continued into 2007. Inflation (uplift) in N part of Atka Island that began in June 2006 totaled 9-10 cm and began to taper off in 2007
11 January 2007- M3.5 earthquake considered large for volcano-generated seismicity.
23 January- Series of tremor bursts
24 January- Resident took pictures of steam column rising from SE crater and reported similar steam columns rose ~300 m every 15-80 minutes
14 February 2007- Pilot reported a steam plume extending 1.5-2.4 km over Korovin
3 March- Residents photograph ash deposit on W flank. Residents observed steam from SE summit vent. Flurry of low-frequency seismicity in morning
May, June & August- Episodes of tremor lasted several days
27 July 2007- Steam plumes observed by residents (figure 7)
5 August- OMI detected small SO2 cloud, 300 km N of Cleveland volcano. Based on wind dispersal models, cloud believed to be from Korovin. Aerial photo (figure 5) showed steam rising from SE crater
20 August- OMI detected small emission of SO2 from Korovin
7 September- ACC/VAAL downgraded to Green/Normal due to decreasing trends in seismicity and uplift
October-December 2007- uneventful
References. Alaska Volcano Observatory, the U.S. Geological Survey, BigTopo 7, and AllTopo 7, Topographic shaded relief image of the northern part of Atka Island (Image 2906), accessed on 14 April 2005, (URL: http://www.avo.alaska.edu/images/image.php?id=2906).
McGimsey, R. G., Neal, C. A., and Girina, O., 2003, 1998 volcanic activity in Alaska and Kamchatka: Summary of events and response of the Alaska Volcano Observatory: U.S. Geological Survey Open-File Report OF 03-0423, 35 pp, (URL: http://pubs.usgs.gov/of/2003/of03-423/).
McGimsey, R.G., Neal, C.A., Dixon, J.P., and Ushakov, S., 2008, 2005 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 2007-5269, 94 pp, (URL: http://pubs.usgs.gov/sir/2007/5269/).
McGimsey, R.G., Neal, C.A., Dixon, J.P., Malik, N., and Chibisova, M., 2011, 2007 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 2010-5242, 110 pp, (URL: http://pubs.usgs.gov/sir/2010/5242/).
Myers, J.D., Marsh, B. D., Frost, C. D. and Linton, J.A., 2002, Petrologic constraints on the spatial distribution of crustal magma chambers, Atka Volcanic Center, central Aleutian arc, Contributions to Mineralogy and Petrology, vol. 143, issue 5, pp. 567-586, DOI 10.1007/s00410-002-0356-7 (URL: http://link.springer.com/article/10.1007/s00410-002-0356-7).
Neal, C.A., McGimsey, R.G., Dixon, J.P., Manevich, A., and Rybin, A., 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 pp, (URL: http://pubs.usgs.gov/sir/2008/5214/).
Geological Summary. The Atka Volcanic Complex consists of a central shield and Pleistocene caldera with several post-caldera volcanoes. A major dacitic explosive eruption accompanied formation of the caldera about 500,000 to 300,000 years ago. The most prominent of the post-caldera stratovolcanoes are Kliuchef and Sarichef, both of which may have been active in historical time. Sarichef has a symmetrical profile, but the less eroded Kliuchef is the source of most if not all historical eruptions. Kliuchef may have been active on occasion simultaneously with Korovin volcano to the north. Hot springs and fumaroles are located on the flanks of Mount Kliuchef and in a glacial valley SW of Kliuchef. Korovin, at the NE tip of Atka Island, is the most frequently active volcano of the complex, and contains a double summit with two craters. The NW summit has a small crater, but the 1-km-wide crater of the SE cone has an open cylindrical vent of widely variable depth that sometimes contains a crater lake or a high magma column. A fresh-looking cinder cone lies on the flank of the partially dissected Konia volcano, located on the SE flank of the dominantly basaltic Korovin. Some late-stage dacitic lava flows are present on both Korovin and Konia.
Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA; Game McGimsey, AVO.