Initial newspaper accounts of this eruption exclaim "City blacked out by 3 volcanoes!" in large bold type, but in reality, only one volcano, Mt. Spurr, was actually erupting. "Mt. Torbert," as well as the third "unnamed volcano" are not volcanic, and were not erupting. Precursory activity to this eruption may have been observed in mid-May, 1953, when Northern Consolidated Airline pilots reported increased steaming from the summit of Spurr (Unknown, 1953; Fairbanks News-Miner, May 21, 1953).
From Waythomas and Nye (2002): "The first known historical eruption of Crater Peak occurred at about 5 a.m. on July 9, 1953 (Juhle and Coulter, 1955; Miller and others, 1998). For at least 30 years prior to the 1953 eruption, plumes of whitish steam commonly were observed rising from the summit of Crater Peak;" [Note: Although Waythomas and Nye report steaming from Crater Peak, newspaper accounts and pilot observations of the area state that the steaming came from the summit of Spurr.] Waythomas and Nye continue: "pilots reported an increase in the vigor of steaming in late spring 1953 (Juhle and Coulter, 1955). At the time of the 1953 eruption, instruments to monitor the seismic activity were not available. The 1953 eruption was a single explosive burst lasting about one hour, and it generated an ash cloud that rose more than 10,000 meters above sea level (Juhle and Coulter, 1955). Ash fall occurred east of the volcano [see fig. 6 in original text] and approximately 6 millimeters of ash accumulated in Anchorage. A light dusting of ash was reported as far away as Valdez and as close as 48 km to Cordova (Juhle and Coulter, 1955). Pyroclastic flows mixed with snow and ice high on the crater rim and combined with heavy rainfall to produce lahars that inundated tributaries to the Chakachatna River on the south flank of Crater Peak. The lahars flowed into the Chakachatna River and formed a substantial debris dam across the river (Juhle and Coulter, 1955; Meyer and Trabant, 1995)."
Wilcox (1959) gives detailed eruption descriptions: "On July 10 at 5:00 am the vent was only steaming. At 3:30 pm an especially strong surge of ash-laden steam rose to 20,000 feet." Juhle and Coulter (1955) state that the eruption continued with steam and small bursts of ash from July 11 to July 16, 1953.
Ash began to fall in Anchorage at about noon on July 9, 1953, and darkened the sky from 1 p.m. until about 3 p.m. (Wilcox, 1953; Juhle and Coulter, 1955; Wilcox, 1959). This ashfall was disruptive to traffic at Elmendorf Air Force Base and Anchorage International Airport. Three jet aircraft that were sent to investigate the ash plume returned with sandblasted wing leading edges, windshields, side panels, and front portions of their canopies. Elmendorf Air Force Base was closed to air traffic from July 9 -17 due to the eruption (Kienle, 1994). See Wilcox (1959) for detailed pilot descriptions of the ash cloud.

For 220 pages of information on the three 1992 eruptions of Crater Peak, please see the USGS Bulletin 2139, available online at: www.avo.alaska.edu/pdfs/B2139.… ; this file is 9 MB.
From McGimsey and others (1995): "On June 27, after 39 years of quiescence, the Crater Peak vent on Spurr volcano began the first of 3 eruptions (June 27, August 18, and September 16-17) in 1992 (Alaska Volcano Observatory, 1993; Eichelberger and others, 1995). The eruption was preceded by 10 months of gradually increasing seismicity that culminated in 19 hours of precursory volcanic tremor. Upwellings in the crater lake and a color change from green to gray were observed three weeks prior to eruption onset. In response to increasing seismicity and changes in the crater lake, AVO issued an alert on June 8 and observatory scientists briefed local officials on June 17 about potential volcanic activity."
From Eichelberger and others (2005): "Seismic behavior changed ominously on June 24 when a tremor episode lasted 154 minutes, followed 12 hours later by a similar episode that lasted 142 minutes. Eight additional tremor bursts occurred within the next 8 hours. The weekly update of 10:30 a.m. Alaska daylight time (ADT) on June 26 reported 'well above normal' seismic activity but still cautioned that an eruption might not be imminent in view of an absence of long-period (LP) earthquakes. At about the same time, aerial observations of the crater revealed that the lake had almost completely drained and that several large rocks had impacted the resulting mud flat. At 12:04 p.m. ADT, tremor that was continuous and stronger than earlier bursts began. AVO formally issued a warning of level of concern color code Yellow at 4:30 p.m. on ADT and went on 24-hour duty. At 3:00 a.m. ADT on June 27, a swarm of VT (volcano-tectonic) earthquakes struck at 0- to 2-km depths beneath Crater Peak; their rate soon increased to about one every 2 minutes. Three LP events accompanied this swarm. Tremor amplitude abruptly doubled at 7:04 a.m. ADT. This increase in amplitude was later interpreted to represent the onset of eruption, although weather clouds prevented visual verification. At 7:16 a.m. ADT, AVO began an emergency calldown announcing level of concern color code Orange. About the same time, telemetry was lost from the seismic station 400 m from the vent and an Alaska Airlines pilot reported that an eruption plume had risen 5,000 m above the cloud cover. AVO announced color code Red at 9:10 a.m. ADT. Tremor amplitude gradually increased, peaking between 9:35 a.m. and 10:25 a.m. ADT and registering on stations more than 100 km away. Pilots estimated the plume at mid-morning as high as 9,000 m and the National Weather Service (NWS) measured a maximum plume height of 14,500 m with C-band radar (Alaska Volcano Observatory, 1993; Rose and others, this volume [USGS Bulletin 2139]). The tephra cloud moved northward and ash began falling on Denali National Park at 10:30 a.m. ADT. Debris flows swept southward down narrow drainages and entered the Chakachatna River in three places. Most debris followed the course of the 1953 lahar. At about 11:30 a.m. ADT, seismicity decreased abruptly and the eruption was over. Weather and steam obscured Crater Peak and the eruption plume track from aerial observation on the afternoon of June 27, but paths of the debris flows were visible on the lower flanks of the volcano (Meyer and Trabant, this volume [USGS Bulletin 2139]).
"At 9:00 a.m. ADT on June 28, the level of concern was downgraded to Yellow. Aerial observation revealed a black northward-broadening swath of tephra on snow fields and glaciers. Ash thickness was about 1 to 2 mm at Denali National Park and Manley Hot Springs, 260 and 420 km north of Crater Peak (Neal and others, this volume [USGS Bulletin 2139]). This region is sparsely populated and there were no other reports of tephra there. The ash cloud continued northward to the Beaufort Sea, then it turned southeast into Canada and the coterminous United States, where it became indistinguishable from weather clouds about July 2.
"The level of concern color code was downgraded to Green on July 8. This was done partly on the basis of greatly reduced seismicity and SO2 emission, but also on the basis of analogy to the single-eruption pattern of 1953. The downgrading to color code Green proved to be premature." The next eruption was on August 18, 1992.
Eichelberger and others (1995) state that the June 27, 1992 eruption produced 44 million cubic meters of tephra, with a Dense Rock Equivalent (DRE) of 12 million cubic meters.

For 220 pages of information on the three 1992 eruptions of Crater Peak, please see the USGS Bulletin 2139, available online at: www.avo.alaska.edu/pdfs/B2139.… ; this file is 9 MB.
From Eichelberger and others (1995): "Following the June [June 27, 1992] eruption, seismicity remained low through the first half of August. Only one shallow and two deep earthquakes were recorded between August 12 and 17. Because the closest operational seismic station at that time was 5 km from the vent, several attempts were made to reestablish a seismic station on the crater rim. These were unsuccessful because of poor weather conditions. At 3:37 p.m. ADT on August 18, a 16-minute episode of weak tremor and several LP [long-period] events began, but these rather obscure events were not identified until post-eruption analysis of the data. At 3:48 p.m. ADT, a pilot reported an ash-rich plume. With confirmation of this plume at 4:25 p.m., AVO began a calldown announcing level of concern color code Yellow. The main eruption began at 4:42 p.m. ADT, when strong tremor was recorded by all Mount Spurr seismic stations. AVO began a calldown announcing color code Orange at 4:47 p.m. ADT, but repeated the calldown process 11 minutes later to raise the color code to Red. By 4:58 p.m. ADT, a subplinian column had risen through low clouds to a height of 11,000 m, and it ultimately reached nearly 14,000 m. From an aircraft only 2.5 km away, AVO staff observed and videotaped a dark roiling cloud that was periodically surrounded by lenticular shock waves. Large bombs were thrown 800 m above the vent. Small-volume pyroclastic flows of breadcrusted blocks descended the east and southeast flanks of Crater Peak; these flows formed coarse, clast-supported lobate deposits with steep-fronted margins. Other flows mixed with snow and ice high on the cone and became lahars. A late fusillade of mostly lithic ballistic projectiles, some as large as 1 m, were hurled as far as 10 km southeastward (Waitt and others, this volume [USGS Bulletin 2139]). More than 170 lightning strikes were detected by the AVO lightning detection system (LDS) during the second half of the eruption (Paskievitch and others, this volume [USGS Bulletin 2139]). The eruption ended at 8:10 p.m. ADT.
"Upper level winds moved the eruption plume east-southeast directly over Anchorage, where it deposited as much as 3 mm of sand-sized ash (Neal and others, this volume [USGS Bulletin 2139]). A satellite image 44 minutes after the onset of the eruption shows the plume extending 80 km east from the volcano over an area of 20,000 square km. Three hours after onset of eruption, the leading edge of the plume was 300 km southeast of Mount Spurr, and its area had grown to 21,000 square km.
"Ashfall forced the closing of Anchorage International Airport for 20 hours (N.W. Gibson, Anchorage International Airport, written commun., 1993). Air quality alerts were issued in Anchorage during the fallout period and also on the following day, as vehicle traffic stirred up ash again (R.B. Stewart, Office of Emergency Management, Municipality of Anchorage, written commun., 1993). Reworked windblown ash continued to reduce air quality until the first snow of autumn, and then it reappeared during the summer of 1993."
Eichelberger and others (1995) state that this eruption produced 52 million cubic m of tephra (14 million cubic m Dense Rock Equivalent).

For 220 pages of information on the three 1992 eruptions of Crater Peak, please see the USGS Bulletin 2139, available online at: www.avo.alaska.edu/pdfs/B2139.… ; this file is 9 MB.
From Eichelberger and others (1995): "Following the August eruption, deep seismicity gradually increased, and by mid-September it had returned to levels comparable to mid-June. AVO teams visiting the crater on September 7 and 16 noted nothing unusual. At about 7:30 p.m. ADT on September 16, however, discrete seismic events and weak tremor were detected by the newly reinstalled crater rim station. Tremor amplitude increased at 10:25 p.m. ADT, and at 10:33 p.m. ADT, AVO declared concern color code Red and began the emergency calldown. An eruption began at 10:36 p.m. ADT that lasted 11 minutes. Incandescence was recorded on the video camera at AVO-Anchorage and on the telemetered slow-scan television camera at Kasilof, 120 km southeast of Crater Peak just south of Kenai on the Kenai Peninsula. Weak tremor through the next hour foreshadowed the main phase of the eruption, which began at 12:03 a.m. ADT on September 17. Intermittent bright incandescence could be seen from Anchorage.
"The September 17 eruption lasted 3.6 hours. Pyroclastic flows swept down the south-southeast and southeast flanks of Crater Peak and mixed with snow and ice to become lahars. These flows were similar in appearance to pyroclastic flows, but they were cool and water saturated hours after emplacement. Tephra fallout on the Kidazgeni Glacier generated a debris flow that temporarily dammed the Chakachatna River. Once again, a narrow ballistic field extended at least 10 km from the vent along the south margin of the tephra plume. The eruption closed with a strong swarm of about 50 VT [volcano-tectonic] shocks between 5 and 10 km in depth, which may reflect readjustment of the conduit after magma withdrawal.
"The plume moved eastward, dusted the north edge of Anchorage and deposited about 1.5 mm of ash in Palmer, Wasilla, and nearby communities in the Matanuska-Susitna Valley north of Anchorage. Very light ashfall was reported in the town of Glenallen, 350 km east of Crater Peak."
Eichelberger and others (1995) state that this eruption produced 56 million cubic m of tephra (15 million m Dense Rock Equivalent).

For a complete report of the unrest at Spurr between 2004 and 2006, please see Coombs and others (2006), available online at pubs.usgs.gov/pp/pp1732/pp1732….
From Neal and others (2005): "In early July 2004, AVO seismologists noted an increase in volcano-tectonic and long-period earthquake activity beneath the summit of Mount Spurr Volcano (Power, 2004; Power and others, 2004). About the same time, AVO was contacted by a long-time Alaskan pilot who flew near the volcano on July 11 and saw a small steam plume from the approximate 5,500 foot level of the east side of Crater Peak. She also reported an unusual sulfur dioxide odor. Based on this pilot report and the increase in seismicity, AVO launched a fixed-wing observation flight on July 15. Clouds prevented a view of the summit of Spurr, but Crater Peak and the lower south and east flanks of the Spurr summit dome were clear. Crater Peak appeared unchanged from previous views following the 1992 eruption and nothing unusual was noted along any of the glacier margins or termini around Crater Peak. The east flank of the Spurr summit dome, however, was marked by as many as a dozen dark debris flow lobes that emanated primarily from point-sources within the glacial cover [see fig. 5 in original text] (McGimsey and others, 2004).
"Increased daily counts of shallow (5-10 km or 3-6 mi below sea level) earthquake activity combined with observations of debris flows from the summit prompted concern about the possibility of volcanic unrest at Spurr. On Monday July 26, AVO elevated the Level of Concern Color Code to YELLOW. A second AVO overflight on August 2 revealed a circular depression in the Spurr summit ice cap, approximately 50-60 m (165-200 ft) in diameter and 25 m (82 ft) deep [see figs. 6A and B in original text]. The pit contained an ice-encrusted pond with small areas of open water that were distinctly blue-gray in color [see fig. 6C in original text]. This feature became known as the 'ice-cauldron' following usage of the term at ice-covered Icelandic volcanoes.
"From early August though early December, the summit ice-cauldron gradually enlarged as blocks of ice ringing the depression sagged and then collapsed into the pit [see figs. 6A, B in original text]. Careful measurements from images taken on August 10 and October 30 indicate that the pit enlarged from about 65 x 95 m (210 x 310 ft) across to 130 x 130 m (430 ft x 430 ft) across in two months' time (M. Coombs, written commun., 2004). Overflights throughout the late summer and fall documented the changing size of the feature, continuing deformation and collapse of surrounding ice walls, and the variability of open water on the surface of the lake. The lake remained a dark battleship gray color, and circular ice-free zones perhaps 5-10 m (16 x 33 ft) across occurred near bedrock lake shoreline and at several points further from the shore [see fig. 6C in original text]. By early December, the areas of exposed bedrock near the bottom of the cauldron had grown and were occasionally observed steaming. Yellow-tinted snow, ice, and rock outcrops in the vicinity of the lake reflected sulfur deposition near the lake margin.
"AVO staff conducted several airborne Forward Looking Infrared Radiometer (FLIR) measurements using both a hand held and helicopter-mounted camera and video system. FLIR data confirmed the presence of at least two prominent areas of warm bedrock -- with temperatures as high as ~39o C or 102o F -- on the margins of the lake [see fig. 7A in original text] and on the outer flanks of the summit dome. Lake surface temperatures as measured by FLIR ranged from -10o to 0o C (14o to 32o F) for areas of floating ice and snow debris as well as open water [see fig. 7B in original text].
"AVO also gathered an extensive library of satellite imagery of the Spurr edifice and increased satellite analysis frequency using the standard AVO monitoring imagery (Geostationary Operational Environmental Satellites [GOES], Advanced Very High Resolution Radiometer [AVHRR]) and higher resolution imagery (Advanced Spaceborne Thermal Emission and Reflection Radiometer [ASTER], Moderate Resolution Imaging Spectroradiometer [MODIS]). ASTER imagery showed the first signs of a summit thermal anomaly in nighttime thermal infrared data on August 17, 2004; as the summit lake grew in size, the intensity of the ASTER thermal infrared anomaly increased (R. Wessels, oral commun., 2005).
"Five fixed-wing gas measurement flights of the Mount Spurr plume were conducted between early August and the end of October. Emission-rate measurements of SO2, H2S, and CO2 gas were made during each of these flights following protocols developed by the USGS (Gerlach and others, 1997; Gerlach and others, 1999; McGee and others, 2001 -- see original paper for complete references). Preliminary results show that CO2 degassing from the summit of Mount Spurr increased from 600 tonnes/day (t/d) in August to 1,300 t/d in September and finally to 1,400 t/d in October. At Crater Peak, CO2 emission rates were 160 t/d, 1,000 t/d and 120 t/d for the same measurement periods. Very small amounts of H2S (=3 t/d) were consistently measured on all of the flights at both degassing locations while no SO2 was detected at all.
"Crater Peak has consistently degassed a small amount of CO2 since 1994 that, except for an anomalously higher value in 1997, is typically <200 t/d (Doukas, 1995; M. Doukas, pers. commun., 2004). Carbon dioxide degassing from the summit of Mount Spurr had previously not been detected, although airborne measurements directed specifically at the summit have been rare. The absence of SO2 throughout this period is likely caused by the extremely wet environment at this glacier-clad volcano, where abundant groundwater dissolves SO2 (Doukas and Gerlach, 1995). This scrubbing process would also be greatly enhanced by the presence of the lake at the summit, and the distinctive battleship gray color of this lake might be partly due to dissolved sulfur compounds. The low but positive values for H2S can reflect the release of H2S from a boiling hydrothermal system (Symonds and others, 2001 -- see original text for full citation). This is consistent with historical reports of pressurized fumaroles described by climbers in the summit region and the presence of diffuse boiling-point fumaroles on outcrops of bedrock on the east side of the Mount Spurr summit dome (Turner and Wescott, 1986; C.J. Nye written commun., 2004).
"Seismicity at Mount Spurr remained consistently above the pre-July 2004 background level for the remainder of the year, although daily rates of seismicity varied considerably from several to several tens of volcano-tectonic (VT) events per day. The largest tally of identifiable earthquakes in one day was 80 on October 26. Particularly energetic swarms of VT earthquakes located within 20 km (12 mi) of Mount Spurr occurred on October 26 (6.6 earthquakes per hour), November 4 (5.8 earthquakes per hour), August 14 (2.6 earthquakes per hour), and August 21 (1.8 earthquakes per hour). Throughout the unrest in 2004, VT seismicity was concentrated within 5 km (3 mi) of the Mount Spurr summit, in stark contrast to the pre-1992 seismicity (Power, 2004; Power and others, 2004). Located long-period (LP) events occurred at an average depth of approximately 7 km (4 mi) and at variable rates, peaking in November. Deep earthquakes (> 20 km or 12 mi) were located beneath and south of Crater Peak in the same area as the deep seismicity associated with the end of the 1992 eruption of Crater Peak.
"Although no eruptive activity ensued in 2004, AVO did experience an eruption response drill. A pilot report of possible ash from Mount Spurr on August 12, followed by a public ash fall advisory issued by the NWS, prompted a daylong flurry of calls, inquiries, and media attention. AVO issued a special Information Release stating that no eruption had occurred. This event— certainly not the first or last of its kind in AVO history—underscored the level of public concern regarding the situation at Mount Spurr and likely reflected a fresh memory of ash fall in 1992. The drill also facilitated review and improvement of communication protocols between AVO and its partner in ash warnings, the National Weather Service.
"How unusual is this drastic change in the summit morphology at Mount Spurr? To our knowledge, this is the first documented episode of significant geothermal heating and generation of a substantial lake at the summit, as well as the first known occurrence of watery debris flows from the summit. Historical reports and aerial photographs from the 1950s, 60's and 70's, however, document significant variability in the snow and ice cover at the Mount Spurr summit. During periods of lower-snow levels, a crater-like structure becomes visible. This feature was described in March and others (1997) as a ~200 to 300 m (650-1,000 ft) diameter feature open to the east-northeast. In this same 1957 aerial photograph, a steep-walled, snow and ice pit, 20-30 m (65-100 ft) wide, is located in the ice cap near the base of the north summit crater wall. No open water can be seen in the bottom of the pit, however, several dark patches occur and could possibly represent warm bedrock.
"AVO interprets this 2004 period of elevated seismicity and heat flux, summit melting, debris flow generation, and magmatic gas emission from both Spurr and Crater Peak to be the result of new injection of magma to a shallow level beneath the Spurr edifice (Power, 2004; Power and others, 2004). Magmatic gas flux from both Crater Peak and Mount Spurr suggests an open connection to the surface from the zone of intrusion or magma storage along two conduits. An alternative interpretation invokes release of volatiles from the still-cooling intrusions from the 1992 eruption series (Power and others, 1998; 2002).
"Mount Spurr remained at Level of Concern Color Code YELLOW through the end of the year. Nearly all information release statements, weekly summaries, and daily status reports emphasized that despite the departure from background activity at Spurr, there were no signs of imminent eruptive activity. As part of this response, AVO mounted a number of observation flights, gas measurement and FLIR imaging flights, increased the frequency of satellite analysis, and installed six new seismometers and 3 permanent, continuous GPS receivers to improve seismic monitoring and track deformation of the volcanic edifice. On October 8, AVO announced the public availability of Internet web camera images of Mount Spurr on the AVO web site (www.avo.alaska.edu).
"AVO issued three Information Releases on Mount Spurr activity in 2004 in addition to summarizing the Spurr situation in standard weekly updates on all Alaskan volcanoes. A number of articles appeared in the Anchorage Daily News (Anchorage Daily News 2004). In response to the YELLOW Level of Concern Color Code declaration, NWS issued a one-time Volcanic Ash Advisory (VAAS) and the FAA issued a Notice to Airmen (NOTAM) on July 26. The NOTAM was cancelled on November 9 (NOTAM 4/2284; B. Brown, FAA, pers. commun., 2005)."
From McGimsey and others (2007): "During 2005, elevated seismicity continued beneath Mt. Spurr, and the summit ice-collapse pit enlarged - becoming a large cauldron - as heat was supplied to the summit area. The lake changed in size, and the amount of ice debris on the lake varied. Lake level declined in May, seemingly associated with the generation of a small debris flow on the upper southeast flank. With the decline in water level, subaqueous fumaroles emerged and the area of hot, steaming wall rock increased. Temperatures of the warm zones measured with Forward-Looking Infrared Radiometer (FLIR) increased somewhat over the year. Emissions of CO2 and SO2 decreased. The Level of Concern Color Code for Mount Spurr remained at Yellow for all of 2005 (see table 6 in original text)."
Neal and others (2009) report that the"Level of Concern Color Code for Mount Spurr at the beginning of 2006 was YELLOW due to continued above-background seismicity, magmatic degassing, and the presence of an open, warm lake within a 300-m-diameter (980 ft) rock- and ice-walled cauldron atop the summit cone. Following months of no significant change in activity, AVO downgraded the Level of Concern from YELLOW to GREEN on February 21 [2006]. The information release cited a steady decrease in shallow seismicity between April and June 2005, after which earthquake activity remained slightly elevated above background levels through the remainder of 2005 and into 2006. By May 2006, seismicity at Mount Spurr ahd returned to background levels and remained there with few exceptions through the end of 2006. Intermittent observations permitted sporadic documentation of ongoing changes in the summit area as the geothermal activity continued to disrupt the ice field around the summit cone [see table 5 in original text]."

From Cameron and others, 2017: "A swarm of low-frequency earthquakes began in early June, following a M3.8 earthquake 13 km (8 mi) west of Mount Spurr. A total of 300 earthquakes were located in this swarm, which ended in mid-October. A swarm in the same area occurred in late 2012. The cause of the swarm remains undetermined. In 2004, seismicity, surface heat flux, and gas emissions suggested a magmatic intrusion (Power, 2004; Neal and others, 2005; Coombs and others, 2006).
"At 20:20 UTC (11:20 a.m. AKDT) on September 10, the Spurr seismograph network recorded a signal interpreted by AVO seismologists as a glacial outburst flood. The flow appears as a single event lasting about 20 minutes. Similar events, but of longer duration, have been recorded at Mount Spurr on several occasions, most recently in 2012 (Herrick and others, 2014). AVO was unable to visually confirm the inferred outburst event."

From Dixon and others, 2017: "No volcanic activity was reported at Mount Spurr in 2015; the only activity noted was an earthquake swarm 12 km (6.5 mi) north of the summit. First noted in the AVO internal logs in mid-October, earthquakes in this area occurred sporadically for the previous 5 months with the rate increasing from 1-2 per week in July to several per day in October. The swarm peaked in November, with 47 earthquakes during the month. The rate of located earthquakes decreased by one-half in December and the swarm continued into 2016 at a much-reduced level of activity. The earthquakes in this cluster were shallow with 90 percent occurring between 3 and 5 km (1.6 to 2.7 mi) below sea level. The Aviation Color Code and Volcano Alert Level remained at GREEN/NORMAL through the year at Spurr."
In 2016, there were four distinct clusters of seismicity at Spurr: "the typical Mount Spurr summit earthquakes that occurred throughout the year, earthquakes near Pothole Glacier (west of Mount Spurr) in late summer, an ongoing swarm of low-frequency earthquakes 10–15 km (6–9 mi) north of the summit (north Spurr earthquakes in fig. 5), and a cluster of earthquakes located 5 km (about 3 mi) east of the summit in May (east Spurr earthquakes in fig. 5). In addition to these areas of high activity, there are three, less-distinct zones of activity. These zones are 10 km (6.2 mi) south, 5 km (3 mi) west, and 20–30 km (12–18.5 mi) northeast of Mount Spurr and are in the area of the 1996 Strandline earthquake (Kilgore and others, 2011). The Aviation Color Code and Volcano Alert Level remained at GREEN and NORMAL, respectively, throughout the year for Spurr." (Cameron and others, 2020).
Dixon and others (2020) report the seismicity at Spurr continued into 2017, including the unusual earthquake sequence that began in 2015. "This cluster of low-frequency earthquakes (north Spurr earthquakes), was located 12 kilometers (km; 7 mi) north of Mount Spurr and continued to show activity throughout 2017. Although the character of the earthquakes is similar to glacial earthquakes, AVO has not determined a definite cause for this cluster of seismicity. The other four clusters (Mount Spurr summit, south Spurr, west Spurr, and the Strandline Lake earthquakes) are typical seismicity seen year-round in the vicinity of Mount Spurr (fig 2). An April 20 gas observation flight noted that the small plume emanating from the fumaroles in Spurr’s summit crater contained detectable quantities of SO2, H2S, and HCl. The Aviation Color Code and Volcano Alert Level remained at GREEN and NORMAL throughout the year at Mount Spurr."

From Orr and others, 2023: "On July 15, 2019, at 16:32 UTC (08:32 AKDT), a large ice and rock avalanche took place on the southeast flank of Mount Spurr. A retrospective analysis of satellite imagery indicated the starting zone of the avalanche was less than 1 km from the summit of the volcano. Clear satellite images of the flow deposit showed that it widened before splitting into two lobes that flowed around an elevated lateral moraine dividing the west and east branches of K’idazq’eni Glacier (March and others, 1997; Molnia, 2008). One lobe flowed down the west branch between the moraine and the Crater Peak cone, while the other traveled slightly farther down the east branch of the glacier. Satellite imagery indicated the ice and rock avalanche spanned an area of approximately 2.3×10^6 square meters (m2) [25,000,000 square feet]. Assuming an average deposit thickness of 0.5 m [1.6 feet] yields a volume of about 1.2×10^6 cubic meters (m3) [42,000,000 cubic feet].
"The ice and rock avalanche generated energetic seismic and acoustic signals, recorded both locally and regionally. High-frequency signals were detected on the local seismic network and long-period (LP) seismic signals were recorded more than 700 km [435 mi] away. Several local seismic stations also recorded approximately 10 minutes of precursory seismicity. Pre-avalanche seismicity has been previously documented at Iliamna Volcano (Caplan-Auerbach and Huggel, 2007). In addition to the recordings of seismic signals, an infrasound array in Dillingham, Alaska, detected acoustic waves from the event.
"During an overflight on August 27, AVO staff noted the terrain of the source area consisted of exposed 'slope-parallel lava, with rivulets of meltwater running on its surface.' They found no evidence of increased non-meteorological heating at the summit area (a phenomenon which can trigger ice and rock avalanches) and observed nothing unusual on the other flanks of the summit cone (M. Coombs, USGS, written commun., 2019). The July 15 avalanche took place in an area known for debris flows, as documented by Coombs and others (2006), but previous flows were smaller and more water-rich than the July 15 event. Mount Spurr remained at an Aviation Color Code and Volcano Alert Level of GREEN and NORMAL throughout 2019."

On October 16, 2024, AVO raised the color code and alert level to YELLOW/ADVISORY, stating: "AVO has observed a gradual increase in volcanic unrest over a period of several months at Mount Spurr, located about 120 km (75 miles) west of Anchorage (avo.alaska.edu/image/view/1961…). GNSS receivers have detected sustained upward and outward ground deformation since March 2024. An increase in seismic activity has also been noted since April (avo.alaska.edu/image/view/1961…). Other indications of elevated activity include the development of a small lake in the summit crater in early summer of 2024.
"The largest magnitude earthquake detected in this current period of unrest is a M2.3 earthquake on October 6th. This increase in activity was described in detail in an Information Statement (avo.alaska.edu/news/hans/DOI-U…) that AVO released on October 9th. Analysis of seismic data indicates a subtle increase in the rate and size of earthquakes over the past few weeks. Because this is a notable departure from the normal background seismicity of the volcano, AVO is raising the Aviation Color Code to YELLOW and the Volcano Alert Level to ADVISORY. However, there are no indications that an eruption is imminent. Often this type of seismicity and ground deformation will decline without producing an eruption.
"AVO continues to closely monitor activity at Mount Spurr for signals that would indicate that the volcano is moving closer to an eruption. Based on previous eruptions, changes from current activity in the earthquakes, ground deformation, summit lake, and fumaroles would be expected if magma began to move closer to the surface. Therefore, it is very likely that if an eruption were to occur it would be preceded by additional signals that would allow advance warning. "
Over the following two weeks, there were more than 180 small earthquakes at Mount Spurr. Over the week of November 1st, there were also a few episodes of possible volcanic tremor, which might indicate deep fluid movement. No unusual activity or surface changes were observed in satellite data or webcam views. AVO staff visited on October 24th to conduct pre-winter maintenance on Spurr’s monitoring network and noted that the fumaroles (steam/gas vents) in Spurr summit’s crater were steaming.
Over the following weeks, earthquakes continued at varying rates, as is typical during periods of unrest. Steam was occasionally visible rising from Spurr’s summit during clear weather. On December 10, there was a M2.8 earthquake beneath the summit, and a few more episodes of tremor were recorded that week.
On Wednesday, December 18, AVO staff conducted a gas flight at Mount Spurr. Measurements of H2O, SO2, H2S, and CO2 were collected. Results were similar to the previous gas flight conducted on June 23, 2024. Personnel also took images and video during the flight that allowed accurate measurements of the crater lake that formed this year, showing that it has grown considerably since June despite the transition into winter. No activity was observed at Crater Peak.
As the new year turned, there were some notable periods of increased earthquake activity within the context of the larger unrest episode. The week of January 3, 2025, over 260 earthquakes were located, the largest being an M2.9 on January 2. Meanwhile, GPS data continued to show slow, steady inflation of the ground surface. Satellite radar data the week of January 10 showed that the crevasses in the summit crater were widening, demonstrating continued heat input to the area.
During late January, the monitoring network at Mount Spurr experienced some issues transmitting data back to AVO due to poor weather, not unusual for this time of year.
On January 31, AVO reported that over the past few weeks more of the ongoing earthquakes had clustered under Crater Peak, the vent that produced the 1953 and 1992 eruptions.
On February 6, AVO released an Information Statement detailing the activity since the color code change in October. The statement noted that over 2700 earthquakes had been detected to date during the period of unrest, which as of this date was ten months long. Movement of the ground surface near the area of Spurr was now about 2.4 inches total, as measured at the closest monitoring station to the mountain. Based on the earthquakes, deformation, growth of the lake in the Spurr summit crater, and low levels of volcanic gases measured, AVO rated the odds of no eruption and a future eruption at the Crater Peak vent as equally likely, with an eruption from Spurr summit less likely. However, additional signs of unrest would be expected in the lead up to an eruption.
On February 7, AVO staff visited the Spurr monitoring network to clear snow and ice from the instruments. They also collected additional volcanic gas measurements which showed no significant changes since the previous gas flight in December.
The remaining weeks of February followed the same general trends, with earthquake rates varying quite a bit while other signs of unrest-deformation and occasional steaming from the summit-remaining consistent. Fewer earthquakes were located close to Crater Peak.
On March 7 and March 11, AVO conducted flights to once again measure any volcanic gases emitted by Spurr. These flights, while consistent with one another, yielded considerably altered results from the previous flights. Elevated levels of sulfur dioxide and carbon dioxide were measured at Spurr summit, while very high levels of carbon dioxide were measured at Crater Peak. Staff also observed newly reactivated fumaroles within Crater Peak. These new changes led AVO to release an Information Statement on March 12 stating that likelihood of an eruption had increased and that AVO considered an eruption similar to 1953 and 1992 at Crater Peak to be the most likely outcome of the current unrest episode.
On March 17, AVO staff visited the Spurr monitoring network to conduct maintenance and clear the snow and ice from the CKT webcam.