Golovnin (translated in 1979 by Ella Wiswell, from the 1822 and 1819 versions) contains this information about Atka: "* * * a very high volcano situated at that end of the island [northeastern]. Occasionally it causes dangerous earthquakes, and in 1812, when Vasiliev spent the winter here, it erupted and caused such strong earthquakes that the inhabitants were afraid of being buried in their yurtas (earthen huts)."
Grewingk (1850, translated 2003 by Fritz Jaensch) also contains this report from Vasiliev, but attributes the eruption to Sarichef instead of Kliuchef or Korovin. Dall (1870) reports that the earthquakes were "most violent and terrified the inhabitants."
Bank and others (1950) reports the following, which may pertain to this eruption: "During the early eighteen hundreds Sarychef and Korovin volcanos [sic] on Atka commenced throwing off increasing amounts of ash, so that the priest decided that Korovinsky must be abandoned. The seat of the Russian Church was transferred to Unalaska as was the trading center, and the villagers were moved to the site of the present village on Nazan Bay. An interesting story concerning this forced move was told to me by a young Aleut hunchback, Johnny Prokopeuff, whose father had related it to him before he died. I quote the story as we recorded it: 'Long time ago before peoples lived in this village Akta peoples live over at Old Harbor. Was a big village with lots of barabaras and big Russian buildings. There was man, Russian priest, name of Father Salamatoff who was kind to people. He brought peoples from all around, Chugul, Kagalaska villages, Adak, to live at Old Harbor. Another priest after Father Salamatoff died, I don't remember his name, told peoples they had to move village, said that mountain was going to come down and cover Old Harbor. All the time at night the sky was red, and lost of little rocks (ash) in the air so that peoples sick. Everyone moved over to this place and build village on Nazan Bay side. Priest, he say that peoples safe here. Mountain not come down on Old Harbor, but all the time at night lots of noise and red fire in the sky. Big rocks roll down mountain. Lots better on Nazan Bay, more fish.'" It is difficult to know which eruption this account is describing - Father Salamatoff died in 1864, so he was not already deceased with a different priest serving on Akta in 1812. Korovin is reported as smoking and with fire in 1844, and this account may pertain to that eruption instead.
Wood and others (1990), Simkin and Siebert (1994), and Miller and others (1998) attribute this eruption to Kluichef rather than Sarichef, due to a younger looking vent on Mt. Kluichef, but Golovnin's report of the volcano being on the "northeastern side" of the island argues that this event could be from Korovin instead.

Grewingk (1850, translated 2003 by Fritz Jaensch) writes that Ingenstrom reported Korovin smoking in 1829 and 1830. Petroff (1884) reports Korovin as "in eruption and smoking" during 1829 and 1830. However, because Petroff (1884) is an incomplete translation of Grewingk (1850) the smoke-only reports are probably more accurate.
Additionally, the following account written by Bank and others (1950) may pertain to this eruption: "During the early eighteen hundreds Sarychef and Korovin volcanos [sic] on Atka commenced throwing off increasing amounts of ash, so that the priest decided that Korovinsky must be abandoned. The seat of the Russian Church was transferred to Unalaska as was the trading center, and the villagers were moved to the site of the present village on Nazan Bay. An interesting story concerning this forced move was told to me by a young Aleut hunchback, Johnny Prokopeuff, whose father had related it to him before he died. I quote the story as we recorded it: 'Long time ago before peoples lived in this village Akta peoples live over at Old Harbor. Was a big village with lots of barabaras and big Russian buildings. There was man, Russian priest, name of Father Salamatoff who was kind to people. He brought peoples from all around, Chugul, Kagalaska villages, Adak, to live at Old Harbor. Another priest after Father Salamatoff died, I don't remember his name, told peoples they had to move village, said that mountain was going to come down and cover Old Harbor. All the time at night the sky was red, and lost of little rocks (ash) in the air so that peoples sick. Everyone moved over to this place and build village on Nazan Bay side. Priest, he say that peoples safe here. Mountain not come down on Old Harbor, but all the time at night lots of noise and red fire in the sky. Big rocks roll down mountain. Lots better on Nazan Bay, more fish.'" It is difficult to know which eruption this account is describing - Father Salamatoff died in 1864, and this account may somehow refer to the 1812 eruption of Kliuchef, the 1829-1830 eruption of Korovin, or another eruption entirely.

Grewingk (1850, translated 2003 by Fritz Jaensch) writes that Voznesenskii reported weak smoke from Korovin's crater in 1844.

Jaggar (1927) reported "fresh volcanic cinder" on the snowfields near Mt. Kliuchef during 1907, and a boiling spring. Whether the "fresh volcanic cinder" came from Korovin or Kliuchef is uncertain.

Eakle (1908) reported "dense clouds of vapor" from the summit of Korovin. Jaggar (1927) reported "fresh volcanic cinder" on the snowfields near Mt. Kluichef during the same year, and a boiling spring. Hot springs and fumaroles are well-known in the vicinity of Korovin and Kliuchef, and this report may be nothing more than the usual fumarolic and hydrothermal activity.

Jones (1952) reports steaming from Korovin in November 1951. This steam may be from normal fumarolic and hydrothermal activity at Korovin, and not part of a volcanic eruption.

The following observations of Korovin are compiled from individual observation sheets filled out by members of the public and U.S. military.
19 June 1953: "Steam, slightly darker than low lying fog was spilling over northwestern lip - wind prevented formation of column. Snow on eastern face appeared to have been darkened by cinders of soot to almost black. It was not bare rock showing. It was a darkened snow coverage." -- observed by USCG ship Pioneer
25 June 1953: "All snow covering mountain darkened by thin coating ash in sharp contrast with brilliantly shining snow on hills to south; steam seen emitted from fumarole on N crater rim to about 100 feet; no steam being emitted from crater proper (or at least that portion visible from plane). -- R R McDonald
13 February 1954: "White smoke rising to height of approximately 50 feet. No lava flow visible." -- J.:. Thurman, LCDR, USNR
18 March 1954: "Steaming good." -- Report of Reeve's Aleutian Airways pilot
25 March 1954: "Column of steam rising 100 to 150 feet above peak, no dispersal evident. Closer view showed no signs of activity in form of smoke or fire." -- John Mays, Lt, USNR
5 April 1954: "Steam and smoke rising one thousand feet from floor of crater on NE corner. No lava or fire visible." -- E.L Burdick
14 May 1954: "Steam with strong sulfur odors rising from northern edge inside the crater, about 300' down from the rim. Rises about 1000'." -- R.L. Kopps
15 June 1954: "Some steam from center of volcano - 100-200 ft. high before dissipating." -- D.C. Curran Lt.
17 June 1954: "No apparent activity." -- C.R. Pendell LTJG
15 July 1954: "Faint vapor fresh snow (on cone dirtied by this showering of ash)" -- Austin E. Jones
14 September 1954: "No smoke or other visible signs of activity." -- E.D. Jezek

From Reeder (1988): "In the evening (just at dusk) of 25 (+/- 2) August 1973, eruptive activity was seen by numerous residents of Atka village while they were on a U.S. Navy harbor tug that was transporting them from Atka village to Adak. The harbor tug maintained a distance of about 9 km from the northern shore of Atka Island as it passed Korovin volcano. An incandescent 10+ m wide active lava-flow channel was observed that extended from a fissure vent the northern summit of Korovin volcano to about half of the way down the northern flank of the volcano. The incandescent lava-flow channel then ended or went out of view underneath the surface. Some minor rock avalanching down the northern side of the volcano to the Bering Sea was remembered by some of the passengers. No steam emission from the shoreline and no ash emission from the summit of the volcano were noted."

From Miller and others (1998): "'Smoke' was observed in 1976 at Korovin from Atka village, located 20 km to the south (Arctic Environmental Information and Data Center, 1978).

From Miller and others (1998): "Steam emission was observed in early May, 1986, and on May 23rd a 600 m steam plume containing some ash reportedly occurred soon after a 7.7 magnitude earthquake struck about 100 km to the southwest (Smithsonian Institution, 1986)."
From Smithsonian Institution (1986): "On 6 May], James Dickson noted a 500-m vertical steam plume over the SE part of the summit [of Korovin]. On 23 May at about 1730, Aleutian Air pilot Thomas Madsen noted a 600-m steam plume containing traces of ash rising above the rim of a 240-m-deep crater in the SE part of the summit area. A shallow magnitude 7.7 earthquake centered roughly 100 km [SSW] of Korovin at [51.52N, 174.78W] occurred 7 May [at 2247 GMT].
John Reeder and Kirk Swanson climbed [Korovin] in July 1983, observing only minor steaming from deep within the crater, rising to only 60 m above its floor."
Reeder (1989) adds the following information: "Pilot Harold Wilson of Peninsula Airways Inc. on 17 December 1986 observed an impressive above average steam plume from Korovin volcano that contained no detectable ash. The steam plume completely filled the crater of the volcano and it rose to a 2,250 m altitude (above 800 m above the crater rim) as measured by his Piper T1040 Navaho altimeter."

From Smithsonian Institution (1987): "On 18 March at 1954 a NOAA 10 satellite image showed three distinct plumes, each 95 km long, drifting ENE. The estimated vent locations were: 52.38N, 174.15W (Korovin's summit); 52.31N, 174.24W; and 52.29N, 174.21W (5.5 km WSW and 6.5 km SW of Mt. Kliuchef, a cone on Korovin's S flank). More accurate locations will be determined by USGS Anchorage. Just before midnight on the same day US Navy pilot Jeffrey Sullivan observed a southward-drifting ash plume rising to at least 3,000 m altitude, lit by an orange 'flame' from Korovin. Smaller orange flickering 'flames' from two other vents at lower elevation were visible. Two of the vents were ~2 km apart and the third vent was ~10 km NE of the other two vents.
Earlier in the day (at 1300) Julie Dirks and other Atka residents noticed sulfur smells (~18 km from the volcano). Although the weather was clear Dirks did not notice any 'unusual' eruptive activity. On 19 March a SIGMET notice was issued to warn pilots of volcanic ash 185 km on either side of a line from 52N, 175W to 54N, 172W. The warning remained in effect until 0930. Pilots reported that the ash cloud reached 3,600 m."
Additional information from Reeder (1990, Kliuchef): "Lieutenant Jeffrey Sullivan flying his U.S. Navy P3 Electra from Dutch Harbor to Adak at a 8,200 m altitude, noted about 240 km E of Adak just before midnight on 18 March a large orange flame with smoke to the south that was determined from the satellite imagery to be from Korovin volcano. Then, about 5 minutes later, Jeffrey could see two more smaller orange flickering flames that were farther to the south and were at a lower elevation than the first flame. These lower and smaller two flames would have been the two Mount Kliuchef SW flank vents."

From Smithsonian Institution (1993): "On 10 December AVO reported the following. 'On 4 December, following a M 5.1 earthquake at 1836 beneath the . . . island of Atka, residents of Atka village reported "rumbling" from the cluster of volcanoes that forms the N part of the island. At the same time, residents observed increased steaming from a fumarolic area on the flank of Kliuchef volcano and noted a distinct sulphur smell. A check of satellite imagery did not confirm any change in the surface state of the volcanoes. Late this week, the weather had deteriorated and no visual observations of the volcanoes were possible. . . .'"

From McGimsey and Neal, 1996: "Observers in the village of Atka, located 15 km (9 mi) to the south, reported a very strong sulfur smell on Monday, May 1 [1995], and a substantial, but lesser, sulfur smell on Thursday, May 4 coincident with the sighting of a small plume-like cloud over Kliuchef volcano. Inclement weather on May 1 prevented direct observation of the volcano. The plumes did not appear on satellite images AVO analyzed that week. The smell of sulfur has been reported previously in Atka village, however, the odors in May were regarded as particularly strong. Satellite images on May 3 showed a hot spot on Korovin, possibly corresponding to one of the fumarolic fields.
From Smithsonian Institution (1995): "Observers in the village of Atka on Atka Island in the central Aleutians reported a very strong sulfur smell on 1 May, and to a lesser extent on 4 May when they observed a small plume-like cloud over Kliuchef. Fumarolic areas exist on or near both Korovin and Kliuchef volcanoes, N of the village. Korovin was active most recently in 1987, and Kliuchef has had Holocene activity. Satellite images did not reveal any plume-like clouds associated with the island, however, a "hot-spot" possibly of fumarolic areas, was observed. A similar sulfur smell was reported by residents in December 1993, at about the same time they felt rumbling from a M 5.1 earthquake (Global Volcanism Network Bulletin v. 18, no. 11)."

From Neal and McGimsey (1997): "Following a pilot report of volcanic ash at 37,000 feet east of Adak, NOAA/SAB detected a plume-like cloud on an AVHRR image of the Atka Island area on June 29, 1996. Subsequent analysis and lack of any confirming observations of eruptions by pilots led AVO to the conclusion that the cloud was meterologic in nature. The cloud had suggested possible activity at Korovin, the most historically active stratocone on Atka Island in the central Aleutians (Marsh, 1991).
From Smithsonian Institution (1996): "On 29 June, Japan Airlines reported volcanic ash erupting from Atka. In addition, GEOS-9 satellite images showed a possible small ash cloud in the immediate vicinity of Atka. In early May 1995 residents of Atka village observed a small plume-like cloud over Kliuchef and reported a strong sulfur smell (Bulletin v. 20, no. 5)."
Although AVO discredits this eruption account, the Smithsonian Global Volcanism Program assigns it a VEI of 2, and attributes it to Kliuchef.

From McGimsey and others (2003): "On the morning of June 30, 1998, AVO received a call from the Village Public Safety Officer (VPSO) in the village of Atka with a report of a dark ash cloud rising to 30,000 feet. The VPSO had observed two separate clouds, the first at approximately 07:30 local (Hawaii-Aleutian Time Zone is one hour behind ADT) and the second at approximately 08:30 local. The second cloud was the larger of the two reaching an estimated 30,000 ft and tinted orange 'as if illuminated from within', according to another observer in Atka. At 11:15 local, AVO received a pilot report from a USCG C-130 aircraft in the vicinity who noted an apparent volcanic cloud reaching about 16,000 feet ASL. At 17:20 local, AVO received a United Airlines pilot report of a cloud to 30,000 feet near the volcano. Coincident satellite imagery did not show an obvious volcanic cloud, however a plume-like meteorologic cloud was evident. The Atka VPSO stated further that both events produced dustings of ash in Atka, the first coarser grained than the second. AVO also learned that an individual had observed a dark ash plume over Korovin two days earlier on June 28. In addition, a commercial pilot very familiar with the volcanoes in the Aleutians contacted AVO to report his mid-May observation of the 'southeast slope blackened by ash' during a fly-by on May 10. He had not seen this during the previous week and speculated that it had occurred only a few days prior to May 10 because of weather conditions and wind directions. Thus, the timing of this activity remains poorly constrained; intermittent ash emission may, in fact, have occurred for weeks or prior to June 30.
"AVO conducted a call-down after receiving the initial report from Atka and solicited pilot reports from the FAA. FAA officials issued a Significant Meteorological Information statement (SIGMET), a Temporary Flight Restriction (TFR) around the volcano (20 mi radius from sea level to 25,000 ft) and decided to route aircraft well to the north of Korovin. The Atka Pride Seafood processing plant was closed for the day out of concern for the effects of ash on workers and the quality of fish. Reeve Aleutian Airways had an airplane en route from Dutch Harbor to Adak when the late afternoon pilot report of a cloud to 35,000 feet was received. Based on the report, the Reeve plane returned to Dutch Harbor. The Marine Radio Operator issued an ash advisory to mariners in the vicinity of Atka.
"Over the next several days, poor weather largely precluded any good views of the volcano. One Atka observer reported a 'rusty' cloud estimated to reach 16,000 feet ASL moving southeast from the volcano on the evening of July 2. On July 3, a pilot familiar with the volcano reported profuse steaming from the summit crater, typical of the past few months (cover photo). He noted new ash on the south, southeast, and east flanks. A thin trail of ash extended to the southwest, towards the village of Atka. On July 8, AVO noted minor, weakly ash-bearing clouds over Korovin on Advanced Very High Resolution Radiometer (AVHRR) satellite images. On July 10, Environment Canada contacted AVO to relay a pilot report of a possible ash cloud over the general vicinity of Vancouver Island; a number of SIGMETs and other official notices were released. Several additional pilot reports of possible ash were logged by Canadian aviation authorities who also recorded many aircraft diversions in Canadian airspace. It remains possible that this cloud was related to an undetected Korovin eruption several days prior to the pilot report. A more likely scenario, however, is that smoke from numerous fires in the heavily forested area of western Canada and even Siberia generated a far-traveled haze mistaken for volcanic ash (Little and others, 1999).
"Over the course of this episode of unrest, AVO issued Information Releases on June 30 and July 1, and mentioned Korovin in the Weekly Updates of July 3 and July 10."

From McGimsey and others (2008): "On September 13, 2005, a long sequence of strong seismicity was recorded on the newly operational Korovin seismic network. The sequence began with two small local events followed by about 30 minutes of weak tremor, and then about 20 weak local events. Nothing unusual was detected on satellite images of the time period.
"Although a network of seismic stations was installed on northern Atka Island during the summer of 2004, data were not accessible until early March 2005, and Korovin was not considered to be seismically monitored until late 2005 - announced in the December 2, 2005, Information Release - when a sufficient period of background seismicity had been recorded, and equipment/communications problems resolved (see table 1 in original text). On December 2, Korovin, which previously had been listed as UA, was formally assigned Color Code Green."

From Dixon and others (2015): "Starting on March 29, Korovin Volcano experienced a 2-week-long swarm of small earthquakes located 2-4 km (1.2-2.4 mi) northwest of the summit of Korovin. Earthquake activity peaked on April 10, with a rate of 10 earthquakes per hour, and the swarm ended by April 12 (fig. 45 in original text). Throughout 2013, AVO noted isolated tremor at Korovin. In comparison, this tremor released about one-third of the energy level of tremor associated with a 2006 period of unrest at Korovin. The Aviation Color Code and Volcano Alert Level remained UNASSIGNED/UNASSIGNED throughout the year."

From Cameron and others (2020): "AVO received a report of steam coming from Korovin Volcano on February 2, 2016, from an Atka, Alaska, resident (fig. 39). A check on seismic data revealed no evidence of any increased activity, and the steaming source was from an area near the volcano with known fumarolic vents that often steam (Motyka and others, 1993). Thus, the February report is considered part of typical Korovin Volcano activity. From April through August, multiple tremor bursts were noted in the seismograph data (fig. 40), and April and May recorded more tremor bursts than the later months. AVO kept the Aviation Color Code and Volcano Alert Level GREEN and NORMAL, respectively, for Korovin Volcano but maintained increased awareness and data checks during periods of increased tremor."