Steam plumes were observed at Mt. Hague on July 14, 1990. This activity probably does not constitute a volcanic eruption.
From Smithsonian Institution (1990): "On 14 July at about 2100, Richard Mack observed and photographed a white plume that had risen 350-500 m from the SW side of the summit crater of Mt. Hague, near the E margin of Emmons Lake Caldera. A series of pulses slowly diminished in size until sunset at about 2200. Traces of material trailed SSW from the top of the plume.
"Mack stated that he had not seen such activity during his 57 years on the Alaska Peninsula. However, during fieldwork in 1946, Kennedy and Waldron (1955) observed six large fumaroles and many other small ones in a steep gully on the SW side of Mt. Hague, at altitudes of ~975-1,150 m. They did not give plume heights, but reported clouds of SO2 and steam rising from the major vents, with a locomotive-like noise that was audible 1/2 km away. The volume of sulfur fumes prevented the geologists from approaching nearer than roughly 100 m from the vents. Sulfur odors were strong many kilometers downwind. Sulfur cones ~1 m high had developed around the vents and extensive deposits of native sulfur were found in the gully. Miller (in Wood and Kienle, 1990) also reported a large fumarolic area on the S side of Mt. Hague."
From Reeder (1993): "At about 2100 on July 14, 1990, Richard Mack of King Cove observed an eruption plume of smoke (steam with ash or with at least particulate matter) that had just risen at least 500 m (based on photographs, estimated to have risen about 600 m) above the crater rim from the very SW inner side of the summit crater of Mount Hague. * * * The plume emission location was determined by J. Reeder based on photographs, air photographs, and 1:63,360 U.S.G.S. topographic maps to be 55 degrees 22 minutes 21 seconds N, 161 degrees, 58 minutes, 43.3 seconds W. Traces of particulate matter and/or tephra trailed to SSW from the top of the plume beyond the shore of the Pacific Ocean from the previous apparently continuous emissions from the summit crater. The emission was fairly continuous, as represented by a series of belches that slowly decreased in size by the time the sun had gone down just before 2200. Richard made his observations from his fishing boat on the S part of Pavlof Bay just SW of Bluff Point along Long Beach.
"Richard Mack noted some emissions from the same point of Mount Hague during the next morning (July 15), but due to strong winds the emissions did not rise to form impressive plumes like the evening before. But, the emissions were there. Richard then left the region."

Steam plumes were observed at Mt. Hague on July 13, 1991. This activity probably does not constitute a volcanic eruption.
From Reeder (1994): "At about 1100 on July 13, 1991, Richard Mack of King Cove observed from his fishing boat, Janice, in the region of Volcano Bay a white plume that was being emitted from within the summit crater of Mt. Hague. The plume reached a height of about 300 m above the peak of Mt. Hague and had drifted to the SW just beyond the crater rim. The day was unusually cloudless. The white plume could be seen all day. By 2100, the plume was slightly smaller and was drifting WSW beyond the summit crater, but the plume was barely rising above the summit of the volcano. The plume was visible from Pavlof Bay until about 2145 when darkness occurred."

McGimsey and others (2004) report that "NWS observers in Cold Bay contacted AVO on the morning of November 7, 2001 to report a small steam plume originating from the south side of Pavlof; they also received several Pilot Weather Reports (PIREPS) describing the same observation. About a month later, on December 13, 2001, NWS personnel in Cold Bay reported steam issuing from a point about half-way down the south flank of the volcano. The plume rose to a height of about 6,000 ft (~1,830 m) before dissipating. A Pen Air pilot corroborated the report and added that the steaming was coming from a 'hill' on the southwest flank; this pilot added that he encountered a strong sulfur smell on a flight by the volcano that day. AVO detected no unusual seismicity or thermal anomalies. Based on conversations with the Pen Air pilot, AVO determined that the source of steaming was likely the fumarole field on nearby Mt. Hague, a late Pleistocene volcano with no historic activity."

From Neal and others (2005): "On February 15, 2002, AVO received a pilot report of steaming from the vicinity of Pavlof Volcano on the Alaska Peninsula. AVO determined that the pilot had most likely spotted a steam plume from the summit crater of Hague, a youthful volcanic cone about 7 km (4 mi) southwest of Pavlof Volcano on the Alaska Peninsula. The pilot reported that snow had melted in a crater at the site of this steaming, but the 'activity was not significant.' AVO had received a similar report in mid-December, 2001 (steam was reported emanating from a 'hill' southwest of Pavlof, rising to about 6,000 ft [1,830 m] and dissipating, accompanied by a strong sulfur smell; McGimsey and others, 2005). The Pavlof seismic network showed nothing unusual in conjuction with any of the reports, and no anomalies were observed in satellite images.
"'Steaming' reports for the vicinity of Hague on the Alaska Peninsual continued into the spring. In early April, AVO received email from a teacher in King Cove (35 km [20 mi]) south-southwest of Hague) describing 'steam from a large crater offset on the southwest side of Pavlof.' Based on the position of the reported activity, it appears likely that the source was also a crater at the summit of Hague. This same observer got a better look from the air on April 18 and confirmed that the crater was still steaming and releasing notable amounts of sulfur-bearing gas. On May 1, USFWS personnel in Cold Bay shared photographs of steaming from the vicinity of Hague and noted that this was the first such observation in at least three years.
"In mid-April, AVO seismologist examined records from the adjacent Pavlof Volcano network and noted that a family of shallow long-period events had been recorded in the general vicinity of Hague (J. Caplan-Auerback, written comm., 2002). A second swarm of similar events occurred in May. While the significance of this seismicity remains unclear, its coincidence in time with reports of increased steaming from the Hague crater does suggest a transient increase in heat flux and resulting hydrothermal activity."

From McGimsey and others (2005): "On July 7, 2003, AVO scientists conducting seismic network maintenance near Mt. Hague on the rim of Emmons Lake Caldera noticed that the crater lake typically present was almost completely gone and all that remained was a few isolated pools surrounded by several vigorously venting fumaroles, and yellow sulfur deposits in the center of the crater. Mud cracks suggested that the lake had drained or evaporated rather recently. A photograph taken a week later, August 16, 2003, shows a full lake. Photographs taken of the crater lake on August 16, 2002 also show the lake filled with water.
"The Hague crater lake apparently has a history of draining and refilling. Sporadic checks of the crater since 1973 have found it empty about as often as full (T. Miller, written communication, 2003). The most recent observations [2003] verify that the lake is capable of reforming within days or weeks."

From McGimsey and others (2007): "National Weather Service personnel in Cold Bay reported a steam plume emanating from the side of Pavlof on April 16, 2005. Subsequent analysis of the photographs sent to AVO indicated that the steam cloud originated instead from adjacent Mount Hague (see fig. 35 in original text), possibly from the fumarolic field located on the south flank - instead of the crater lake - based on the plume position; however, no direct observations confirmed the source. Seismicity was determined to be normal.
"On May 23 and 24, 2005, observations of steam - this time possibly containing some ash - rising to as much as 3,000 ft (~900 m) above Pavlof were again reported to AVO, as well as to FAA and AAWU. Photographs revealed that the plume originated instead from Mount Hague (see fig. 36 in original text). Analysis of satellite images revealed no evidence of ash, and no unusual seismicity was recorded. One of the two summit craters on Mount Hague contains vigorous fumaroles and has produced strong steam emissions in previous years (see table 7 in original text). The activity was interpreted to result from normal fluctuation of the hydrothermal system at Mount Hague and was reported in the AVO Weekly Update on May 27, 2005."