Alaska Volcano Observatory

From Associated Press (1974): "A spokesman for the Adak Seismological Observatory, a mere 23 miles away from the volcano, said the eruption was reported at 6:58 p.m. BDT and created 'a perfect mushroom cloud.' He said the clouds arose to at least 10,000 to 12,000 feet within four minutes of the eruption and was colored a dirty white to a light beige." AVO has several photographs of a Great Sitkin eruption plume, taken from Adak.. . .
"'It was a very spectacular explosion,' he said, 'but we don't know its type yet. It could be a steam explosion or a genuine volcanic eruption.'"
"The spokesman said witnesses saw a number of bright flashes as the mushroom cloud boiled its way up lending credence to the possibility of volcanic origin."
"He said it was not known if anyone actually heard the blast but he noted a number of witnesses said they heard a deep rumble shortly before the eruption."
From Smithsonian Institution, 1974, CSLP Report 1804: (22 February 1974): Explosive activity and light-colored plume
The following was cabled from the Geophysical Institute on 22 February 1974. "Explosive activity was observed at 1855 local time from Adak, 48 km WSW of Great Sitkin volcano. An earthquake originating at the volcano of Richter magnitude 2.6 occurred at the time of onset. An estimated 10,000-foot light-colored plume was reported over the summit at dusk. Since that time bad weather has obscured the island."

Smithsonian Institution, 1974, CSLP Report 1938: (30 September 1974): Lava dome still growing, overspilling crater rim
"D. Glover reported that, on a helicopter inspection trip to the volcano on 22 February, he '. . . Found that a large lava dome had been emplaced in the crater, with mostly steam and gas being emitted.' Foul weather prevented observations on all but three occasions between then and 29 March. About one week after the eruption, he noted, through a high-power telescope, '. . . That the dome had been extruded a considerable extent, with some ash being emitted. Since then activity has decreased to steam and gas emissions.'
"In mid-September, he reported that he had '. . . Only been able to observe Great Sitkin volcano by high-power telescope and a few times from aircraft. The lava dome appears to continue to extrude with minor lava flows spilling over the lip of the crater. The size of the dome is hard to estimate but it is probably close to 700 m in diameter and 200-300 m high. We have recently installed seismic instrumentation on the volcano but we have not noticed any unusual activity.' In summary, it appears that, following the initial release of the pressure head of volatiles on 19 February a dome has been extruded in the caldera of Great Sitkin. The new dome appears to be about the size of that extruded in 1945. Further, the dome is still active, overspilling the lip of the caldera as it grows. The extrusion has been quiet, with little of no associated explosiveness."
Newhall and Melson (1983) estimate the size of this dome at 96x10^6 cubic meters.