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Okmok reported activity




Event Name : Cone A 1945/6

Start:June 1, 1945 Observed
Stop:December 1945 Observed

Lava flow: BibCard BibCard BibCard BibCard
Central eruption: BibCard BibCard BibCard BibCard
"Fire", "Glowing", or incandescence: BibCard BibCard
Eruption Type:Explosive
Duration: 7 months BibCard
Eruption Product: basalt BibCard
MaxVEI: 2 BibCard
ColHeight: 3000 m BibCard

Description: From Grey (2003): "The 1945 eruption was fairly well documented (Miller and others, 1998; Robinson, 1948; Wilcox, 1959; Byers, 1947). Robinson gave a detailed account of his visit to Okmok at the request of Lt. Gen. Delos C. Emmons, Commanding General of the Alaskan Department, who was concerned for the safety of Ft. Glenn army base. The eruption is believed to have begun on June 1, when a sharp earthquake was felt at Ft. Glenn. Cloud cover delayed the first observation until June 4, when pilots reported black ash rising to 3000 m. Weather precluded further observations until June 10, when the clouds and fog finally cleared. Robinson and his fellow party members witnessed strombolian activity of Cone A from the caldera rim, along with the accompanying lava flow [see figure 4.2 in original text]. An excerpt from Robinson's description:

"'A steady roar, like that of a railroad locomotive at the far end of a long tunnel, was punctuated every 10 to 15 seconds by a violent explosion which threw red-hot blobs of lava more than a thousand feet above the cone * * * About once a minute there was a particularly violent explosion in which bombs, some several feet long, were thrown far out on the caldera floor * * * A stream of lava, glowing red even in the bright sunlight, issued from a fissure in the southwest base of the cone, poured over a cliff as a "lava fall," and turned down a depression to the northeast toward the center of the caldera * * * Near the lava vent were three miniature volcanoes only a few feet high, throwing innumerable blobs of bright orange-hot lava into the air like many-armed jugglers and giving off, with a high-pitched hiss, large volumes of faintly bluish gases. The sides of the tiny volcanoes were spectacularly colored with white, yellow, orange, and red deposits made by the gases.'

"Robinson's crew also noticed 5 cm of ash accumulated on the caldera rim on June 10, and observed that the lava flow rate was about 0.15 m/s, and the flow had reached 1200 m long. By the end of the eruption, which continued intermittently until December, 1945, the main flow lobe reached about 6 km in length, with a second flow lobe about 2.5 km long to the north of the cone [see figure 1.2 in original text]. The estimated average thickness of the first lava lobe is 12 m. Estimated lava flow volume is 1x10^7 cubic m (Reeder, 1984) to 2x10^7 cubic meters (Byers and others, 1947). The summit of Cone A had two craters before the eruption (Robinson, 1948), whose rim heights were estimated at 150 m for the NW vent and 120 m for the SE vent. After the eruption, the SE vent, which had been the active vent for the duration of the 1945 eruption, had grown by an estimated 30 m (Robinson, 1948)."

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