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Okmok reported activity

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EVENT SPECIFIC INFORMATION

Event Name : Cone A 1960/10

Start:October 15, 1960 Observed
Stop:April 15, 1961 ± 45 DaysObserved

Tephrafall: BibCard BibCard BibCard
Central eruption: BibCard BibCard
"Fire", "Glowing", or incandescence: BibCard
Eruption Type:Explosive
MaxVEI: 3 BibCard
Duration: 4 to 8 months BibCard
ColHeight: 2900 m BibCard

Description: From Grey (2003): "An eruption that began in October, 1960 produced enough ash to reach Chernofski Sheep Ranch on western Unalaska Island [see figure 4.8 in original text] (Holmes, 1994). According to John Reeder of the Alaska Division of Geological & Geophysical Surveys, who interviewed Milton Holmes, resident Chernofski rancher, 'there were times when Milton could see lava shooting above the Okmok caldera only to fall back in. When the wind was not blowing, a red glow could be seen from the crater. At one time, he had to wear goggles while riding range because the ash was so thick' (Reeder, 1986). A concurrent report in the Anchorage Daily Times on October 17, 1960, states that Reeve Aleutian Airways passengers and crew 'were treated to an unexpected show of fireworks - the eruption of Tulik volcano' on October 15, involving a 'black cloud 9,500 feet into the air' and 'a 15-mile lava flow.' The flight attendant was quoted as seeing 'red lava and chunks of rock flying through the air at the base of the volcano.' This report is perplexing because in distinguishing between Tulik and 'Okmak Crater,' it limits the probability of misidentifying the active vent; yet as mentioned earlier [in other eruption descriptions], there is no geologic evidence to suggest an eruption from Tulik in historic times.

"Furthermore, there are no young lava flows associated with Tulik, and the maximum length of any lava flow exposed within the caldera is 7.8 km (the 1958 flow); there is no lava flow reaching 15 mi (25 km) in length anywhere on Okmok. Either the report was exaggerated or the number is a misprint and should have read '5-mile,' which would be reasonable. However, despite the vigorous level of activity implied by Holmes' observations and the Times report, no lava flow has been identified associated with this activity. It is probable that this was a brief burst of lava fountaining and the flow the Reeve passengers saw was the fresh 1958 flow.

"There is also one report of light ash fall in the community of Unalaska, 120 km ENE of Okmok in the late fall of 1960 (Reeder, 1986). Since neither Makushin nor Akutan volcano was erupting at the time, nor were those volcanoes immediately west of Okmok, that ash probably came from Okmok. Simkin and Siebert (1994) list the end date for this eruption as April 15, 1961. Based on measurements of tephra thickness within Okmok caldera by Reeder in 1980 and on western Unalaska Island by Holmes in 1961, the estimated total bulk volume of tephra from this eruption is 'greater than 1 x 10^7 cubic meters' (Reeder, 1986). It is possible that Reeder may have included tephra from the 1958 eruption in his calculations and overestimated the 1960 eruptive volume, since no lava flow is identified associated with this event."

From Black (1981): "Stanley Holmes, Unalaska, reports that when Tulik (Okmok) caldera erupted in 1960, lava ran across Crater Creek. The temperature of the water in the creek remained above normal for a year, disrupting the salmon run (personal communication, March 22, 1978)."

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