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Okmok reported activity





Event Name : Cone A 1983/7

Start:July 8, 1983 ± 16 HoursObserved
Stop:July 8, 1983 Observed

Tephrafall: BibCard
Fumarolic or hydrothermal activity: BibCard
Steam: BibCard
Tephra plume: BibCard BibCard
Central eruption: BibCard BibCard
Eruption Type:Explosive
MaxVEI: 2 BibCard
Duration: Less than 24 hours BibCard

Description: From Grey (2003): "A 100 km long plume was recognized in one NOAA 7 image at 1716 local time on July 8 [1983] (0216 UTM on July 9), but was not seen on images 12 hours earlier or later. This was apparently only a brief puff of ash and steam, accompanied by sulfurous gases, as reported by Aleutian Air pilot Tom Madsen (Reeder, 1986)."

From Reeder (1986), describing what Tom Madsen saw on his flight to Atka from Dutch Harbor on July 8: "Upon reaching Driftwood Bay, which is about 23 km WNW of Dutch Harbor, Tom could clearly see a hazy yellowish-brown smoke horizon straight west in the Okmok region. This smoke horizon was at an altitude of about 1,000 m and higher. The smoke was densest at Okmok, and the smoke horizon extended north across the Bering Sea as far as Tom could see (about 100 km). Due to thick fog and rain, Tom could not see the extent of the cloud to the south. Because Tom could not recognize the top altitude of this smoke cloud and because it appeared to extend over a very broad region, he elected to continue his normal route along the Bering Sea side of the Aleutian Island at an altitude of 500 m. Upon reaching Cape Idak of the most eastern part of Umnak Island, which is about 25 km NE of Okmok caldera, he was beneath the eastern edge of the cloud. Tom could detect sulfur gases. The cloud above him had a definite yellow tinge and at a distance was yellowish brown. He did not reach the other end of the cloud until he reached Inaudak Bay along the central Bering Sea side of Umnak Island, which is about 25 km SW of Okmok caldera and about 50 km SW of Cape Idak. No damage occurred to the Twin Beechcraft. Tom continued his normal route to Atka, arriving at about 1100. He then returned to Dutch Harbor by the same route, leaving Atka at about 1400 and arriving at Dutch Harbor at about 1600. During this return, he again had the same experience of flying under the Okmok eruption cloud, which started at about Inanudak Bay and ended at Cape Idak. During Tom's previous 3 years of flying in the Aleutian Islands, he has never had such an experience."

From Reeder (1986): "On 9 August, J.W. Reeder, while flying with Tom Madsen, made examinations of Okmok caldera. No new lava flows were recognized within Okmok caldera. Cinder Cone A, which is located in the SW region of Okmok caldera was teaming and some ash was noticeable over remaining winter-snow up to a 2 km radius from Cone A. A nearly transparent blueish smoke was also detected drifting to the east from the cone. J.W. Reeder and Tom Madsen have made several independent observations of the caldera during the previous 3 years. Cinder Cone A appeared to be similar in physical appearance, except it was steaming and smoking above average."

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