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Description

Augustine Volcano in Lower Cook Inlet, southern Alaska, erupted after 12 years of dormancy in January, 1976. By April, when the eruption ended, a minimum of 0.5 km³ of ejecta had been deposited as pyroclastic flows, ash falls and lava, which formed a new summit dome. The mass of the eruption was about 7.6 x 10¹⁴ g, and the corresponding thermal energy released about 3.8 x 10²⁴ ergs. In this paper we compiled all available observational data for the highly explosive vent-clearing phase of the eruption in order to estimate its effect on the atmosphere. We discuss radar and visual observations – aerial, ground and satellite photography – regional ash fall and damage to aircraft – and infrasonic and seismic data. The eruptive plumes stayed intact for long distances and could be easily traced for 700 km downwind. The plumes consisted of three parts: (1) a homogenous layer of ash and some condensed (frozen) water at 3 to 4 km altitude, giving rise to extensive regional ash falls; (2) puffs of ash, travelling at heights of 6 to 8 km to great distances (Arizona and Virginia); and (3) stratospheric dust, which eventually appeared over the tropics and was detected with a pyroheliometer up to 5 months after the eruption at Mauna Loa, Hawaii. Injection of material into the stratosphere was probably through occasional high speed gas jets. From visual ranges reported by airplanes inside the eruption clouds we calculated a minimum mass loading of 0.3 g m⁻³. The mass of suspended material in the troposphere, 7.5 x 10¹³ g, represents 10% of the total mass erupted in the 1976 eruptive cycle. An additional 0.4% of the total erupted mass ended up in the stratosphere. We speculate that over the past 10,000 years Augustine’s particulate mass input was 225 megatons/century into the troposphere and 9 megatons/century into the stratosphere. The mean global injection rate of volcanic dust into the troposphere and stratosphere is estimated to be one order of magnitude higher than previously assumed.

Publication Date

11-17-1977

Keywords

Volcanoes, Seismology, Alaska, Augustine Volcano

Handle

http://hdl.handle.net/11122/15493

Augustine Volcano eruption : initial explosive phase, January 1976 : impact on the atmosphere

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