Kaitoku Seamount and the Mystery Cloud of 9 April 1984

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Abstract
On 9 April 1984, commercial airlines enroute from Tokyo, Japan, to Anchorage, Alaska, reported an unusual mushroom-shaped cloud at about 38.5°N, 146.0°E. On 8 and 9 April the intensity of volcanism from Kaitoku Seamount (26.0°N, 140.8°E), as indicated by T-phase recordings on an array of ocean bottom hydrophones, reached a maximum level and then declined rapidly. An examination was made of the possible relation of the cloud to eruptions of Kaitoku through an analysis of pilot depositions, satellite photos, wind charts, signal strengths and spectra of known man-made underwater explosions, as well as ascent rates of volcanic plumes and cumulonimbus clouds.