Alaska Volcano Observatory

From Grey (2003): "After a 13-year hiatus in reported eruptive activity, Okmok returned to life the evening of August 14, 1958. Eruptive activity was first reported by sheep ranchers on northeastern Umnak, and by Reeve Aleutian Airways personnel on the island (Anchorage Daily News/Times, August 15, 16, and 19, 1958). Reeve pilot Everett Skinner flew from Dutch Harbor to Nikolski on the SW end of Umnak Island on the morning of August 15 and observed an ash plume over Okmok reaching 5.5-6.0 km (Reeder, 1984). On his return flight from Nikolski, Skinner flew inside the caldera to photograph and observe the eruption [see figure 4.6 in original text]. The active vent was Cone A, where two ~35 m-high lava fountains at the NE base of the cone fed a basaltic a'a lava flow extending to the NNE, eventually reaching 7.8 km in length and covering 9.36 square km [see figure 4.7 in original text] (Reeder, 1984). According to James Bynum (Anchorage Daily News, August 29, 1958) the flow was still active on August 29, but when Skinner flew by Okmok again on September 5, he saw only steam rising from the cone and flow [see figure 4.6 in original text]. Thus, the effusion rate must have been relatively high in order for the flow to reach its full length in only two weeks. John Reeder estimated a mean thickness of 12.8 m and a volume of 1.2 x 10^8 cubic meters, which is 6-12 times larger than the estimated volume of the 1945 flows at 1-2 x 10^7 cubic meters (Reeder, 1984)."