Steam-and-ash explosions . . . continued in late July and early August. A gas-and-ash plume was rising as high as 3 km above the crater (8 km altitude) and extending to the NW at 1400 on 25 July according to visual observations made from a helicopter by S. Zharinov and O. Braitseva. Lava flows were observed to extend from the summit crater down the W slope of the volcano, entering and melting the glacier at ~3,000 m elev. Seismic activity, including tremor, was stable but at a high level. The direction and height of the plume was about the same the next day as seen from a helicopter, and ashfall took place in Kliuchi [(30 km NNE)]. On 27 July at 2200, the gas-and-ash plume was as high as 5 km above the crater, extending to the S for an unknown distance. A W-flank lava flow was observed at 0030 on 28 July as well as lava fountains 600-700 m above the crater. On July 29 at 1500, the gas-and-ash cloud was 5 km above the crater and extended SW.

Airborne observations in early August indicated that the gas-and-ash plume was generally 1-3 km above the crater, extending to the N or NW for ~50 km. On 3 August, the gas-and-ash plume, as observed from a helicopter by V. Dvigalo and A. Belousov, rose to 6-7 km altitude and extended to the E in the afternoon and to the N that night. Lava continued to flow down the W slope of the volcano, and ash fell again on Kliuchi. Volcanic tremor remained high and steady in late July and early August.

Geological Summary. Klyuchevskoy is the highest and most active volcano on the Kamchatka Peninsula. Since its origin about 6,000 years ago, this symmetrical, basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without major periods of inactivity. It rises above a saddle NE of Kamen volcano and lies SE of the broad Ushkovsky massif. More than 100 flank eruptions have occurred during approximately the past 3,000 years, with most lateral craters and cones occurring along radial fissures between the unconfined NE-to-SE flanks of the conical volcano between 500 and 3,600 m elevation. Eruptions recorded since the late 17th century have resulted in frequent changes to the morphology of the 700-m-wide summit crater. These eruptions over the past 400 years have originated primarily from the summit crater, but have also included numerous major explosive and effusive eruptions from flank craters.

Information Contacts: S. Zharinov, IVGG.