In December the plume typically rose up to 1 km above the crater, and was mainly composed of gas and steam shed off the extrusive dome. In some cases (for example in late December), it remained conspicuous for over 40 km downwind. In comparison, when visible in early to mid-November, the plume was slightly higher (2-2.5 km), and conspicuous only slightly farther downwind (50 km). These plume observations in early November were coincident with nearly continuous tremor; minor explosions were observed, although a clear eruption was not, possibly due to poor visibility. The strong 22 April eruption was preceded by explosions and clear increases in both tremor and earthquakes.

. . . during the week ending on 3 January, tremor progressively increased; on 3 January it prevailed for 6 hours/day. For the interval 4-12 January tremor durations were in the range of 9-16 hours/day.

For the first half of October, and the interval from late-November to mid-December, 2-8 earthquakes/day were typically recorded near the volcano. Earthquakes in the second half of October, and some periods in September, increased sharply and reached >40 events/day; in early January they varied from 7 to 23 events/day.

Geological Summary. The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1,300 km3 andesitic volcano is one of Kamchatka's largest and most active volcanic structures, with at least 60 large eruptions during the Holocene. The summit of roughly 65,000-year-old Stary Shiveluch is truncated by a broad 9-km-wide late-Pleistocene caldera breached to the south. Many lava domes occur on its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large open caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. Widespread tephra layers from these eruptions have provided valuable time markers for dating volcanic events in Kamchatka. Frequent collapses of dome complexes, most recently in 1964, have produced debris avalanches whose deposits cover much of the floor of the breached caldera.

Information Contacts: V. Kirianov, IVGG.