During 6 March-8 April there was a significant increase in seismic activity. Most of the 43 seismic events recorded took place at a depth of 5 km beneath the volcano. The three strongest earthquakes occurred on 4 April. The level of seismic activity beneath the volcano decreased during the second week of April; only a few weak earthquakes were registered at depths of 5-10 km. On 8 April the Level of Concern Color Code was upgraded to Yellow from Green, indicating that an eruption is possible with little or no additional warning.

Geological Summary. The large symmetrical Koryaksky stratovolcano is the most prominent landmark of the NW-trending Avachinskaya volcano group, which towers above Kamchatka's largest city, Petropavlovsk. Erosion has produced a ribbed surface on the eastern flanks of the 3430-m-high volcano; the youngest lava flows are found on the upper W flank and below SE-flank cinder cones. Extensive Holocene lava fields on the western flank were primarily fed by summit vents; those on the SW flank originated from flank vents. Lahars associated with a period of lava effusion from south- and SW-flank fissure vents about 3900-3500 years ago reached Avacha Bay. Only a few moderate explosive eruptions have occurred during historical time, but no strong explosive eruptions have been documented during the Holocene. Koryaksky's first historical eruption, in 1895, also produced a lava flow.

Information Contacts: V. Kirianov, IVGG.