The largest Plinian eruption of our era and the latest caldera-forming eruption in the Kuril-Kamchatka region occurred about cal. A.D. 240 from the Ksudach volcano. This catastrophic explosive eruption was similar in type and characteristics to the 1883 Krakatau event. The volume of material ejected was 18–19 km3 (8 km3 DRE), including 15 km3 of tephra fall and 3–4 km3 of pyroclastic flows. The estimated height of eruptive column is 22–30 km. A collapse caldera resulting from this eruption was 4 × 6.5 km in size with a cavity volume of 6.5–7 km3. Tephra fall was deposited to the north of the volcano and reached more than 1000 km. Pyroclastic flows accompanied by ash-cloud pyroclastic surges extended out to 20 km. The eruption was initially phreatomagmatic and then became rhythmic, with each pulse evolving from pumice falls to pyroclastic flows. Erupted products were dominantly rhyodacite throughout the eruption. During the post-caldera stage, when the Shtyubel cone started to form within the caldera, basaltic-andesite and andesite magma began to effuse. The trigger for the eruption may have been an intrusion of mafic magma into the rhyodacite reservoir. The eruption had substantial environmental impact and may have produced a large acidity peak in the Greenland ice sheet.

Four Plinian eruptions of Ksudach have been reconstructed and dated by the carbon-14 method. The eruptions produced three collapse calderas: the KS1 eruption formed Caldera V 1700-1800 years ago, the KS2 and KS3 events produced Caldera IV 6000-6100 years ago, and the KS4 eruption formed Caldera III 8700-8800 years ago. The most violent eruption was the KS1 event. The sizes of the calderas were 4 × 6.5 km (V), 5 × 6 km (IV), and presumably 2-3 km across (III). Juvenile material was erupted in a rhythmic manner. The composition of the products was dominated by andesite (KS2 and KS4), dacite and rhyodacite (KS3), and rhyodacite (KS1). It is assumed that all caldera-forming eruptions were triggered by the injection of a new portion of high-temperature basic magma and its mixing with the cooling acid magma of the preexisting source. -from Journal summary

Remnants of five catastrophic lahars have been discovered, described, and dated by the carbon-14 method. They occurred during eruptions of Avacha (violent explosions with voluminous juvenile pyroclastics) and Koryakskiy (large fissure lava flows): 3500 to 3200 14C years ago or 1900-1500 years B.C. These lahars were much higher in vigor, hazard, and effect on the environment than the lahars generated by the historic eruptions of these volcanoes. -from Journal summary

Предлагаемая статья продолжает серию работ, описывающих деятельность вулканов Северной группы, начиная с 1935 г. Статья охватывает период с 1990 по 1992 г. включительно. Описана динамика извержений вулканов Ключевской, Безымянный и Шивелуч.