Three stages of study of active and potentially active volcanoes on Kamchatka and the Kurile Islands were distinguished: the anterior stage (1700-1935), the new stage (1935-1962) and the recent stage (from 1962 till present time).
This paper provides a new, for the first time scientifically based term of «active volcano». Updated catalogues display active and potentially active volcanoes of Kamchatka and the Kurile Islands. Here we propose a long-term forecast of behavior and parameters of impending eruptions and related volcanic hazards for the typical volcanoes of the 1st and the 2nd stages of evolution.

It is shown that the young andesite-basaltic cone of Avacha Volcano was more complex, of the "cone-in-cone" type, in the 18th and early 19th century than is now the case. The upper cone was then nested in a crater of diameter 350-400 m, its base being at absolute heights of 2720 m, while the summit crater had a diameter of 50-100 m at absolute heights of 2800-2850 m. Since the summit crater was small, S.P. Krasheninnikov was induced to call Avacha Volcano a "peaked" one in 1738. The major eruption of 27-29 June, 1827 nearly anni-hilated the nested upper cone, while Young Cone of Avacha Volcano acquired nearly the present-day outward shape.

The old views on the style of the Avachinsky eruptions during 1737- 1909 have partially been revised based on new data obtained by the authors. We specified their types and geological-geomorphological effect and made an assessment of the related volcanic hazards. All the eruptions were merely explosive except for the effusive-explosive eruption of 1894-1895. The eruptions of 1737, 1779 and 1827 are referred to large for this historical eruptive stage, the rest (of 1772, 1851-1855, 1878, 1881, 1894-1895 and 1909) are regarded as small and moderate.

We have summed up and supplemented new data on the eruptions of 1926-1927, 1938 and 1945 plus added the description of the last eruption of the volcano in January 1991. Considering the dynamics of the eruptive activity of the Avachinsky volcano in 1737-1991 we have presented a classification for these eruptions. Also we made a forecast of the type and parameters of possible future eruption as well as estimated the volcanic hazard associated with it. Because of high degree of volcanic hazard in the SW and S sectors of the base of the volcano it is proposed to prohibit constructions of any kind in these areas.

We have identified, and describe in this paper, a phase of multifactor natural catastrophism that has been the greatest during our era in Kamchatka, to be dated 0-650 A. D. Its chief components were. The last catastrophic eruptions to have occurred (a caldera-generating one at about 240 A. D., the pyroclastics volume being 18-19 km3 and a subcaldera one around 600 A. D. with the volume of lava and pyroclastics 9.5-10.5 km3) which were followed by irreversible relief changes over areas of hundreds of square kilometers and have affected rather injuriously many other environmental components. An exceptionally intensive activity of the other volcanoes (at least 75-80% of all active and potebtially active Kamchatkan volcanoes were erupting, tens of large and catastrophic eruptions occurred). Regional catastrophic and large ashfalls. A sharp, large-amplitude (between 1.5-2 and 12-15 m) tectonic uplift of various blocks in Kamchatka. Large earthquakes accompanied by large-volume rockfalls, landslides, large and frequent tsunamis. The catastrophic events of that time are argued to have been part of a worldwide phase of natural catastrophism that we hypothesize to have occurred at the beginning of our era.

Through radiocarbon techniques we determir the age (30 000 yrs) of the latest in the Late Pleistocene directed blast at the Avachinsky volca and approximately calculated the age of the previous large catastrophic eruption of the same type (35 00( 40 000 yrs). Coarse debris deposits produced by the eruption originally covered the area of 400 km2 a their volume was 16-20 km3. As a result of these eruptions the relief cardinally changed to the south of t Avachinsky and the lower part of the Avacha river channel was transported to the distance of 6-10 km. 11 believed that in the nearest hundreds of years such blasts will not take place but this forecast does not apply the adjacently located Koryaksky volcano.