В течение 1997-1999 гг. вблизи вулкана Карымский (∆ = 1.5 км) в рамках Российско-Американской экспедиции (начальник экспедиции с Российской стороны А.Ю. Озеров, научный руководитель Е.И. Гордеев) проводились комплексные наблюдения за сейсмическими и инфразвуковыми волнами, сопровождавшими эксплозивную активность вулкана. Регистрация сигналов осуществлялась цифровой аппаратурой с частотой дискретизации сигнала 125 Гц, амплитудно-частотные характеристики аппаратуры и ее калибровка приведены в работе [13]. В данной статье сделан предварительный анализ особенностей генерации акустических сигналов (АС) в атмосфере, сопровождавших эксплозивную деятельность вулкана.

The temperature and hydrogen isotope composition of the fumarolic gases have been studied at Kudriavy volcano, Kurile Islands, which is unique for investigating the processes of magma degassing because of the occurrence of numerous easily accessible fumaroles with a temperature range of 100–940°C. There are several local fumarolic fields with a total surface area of about 2600 m2 within the flattened crater of 200×600 m. Each fumarolic field is characterized by the occurrence of high- and low-temperature fumaroles with high gas discharges and steaming areas with lower temperatures. We have studied the thermal budget of the Kudriavy fumarolic system on the basis of the quantitative dependences of the hydrogen isotope ratio (D/H) and tritium concentration on the temperature of fumarolic gases and compared them with the calculated heat balance of mixing between hot magmatic gas and cold meteoric water. Hydrogen isotope composition (δD and 3H) shows a well expressed correlation with the gas temperature. Since D/H ratio and 3H are good indicators of water sources in volcanic areas, it suggests that the thermal budget of the fumarolic system is mostly controlled by the admixing of meteoric waters to magmatic gases. The convective mechanism of heat transfer in the hydrothermal system governs the maximum temperatures of local fumaroles and fumarolic fields. Low-temperature fumaroles at Kudriavy are thermally buffered by the boiling processes of meteoric waters in the mixing zone at pressures of 3–12 bar. These values may correspond to the hydrostatic pressure of water columns about 30–120 m in height in the volcanic edifice and hence to the depth of a mixing/boiling zone. Conductive heat transfer is governed by conductive heat exchange between gases and country rocks and appears to be responsible for the temperature distribution around a local fumarolic vent. The temperature and pressure of shallow degassing magma are estimated to be 1050°C and 2–3 bar, respectively. The length of the ‘main’ fumarolic gas conduit is estimated to be about 80 m from the linear correlation between maximal temperatures of fumarolic fields and distances to the highest-temperature ‘F-940’ fumarole. This value may correspond to the depth of an apical part of the magmatic chamber. The geometry of the crater zone at the Kudriavy summit and the model of convective gas cooling suggest different hydrostatic pressures in the hydrothermal system at the base of high- and low-temperature gas conduits. The depths of gas sources for low-temperature fumaroles are evaluated to be about 200 m at the periphery of the magma chamber.

Temporal irregularity of the output of volcanic material is studied for the sequence of large (V ≥ 0.5 km3, N = 29) explosive eruptions on Kamchatka during the last 10,000 years. Informally, volcanic productivity looks episodic, and dates of eruptions cluster. To investigate the probable self-similar clustering behavior of eruption times, we determine correlation dimension Dc. For intervals between events 800 and 10,000 years, Dc ≈ 1 (no self-similar clustering). However, for shorter delays, Dc = 0.71, and the significance level for the hypothesis Dc < 1 is 2.5%. For the temporal structure of the output of volcanic products (i.e., for the sequence of variable-weight points), a self-similar “episodic” behavior holds over the entire range of delays 100–10,000 years, with Dc = 0.67 (Dc < 1 at 3.4% significance). This behavior is produced partly by the mentioned common clustering of event dates, and partly by another specific property of the event sequence, that we call “order clustering”. This kind of clustering is a property of a time-ordered list of eruptions, and is manifested as the tendency of the largest eruptions (as opposed to smaller ones) to be close neighbors in this list. Another statistical technique, of “rescaled range” (R/S), confirms these results. Similar but weaker-expressed behavior was also found for two other data sets: historical Kamchatka eruptions and acid layers in Greenland ice column. The episodic multiscaled mode of the output of volcanic material may be a characteristic property of a sequence of eruptions in an island arc, with important consequences for climate forcing by volcanic aerosol, and volcanic hazard.

In 1998 the Alaska Volcano Observatory responded to eruptive activity or suspect volcanic activity at 7 volcanic centers--Shrub mud, Augustine, Becharof Lake area, Chiginagak, Shishaldin, Akutan, and Korovin.

In addition to responding to eruptive activity at Alaska volcanoes, AVO also disseminated information for the Kamchatkan Volcanic Eruption Response Team about the 1998 activity of 4 Russian volcanoes-Sheveluch, Klyuchevskoy, Bezymianny, and Karymsky.

A model is proposed to explain temporal patterns of activity in a class of periodically exploding Strombolian-type andesite volcanoes. These patterns include major events (explosions) which occur every 3–30 min and subsequent tremor with a typical period of 1 s. This two-periodic activity is thought to be caused by two distinct mechanisms of accumulation of the elastic energy in the moving magma column: compressibility of the magma in the conduit and viscoelastic response of the almost solid magma plug on the top. A release of the elastic energy occurs during a stick–slip dynamic phase transition in a boundary layer along the walls of the conduit; this phase transition is driven by the shear stress accumulated in the boundary layer. The intrinsic hysteresis of this first-order phase transition explains the long periods of inactivity in the explosion cycle. Temporal characteristics of the model are found to be qualitatively similar to the acoustic and seismic signals recorded at Karymsky volcano in Kamchatka.

Рассмотрены два сближенных во времени катастрофических плинианских извержения (IIAB1 - 3500 и IIAB3 - 3280 14C лет назад) Авачинского вулкана, положивших начало деятельности его Молодого конуса. Изучена стратиграфия продуктов извержений, реконструированы их хронология и параметры, оценено воздействие на природную среду. Среди изверженных продуктов в обоих случаях преобладала тефра объемом соответственно >3 и >1.1 км3. Высоты эруптивных колонн достигали 21-28 км. Пепел извержения IIAB1 прослежен на 300 км к СВ от вулкана, площадь пеплопада по изопахите 1 см -около 50000 км2. Оба извержения сопровождались пирокластическими потоками, пирокластическими волнами и катастрофическими лахарами. Состав ювенильной пирокластики андезибазальтовый. По общему объему продуктов (>3.6 км3 для IIAB1 и >1.21 км3 - IIAB3) эти извержения относятся к крупнейшим за всю эруптивную историю Молодого конуса.

Проанализирована динамика исторических извержений вулкана Чикурачки. Показано, что для этого вулкана характерны как слабые вулканско-стромболианские (интервал годы-десятилетия), так и мощные плинианские (интервал 100-200 лет) извержения базальтовой магмы (50-54% SiO2). Изучены отложения тефры и восстановлены параметры плинианских стадий извержений 1853 и 1986 гг., значения которых оказались очень близки: минимальный объем изверженной магмы составил соответственно 0.03 и 0.04 км3, расход магмы для обоих извержений составлял 5 х 106 кг/с, высоты эруптивных колонн - около 13-14 км при скорости ветра 35-40 и 15 м/с, продолжительность плинианских стадий 5 и 7 ч. Приведены сведения о морфологии постройки вулкана и строении почвенно-пирокластического чехла района. Описано состояние кратера вулкана летом 2000 г. Сделан вывод о том, что высокие, сильно нагруженные пирокластикой облака плинианских извержений являются главным фактором риска, связанным с вулканом Чикурачки.