DISTINCTIVE FEATURES OF FUMAROLIC ACTIVITY AT KUDRYAVYI VOLCANO IN 1991-1999 AND ITS 1999 PHREATIC ERUPTION

Abstract

The paper reports the results of detailed studies (in 1990-1999) of the fumarolic activity at Kudryavyi volcano. The highest temperature of the fumarolic gages of 940degreesC was registered in 1992, after which the gas temperature gradually decreased to 907degreesC. Simultaneously, the gases became higher in water and lower in other gas components and deuterium. Such trends of gas temperature and composition may be indicative of the fact that, early in the 1990s, the near-surface chamber of Kudryavyi volcano underwent insignificant reactivation, which could be caused by the ascent of a new melt portion. In spite of this, fumarolic activity at the volcano remained relatively stable over the past 100 years, since no new eruptions of this volcano were observed throughout this time period, and the modern contours of its fumarole fields are generally identical to those documented in 1948. Our detailed studies in 1998 and 1999 have revealed short-term variations in the fumarolic activity of this volcano, which were most probably triggered by meteoric precipitates. Weak rains resulted in an insignificant rise in the temperature and pressure of gas in the high-temperature fumaroles, while extensive precipitates caused, a significant increase in the gas pressure, changes in the gas composition, and enhancement of seismic activity at the volcano. The October 7, 1999, phreatic eruption of the volcano was caused by the following sequence of events observed that same year: an unusual dryness (which is atypical of the southern Kurils), regional earthquakes, and uncharacteristically abundant meteoric precipitates. The onset of active water boiling within the volcanic edifice resulted in an increase in the gas pressure in the fumarolic system and, as a consequence, the ejection of crater material and the origin of a new crater.