NONLINEAR OSCILLATIONS IN THE VENT FUNNEL OF THE KLYUCHEVSKIY VOLCANO

Abstract

During the eruption of the Klyuchevskiy volcano in March-June 1983, acoustic signals associated with explosive action in the Predskazannyy secondary crater and the summit crater were recorded. The activity of the summit crater consisted of emissions of gas with a little ash from a vent about 120 m in diameter. The recordings of the acoustic signals (AS) from the summit crater, made at the Apakhonchich station, can be tentatively divided into three types. The first type (AS1) is a double or triple pulse, with the maximum overpressure in the compression wave ΔP = 10 Pa. The second type (AS2) is also a double or triple pulse; in addition, damped vibrations with f = 1.5 and 3 Hz are superimposed on it. The third type (AS3) is a train of three quasisinusoidal oscillations with f = 1 Hz; the first train is followed by a second, 1/2 to 1/4 as strong. The set of characteristic frequencies observed in the spectra of the acoustic signals is well explained by the set of resonant frequencies predicted by the theory of nonlinear oscillations in a pipe open at one end. Additional aspects of the study are discussed. …