Weak shock waves in the eruption column

Abstract

RECENTLY Nairn¹ has made a study of the visible air shock waves which propagate above a volcanic vent in the form of luminous arcs and are closely followed by violent projections of gas and solid ejecta. In ref. 1 it is suggested that this event is caused by a strong explosion within the volcano due to a rapid heating of meteoritic water enclosed in lava pockets. Another type of shock wave formation accompanying volcanic eruption was recorded by one of us (L.D.L.) during an explosive phase of eruption in the Tolbatchik volcanic area (Kamchatka 1975). These waves were smoke and ash which could be observed as optically denser layers rising in the eruption column and probably cannot be attributed to burst phenomena. The present note is based on observations made near the end of the activity of cone II (the middle one in the photographs) when other newly-built pyroclastic cones already showed only weak fumarolic activity.