Lava lake oscillations and the magma reservoir beneath a volcano

Abstract

Stagnation of magma beneath a volcano very likely produces a considerable body of magma, the so called magma reservoir. Assuming an active lava lake being connected with an underneath magma reservoir through a vertical conduit, the height of the surface of the lava lake may be expected to show tidal fluctuations which are caused by squeezing out and draining back of magma from a magma reservoir due to earth tides. Examples are shown in the case of Halemaumau lava lake, Kilauea, in 1919. A similar behaviour also appeared in 1968 which showed semidiurnal tilt of the summit area. It is interesting to notice that the semidiurnal oscillation of the surface of the lava lake appeared only at the heighest level of the lava lake activity. This evidence implies that during the early stage of the activity, a part of the lava filled feeding dikes and open cracks and consequently tidal oscillations of the lava lake were masked and could not be observed.