The Dynamics of Prolonged Low Fountaining Behaviour at Halemaumau, Kilauea, in December 2013.

Abstract:

Episodes of low-fountaining eruption lasting minutes to tens of minutes alternated with passive degassing at Halema`uma`u during 5 days of observations in December 2013. Some low fountains were triggered by small collapses from the vent walls and originated close to the margin of the lava lake. Others began in the lake interior and migrated to its margins without any obvious link to rock falls.

Observations using high-frequency (50-500 Hz) thermal and visible imaging reveal that the fountains consist of sequences of close-spaced, meter-scale pockets of gas that burst through the free surface. Bursts lasted between 0.15 and 1.5 seconds, often partially overlapping in time and space. Bursts entrain both relatively brittle plates from the crust of the lava lake and very ductile thin crust that formed between successive pockets. The latter form spectacular ‘lace-work’ pyroclasts, of meter-scale diameter, which rise, deform, tear, and fall back into the lava lake.

 The process can be treated as a form of hydrodynamic fragmentation involving the transformation of masses of accelerating liquid into jets via the generation of liquid films that experience strong stretching during highly non-linear fluid motion.