Laboratory models of Hawaiian and Strombolian eruptions

Abstract

Basaltic eruptions are often characterized by cyclic changes of activity. At Hawaii, periods of continuous fountaining alternate with much longer periods of effusive outflow^1,2. In Strombolian eruptions, activity proceeds through intermittent discrete bursts^2–5. We report laboratory experiments that simulate the degassing process in basaltic eruptions. Gas bubbles are generated at the bottom of a tank filled with viscous liquid and topped by a small open conduit. The bubbles rise and accumulate at the roof in a foam layer whose thickness increases. At a critical thickness the bubbles coalesce and the foam collapses, generating gas pockets whose size depends on liquid viscosity and surface tension. At low viscosity a single large gas pocket is formed, which flows into the conduit. This erupts in an annular flow configuration where a central jet expels the liquid films that wet the conduit walls⁶. At higher viscosity many smaller pockets are formed, which rise as slugs and burst out intermittently at the vent. The experiments imply that the presence of constrictions in the chamber and conduits plays a major role in determining eruption behaviour.