The Role of Macroscopic and Microscopic Processes Relating to the 2008 series of Explosions from Halemaumau Crater, Kilauea, Hawaii

A short series of 8 pyroclastic eruptions from Halemaumau crater in 2008 represented part of the first eruptive activity from the summit of Kilauea since 1982, and first explosive events since 1924. The explosive phases occurred at irregular intervals during an on-going period of continuous outgassing and ash emission. Together this activity represents conditions of relatively open-system degassing at the summit vent. Throughout this period, the geometry of the vent has changed: becoming wider with time due to frequent vent wall collapses leading to a shift from a vent diameter of 35 m to 130 m. The larger explosive events from Halemaumau in 2008 were coupled with vent wall collapse, however the role of vent wall collapse as an accompaniment to explosive behavior or a trigger to the heightened activity is currently under debate. We describe here the characteristics of the deposits erupted from each explosive event in terms of clast morphology, density, bubble size distribution and vesicle number density, tied to observations of the proportions of juvenile versus lithic ejecta during a) explosive phases; b) persistent degassing periods and c) periods of elevated tremor (VLF events). The early juvenile products from 2008 explosions represent magma that was stagnant and outgassed in the vent and shallow conduit region prior to eruption, suggesting an external trigger for the initial explosion. However subsequent explosive events produced significant amounts of microvesicular juvenile ejecta that suggest the arrival of volatile-rich and actively vesiculating magma to shallow levels in the conduit and contributing to processes of explosive fragmentation.