EXPLAINING DIVERSITY IN RECENT PYROCLASTIC ERUPTIONS AT KĪLAUEA, HAWAII

Kīlauea shows diverse eruptive behaviors that span from explosive subplinian events through Hawaiian fountaining to passive lava effusion; timescales range from short-lived (seconds to minutes) to persistent (months to years), while effusion rates vary from sustained to intermittent, and from steady to unsteady. We offer here snapshots of magmatic pyroclastic activity over the last 500 years which include:

• A short-lived subplinian eruption in c. 1650 CE
• An intensely powerful Hawaiian fountaining eruption from c. 1500 CE
• The most powerful 20^th century Hawaiian fountain (1959)
• Weak impulsive explosive eruptions from Halema‘uma‘u in 2008
• Prolonged spattering episodes from Halema‘uma‘u in 2013-2016
• Transitions between spattering and low fountaining behavior at Kamoamoa in 2011.

A first-order control on Kīlauea’s eruptive activity relates to the patterns of shallow-level release (‘exsolution’) and retention or escape (‘outgassing’) of initially dissolved gases from magma; these processes drive much of the rich diversity in eruptive behavior cited above and modulate both the abrupt and progressive changes of eruption dynamics between and within eruptive episodes. Processes driving the sometimes coupled and sometimes independent behavior of volcanic gases are, in turn, strongly influenced by the properties and behavior of the melt and the initial dissolved volatile species. Three endmember styles of ascent and vesiculation map to the styles of eruption observed at Kīlauea. Partial coupling of the fraction of relative small late-exsolved bubbles permits the sustained but unsteady fountaining behavior associated with classical Hawaiian episodes. Weak short-lived impulsive explosions when the majority of the volatile phase rises as decimeter-to-meter sized bubbles decoupled from the adjacent melt. Conditions of very rapid ascent and delayed but vigorous disequilibrium exsolution of large numbers of very small bubbles promote the rarer subplinian eruption.