GSA Connects 2021 in Portland, Oregon

Paper No. 37-12
Presentation Time: 4:50 PM


LERNER, Allan, Department of Earth Sciences, University of Oregon, 100 Cascade Hall, 1272 University of Oregon, Eugene, OR 97403 and WALLACE, Paul J., Department of Earth Sciences, University of Oregon, Eugene, OR 97403

Kīlauea (Hawaiʻi, USA) has intermittently operated as an open-system volcano throughout its ~200 years of recorded history. The most obvious open-system behavior is convecting lava lake activity within Kīlauea’s summit caldera (e.g., from 1823–1894, 1906–1924, 2008–2018). Another open-system phenomenon at Kīlauea is lava drain-back, where ponded lava returns to the deeper magmatic system by flowing down through fissures or cracks. Lava drain-back has been observed during a number of Kīlauea eruptive episodes, including the 1959 Kīlauea Iki eruption (Richter et al. 1970) and most recently in the early weeks of the 2020 summit eruption. H2O and sulfur (as SO2) significantly degas from Kīlauea magmas only at very low pressures (<200 m depth) and lava lake convection and lava drain-back are therefore key processes that recycle shallowly-degassed, H2O- and sulfur-depleted melts back into Kīlauea’s plumbing system.

Primary Kīlauea magmas are estimated to contain 0.5–0.7 wt% H2O and 1300–1600 ppm S (e.g., Anderson and Brown 1993; Edmonds et al. 2013), but mixing with recycled volatile-depleted melts could cause significant variations in volatile concentrations between magma batches. H2O- and sulfur-poor submarine glasses from the Puna Ridge, which erupted at depths where hydrostatic pressure would have prevented most degassing, provide strong evidence for the recycling of shallowly-degassed magma (Dixon et al. 1991). Additionally, melt inclusions from the 2018 Lower East Rift Zone eruption are commonly sulfur-poor (400–800 ppm S) and have isotopically light sulfur signatures (0 to -2‰ δ34S) consistent with sulfur-loss by shallow SO2 degassing (Lerner et al. 2021). Many of these sulfur-depleted melt inclusions are hosted in Fo86-89 olivine grains, indicating that at times in the past, highly primitive Kīlauea magmas (1200–1300 °C) reached very shallow depths and underwent substantial degassing before being recycled back into the magmatic system.

We propose that Kīlauea’s long history of lava lake activity and lava drain-back events have recycled substantial volumes of degassed magma, including primitive magmas, into the shallow magmatic system. Hybridization between fresh magmas and recycled volatile-depleted magmas may control important eruption properties such as fire fountain height and lava viscosity.