Vesiculation of high fountaining Hawaiian eruptions: episodes 15 and 16 of 1959 Kīlauea Iki

Abstract

The 1959 summit eruption of Kīlauea volcano produced the highest recorded Hawaiian fountain in Hawai'i. Quantitative analysis of closely spaced samples from the final two high-fountaining episodes of the eruption result in a fine-scale textural study of pyroclasts and provide a record of postfragmentation processes. As clast vesicularity increases, the vesicle number density decreases and vesicle morphology shifts from small and round to larger and more irregular. The shift in microtexture corresponds to greater degrees of postfragmentation expansion of clasts with higher vesicularity. We suggest the range of clast morphologies in the deposit is related to thermal zonation within a Hawaiian fountain where the highest vesicularity clasts traveled in the center and lowest traveled along the margins. Vesicle number densities are greatest in the highest fountaining episode and therefore scale with intensity of activity. Major element chemical analyses and fasciculate crystal textures indicate microlite-rich zones within individual clasts are portions of recycled lava lake material that were incorporated into newly vesiculating primary melt.

Externally triggered renewed bubble nucleation in basaltic magma: The 12 October 2008 eruption at Halema‘uma‘u Overlook vent, Kīlauea, Hawai‘i, USA

“…The high number density of small bubbles is comparable to that in the most powerful basaltic eruptions (Figure 6) [e.g., Mangan and Cashman , 1996; Mangan et al , 1993; Lautze and Houghton , 2005, 2007; Sable et al , 2009; Stovall et al , 2011, 2012]. The presence of a high number of small bubbles (<50 μ m) implies rapid nucleation as a response to decompression.…”

“…High magma ascent rates and lower degrees of vapor segregation lead to reduced timescales for bubble nucleation and growth, generating supersaturation of volatiles, bubble overpressure and rapid late stage acceleration of the magma [e.g., Proussevitch and Sahagian , 1996, 1998]. Fountaining episodes of Pu‘u ‘Ō‘ō [ Heliker et al , 2003], Mauna Ulu [ Swanson et al , 1979], and Kīlauea Iki [ Stovall et al , 2011, 2012] are representative of such systems. Our goal here is to assess the dynamics of vesiculation during the 12 October 2008 event using the only physical record of the ascent, degassing and fragmentation of the magma—the juvenile ejecta.…”

MeMoVolc consensual document: a review of cross-disciplinary approaches to characterizing small explosive magmatic eruptions

“…In basaltic magma, post-fragmentation effects can be a complication even for these sizes (e.g. Szramek et al 2006;Costantini et al 2010;Gurioli et al 2008;Pioli et al 2014;Pistolesi et al 2008Pistolesi et al , 2011Stovall et al 2011Stovall et al , 2012. In these cases, the challenge is to identify, quantify and remove post-fragmentation effects in order to isolate textures preserved across the fragmentation zone.…”

“…The textural signature that was quenched immediately at the fragmentation level has to be distinguished from the textural effects of post-fragmentation processes, including microlite formation and bubble nucleation, expansion, collapse, coalescence and Ostwald ripening that will change clast vesicularity or vesicle size and shapes once the pyroclast has been formed (e.g. Thomas et al 1994;Herd and Pinkerton 1997;Larsen and Gardner 2000;Gurioli et al 2008;Costantini et al 2010;Stovall et al 2011Stovall et al , 2012. The time window for post-fragmentation changes depends on magma composition, viscosity and fragmentation depth.…”

Dynamics of an open basaltic magma system: The 2008 activity of the Halema‘uma‘u Overlook vent, Kīlauea Caldera

“…External triggering is not a feature of either Hawaiian or Strombolian explosivity or any of the less formally defined variations on these styles. The rock-falls also induced a second nucleation of bubbles in parts of the Halema'uma'u magma within the shallow magmatic system , not seen during Hawaiian fountaining (Stovall et al, 2011(Stovall et al, , 2012 or explosions at Stromboli (Lautze and Houghton, 2007). This suggests that the eruption at Kīlauea in 2008 would, except for the instability of the newly-formed vent walls, have rapidly evolved to a passively outgassing stable lava pond, perhaps reminiscent of the long periods of such activity that characterised much of the 19th and early 20th centuries.…”