Clark, Acacia1; Carey, Rebecca1; Jutzeler, Martin1; Mitchell, Samuel2
1University of Tasmania, Hobart, Australia, 2University of Bristol, Bristol, United Kingdom
Submarine eruptions are poorly understood compared to their subaerial counterparts due to challenges accessing and observing them. The 2012 silicic submarine eruption of Havre Volcano in the Kermadec Arc was the largest deep ocean eruption (~900 – 1220 meters below sea level) ever recorded.
The main vent transitioned in eruption style during the event. The current eruption framework describes the onset of magma disruption on the seafloor at high (107 kgs-1) eruption rates, which produced a large pumice raft (~1 km3) accompanied with a giant pumice seafloor deposit. This phase transitioned to an intermediate phase of unknown intensity that produced an ash-lapilli-block (ALB) deposit proximal to the vent. The final eruptive phase was low intensity (104 kgs-1) effusive magma emplacement that produced a 250 m-high dome complex (Dome OP) over the vent. Previous studies have focused on microtextures of these main phases to understand shallow conduit processes.
We have identified lobe deposits around Dome OP which stratigraphically sit above the ALB deposit but were emplaced prior to the end of the effusive phase. These deposits represent a transitional phase between high to low eruption rates. Detailed microtextural studies were conducted on four representative clasts from in-situ Dome OP together with three clasts from surrounding lobe deposits, and two dense end-member ALB clasts not previously studied.
Microlites of the same crystal types and habits are present in lobe deposits and in-situ Dome OP clasts, where they are most abundant. ALB clasts are microlite free with almost spherical vesicles. Clasts from lobe deposits have elongated vesicles with round edges and in-situ Dome clasts have elongated and flattened vesicles. ALB clasts have the highest vesicle number density, followed by lobe deposits and then in-situ Dome clasts. Rounded vapor-phase cristobalite is present in lobe deposits and in-situ Dome O clasts, whereas in-situ Dome P clasts contain an abundance of oblong cristobalite crystals that exist entirely within the groundmass. No discernible correlation could be made between vesicle size and cristobalite crystal size. Silicic submarine domes are morphologically and texturally similar to subaerial domes, indicating hydrostatic pressure has a minor role in outgassing and emplacement processes of lava domes.
Acacia graduated with a Bachelor of Science from the University of Sydney in 2015. After taking some time to explore Canada she returned to undertake her Honours at the University of Tasmania (UTAS) and graduated with First Class. She intends to begin her PhD at UTAS in late 2020.