Submarine terraced deposits linked to periodic collapse of caldera-forming eruption columns

Gilchrist, J. T., Jellinek, A. M., Hooft, E. E. E., and Wanket, S. (2023). Submarine terraced deposits linked to periodic collapse of caldera-forming eruption columns. Nature Geoscience.

Catastrophic caldera forming (CCF) eruptions are the most impressive of volcanic phenomena in the geological record. However, relationships between the size of CCF eruptions and the magnitudes as well as types of their associated hazards are equivocal and intensely debated. The character and intensity of hazards predominantly depend on the extent to which mixtures of erupted ash and entrained gases are delivered to the atmosphere and to the ground. Using the results of analog experiments and spectral analyses of well-preserved periodic terracing observed at the Sumisu and Santorini CCF eruption deposits we constrain the dynamics governing these CCF eruptions. We show that submarine eruptions in a `total collapse' (TC) regime deliver material to the water surface and seabed in periodic annular “sedimentation waves" (SW). Depending on the period between successive SWs, their impact and spread at the sea surface and seabed can excite tsunamis, drive radial PDCs, and deliver material to form concentric backward facing terraces with a wavelength that decreases with distance, or deposits that thin monotonically. In particular, SWs descending from powerful “deep water” eruption columns with heights comparable to the water depth, involve minimal interactions with the water surface and produce a deposit architecture similar to that observed at Sumisu caldera. SWs from similarly strong “shallow water” eruptions with tall subaerial columns, however, are strongly modified by the dynamics of their impact and spread at the water surface. Where these SWs enter the water as jets and impact the seabed, intensive scouring and deposition produce relatively broad and concave terraces consistent with observations from Santorini and Macauley calderas. Our results enable a novel explicit classification of submarine CCF eruption dynamics and mass eruption rates from the architectures of their deposits and will inform studies of hazards of CCF events and ongoing and future ocean drilling expeditions. 

Catastrophic caldera-forming eruptions

Gilchrist, J. T., & Jellinek, A. M. (2021). Sediment waves and the gravitational stability of volcanic jets. Bulletin of Volcanology, 83(10), 1-59.

The meticulous field work of Walker (1980), Self and Rampino (1981), Self et al. (1984), Rose and Chesner (1987), Hildreth and Mahood (1986), Branney (1991) and Druitt and Francaviglia (1992) demonstrated the destructive potential of catastrohpic caldera-forming eruptions, the largest known explosive eruptions in the geologic record. Using insights from this pioneering volcanology work and combining it with seminal studies on turbulent plumes by Morton et al. (1956) and analog experiments on volcanic jets by Carey et al. (1988), I conduct new analog experiments that test the effect of intermediate-sized "inertial" particles modeling pumice lapilli on the gravitational stability of jet columns modeling catastrophic caldera-forming eruptions. Inertial particles have a complex two-way momentum transfer coupling with the fluid they are suspended in and this coupling affects the ability of an eruption column to ingest and mix in the surrounding atmosphere, which is a crucial process for determining whether an eruption column collapses or rises buoyantly. Consequently, inertial particles play an important role in the dynamics of eruption columns and, in turn, determining the initial conditions of spreading ash clouds in the atmosphere, which serve as key input parameters for sophisticated ash transport models that predict hazards for air traffic and volcano-climate cooling effects on Earth's surface

Are eruptions from linear fissures and caldera ring dykes more likely to produce pyroclastic flows?

Jessop, D. E., Gilchrist, J., Jellinek, A. M., & Roche, O. (2016). Are eruptions from linear fissures and caldera ring dykes more likely to produce pyroclastic flows?. Earth and Planetary Science Letters, 454, 142-153.

My previous work performed with Dr. David Jessop, Dr. Mark Jellinek and Dr. Olivier Roche investigated the effect of these particles when injected from annular vent geometries as expected to occur during catastrophic caldera eruptions. We have shown that these particles can enhance entrainment and in turn inhibit column collapse during Catastrophic Caldera-Forming explosive eruptions, whereas lower aspect ratio caldera ring vent geometries can do the opposite. The largest of these caldera-forming eruptions have not been witnessed with modern scientific instrumentation, therefore our understanding relies on analyses of their deposits, computer simulations and our analog laboratory experiments. Further analog experiments investigating this style of eruption can help us predict their effects on the global climate and in turn their threat to life on Earth.