Rapid heat discharge during deep-sea eruptions generates megaplumes and disperses tephra

Samuel S Pegler,David J Ferguson

doi:10.1038/s41467-021-22439-y

Abstract

Deep-marine volcanism drives Earth’s most energetic transfers of heat and mass between the crust and the oceans. While magmatic activity on the seafloor has been correlated with the occurrence of colossal enigmatic plumes of hydrothermal fluid known as megaplumes, little is known of the primary source and intensity of the energy release associated with seafloor volcanism. As a result, the specific origin of megaplumes remains ambiguous. By developing a mathematical model for the dispersal of submarine tephras, we show that the transport of pyroclasts requires an energy discharge that is sufficiently powerful (~1-2 TW) to form a hydrothermal plume with characteristics matching those of observed megaplumes in a matter of hours. Our results thereby directly link megaplume creation, active magma extrusion, and tephra dispersal. The energy flux at the plume source required to drive the dispersal is difficult to attain by purely volcanogenic means, and likely requires an additional input of heat, potentially from rapid evacuations of hot hydrothermal fluids triggered by dyke intrusion. In view of the ubiquity of submarine tephra deposits, our results demonstrate that intervals of rapid hydrothermal discharge are likely commonplace during deep-ocean volcanism.

Highlights

Deep-marine volcanism drives Earth’s most energetic transfers of heat and mass between the crust and the oceans
The apparent ubiquity of widely dispersed submarine tephras (Fig. 1), and the aforementioned correlation between lava extrusion and megaplume detection, both indicate that syn-eruptive energy transfers of a magnitude comparable to that predicted for the Northern Escanaba (NESCA) eruption are an intrinsic characteristic of many volcanic events occurring in the deep oceans
If the energy transfer driving megaplume creation is primarily associated with rapid evacuation of intracrustal fluid reservoirs rather than magmatic heating we anticipate that the processes that instigate this fluid release will generally produce lava extrusion

Summary

Introduction

Deep-marine volcanism drives Earth’s most energetic transfers of heat and mass between the crust and the oceans. While models of the dynamics of megaplumes have suggested they form rapidly[17], little is known of the rates of energy or volume discharge feeding the plume during a seafloor eruption, of the primary source of the hydrothermal input, nor of the role of eruption dynamics on plume formation Another open question regarding seafloor volcanism is the process responsible for the dispersal of pyroclastic deposits in the deep ocean. Older tephra-bearing sediments recovered from sediment cores taken on the flanks of MORs indicate similar dispersal scales[29,30] These tephras provide evidence for explosive pyroclastic eruption styles[15,19], something that has traditionally been considered extremely rare due to the high hydrostatic pressure[31,32] (we note that some debate exists as to the potential for tephra to be generated by magmatic fragmentation of fluid magma[15] versus other brecciation processes such as thermal granulation[33] and/or hydrovolcanic fragmentation[28]). With the exception of the pyroclastic deposit studied here (sampled and mapped by15), no detailed information exists on

Methods

Results

Conclusion