Abstract
Abstract. Submarine volcanism accounts for ca. 75 % of the Earth's volcanic activity. Yet difficulties with imaging their exteriors and interiors mean that the extrusion dynamics and erupted volumes of deepwater volcanoes remain poorly understood. Here, we use high-resolution 3-D seismic reflection data to examine the external and internal geometry and extrusion dynamics of two late Miocene–Quaternary deepwater (> 2 km emplacement depth) volcanoes buried beneath 55–330 m of sedimentary strata in the South China Sea. The volcanoes have crater-like bases, which truncate underlying strata and suggest extrusion was initially explosive, and erupted lava flows that feed lobate lava fans. The lava flows are > 9 km long and contain lava tubes that have rugged basal contacts defined by ∼90±23 m high erosional ramps. We suggest the lava flows eroded down into and were emplaced within wet, unconsolidated, near-seafloor sediments. Extrusion dynamics were likely controlled by low magma viscosities as a result of increased dissolved H2O due to high hydrostatic pressure and soft, near-seabed sediments, which are collectively characteristic of deepwater environments. We calculate that long-runout lava flows account for 50 %–97 % of the total erupted volume, with a surprisingly minor component (∼3 %–50 %) being preserved in the main volcanic edifice. Accurate estimates of erupted volumes therefore require knowledge of volcano and lava basal surface morphology. We conclude that 3-D seismic reflection data are a powerful tool for constraining the geometry, volumes, and extrusion dynamics of ancient or active deepwater volcanoes and lava flows.
Highlights
The external morphology of volcanoes and their eruptive products reflect, and provide insights into, the processes controlling magma extrusion and volcano construction (e.g. Walker, 1993; Planke et al, 2000; Grosse and Kervyn, 2018)
We suggest that the high hydrostatic pressure of the deepwater environment controlled melt H2O content and internal lava viscosity, effusion rate, and volcano and lava flow morphology and runout distance
We show that the accuracy of total erupted volume estimates can be improved by constraining basal volcano and lava morphologies, seismic images capturing the geological record of deepwater volcanoes cannot determine how much, if any, clastic volcanic material was transported away from the eruption site as pumice rafts or through ocean current clast suspension and subsequent transport (e.g. Jutzeler et al, 2014; Carey et al, 2018)
Summary
The external morphology of volcanoes and their eruptive products reflect, and provide insights into, the processes controlling magma extrusion and volcano construction (e.g. Walker, 1993; Planke et al, 2000; Grosse and Kervyn, 2018). The external morphology of volcanoes and their eruptive products reflect, and provide insights into, the processes controlling magma extrusion and volcano construction Walker, 1993; Planke et al, 2000; Grosse and Kervyn, 2018). By collecting high-resolution quantitative data on the morphology of modern volcanic edifices and surrounding lava flows from airborne–shuttle radar topography or time-lapse multibeam bathymetry, we can estimate erupted volumes, at least for individual eruptive episodes Whilst remote sensing data capture the external morphology of volcanoes and lava flows both before, during, and after eruptions, they do not image their basal surface or internal architecture. Sun et al.: Extrusion dynamics of deepwater volcanoes revealed by 3-D seismic data to test long-term volcano growth and lava emplacement models
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