External surface water influence on explosive eruption dynamics, with implications for stratospheric sulfur delivery and volcano-climate feedback

Abstract

Explosive volcanic eruptions can inject sulfur dioxide (SO2) into the stratosphere to form aerosol particles that modify Earth’s radiation balance and drive surface cooling. Eruptions involving interactions with shallow layers (< 500 m) of surface water and ice modify the eruption dynamics that govern the delivery of SO2 to the stratosphere. External surface water potentially controls the evolution of explosive eruptions in two ways that are poorly understood: (1) by modulating the hydrostatic pressure within the conduit and at the vent, and (2) through the ingestion and mixing of external water, which governs fine ash production as well as eruption column buoyancy flux. To make progress, we couple one-dimensional models of magma flow in the conduit and atmospheric column rise through a novel ”magma-water interaction” model that simulates the occurrence, extent and consequences of water entrainment depending on the depth of a surface water layer. We explore the effects of hydrostatic pressure on magma ascent in the conduit and gas decompression at the vent, and the conditions for which water entrainment drives fine ash production by quench fragmentation, eruption column collapse, or outright failure of the jet to breach the water surface. We show that the efficiency of water entrainment into the jet is the predominant control on jet behavior. For an increase in water depth of 50 to 100 m, the critical magma mass eruption rate required for eruption columns to reach the tropopause increases by an order of magnitude. Finally, we estimate that enhanced emission of fine ash leads to up to a 2-fold increase in the mass flux of particles < 125 microns to spreading umbrella clouds, together with up to a 10-fold increase in water mass flux, conditions that can enhance the removal of SO2 via chemical scavenging and ash sedimentation. Overall, compared to purely magmatic eruptions, we suggest that hydrovolcanic eruptions will be characterized by a reduced delivery of SO2 to the stratosphere. Our results thus suggest the possibility of an unrecognized volcano-climate feedback mechanism arising from modification of volcanic climate forcing by direct interaction of erupting magma with varying distributions of water and ice at the Earth’s surface.

Quantifying the Water‐to‐Melt Mass Ratio and Its Impact on Eruption Plumes During Explosive Hydromagmatic Eruptions

“…For high conversion factors, β > 10%, only a few centimeters of meltwater is required to match the measured surface energy, whereas for β = 2%, the required height of meltwater column is greater than 70 m. Among this wide range of estimated meltwater column heights, however, only model simulations with Z w < 35 m produce plume heights that are comparable with the interpretations from fallout deposits. At meltwater depths of greater than 35 m our model predicts that the plume will collapse because the increase in density due to vapor condensation does not allow the jet to become buoyant (Koyaguchi & Woods, 1996; Rowell et al., 2021).…”

“…However, our simulation results show that, with identical exit conditions at the vent, mixtures that pass through meltwater can reach higher elevations than dry plumes (Figure 4). This is true for situations where the thermal energy of the jet is high enough to vapourize all, or most of, the entrained meltwater (Koyaguchi & Woods, 1996; Rowell et al., 2021). Our findings therefore suggest that the relative increase in the plume height in the subglacial phase might be due the entrainment of glacial meltwater.…”

“…Interaction of volcanic jets with external water, that is water other than that originally dissolved within the erupting magma, can impact the jet dynamics. The entrained ambient water into the jet may condense and cause the jet to collapse or the water may vaporize and increase the jet buoyancy and thus the stability of the eruption (Cahalan & Dufek, 2021; Head & Wilson, 2003; Koyaguchi & Woods, 1996; Rowell et al., 2021; Van Eaton et al., 2012). Moreover, interaction of volcanic jets with external water can further fragment primary magmatic pyroclasts, by secondary hydrofragmentation processes.…”

“…Moreover, we examine the impact of this ratio on the ascent of the eruption plume in the atmosphere. The water-to-melt mass ratio directly controls how much of the water condenses in the jet, which itself determines whether the jet becomes a stable buoyant plume or collapses (Koyaguchi & Woods, 1996;Rowell et al, 2021). A schematic of a subglacial explosive eruption with a pyroclastic jet erupting within an ice cauldron.…”

Volatile trace metals deposited in ice as soluble volcanic aerosols during the 17.7.ka eruptions of Mt Takahe, West Antarctic Rift

“…During hydrovolcanic activity, external ice-water may modulate pressure at the vent as well as interact directly with magmatic gases. The production of fine hydrovolcanic ash may also promote chemical scavenging processes on ash surfaces by adsorption (Ayris et al, 2013;Rowell et al, 2021). Large explosive eruptions, such as the early ash-producing eruptions associated with the 17.7 ka event, may generate rapidly ascending plumes that can reach heights in excess of 30-40 km, although the eruption column heights for this series of eruptions are unconstrained.…”