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 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 and eruption column buoyancy flux. To make progress, we couple one-dimensional models of conduit flow 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 50–100 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 μm 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. On average, compared to purely magmatic eruptions, we suggest that hydrovolcanic eruptions will be characterized by reduced climate forcing. Our results suggest one possible mechanism for volcano-climate feedback: temporal changes with climate in surface distributions of water and ice may modify the relative global frequency or dominance of hydrovolcanic eruption processes, modulating, in turn, global patterns in volcano-climate forcing.

Out of the blue: Volcanic SO2 emissions during the 2021–2022 eruptions of Hunga Tonga—Hunga Ha’apai (Tonga)

“…Assuming the same contributions from spectral fitting errors (~15%), the total uncertainty on lower tropospheric OMPS SO 2 measurements is ~54%. Finally, as mentioned earlier, we stress that all SO 2 data for the HTHH eruption plumes must be evaluated in the context of potentially significant SO 2 removal by hydrometeors and volcanic ash (Rowell et al, 2022), and rapid conversion of volcanic SO 2 to sulfate aerosol in the water-rich plumes (Sellitto et al, 2022). A complete appraisal of the sulfur budget of the HTHH eruptions will require…”

“…There are at least two plausible interpretations of the EPIC SO 2 data (Figure 3). The observed SO 2 distribution may be diagnostic of the water-rich, phreatomagmatic HTHH eruption in which SO 2 in the plume core was significantly scrubbed or entirely stripped from the plume by co-emitted water (derived from the magma, seawater and/or entrained atmosphere), as modeled by Rowell et al (2022). Alternatively, the EPIC SO 2 observations may reflect temporally variable magmatic SO 2 emissions during the eruption, e.g., due to pre-eruptive accumulation of magmatic gases (including SO 2 ) at the top of the magma reservoir supplying the eruption.…”

“…Prior to 2021-22, confirmed eruptions of HTHH occurred in June 1988March 2009, and December 2014-15 (Global Volcanism Program, 2013, with the latter two eruptions including periods of island growth and erosion (Vaughan and Webley, 2010;Garvin et al, 2018). The typical eruption style of HTHH is the rarely observed Surtseyan style of activity, involving magma-seawater interaction, ephemeral island growth, and emission of volcanic plumes rich in water vapor, condensed water and fine volcanic ash, with the potential for significant scrubbing of SO 2 emissions via chemical scavenging and ash sedimentation (e.g., Rowell et al, 2022).…”

“…Our goals are to analyze SO 2 emissions prior to the paroxysmal January 15 eruption, to estimate total SO 2 emissions during the HTHH eruptions and aid assessment of potential impacts on the atmosphere and climate, and to gain insight into the fate of volcanic SO 2 emissions during water-rich, explosive submarine eruptions. Whilst the potential for scavenging of volcanic SO 2 by hydrometeors (derived from water of magmatic and atmospheric origin) and volcanic ash particles in subaerial volcanic eruption plumes is well known (e.g., Rose et al, 1995;Textor et al, 2003;Zhu et al, 2020), recent modeling work suggests that such scavenging is enhanced in submarine eruptions involving external surface water (Rowell et al, 2022). As the largest submarine explosive eruption to date in the era of UV satellite observations (since 1978), the 2022 HTHH eruption provides some unique observational constraints on these processes.…”

Cryospheric Impacts on Volcano-Magmatic Systems

“…Outstanding questions concern how the cryospheric environment impacts magma fragmentation and explosivity. Recent work on eruptions in aqueous (englacial) environments by Rowell et al (2021) suggests that magma-water interactions can produce more energetic eruption columns. As discussed above, the presence of ice and water can increase rates of heat transfer from the magma (and its fragments) to its environment.…”