Nature of Explosive Activity in the 10th Century Eldgja Eruption, Iceland

Moreland, William; Thordarson, T.; Houghton, B. F.

doi:10.1130/abs/2017cd-292830

Cited by 5 publications

(14 citation statements)

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“…Such effects are beyond the capability of a 1D integral model and could further contribute to partial column collapse or particle shedding events, with consequently reduced mass flux of particles and gas in the rising column. An additional consequence of incomplete mechanical and thermal mixing is that the column may retain a hot core of particles that do not supply thermal energy to entrained external water to drive quench fragmentation, which is consistent with observations of pyroclast textures and particle sizes (e.g., Moreland, 2017). Our assumed complete mixing and parameterized fragmentation efficiency thus probably provides an upper bound to the extent of quench fragmentation and ash production.…”

Section: Water Entrainment and Mixing Efficiency Governs Eruption Col...supporting

confidence: 83%

“…Consequently we restrict our analysis and modelling efforts to a class of powerful eruptions driven by magmatic vesiculation and fragmentation in the conduit, where the gas-pyroclast mixture is modified by the entrainment and mixing of external water that is primarily confined to the surface environment. This approach is motivated by observations of pyroclast textures and particle size distributions from several hydrovolcanic eruptions, including the 25 ka Oruanui and 1.8 ka Taupo eruptions, New Zealand (Self and Sparks, 1978;Wilson and Walker, 1985), the 2500 BP Hverfjall Fires eruption (Liu et al, 2017), the 10 th century eruption of Eldgjá Volcano, Iceland (Moreland, 2017;Moreland et al, 2019), the 1875 eruption of Askja Volcano, Iceland (Self and Sparks, 1978;Carey et al, 2009), and the 2011 eruption of Grímsvötn (Liu et al, 2015). Whereas airfall deposits from dry phases of each of these eruptions have total PSDs and porosities typical of Plinian events (Cas and Wright, 1987;Fisher and Schmincke, 2012), PSDs from wet eruption phases are relatively fines-enriched.…”

Section: A Model Of Sustained Explosive Hydrovolcanismmentioning

confidence: 99%

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External Surface Water Influence on Explosive Eruption Dynamics, With Implications for Stratospheric Sulfur Delivery and Volcano-Climate Feedback

et al. 2022

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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.

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Section: Water Entrainment and Mixing Efficiency Governs Eruption Col...supporting

confidence: 83%

Section: A Model Of Sustained Explosive Hydrovolcanismmentioning

confidence: 99%

External Surface Water Influence on Explosive Eruption Dynamics, With Implications for Stratospheric Sulfur Delivery and Volcano-Climate Feedback

et al. 2022

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“…Consequently, an important question is whether using EVA_H would significantly affect forcing data sets used in VolMIP or PMIP. We test this hypothesis using the following: A Tambora (1815)‐like eruption with the same injections conditions as those used in Zanchettin et al, (; Figure ), that is, 60 Tg of SO

_{2}

at 0°N and 24 km altitude in April. An Eldgjá (939)‐like eruption with 32 Tg of SO

_{2}

(Toohey & Sigl, ) at 63.6°N and 12.5 km altitude (Moreland, ; 17.5 km for plume top which corresponds to

\sim

12.5 km for the umbrella cloud) in April. …”

Section: Examples Of Application Of Eva_h: Reconstruction Of Past Volmentioning

confidence: 99%

“…This difference is solely due to differences in model structure (including sensitivity to eruption latitude) and calibration processes. When we use the estimated injection height of 12.5 km for this eruption (Moreland, ), the resulting SAOD is significantly lower than the one predicted by EVA_H with a 25 km injection height or the one predicted by EVA. In particular, the predicted SAOD is 50–90% smaller than the one predicted by EVA.…”

Section: Examples Of Application Of Eva_h: Reconstruction Of Past Volmentioning

confidence: 99%

A New Volcanic Stratospheric Sulfate Aerosol Forcing Emulator (EVA_H): Comparison With Interactive Stratospheric Aerosol Models

et al. 2020

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Idealized models or emulators of volcanic aerosol forcing have been widely used to reconstruct the spatiotemporal evolution of past volcanic forcing. However, existing models, including the most recently developed Easy Volcanic Aerosol (EVA; Toohey et al., doi: 10.5194/gmd‐2016‐83), (i) do not account for the height of injection of volcanic SO 2; (ii) prescribe a vertical structure for the forcing; and (iii) are often calibrated against a single eruption. We present a new idealized model, EVA_H, that addresses these limitations. Compared to EVA, EVA_H makes predictions of the global mean stratospheric aerosol optical depth that are (i) similar for the 1979–1998 period characterized by the large and high‐altitude tropical SO 2 injections of El Chichón (1982) and Mount Pinatubo (1991); (ii) significantly improved for the 1998–2015 period characterized by smaller eruptions with a large variety of injection latitudes and heights. Compared to EVA, the sensitivity of volcanic forcing to injection latitude and height in EVA_H is much more consistent with results from climate models that include interactive aerosol chemistry and microphysics, even though EVA_H remains less sensitive to eruption latitude than the latter models. We apply EVA_H to investigate potential biases and uncertainties in EVA‐based volcanic forcing data sets from phase 6 of the Coupled Model Intercomparison Project (CMIP6). EVA and EVA_H forcing reconstructions do not significantly differ for tropical high‐altitude volcanic injections. However, for high‐latitude or low‐altitude injections, our reconstructed forcing is significantly lower. This suggests that volcanic forcing in CMIP6 last millenium experiments may be overestimated for such eruptions.

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“…Unit 7 originated from the subaerial southern Eldgjá fissure segment (Figure 2) and formed a poly-lobate deposit (Moreland et al, 2019). The tephra of Unit 7 is black to metallic blue in color, is very well to well sorted (Moreland, 2017) in the proximal to medial regions (<20 km from source). Unit 8 has a brown color and is lacking in achneliths, consistent with a cooler and wetter eruption environment.…”

Section: The 10th Century Eldgjá Eruptionmentioning

confidence: 99%

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

Hajimirza

Jones

Moreland

et al. 2022

Geochem Geophys Geosyst

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The interaction of magma with external water commonly enhances magma fragmentation through the conversion of thermal to mechanical energy and results in an increased production of fine‐grained volcanic tephra. Magma‐water interaction is thus of importance for hazard mitigation on both a local and a regional scales. The relative proportion of water that interacts with magma, quantified as the water‐to‐melt mass ratio, is thought to determine the efficiency of thermal to mechanical energy conversion, termed the fragmentation efficiency. Here, we analyze the pyroclast size distributions from the 10th century Eldgjá fissure eruption in Iceland, where parts of the fissure erupted subglacially and other erupted subaerially. The subglacially erupted magma passed through a column of glacial meltwater, resulting in a larger proportion of finer pyroclast sizes relative to the subaerially erupted, purely magmatic tephra. This finer grain size distribution has been attributed to quench‐granulation induced by enhanced cooling upon interaction with external water. We hypothesize that the additional fragmentation (surface) energy required to produce the finer grained hydromagmatic deposits is due to the conversion of thermal to mechanical energy associated with the entrainment of water into the volcanic jet, as it passed through a column of subglacial melt water. Based on field and granulometry data, we estimate that the interaction of the volcanic jet with the meltwater provided an additional fragmentation energy of approximately 3–14 kJ per kg of pyroclasts. We numerically model the hydrofragmentation energy within a jet that passes through a layer of meltwater. We find that the water‐to‐melt mass ratio of entrained water required to produce the additional fragmentation energy is in the range of 1–2, which requires a minimum ice melting rate of 104 m3 s−1. Our simulation results show that the water‐to‐melt ratio is an important parameter that controls the ascent of plume in the atmosphere.

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Nature of Explosive Activity in the 10th Century Eldgja Eruption, Iceland

Cited by 5 publications

References 0 publications

External Surface Water Influence on Explosive Eruption Dynamics, With Implications for Stratospheric Sulfur Delivery and Volcano-Climate Feedback

External Surface Water Influence on Explosive Eruption Dynamics, With Implications for Stratospheric Sulfur Delivery and Volcano-Climate Feedback

A New Volcanic Stratospheric Sulfate Aerosol Forcing Emulator (EVA_H): Comparison With Interactive Stratospheric Aerosol Models

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

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