Rapid and slow: Varying magma ascent rates as a mechanism for Vulcanian explosions

Cassidy, Michael; Cole, Paul; Hicks, Kelby E.; Varley, Nick; Peters, Nial; Lerner, Allan

doi:10.1016/j.epsl.2015.03.025

Cited by 58 publications

(51 citation statements)

References 57 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Assuming that the June batch caused the October 18 explosion, the averaged ascent rate over this period is ~3 m h -1 . This is consistent with tilt signal modelling (Neuberg et al, 2018) but it is at the low end (Cassidy et al, 2018) of effusive eruptions with intermittent explosive activity, such as at Soufrière Hills (Edmonds et al, 2003), Unzen (Hirabayashi et al, 1995), Mt St Helens (Gerlach and McGee, 1994), and Colima (Cassidy et al, 2015). This low ascent rate nevertheless gave rise to one of the most powerful recent event at…”

Section: Explosion Trigger and Eruptive Intensitysupporting

confidence: 83%

Triggering of the powerful 14 July 2013 Vulcanian explosion at Tungurahua Volcano, Ecuador

Gaunt

Burgisser

Mothes

et al. 2020

Journal of Volcanology and Geothermal Research

View full text Add to dashboard Cite

The 14 July 2013 Vulcanian explosion at Tungurahua occurred after two months of quiescence and was extremely powerful, generating some of the highest infrasound energies recorded worldwide. Here we report on how a combination of geophysical data, textural measurements, and physical and mechanical tests on eruptive products allowed us to determine the processes that led to the pressurization of the conduit and triggering of this large Vulcanian event. Two weeks prior to the 14 July event, daily seismic counts and radial tilt began to steadily increase, indicating the probable intrusion of a new batch outgassing, formed a dense (< 2 % porosity), highly crystalline plug. This plug had a very low matrix permeability (10-17 to 10-18 m 2) and high tensile strength (9 to 13 MPa), forming an efficient rigid seal and preventing significant outgassing from the conduit. 2) Just below the plug, a high porosity zone (up to 50%) formed, acting as a gas storage zone, with pressurisation occurring partly under closed-system degassing. 3) The shallow conduit became pressurised due to the combination of both gas accumulation and the resistance of the plug to magma column extrusion in response to a new influx of magma. 4) On the 14 th of July a critical gas over-pressure was reached, overcoming the strength of the dense plug of magma, trigging extreme decompression and evacuation of the top two kilometres of the conduit. 5) The newly intruded magma was not directly involved in the explosion and continued to ascend during the week following the explosion.

show abstract

Section: Explosion Trigger and Eruptive Intensitysupporting

confidence: 83%

Triggering of the powerful 14 July 2013 Vulcanian explosion at Tungurahua Volcano, Ecuador

Gaunt

Burgisser

Mothes

et al. 2020

Journal of Volcanology and Geothermal Research

View full text Add to dashboard Cite

show abstract

“…We infer that pressure changes related to vein opening triggered either fragmentation or vesiculation of neighboring magma, depending upon the rate and amount of decompression, and the porosity-controlled fragmentation threshold (Spieler et al, 2004). Magma porosity within the shallow conduit was heterogeneous over short spatial scales, resulting from the integrated effects of strain localization and trapping of volatile-rich deeper magma fragments within tuffisite veins (Schipper et al, 2013;Castro et al, 2014;Cassidy et al, 2015). As a result, individual decompression events could simultaneously elicit fragmentation and vesiculation responses in jutxaposed, decimeter to meter-scale magma domains, with preferential "quarrying" of vesicular domains promoting release of batches of exsolved gas, and boosting the efficiency of gasmagma separation (Castro et al, 2012.…”

Section: Broader Implications For Shallow Conduit Processesmentioning

confidence: 99%

“…Direct measurement of exsolved gas fluxes and ejected particle velocities during silicic eruptions, combined with petrological characterization (Cassidy et al, 2015), and investigation of trace metal and short-lived radionuclides within tuffisites (Berlo et al, 2013) may be better approaches. The glassy tuffisite veins, however, provide rich textural and volatile records that belie a multi-scale evolutionary complexity that cannot be ignored in the description of silicic conduits that are in transitional explosive-effusive activity.…”

Section: Broader Implications For Shallow Conduit Processesmentioning

confidence: 99%

Conduit Dynamics in Transitional Rhyolitic Activity Recorded by Tuffisite Vein Textures from the 2008–2009 Chaitén Eruption

et al. 2016

View full text Add to dashboard Cite

The mechanisms of hazardous silicic eruptions are controlled by complex, poorly-understood conduit processes. Observations of recent Chilean rhyolite eruptions have revealed the importance of hybrid activity, involving simultaneous explosive and effusive emissions from a common vent. Such behavior hinges upon the ability of gas to decouple from magma in the shallow conduit. Tuffisite veins are increasingly suspected to be a key facilitator of outgassing, as they repeatedly provide a transient permeable escape route for volcanic gases. Intersection of foam domains by tuffisite veins appears critical to efficient outgassing. However, knowledge is currently lacking into textural heterogeneities within shallow conduits, their relationship with tuffisite vein propagation, and the implications for fragmentation and degassing processes. Similarly, the magmatic vesiculation response to upper conduit pressure perturbations, such as those related to the slip of dense magma plugs, remains largely undefined. Here we provide a detailed characterization of an exceptionally large tuffisite vein within a rhyolitic obsidian bomb ejected during transitional explosive-effusive activity at Chaitén, Chile in May 2008. Vein textures and chemistry provide a time-integrated record of the invasion of a dense upper conduit plug by deeper fragmented magma. Quantitative textural analysis reveals diverse vesiculation histories of various juvenile clast types. Using vesicle size distributions, bubble number densities, zones of diffusive water depletion, and glass H 2 O concentrations, we propose a multi-step degassing/fragmentation history, spanning deep degassing to explosive bomb ejection. Rapid decompression events of ∼3-4 MPa are associated with fragmentation of foam and dense magma at ∼200-360 m depth in the conduit, permitting vertical gas and pyroclast mobility over hundreds of meters. Permeable pathway occlusion in the dense conduit plug by pyroclast accumulation and sintering preceded ultimate bomb ejection, which then triggered a final bubble nucleation event. Our results highlight how the vesiculation response of magma to decompression events is highly sensitive to the local melt volatile concentration, which is strongly spatially Saubin et al.Chaitén Tuffisites Record Conduit Processes heterogeneous. Repeated opening of pervasive tuffisite vein networks promotes this heterogeneity, allowing juxtaposition of variably volatile-rich magma fragments that are derived from a wide range of depths in the conduit. This process enables efficient but explosive removal of gas from rhyolitic magma and creates a complex textural collage within dense rhyolitic lava, in which neighboring fused clasts may have experienced vastly different degassing histories.

show abstract

“…The processes triggering “vulcanian” gas‐and‐ash explosions at active lava domes remain widely debated as competing hypotheses exist at both all‐encompassing (Chouet et al, ) and volcano‐specific (Hall et al, ) scales. Vulcanian events have been attributed to a range of processes, from the ascent of a fresh batch of bubbly magma in the shallow conduit (Cassidy et al, ) and gas pressure accumulation due to fracture sealing (Kendrick et al, ; Okumura & Sasaki, ) healing (Gardner et al, ; Lamur et al, ) and cyclic gas fluxing (Michaut et al, ) to the development of shear fractures along the margins of volcanic conduits during ascent of highly viscous magma (Lavallée et al, ; Lensky et al, ; Tuffen et al, ). On the other hand, there is a general agreement on the processes that result in fracturing of parts of the dome during explosive activity to allow the ejection of ash‐laden plumes.…”

Section: Introductionmentioning

confidence: 99%

Brittle‐Ductile Deformation and Tensile Rupture of Dome Lava During Inflation at Santiaguito, Guatemala

et al. 2019

View full text Add to dashboard Cite

Gas-and-ash explosions at the Santiaguito dome complex, Guatemala, commonly occur through arcuate fractures, following a 5-to 6-min period of inflation observed in long-period seismic signals. Observation of active faults across the dome suggests a strong shear component, but as fault propagation generally proceeds through the coalescence of tensile fractures, we surmise that explosive eruptions require tensile rupture. Here, we assess the effects of temperature and strain rate on fracture propagation and the tensile strength of Santiaguito dome lavas. Indirect tensile tests were conducted on samples with a porosity range of 3-30% and over diametral displacement rates of 0.04, 0.004, and 0.0004 mm/ s. At room temperature, the tensile strength of dome rock is rate independent (within the range tested) and inversely proportional to the porosity of the material. At eruptive temperatures we observe an increasingly ductile response at either higher temperature or lower displacement rate, where ductile deformation is manifest by a reduction in loading rate during constant deformation rate tests, resulting in slow tearing, viscous flow, and pervasive damage. We propose a method to conduct indirect tensile tests under volcanic conditions using a modification of the Brazilian disc testing protocol and use brittleness indices to classify deformation modes across the brittle-ductile transition. We show that a degree of ductile damage is inevitable in the lava core during explosions at the Santiaguito dome complex and discuss how strain leading to rupture controls fracture geometry, which would impact gas pressure release or buildup and regulate explosive activity.Plain Language Summary Using instruments we installed at Santiaguito, an active lava dome complex in Guatemala, we detected repeating cycles of inflation and deflation. The inflation took less time leading up to explosions compared to weak gas puffing, which led us to suspect that lava breaking and flowing might be responsible. To investigate this, we made laboratory tests where we put lava samples under tension, which is the most common way they break. We ran tests where we squeezed lavas at faster and slower rates in a press, and we also heated the lavas to their eruption temperatures-about 800°C-for some tests. Since the lavas contain volcanic glass, in some high temperature tests the glass partially flowed. In other tests the lavas were completely brittle, which means they stored up stress and then broke without flowing. The lava's behavior depends on the temperature and how fast they are squeezed. Finally, we considered how fast dome lavas at Santiaguito would have to be deformed to either break or stay intact during inflation of the dome. This study gives us a better idea of how dome lavas deform and how that affects hazardous activity during eruptions.

show abstract

Rapid and slow: Varying magma ascent rates as a mechanism for Vulcanian explosions

Cited by 58 publications

References 57 publications

Triggering of the powerful 14 July 2013 Vulcanian explosion at Tungurahua Volcano, Ecuador

Triggering of the powerful 14 July 2013 Vulcanian explosion at Tungurahua Volcano, Ecuador

Conduit Dynamics in Transitional Rhyolitic Activity Recorded by Tuffisite Vein Textures from the 2008–2009 Chaitén Eruption

Brittle‐Ductile Deformation and Tensile Rupture of Dome Lava During Inflation at Santiaguito, Guatemala

Contact Info

Product

Resources

About