Seismic monitoring of co-eruptive volcanic processes during the 2021 Fagradalsfjall Eruption, Iceland, using two small-aperture arrays
0
Citation
0
Reference
10
Related Paper
Abstract:
The 2021 Fagradalsfjall eruption in the Reykjanes peninsula, Iceland, was marked by episodes with varying volcanic activity. Our study focuses on the period from eruption start on the 19th March 2021 until the 2nd May 2021. This phase was marked by relatively continuous lava flows and non-periodic lava fountaining observed at up to 12 different vents, increasing in intensity throughout the observation period. Seismic tremor emanating from co-eruptive processes like for example lava fountaining, collapse of crater walls and magma and lava migration is non-impulsive, often with emergent onsets and no defined phase arrivals. Thus it is difficult to locate the tremor sources with traditional network based methods. We show that using small aperture arrays it is possible to locate and monitor several tremor sources that were active simultaneously, providing good spatial resolution on the details of the eruptive fissure. We investigate how array processing of 3-component data can assist with the determination of different seismic wave types and lead to a better understanding of the underlying volcanic processes. We find that seismic arrays are well suited to monitor the location, type and strength of volcanic processes that are active simultaneously. This can have important implications for volcanic hazard monitoring, especially when visual monitoring with webcams is difficult for example due to remoteness or poor visibility.Keywords:
Strombolian eruption
Volcanic hazards
Open-vent activity at volcanoes of low-silica composition, such as Stromboli (Italy), Villarrica (Chile), Mt. Erebus (Antarctica), is characterised by persistent passive gas emission and recurrent mild explosive outgassing. Four styles of bubble bursting activity have been recognised in such volcanoes: seething magma, small short-lived lava fountains, strombolian explosions and gas puffing. At Villarrica, one of the two case study volcanoes, seething magma consists of continual bursts of bubbles up to a few metres in diameter, with varying strength over the entire surface of the lava lake. Small lava fountains, seen as a vigorous extension of seething magma, commonly last 20-120 s and reach 10-40 m above the lava free-surface. Strombolian explosions can last for less than a second in a single bubble burst that erupts mainly bombs, as seen at the lava lake of Mt. Erebus and Villarrica volcanoes, or for more than 30 seconds accompanied by large amounts of ash, as seen at Stromboli and Mt. Etna volcanoes. At Stromboli, the second case study volcano, gas puffing consists of small but repetitive bubble bursts with a generally stable eruption frequency in the range 0.2-1.2 s-1. More vigorous explosive phenomena, such as hundreds-metres high lava fountains or very strong (paroxysmal) explosions, may occur during eruptions or episodes of elevated activity.
Correlations between seismicity and visual observations at Villarrica volcano indicate that the seismic tremor is mostly caused by explosive outgassing. Real-time Seismic Amplitude Measurements (RSAM) and SO2 emission rates (measured by FLYSPEC) show a very good positive linear correlation between periods of background and elevated activity. Higher SO2 emissions appear to be related to higher levels of the lava lake, stronger bubble bursting activity and changes in the morphology and texture of the crater floor. Background (low) levels of activity correspond to a lava lake located >80 m below the crater rim, small and/or blocky morphology of the roof, seismic amplitude (RSAM) lower than 25 units, few volcano-tectonic earthquakes, and daily averages of SO2 emission below 600 Mg d-1.
Convection of magma in the narrow conduits of the plumbing system can explain the sustained degassing with negligible effusion of lava, while supporting the variable outgassing styles at open-vent volcanoes. Theoretical analysis and laboratory experiments carried out with immiscible fluids in vertical and inclined pipes, constrain the convection in terms of a 'flux coefficient' that depends on the viscosity ratio between the liquids, flow regime, angle of inclination of the pipe, and position of the interface between the fluids. Prediction of the flux coefficient is possible within an acceptable range of error. Application of this model to Villarrica and Stromboli volcanoes, along with the analysis of the physical properties of the magma and gas data collated from the literature, allow the estimation of two parameters that constrain the dimensions of the convection: the magma flow rate and equivalent radius. Magma degassing at Villarrica is characterised by the ascent of a relatively degassed magma. Most of the gas exsolves at shallow levels in the system, leading to continuous bubble bursting activity at the lava lake. At Stromboli. magma degassing takes place in an inclined dyke (or dykes). Within this geometry. magma convection adopts a stratified regime of the gas-rich magma overlying the degassed melt, which favours coalescence of bubbles and an efficient convection. Interconnected conduits at the uppermost part of the system constrain the release of the large gas slugs observed during strombolian explosions.
Strombolian eruption
Outgassing
Scoria
Effusive eruption
Lava dome
Volcanic Gases
Cite
Citations (0)
The Etna volcano is renowned worldwide for its extraordinary lava fountains that rise several kilometers above the vent and feed eruptive columns, then drift hundreds of kilometers away from the source. The Italian Istituto Nazionale di Geofisica e Vulcanologia-Osservatorio Etneo (INGV-OE) is responsible for the monitoring of Mt. Etna, and for this reason, has deployed a network of visible and thermal cameras around the volcano. From these cameras, INGV-OE keeps a keen eye, and is able to observe the eruptive activity, promptly advising the civil protection and aviation authorities of any changes, as well as quantifying the spread of lava flows and the extent of pyroclastic and ash plumes by using a careful analysis of the videos recorded by the monitoring cameras. However, most of the work involves analysis carried out by hand, which is necessarily approximate and time-consuming, thus limiting the usefulness of these results for a prompt hazard assessment. In addition, the start of lava fountains is often a gradual process, increasing in strength from Strombolian activity, to intermediate explosive activity, and eventually leading to sustained lava fountains. The thresholds between these different fields (Strombolian, Intermediate, and lava fountains) are not clear cut, and are often very difficult to distinguish by a manual analysis of the images. In this paper, we presented an automated routine that, when applied to thermal images and with good weather conditions, allowed us to detect (1) the starting and ending time of each lava fountain, (2) the area occupied by hot pyroclasts, (3) the elevation reached by the lava fountains over time, and (4) eventually, to calculate in real-time the erupted volume of pyroclasts, giving results close to the manual analysis but more focused on the sustained portion of the lava fountain, which is also the most dangerous. This routine can also be applied to other active volcanoes, allowing a prompt and uniform definition of the timing of the lava fountain eruptive activity, as well as the magnitude and intensity of the event.
Strombolian eruption
Cite
Citations (41)
Abstract We focus on a sequence of 9 lava fountains from Etna that occurred in 2011, separated by intervals of 5 to 10 days. Continuous measurements allowed to discover the occurrence of gravity decreases before the onset of most fountaining episodes. We propose that the gravity changes are due to the pre-fountaining accumulation of a foam layer at shallow levels in the plumbing system of the volcano. Relying on the relationship between amount of gas trapped in the foam and amount of gas emitted during each episode, we develop a conceptual model of the mechanism controlling the passage from Strombolian to lava fountaining activity. Gas leakage from the foam layer during the late stages of its accumulation increases the gas volume fraction at upper levels, thus inducing a decrease of the magma-static pressure in the trapping zone and a further growth of the foam. This feedback mechanism eventually leads to the collapse of the foam layer and to the onset of lava fountaining. The possibility to detect the development of a foam layer at depth and to set quantitative constraints on the amount of trapped gas is important because of the implications for forecasting explosive eruptions and predicting their intensity.
Strombolian eruption
Cite
Citations (40)
The long‐lived 222 Rn decay products 210 Pb, 210 Bi and 210 Po have been monitored in the plumes of several vents at Mount Etna (Sicily) from May to October 1986. The results show that the four main craters of this volcano emit gases whose compositions are different from each other. The 210 Bi/ 210 Pb ratios for the plumes have similar mean values, (close to 25), which correspond to a degassing time of 1.5 to 2.7 days, according to the model of Lambert et al. (1985/86). In contrast, 210 Po/ 210 Pb ratios have very different mean values in each plume: 35 at the Voragine crater, 20 at the Bocca Nuova crater, and 14 at the South East crater. These figures enable us to calculate proportions of deep magma of 50%, 29% and 19% in the degassing cells of these craters respectively. Moreover, the SE crater appears to be a secondary degassing vent, not directly related to the main magma reservoir. The evolution of these ratios has been related to variations in volcanic activity.
Panache
Mount
Crater lake
Cite
Citations (16)
[1] The 11–13 January 2011 eruptive episode at Etna volcano occurred after several months of increasing ash emissions from the summit craters, and was heralded by increasing SO2 output, which peaked at ∼5000 megagrams/day several hours before the start of the eruptive activity. The eruptive episode began with a phase of Strombolian activity from a pit crater on the eastern flank of the SE-Crater. Explosions became more intense with time and eventually became transitional between Strombolian and fountaining, before moving into a lava fountaining phase. Fountaining was accompanied by lava output from the lower rim of the pit crater. Emplacement of the resulting lava flow field, as well as associated lava fountain- and Strombolian-phases, was tracked using a remote sensing network comprising both thermal and visible cameras. Thermal surveys completed once the eruptive episode had ended also allowed us to reconstruct the emplacement of the lava flow field. Using a high temporal resolution geostationary satellite data we were also able to construct a detailed record of the heat flux during the fountain-fed flow phase and its subsequent cooling. The dense rock volume of erupted lava obtained from the satellite data was 1.2 × 106 m3; this was emplaced over a period of about 6 h to give a mean output rate of ∼55 m3 s−1. By comparison, geologic data allowed us to estimate dense rock volumes of ∼0.85 × 106 m3 for the pyroclastics erupted during the lava fountain phase, and 0.84–1.7 × 106 m3 for lavas erupted during the effusive phase, resulting in a total erupted dense rock volume of 1.7–2.5 × 106 m3 and a mean output rate of 78–117 m3 s−1. The sequence of events and quantitative results presented here shed light on the shallow feeding system of the volcano.
Strombolian eruption
Effusive eruption
Cite
Citations (93)
Strombolian eruption
Effusive eruption
Lava dome
Shield volcano
Cite
Citations (31)
Lava dome
Effusive eruption
Dike
Magma chamber
Lava field
Cite
Citations (18)
First posted December 14, 2021 For additional information, contact: Contact HVOHawaiian Volcano ObservatoryU.S. Geological Survey1266 Kamehameha AvenueSuite A-8Hilo, HI 96720 Lava lake surfaces display the tops of active magma columns and respond to eruption variables such as magmatic pressure, convection, degassing, and cooling, as well as interactions with the craters that contain them. However, they are challenging to study owing to the numerous hazards that accompany these eruptions, and they are typically difficult to observe because the emitted gas plumes obscure the lava lake surfaces. The 2008–2018 Overlook crater and lava lake at Kīlauea Volcano, Hawaiʻi, provided a remarkable opportunity to study several high-resolution data streams of eruption variables that impacted the lava lake. To investigate how the crater and associated lava lake responded to changes in these eruption variables, we acquired terrestrial light detection and ranging (lidar) surveys of the Overlook crater and lava lake surface from February 2012 through December 2013, supplemented with several earlier terrestrial and airborne lidar datasets, to quantitatively track changes in the shape of the lava lake surface and the crater walls. Lidar captures high-resolution data even when the lake is completely obscured by thick gas plumes. We used a novel "unrolling technique" to map volumetric changes in crater shape, because standard elevation differencing fails to capture all topographic changes on the nearly vertical, and sometimes overhanging, crater walls. We measured crater perimeter growth rates of approximately 52 meters per year from 2009 to 2013, with the greatest growth occurring along a line linking areas of persistent upwelling and downwelling. We suggest that the development of an oblong crater with a perimeter that grows linearly is best explained by a model where degradation is favored at the sites of persistent upwelling and downwelling and where growth is controlled by a lithology that varies little with respect to rock strength. We also found that most of the Overlook crater growth occurred during a relatively small number of significant rockfall events (~16) over this period. Additional lidar datasets revealed that the lava lake surface has a measurable slope from the areas of persistent upwelling to downwelling, although rockfalls from the crater walls temporarily changed the direction of crustal plate movement along with the magnitude and direction of the lava lake surface slope. Our study demonstrates that lidar is an effective tool for tracking the topography of an active volcanic crater when heavy outgassing renders other tools, such as structure from motion, ineffective.
Crater lake
Lava dome
Lava field
Volcanology
Effusive eruption
Cite
Citations (1)
Strombolian eruption
Lava dome
Effusive eruption
Phreatic eruption
Lava field
Cite
Citations (86)
Volcanology
Lunar craters
Lava dome
Lava field
Cite
Citations (15)