Temporal seismic wave velocity variations at Láscar volcano

González, D.; Bataille, K.; Eulenfeld, Tom; Franco, Luis

doi:10.5027/andgeov43n2-a05

Cited by 3 publications

(3 citation statements)

References 11 publications

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“…Despite the difficulty of forecasting steam-driven explosions, some studies have retrospectively identified unexpected precursor activity associated with Lascar's episodes of unrest. Wooster (2001) described the new rapid cooling behaviour of the Lascar dome as precursor activity following the 1993 eruption, while a recent study of the 2013 explosion utilized seismic wave interferometry to depict variations in the seismic velocity and consequently speculated on the pre-eruptive deformation of a magmatic/hydrothermal reservoir (González et al, 2016). Matthews et al (1997) proposed a continuous deepening of the crater floor associated with a high rate of degassing from fumaroles within the active crater; this degassing phenomenon was subsequently identified by an InSAR investigation (Pavez et al, 2006) and further confirmed by continuous monitoring using the high-resolution German satellite TerraSAR-X (Richter et al, 2018), which also showed that the deformation rate appeared to be largely unaffected by the most recent explosive eruptions in 2013 and 2015.…”

Section: Study Area and Explosive History Of Lascar Volcanomentioning

confidence: 99%

“…A shallow hydrothermal system depicted by magnetotelluric and seismic data (Díaz et al, 2012;Hellweg, 2000) seems to influence the active degassing at Lascar (Bredemeyer et al, 2018;Tassi et al, 2009). These degassing processes have been suggested to be the source of the tremors observed during the 1994-1995 period of unrest (Hellweg, 2000), and they are probably associated with the increase in longperiod (LP) events preceding an eruption (González et al, 2016).…”

Section: Study Area and Explosive History Of Lascar Volcanomentioning

confidence: 99%

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Processes culminating in the 2015 phreatic explosion at Lascar volcano, Chile, monitored by multiparametric data

Gaete¹,

Walter²,

Bredemeyer³

et al. 2019

Preprint

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Abstract. Small steam-driven volcanic explosions are common at volcanoes worldwide but are rarely documented or monitored; therefore, these events still put residents and tourists at risk every year. Steam-driven explosions also occur frequently (once every 2–5 years on average) at Lascar volcano, Chile, where they are often spontaneous and lack any identifiable precursor activity. Here, for the first time at Lascar, we describe the processes culminating in such a sudden volcanic explosion that occurred on October 30, 2015, which was thoroughly monitored by cameras, a seismic network, and gas (SO2 and CO2) and temperature sensors. Prior to the eruption, we retrospectively identified unrest manifesting as a gradual increase in the number of long-period (LP) seismic events in 2014, indicating an augmented level of activity at the volcano. Additionally, SO2 flux and thermal anomalies were detected before the eruption. Then, our weather station reported a precipitation event, followed by changes in the brightness of the permanent volcanic plume and (10 days later) by the sudden volcanic explosion. The multidisciplinary data exhibited short-term variations associated with the explosion, including (1) an abrupt eruption onset that was seismically identified in the 1–10 Hz frequency band, (2) the detection of a 1.7 km high white-grey eruption column in camera images, and (3) a pronounced spike in sulfur dioxide (SO2) emission rates reaching 55 kg sec−1 during the main pulse of the eruption as measured by a mini-DOAS scanner. Continuous CO2 gas and temperature measurements conducted at a fumarole on the southern rim of the Lascar crater revealed a pronounced change in the trend of the relationship between the carbon dioxide (CO2) mixing ratio and the gas outlet temperature; we believe that this change was associated with the prior precipitation event. An increased thermal anomaly inside the active crater observed through Sentinel-2 images and drone overflights performed after the steam-driven explosion revealed the presence of a fracture ~ 50 metres in diameter truncating the dome and located deep inside the active crater, which coincides well with the location of the thermal anomaly. Altogether, these observations lead us to infer that a lava dome was present and subjected to cooling and inhibited degassing. We conjecture that a precipitation event led to the short-term build-up of pressure inside the shallow dome that eventually triggered a vent-clearing phreatic explosion. This study shows the chronology of events culminating in a steam-driven explosion but also demonstrates that phreatic explosions are difficult to forecast, even if the volcano is thoroughly monitored; these findings also emphasize why ascending to the summits of Lascar and similar volcanoes is hazardous, particularly after considerable rainfall.

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Section: Study Area and Explosive History Of Lascar Volcanomentioning

confidence: 99%

Section: Study Area and Explosive History Of Lascar Volcanomentioning

confidence: 99%

Processes culminating in the 2015 phreatic explosion at Lascar volcano, Chile, monitored by multiparametric data

Gaete¹,

Walter²,

Bredemeyer³

et al. 2019

Preprint

View full text Add to dashboard Cite

show abstract

“…Additionally, a magnetotelluric study (Díaz et al 2012) imaged a high-conductivity volume at only ∼1 km beneath the summit, suggesting the presence of a shallow hydrothermal system; Díaz et al (2012) further identified an anomaly at a depth of 6 km, which could be associated with a magma storage zone. Seismic wave interferometry allowed some scholars to speculate on the seismic velocity variations associated with inflation/deflation processes in a magmatic or hydrothermal reservoir during the period of unrest preceding the 2013 eruption (González et al 2016). This velocity variation also coincided with an increase in the number of LPs, an intensification of fumarole degassing, and the phenomenon of crater incandescence.…”

mentioning

confidence: 99%

Seismic activity during the 2013–2015 intereruptive phase at Lascar volcano, Chile

Gaete

Cesca

Franco³

et al. 2019

Geophysical Journal International

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SUMMARY In addition to enabling the physical processes of volcanic systems to be better understood, seismology has been also used to infer the complexity of magma pathways and plumbing systems in steep-sided andesitic and stratovolcanoes. However, in these volcanic environments, the application of seismic location methods is particularly challenging and systematic comparisons of common methods are lacking. Furthermore, little is known about the characteristic seismicity and deep structure of Lascar volcano, one of the most historically active volcanoes in northern Chile known to produce VEI-4 eruptions. To better understand the inner processes and deep structure of Lascar, the local broad-band seismic monitoring network was densified during a temporal installation in 2014–2015. Herein, we focus on the local seismicity during the 2014–2015 unrest episode, during which we recorded numerous seismic events mainly classified as long-period (LP) type, but also denote volcano-tectonic (VT) activity. Specifically, a long-lasting phase of LP activity is observed over a period of ∼14 months that starts in tandem with a pulse of VT activity. The LP rate and amplitude are modulated over time; they are lower in the initial phase, rise during the intermediate period from October 2014 to July 2015, and finally slowly decay while approaching the eruption time. The location of LPs is challenging due to the typical lack of clear seismic onsets. We thus encompass this problem by comparing a broad range of different standard and novel location techniques to map the source region of LPs by fitting the amplitude decay, polarization patterns, coherence of characteristic functions and cross-correlation differential times. As a result, we principally constrain LP locations within the first 5 km depth below the summit extending downward along a narrow, conduit-like path. We identify different regions of complexity: VTs dominate at depth, both VTs and LPs cluster in an intermediate depth region (down to 1.5 km), suggesting a change in the plumbing system geometry, and LPs dominate the shallowest region. Based on these results, we infer the presence of a subvertical conduit extending down to a depth of ∼5 km, and a region of path divergence, possibly accommodating a magma plumbing system, at a depth of ∼3 km beneath the volcano summit. Identifying the locations of complexities in the magma pathways at Lascar may help identify future unrest. The results are compared with independent observations, demonstrating the strength of the location method used herein that will be tested at volcanoes elsewhere.

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Processes culminating in the 2015 phreatic explosion at Lascar volcano, Chile, evidenced by multiparametric data

Gaete

Walter

Bredemeyer

et al. 2020

Nat. Hazards Earth Syst. Sci.

View full text Add to dashboard Cite

Abstract. Small steam-driven volcanic explosions are common at volcanoes worldwide but are rarely documented or monitored; therefore, these events still put residents and tourists at risk every year. Steam-driven explosions also occur frequently (once every 2–5 years on average) at Lascar volcano, Chile, where they are often spontaneous and lack any identifiable precursor activity. Here, for the first time at Lascar, we describe the processes culminating in such a sudden volcanic explosion that occurred on 30 October 2015, which was thoroughly monitored by cameras, a seismic network, and gas and temperature sensors. Prior to the eruption, we retrospectively identified unrest manifesting as a gradual increase in the number of long-period (LP) seismic events in 2014, indicating an enhanced level of activity at the volcano. Additionally, sulfur dioxide (SO2) flux and thermal anomalies were detected before the eruption. Then, our weather station reported a precipitation event, followed by an increase in steaming and a sudden volcanic explosion at Lascar. The multidisciplinary data exhibited short-term variations associated with the explosion, including (1) an abrupt eruption onset that was seismically identified in the 1–10 Hz frequency band, (2) the detection of a 1.7 km high white-gray eruption column in camera images, and (3) a pronounced spike in SO2 emission rates reaching 55 kg s−1 during the main pulse of the eruption as measured by a mini-differential optical absorption spectroscopy (DOAS) scanner. Continuous carbon dioxide (CO2) and temperature measurements conducted at a fumarole on the southern rim of the Lascar crater revealed a pronounced change in the trend of the relationship between the CO2 mixing ratio and the gas outlet temperature; we speculate that this change was associated with the prior precipitation event. An increased thermal anomaly inside the active crater as observed in Sentinel-2 images and drone overflights performed after the steam-driven explosion revealed the presence of a ∼50 m long fracture truncating the floor of the active crater, which coincides well with the location of the thermal anomaly. This study presents the chronology of events culminating in a steam-driven explosion but also demonstrates that phreatic explosions are difficult to predict, even if the volcano is thoroughly monitored; these findings emphasize why ascending to the summits of Lascar and similar volcanoes is hazardous, particularly after considerable precipitation.

show abstract

Temporal seismic wave velocity variations at Láscar volcano

Cited by 3 publications

References 11 publications

Processes culminating in the 2015 phreatic explosion at Lascar volcano, Chile, monitored by multiparametric data

Processes culminating in the 2015 phreatic explosion at Lascar volcano, Chile, monitored by multiparametric data

Seismic activity during the 2013–2015 intereruptive phase at Lascar volcano, Chile

Processes culminating in the 2015 phreatic explosion at Lascar volcano, Chile, evidenced by multiparametric data

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