An overview of recent (1988 to 2014) caldera unrest: Knowledge and perspectives

Acocella, Valerio; Lorenzo, Riccardo Di; Newhall, Chris; Scandone, Roberto

doi:10.1002/2015rg000492

Cited by 152 publications

(179 citation statements)

References 288 publications

(450 reference statements)

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“…The shape of the Askja central volcano is dominated by nested calderas. The 7-9 km wide outer caldera (Askja caldera) developed in the early Holocene, and the 3-5 km wide inner caldera (Öskjuvatn caldera) with the lake Öskjuvatn gradually subsided in the 40 years following a rifting event in 1874-1876 (Acocella et al, 2015). The 5 ring faults of the inner caldera dissect Pleistocene glaciovolcanic deposits of the Austurfjöll and the Thorvaldsfjall mountains at the eastern and southern margin of Lake Öskjuvatn (Fig.…”

Section: Geological Settingmentioning

confidence: 99%

Dynamics of the Askja caldera July 2014 landslide, Iceland, from seismic signal analysis: precursor, motion and aftermath

Schöpa¹,

Chao²,

Lipovsky³

et al. 2017

Preprint

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Abstract. Using data from a network of 58 seismic stations, we characterise a large landslide that occurred at the southeastern corner of the Askja caldera, Iceland, on 21 July 2014, including its precursory tremor and mass wasting aftermath. Our study is motivated by the need for deeper generic understanding of the processes operating not only at the time of catastrophic slope failure, but also in the preparatory phase and during the transient into the subsequent stable state.In addition, it is prompted by the high hazard potential of the steep caldera lake walls at Askja as tsunami waves created by 15 the landslide reached famous tourist spots 60 m above the lake level. Since direct observations of the event are lacking, the seismic data give valuable details on the dynamics of this landslide episode. The excellent seismic data quality and coverage of the stations of the Askja network made it possible to jointly analyse the long-and short-period signals of the landslide to obtain information about the triggering, initiation, timing, and propagation of the slide. The seismic signal analysis and a landslide force history inversion of the long-period seismic signals showed that the Askja landslide was a single, large event 20starting at the SE corner of the caldera lake at 23:24:05 UTC and propagating to the NW in the following 2 min. The bulk sliding mass was 7-16×10 10 kg, equivalent to a collapsed volume of 35-80×10 6 m 3 , and the centre of mass was displaced horizontally downslope by 1260±250 m during landsliding. The seismic records of stations up to 30 km away from the landslide source area show a tremor signal that started 30 min before the main landslide failure. It is harmonic, with a fundamental frequency of 2.5 Hz and shows time-dependent changes of its frequency content. We attribute the complex 25 tremor signal to accelerating and decelerating stick-slip motion on failure planes at the base and the sides of the landslide body. The accelerating motion culminated in aseismic slip of the landslide visible as a drop in the seismic amplitudes down to the background noise level 2 min before the landslide high-energy signal begins. We propose that the seismic signal of the precursory tremor may be developed as an indicator for landslide early-warning systems. The 8 hours after the main landslide failure are characterised by smaller slope failures originating from the destabilised caldera wall decaying in 30 frequency and magnitude. We introduce the term afterslides for this subsequent, declining slope activity after a large landslide.Earth Surf. Dynam. Discuss., https://doi

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Section: Geological Settingmentioning

confidence: 99%

Dynamics of the Askja caldera July 2014 landslide, Iceland, from seismic signal analysis: precursor, motion and aftermath

Schöpa¹,

Chao²,

Lipovsky³

et al. 2017

Preprint

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“…A better understanding of the structural framework of any caldera and its control on fluid and gas ascent are key requirements for a better definition of the role of any hydrothermal system during unrest (Acocella et al 2015). To this regard, we need to define general patterns of the monitoring indicators and their possible relationships during unrest, with particular attention at identifying any general behaviour.…”

Section: Discussionmentioning

confidence: 99%

“…The last few years have seen clear signs of unrest at Solfatara, which have included ground deformation, earthquakes and variations in hydrothermal activity (Acocella et al 2015;Chiodini et al 2015). With the purpose of improving the temporal resolution for identifying and localizing changes in the shallow layers of the crater, we apply the inversion algorithm repeatedly to fractions of the entire data set.…”

Section: N O I S E -B a S E D 4 -D M O N I T O R I N G O F V E L O C mentioning

confidence: 99%

A 3D algorithm based on the combined inversion of Rayleigh and Love waves for imaging and monitoring of shallow structures

2017

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S U M M A R YIn recent years, there has been increasing interest in the study of seismic noise interferometry as it can provide a complementary approach to active source or earthquake-based methods for imaging and continuous monitoring the shallow structure of the Earth. This meaningful information is extracted from wavefields propagating between those receiver positions at which seismic noise was recorded. Until recently, noise-based imaging relied mostly on Rayleigh waves. However, considering similar wavelengths, a combined use of Rayleigh and Love wave tomography can succeed in retrieving velocity heterogeneities at depth due to their different sensitivity kernels. Here, we present a novel one-step algorithm for simultaneously inverting Rayleigh and Love wave dispersion data aiming at identifying and describing complex 3-D velocity structures. The algorithm may help to accurately and efficiently map the shear wave velocities and the Poisson ratio of the surficial soil layers. In the high-frequency range, the scattered part of the correlation functions stabilizes sufficiently fast to provide a reliable estimate of the velocity structure not only for imaging purposes but also allows for changes in the medium properties to be monitored. Such monitoring can be achieved with a high spatial resolution in 3-D and with a time resolution as small as a few hours. In this paper, we describe a recent array experiment in a volcanic environment in Solfatara (Italy) and we show that this novel approach has identified strong velocity variations at the interface between liquids and gas-dominated reservoirs, allowing localizing a region which is highly dynamic due to the interaction between the deep convection and its surroundings.

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“…This sector is marked by the presence of minor, normal faults that subsided the apical dome possibly by diffuse pore fluid circulation along the higher permeability zones [24][25][26][27][28][29][30][31][32]. As regards the thermal state of the caldera, there is surface evidence of the presence of a high temperature geothermal system, which is mainly developed in the central part of the caldera at Solfatara crater [6][7][8][9][10][11]. This roughly corresponds to the zone of major collapse filled by volcano-clastic deposits of post-caldera volcanic activity, as testified by gravity anomalies and seismic and geological surveys [33,34].…”

Section: Geological Setting and Heat Dischargementioning

confidence: 99%

Distributed-Temperature-Sensing Using Optical Methods: A First Application in the Offshore Area of Campi Flegrei Caldera (Southern Italy) for Volcano Monitoring

Carlino

Mirabile²,

Troise

et al. 2016

Remote Sensing

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Abstract:A temperature profile 2400 m along the off-shore active caldera of Campi Flegrei (Gulf of Pozzuoli) was obtained by the installation of a permanent fiber-optic monitoring system within the framework of the Innovative Monitoring for Coastal and Marine Environment (MON.I.C.A) project. The system consists of a submerged, reinforced, multi-fiber cable containing six single-mode telecom grade optical fibers that, exploiting the stimulated Brillouin scattering, provide distributed temperature sensing (DTS) with 1 m of spatial resolution. The obtained data show that the offshore caldera, at least along the monitored profile, has many points of heat discharge associated with fluid emission. A loose association between the temperature profile and the main structural features of the offshore caldera was also evidenced by comparing DTS data with a high-resolution reflection seismic survey. This represents an important advancement in the monitoring of this high-risk volcanic area, since temperature variations are among the precursors of magma migration towards the surface and are also crucial data in the study of caldera dynamics. The adopted system can also be applied to many other calderas which are often partially or largely submerged and hence difficult to monitor.

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An overview of recent (1988 to 2014) caldera unrest: Knowledge and perspectives

Cited by 152 publications

References 288 publications

Dynamics of the Askja caldera July 2014 landslide, Iceland, from seismic signal analysis: precursor, motion and aftermath

Dynamics of the Askja caldera July 2014 landslide, Iceland, from seismic signal analysis: precursor, motion and aftermath

A 3D algorithm based on the combined inversion of Rayleigh and Love waves for imaging and monitoring of shallow structures

Distributed-Temperature-Sensing Using Optical Methods: A First Application in the Offshore Area of Campi Flegrei Caldera (Southern Italy) for Volcano Monitoring

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