NE Crater Research Articles

Thermal Emissions of Active Craters at Stromboli Volcano: Spatio‐Temporal Insights From 10 Years of Satellite Observations

AbstractOpen‐vent volcanoes continuously emit magmatic products and frequently feature multiple adjacent craters. Temporal shifts of thermal emissions between craters are especially detectable by InfraRed satellites. Here, SENTINEL‐2 and LANDSAT‐8/9 Short Wave InfraRed (SWIR) high‐spatial resolution satellite data, are combined to investigate 10 years (2013–2023) of thermal activity at Stromboli volcano (Italy). The correlation between Volcanic Radiative Power (VRP, in Watts) and Volcanic Radiative Energy (VRE, in Joules), retrieved by moderate MODIS and VIIRS Middle InfraRed (MIR) data, with the Thermal Index SWIR (TISWIR) data, allows us to quantify long‐term series of heat fluxes (VRPSWIR) and energy (VRESWIR). Combining moderate and higher spatial resolution data and fitting cumulative trends of TISWIR with VREMIR allows to measure thermal activity sourced by single craters during Strombolian activity. Long‐term results highlight that thermal emissions are clustered in the northern and southern parts of the crater terrace, with total energy emitted (∼12 × 1014 J) equally distributed. The thermal increase since April 2017 marked a reactivation of shallow magma transportation and an intensification of the activity after the 2014 eruption. Distinct thermal behaviors are shown by the NE, C, and SW craters, related to mechanisms of explosions. We found that short‐term thermal variations match well those resolved by ground‐based signals, and the NE crater as the most sensitive to the transition to higher‐intensity activity. Our multispatial/multisensory investigation allows, for the first time, the long‐term quantification of heat flux from Stromboli's craters, with an improved understanding of open‐vent dynamics and a new approach to monitor multiple active craters.

Overflows and Pyroclastic Density Currents in March-April 2020 at Stromboli Volcano Detected by Remote Sensing and Seismic Monitoring Data

Between 28 March and 1 April 2020, Stromboli volcano erupted, with overflows from the NE crater rim spreading along the barren Sciara del Fuoco slope and reaching the sea along the NW coast of the island. Poor weather conditions did not allow a detailed observation of the crater zone through the cameras monitoring network, but a clear view of the lower slope and the flows expanding in the area allowed us to characterize the flow features. This evidence was integrated with satellite, GBInSAR, and seismic data, thus enabling a reconstruction of the whole volcanic event, which involved several small collapses of the summit cone and the generation of pyroclastic density currents (PDCs) spreading along the slope and on the sea surface. Satellite monitoring allowed for the mapping of the lava flow field and the quantification of the erupted volume, and GBInSAR continuous measurements detected the crater widening and the deflation of the summit cone caused by the last overflow. The characterization of the seismicity made it possible to identify the signals that are associated with the propagation of PDCs along the volcano flank and, for the first time, to recognize the signal that is produced by the impact of the PDCs on the coast.

Ground‐based InSAR reveals conduit pressurization pulses at Stromboli volcano

AbstractAt Stromboli volcano (Southern Italy), only few minor precursors (gas output) have been identified for ‘major’ Strombolian explosions. We use ground‐based interferometric synthetic aperture radar (GBInSAR) technology to monitor the displacement rate of the summit area of Stromboli. We analysed the 2009–2011 period. The analysis of the displacement rate has been performed by dividing the summit zone monitored by the GBInSAR into three regions, corresponding to the edge of the crater area (1 and 2), and to the slope of the NE crater (3). Pulses of rapid expansion of sector 3, of variable duration and amplitude, appear in coincidence with periods of intense activity that include lava flows and major explosions. We associate this expansion with the pressurization of the magma column that is recharged by deep‐derived gas, promoting the onset of ‘major explosion‐dominated’ activity.

Magnetic features of the magmatic intrusion that occurred in the 2007 eruption at Stromboli Island (Italy)

Significant changes in the local magnetic field marked the resumption of eruptive activity at Stromboli volcano on February 27, 2007. After differential magnetic fields were obtained by filtering out external noise using adaptive filters and seasonal thermal noise using temperature data, we identified step-like changes of 1–4 nT coincident with the opening of eruptive fissures in the upper part of the Sciara del Fuoco. The magnetic variations detected at two stations are closely related to the propagation of a shallow NE–SW magmatic intrusion extending beyond the summit craters area. These observations are consistent with those calculated using piezomagnetic models in which stress-induced changes in rock magnetization are produced by the magmatic intrusion. No significant magnetic changes were observed when the first fractures opened along the NE crater rim. Indeed, the stress-induced magnetization caused by this magmatic activity is expected to be too low because of the structural weakness and/or thermal state of the summit area. The continuous long-term decay characterizing the post-eruptive magnetic pattern can be related to a time-dependent relaxation process. A Maxwell rheology was assumed and the temporal evolution of the piezomagnetic field was evaluated. This allowed us to estimate the rheological properties of the medium; in particular, an average viscosity ranging between 1016 and 1017 Pa⋅s was a relaxation time τ of about 38 days.

Infrasonic evidences for branched conduit dynamics at Mt. Etna volcano, Italy

On multi‐vents volcanoes changes in activity between different vents reflect a complex fluid‐dynamics of the shallow feeding systems and are often explained numerically and experimentally in terms of conduit branches and bifurcations. We present new geophysical constraints on the shallow feeding system of Etna volcano derived from array analysis of infrasound radiated from two distinct sources, one located in the SE crater and one in the Voragine or NE crater (VNE). These two sources alternated in their behavior, with the VNE crater system radiating low amplitude background infrasound interrupted by episodes of increased infrasound radiation from the SE crater. This switching behavior suggested a branched shallow feeding system strongly controlled by the gas/magma‐flux. Here, the VNE craters represented the preferential and most stable branch of degassing during stationary flux regime, while the SE crater branch activated in response to an increase in the magma/gas supply rate.

The onset of the 2007 Stromboli effusive eruption recorded by an integrated geophysical network

The Stromboli volcano erupted on February 27, 2007, after an intense Strombolian activity lasted about 2 months. The eruption was characterized by a series of rapidly evolving phenomena, like the propagation of an effusive fracture along the crater rim, the opening of lateral effusive vents, an unusually large effusive flux (> 10 m 3/s), the collapse of the crater system, and a major strombolian explosion. This eruption was monitored by an integrated network of multiparameter instruments: broad-band seismometers, infrasonic array, thermal cameras and bore-hole tiltmeters. All the information collected and processed in real-time allowed to draw a clear picture of the eruption dynamics. Thermal imagery documented in real-time how the effusive fracture propagated at 12:24 GMT of February 27 along the northern rim of the NE crater towards the NE direction. The infrasonic array showed that explosive and degassing activity ceased at 10:32 GMT, a couple of hours before the opening of the effusive fractures. The end of the explosive activity coincided with an intense phase of high-frequency (4–22 Hz) tremor which showed two episodes of harmonic spectrum gliding from 4–7 Hz to ~ 22 Hz. The end of this phase was characterized at 18:26 GMT by a strong infrasonic signal located by the array in the Sciara del Fuoco and associated with the landslide induced by the opening of a lateral effusive vent at 400 m of elevation. This eruption provided a clear example on how the strategy of integrating in near-real-time geophysical information can pinpoint the transition from explosive to effusive activity of the shallow volcanic system at Stromboli.

Deformation of Stromboli Volcano (Italy) during the 2007 eruption revealed by radar interferometry, numerical modelling and structural geological field data

The activity of Stromboli volcano is characterized by very low energy explosions, occurring every 10–15 min, throwing out lava above the crater rim. During 2007, the volcano showed an anomalous activity in which new effusive vents developed (27 February and 9 March) and a major explosion took place on 15 March. This paper presents an integrated study based on a structural geological field survey, interferometric radar monitoring and numerical modelling on the deformations of the upper NW flank of the volcano (Sciara del Fuoco — SdF). The field survey carried out during the 2007 events shows the development of mainly NE-striking fissures and fractures on the northern part of the upper SdF. In January 2007, the ground-based synthetic aperture radar (GB-InSAR), installed on the flank of the SdF, showed a progressive acceleration of movement on the NE crater preceding the eruption of 27 February 2007. By the first half of February, the acceleration also involved the upper portion of the SdF and on 27 February the eruption started with the opening of new vents and deformation rates higher than the measurement capability of the radar device. On 8–9 March 2007, the GB-InSAR highlighted the formation of a bulge on the NW sector of the SdF, preceding the opening of an additional vent. To understand the deformation pattern recorded during the eruption, a numerical simulation was carried out by using the FLAC 3D code. Based on the integration of all the data, the deformations observed in the pre-effusive phase (before 27 February) seem to be related to the intrusion of a SW–NE striking dyke. The bulging recorded before the 9 March vent opening is instead to be associated with the intrusion of a sub-horizontal sill.

Coupled thermal oscillations in explosive activity at different craters of Stromboli volcano

Thermal infrared thermometers deployed ∼250 m from Stromboli's active craters can detect thermal emissions during strombolian explosions. Explosions appear as spikes in thermal time series, with variations in the mass erupted during each event revealed by pulses in the time series. During May 2001, Stromboli's NE and SW craters showed consistently different thermal signatures. SW crater events were characterized by long lasting (>10 s), higher amplitude thermal signals with significant fluctuations, whereas the NE crater was characterized by short (<5 s), impulsive, lower amplitude signatures. The two craters showed well‐correlated variations in thermal amplitude evolving over periods of several hours and providing strong evidence for linkage of the craters to a common feeding system affected by cyclic processes that drive steady variations in the style of emission.

Lava effusion rates from hand-held thermal infrared imagery: an example from the June 2003 effusive activity at Stromboli

A safe, easy and rapid method to calculate lava effusion rates using hand-held thermal image data was developed during June 2003 at Stromboli Volcano (Italy). We used a Forward Looking Infrared Radiometer (FLIR) to obtain images of the active lava flow field on a daily basis between May 31 and June 16, 2003. During this time the flow field geometry and size (where flows typically a few hundred meters long were emplaced on a steep slope) meant that near-vertical images of the whole flow field could be captured in a single image obtained from a helicopter hovering, at an altitude of 750 m and ∼1 km off shore. We used these images to adapt a thermally based effusion rate method, previously applied to low and high spatial resolution satellite data, to allow automated extraction of effusion rates from the hand-held thermal infrared imagery. A comparison between a thermally-derived (0.23–0.87 m3 s−1) and dimensionally-derived effusion rate (0.56 m3 s−1) showed that the thermally-derived range was centered on the expected value. Over the measurement period, the mean effusion rate was 0.38±0.25 m3 s−1, which is similar to that obtained during the 1985–86 effusive eruption and the time-averaged supply rate calculated for normal (non-effusive) Strombolian activity. A short effusive pulse, reaching a peak of ∼1.2 m3 s−1, was recorded on June 3, 2003. One explanation of such a peak would be an increase in driving pressure due to an increase in the height of the magma contained in the central column. We estimate that this pulse would require the magma column to attain a height of ∼190 m above the effusive vent, which is approximately the elevation difference between the vent and the floor of the NE crater. Our approach gives an easy-to-apply method that has the potential to provide effusion rate time series with a high temporal resolution.

Dynamic river channels suggest a long‐lived Noachian crater lake on Mars

Recent images of the Noachian‐age Holden Northeast Crater show spectacular meandering channels that form a complex 150 meter thick lacustrine river delta deposit confined to the northwest margin of the crater. We identify 11 major avulsion events in the topmost layer and suggest an avulsion frequency of a few hundred years. The meandering nature of the channels and numerous avulsions is incompatible with deposition on an alluvial fan and clearly reflects a complex history of multiple sustained flows. Assuming an average sedimentation rate of 1mm/year, we suggest that Holden NE Crater contained a lake that persisted for at least 150,000 years. Our analysis is incompatible with this feature being the result of a major bolide impact that would have released a catastrophic flood by groundwater sapping and supports the hypothesis that early Mars was both warmer and wetter during the Noachian.

New integrated geodetic monitoring system at Stromboli volcano (Italy)

Stromboli is a composite volcano, forming the northernmost island of the Aeolian Archipelago volcanic arc (Tyrrhenian Sea). On December 28th 2002, lava flows outpoured from the northern wall of the NE crater and descended into the Sciara del Fuoco (SdF), a deep depression marking the NW flank of the volcano edifice. On December 30th 2002, two landslides occurred on the northern part of the SdF; they moved a mass in the order of tens of millions of cubic meters both above and below sea level. The landslide produced a tsunami causing significant damage to the eastern coast of the island, reaching the other Aeolian Islands and the Sicilian and southern Italian coasts. This event led to the upgrading of the ground deformation monitoring system, already existing on the island; the new requirement was the real-time detection of the deformations related to potential slope failures of the SdF. To this end, a remotely controlled monitoring system, based both on GPS and geodetic techniques, was planned and set up in a few months. The new monitoring system allowed to continuously measure the ground deformations occurring on the SdF, by integrating both terrestrial and satellite geodetic techniques. Although this system was severely damaged during the 7-month long eruption, it allowed to monitor important eruptive phases. For the first time, an accurate data set on the actual mass movements of the SdF and the crater area was available. It provided data that significantly supported the Civil Protection Authorities in making decisions and constrains theories related to landslide movements and volcanic activity. After the end of the eruption, the system was overhauled in order to optimize the instruments and set up a monitoring system aimed at measuring deformations forecasting other flank collapses.

Volcanomagnetic changes accompanying the onset of the 2002–2003 eruption of Mt. Etna (Italy)

Remarkable changes in the local magnetic field were associated with the onset of the 2002–2003 flank eruption at Mt. Etna. After differential magnetic field measurements were filtered from the external noise by using adaptive filters, we recognized two stages in the total intensity changes, which are closely related to different volcanic events: (a) rapid variations of about 4–5 nT associated with October 26 seismic swarm recorded beneath the summit craters; (b) step-like variations of 9–10 nT coincident with October 27 eruptive fissures opening up in the north flank. These observations are generally consistent with those calculated from simple magnetic models of these volcanic processes, in which the magnetic changes are generated by stress redistribution due to magmatic intrusions at different depth. The magnetic data not only allow the timing of the intrusive event to be described in greater detail but also, together with other volcanological and geophysical evidences, permit some constraints to be set on the characteristics of propagation of a shallow dike. Firstly, at around midnight on 26 October magma was rapidly injected to a depth of 3–4 km just below the summit craters. Secondly, after 1:00 on 27 October, continued intrusion magma occurred upward and culminated a few hundred meters below the free surface fractured along a N–E direction. Thirdly, at about 2:28, magma gave rise to an explosive fissural vent at the northern base of the NE crater near 3000 m a.s.l. Finally, at about 5:00, the first eruptive fissure became active along the eastern border of the NE rift at 2500 m a.s.l. The rate of growth of the magnetic anomalies, moreover, leads to the interpretation that the magmatic intrusion travelled northward from base of the NE crater to the NE rift at approximately 14 m/min.

Array tracking of infrasonic sources at Stromboli volcano

Infrasonic arrays are a powerful tool for volcanic monitoring and hazard assessment. Explosions were recorded at Stromboli using a small aperture array of 4 infrasonic stations, allowing precise vent location. The acoustic signals were delayed‐and‐summed, revealing the existence of two main groups of infrasonic waves. The NE crater produces short (<3 s) high amplitude (20–80 Pa) pressure waves while the SW crater produces small acoustic pressure (10–30 Pa) with long (5–15 s) coda. The two groups reflect different in explosive styles and similar spectral content, centered on 5–6 Hz. When stacked together, acoustic waveforms for each crater reveal the same pressure pulse, which indicates a common source process. We infer that the acoustic onset at both craters is generated by the burst of a large gas bubble while the acoustic coda is controlled by a sustained pressure release.

Features of volcanic tremors on Mt. Etna (Sicily) during the March–August 1983 eruption

The seismic analysis of the volcanic tremors preceding and accompanying the Etnean eruption of March–August, 1983 has shown a significant variation in the spectral content before the beginning of the eruption, the tremor peaks at 1.4 and 1.6 Hz — which might be associated with the feeding pipes of the NE crater (Schicket al., 1982a) — being the dominant feature of the spectra.

Mount Etna and the 1971 eruption - Structural implications of the 1971 Mount Etna eruption

The author believes the 1971 eruption has been triggered by an uprise of the magma column which had for several decades fed the persistent activity located in both the NE crater and in the central crater’s chasm. This uprise split open a set of en-echelon fissures first on the southern, then on the eastern upper slopes of Mt Etna. Degassing occurred at the uppermost part of the successive fissure systems, while the degassed lava flows poured out at the lowermost end. When the ENE tectonic fault-system came into operation and controlled the second half of the eruption, it led to the engulfment of the degassing vent and subsequently acted as an undergound channel through which the degassed lavas could flow freely until they poured out at the lower end of the fault zone. This fault zone follows one of the main tectonic trends which intersect below Mt Etna, the main other ones being oriented SW-NE and WSW—ENE.

Mount Etna and the 1971 eruption - The summit of Mount Etna prior to the 1971 eruptions

The summit cone of Mt Etna is cut by an approximately NNE-SSW trending, narrow fissure zone that controls much of the terminal activity of this volcano. Within the central crater, which lies at the top of the summit cone, there are two main vents alined on this fissure zone: the chasm, a deep pit; and the 1964 crater. Both of these vents were blocked before 1971. The NE crater first opened in 1911 on the lower slopes of the summit cone on the same fissure zone, and has had an open conduit from which lava has been erupted at a constant rate from 1966 to the beginning of the 1971 eruption. In 1968 a small gas bocca known as the Bocca Nuova opened near a fissure that had previously erupted lavas in 1956. The Bocca Nuova collapsed in early 1970 to give a 100 m wide crater. It is suggested that collapse resulted from movement of magma at depth into the 1956 fissure causing sudden lowering in the magma column below the Bocca, and that continued migration of magma into the fissure eventually lead to the eruption of April 1971, the site of this eruption being in line with the fissure. A rise in temperature of fumaroles at the edge of the central crater after the Bocca Nuova collapse is attributed to this incursion of magma across the crater.

Mount Etna and the 1971 eruption - Oxygen and sulphur fugacities of magmatic gases directly measured in active vents of Mount Etna

Solid-electrolyte sensors were used to measure the oxygen and sulphur fugacities of magmatic gases in vents located at an elevation of about 3170 m on the northeast flank of the NE crater of Mt Etna in July 1970. The temperature of the gas ranged from 773 to 1057 °C. The least-squares fit of 13 measured lgfo2 values yielded the relation: lg/o2 (atm) = 2.175- 15110/T (K), which gives values of 0.9 to 2.2 lgfo2 units higher than those obtained in the Makaopuhi lava lake, Hawaii, within the temperature range measured, the difference increasing with decreasing temperature. Laboratory study of a water-quenched sample of the Etna lava and calculations of gas equilibria indicate that the difference is due partly to the intrinsically higher f 02 of the Etna magma and partly to the mixing of air with the Etna gases. The measured j^2 value was 10-2 4 atm at 860 °C.