Tilt and strain change during the explosion at Minami-dake, Sakurajima, on November 13, 2017

We herein propose an alternative model for deformation caused by an eruption at Sakurajima, which has been previously interpreted as being due to a Mogi-type spherical point source beneath Minami-dake. On November 13, 2017, a large explosion with a plume height of 4200 m occurred at Minami-dake. During the 3 min following the onset of the explosion (November 13, 2017, 22:07–22:10 (Japan standard time (UTC + 9); the same hereinafter), phase 1, a large strain with changes up to 120 nstrain was detected at the Arimura observation tunnel (AVOT) located approximately 2.1 km southeast from the Minami-dake crater. After the peak of the explosion (November 13, 2017, 22:10–24:00), phase 2, a large deflation was detected at every monitoring station due to the continuous Strombolian eruption. Subsidence toward Minami-dake was detected at five out of six stations, whereas subsidence toward the north of Sakurajima was detected at the newly installed Komen observation tunnel (KMT), located approximately 4.0 km northeast from the Minami-dake crater. The large strain change at AVOT as well as small tilt changes at all stations and small strain changes at the Harutayama observation tunnel (HVOT) and KMT during phase 1 can be explained by a very shallow deflation source beneath Minami-dake at 0.1 km below sea level (bsl). For phase 2, a deeper deflation source beneath Minami-dake at a depth of 3.3 km bsl was found in addition to the shallow source beneath Minami-dake, which turned inflation after the deflation that occurred during phase 1. However, this model cannot explain the tilt change of KMT. Adding a spherical deflation source beneath Kita-dake at a depth of 3.2 km bsl can explain the tilt and strain change at KMT and the other stations. The Kita-dake source was also found in a previous study of long-term ground deformation. Not only the deeper Minami-dake source MD, but also the Kita-dake source deflated due to the Minami-dake explosion.

Tilt and strain change during the explosion at Minami-dake, Sakurajima, on November 13, 2017

We herein propose an alternative model for deformation caused by an eruption at Sakurajima, which have been previously interpreted as being due to a Mogi-type spherical point source beneath Minami-dake. On November 13, 2017, a large explosion with a plume height of 4,200 m occurred at Minami-dake. During the three minutes following the onset of the explosion (November 13, 2017, 22:07–22:10 (Japan standard time (UTC+9); the same hereinafter), phase 1, a large strain change was detected at the Arimura observation tunnel (AVOT) located approximately 2.1 km southeast from the Minami-dake crater. After the peak of the explosion (November 13, 2017, 22:10–24:00), phase 2, a large deflation was detected at every monitoring station due to the continuous Strombolian eruption. Subsidence toward Minami-dake was detected at five out of six stations whereas subsidence toward the north of Sakurajima was detected at the newly installed Komen observation tunnel (KMT), located approximately 4.0 km northeast from the Minami-dake crater. The large strain change at AVOT as well as small tilt changes of all stations and small strain changes at HVOT and KMT during phase 1 can be explained by a very shallow deflation source beneath Minami-dake at 0.1 km below sea level (bsl). For phase 2, a deeper deflation source beneath Minami-dake at a depth of 3.3 km bsl was found in addition to the shallow source beneath Minami-dake which turned inflation after the deflation obtained during phase 1. However, this model cannot explain the tilt change of KMT. Adding a spherical deflation source beneath Kita-dake at a depth of 3.2 km bsl can explain the tilt and strain change at KMT and the other stations. The Kita-dake source was also found in a previous study of long-term ground deformation. Not only the deeper Minami-dake source MD but also the Kita-dake source deflated due to the Minami-dake explosion.

Tilt and Strain Change During the Explosion at Minami-dake, Sakurajima, on November 13, 2017

We herein proposed an alternative model for deformation caused by each eruption at Sakurajima, which have been previously interpreted as being due to a Mogi-type source beneath Minami-dake. On November 13, 2017, a large explosion with a plume height of 4,200 m occurred at Minami-dake. During the three minutes following the onset of the explosion (November 13, 2017, 22:07–22:10 (Japan standard time (UTC+9); the same hereinafter), phase 1, a large strain change was detected at the Arimura observation tunnel (AVOT) located approximately 2.1 km southeast from the Minami-dake crater. After the climax of the explosion (November 13, 2017, 22:10–24:00), phase 2, a large deflation was detected at every monitoring stations due to the continuous Strombolian eruption. Subsidence toward Minami-dake was detected at five out of six stations whereas subsidence toward the north of Sakurajima was detected at the newly installed Komen observation tunnel (KMT), located approximately 4.0 km northeast from the Minami-dake crater. The large strain change at AVOT during phase 1 can be explained by a very shallow deflation source beneath Minami-dake at 0.1 km below sea level (bsl). For phase 2, a deeper source beneath Minami-dake at a depth of 3.3 km bsl deflated in addition to the shallow source beneath Minami-dake, which turned inflationary after the deflation obtained during phase 1. However, this model cannot explain the tilt change of KMT. Adding a spherical deflation source beneath Kita-dake at a depth of 3.2 km bsl can be explain the tilt and strain change at KMT and the other stations. The Kita-dake source was also found in a previous study of long-term ground deformation events. Not only the deeper Minami-dake source M D but also the Kita-dake source deflated due to the Minami-dake explosion.

The Contribution of Multi-Sensor Infrared Satellite Observations to Monitor Mt. Etna (Italy) Activity during May to August 2016

In May 2016, three powerful paroxysmal events, mild Strombolian activity, and lava emissions took place at the summit crater area of Mt. Etna (Sicily, Italy). During, and immediately after the eruption, part of the North-East crater (NEC) collapsed, while extensive subsidence affected the Voragine crater (VOR). Since the end of the May eruptions, a diffuse fumarolic activity occurred from a fracture system that cuts the entire summit area. Starting from 7 August, a small vent (of ~20–30 m in diameter) opened up within the VOR crater, emitting high-temperature gases and producing volcanic glow which was visible at night. We investigated those volcanic phenomena from space, exploiting the information provided by the satellite-based system developed at the Institute of Methodologies for Environmental Analysis (IMAA), which monitors Italian volcanoes in near-real time by means of the RSTVOLC (Robust Satellite Techniques–volcanoes) algorithm. Results, achieved integrating Advanced Very High Resolution Radiometer (AVHRR) and Moderate Resolution Imaging Spectroradiometer (MODIS) observations, showed that, despite some issues (e.g., in some cases, clouds masking the underlying hot surfaces), RSTVOLC provided additional information regarding Mt. Etna activity. In particular, results indicated that the Strombolian eruption of 21 May lasted longer than reported by field observations or that a short-lived event occurred in the late afternoon of the same day. Moreover, the outcomes of this study showed that the intensity of fumarolic emissions changed before 7 August, as a possible preparatory phase of the hot degassing activity occurring at VOR. In particular, the radiant flux retrieved from MODIS data decreased from 30 MW on 4 July to an average value of about 7.5 MW in the following weeks, increasing up to 18 MW a few days before the opening of a new degassing vent. These outcomes, in accordance with information provided by Sentinel-2 MSI (Multispectral Instrument) and Landsat 8-OLI (Operational Land Imager) data, confirm that satellite observations may also contribute greatly to the monitoring of active volcanoes in areas where efficient traditional surveillance systems exist.