Unusually high SO2 emissions and plume height from Piton de la Fournaise volcano during the April 2020 eruption.

Piton de la Fournaise volcano, La Réunion, France, erupted between the 2 and 6 April 2020, one of a series of eruptive phases which occur typically two or three times per year. Here, we use back trajectory analysis of satellite data from the TROPOMI instrument to determine that gas emissions during the June 2020 eruption were of unusually high intensity and altitude, producing 34.9 ± 17.4 kt of SO2 and plume heights up to 5 km a.s.l. The early stages of the eruption (2-4 April 2020) were characterised by relatively low SO2 emission rates despite strong low frequency tremor (LFT); the latter phase followed an increase in intensity and explosivity in the early hours of 5 April 2020. This period included lava fountaining, significantly increased SO2 emission rates, increased high frequency tremor (HFT) and decreased LFT. Using the PlumeTraj back trajectory analysis toolkit, we found the peak SO2 emission rate was 284 ± 130 kg/s on the 6 April. The plume altitude peaked at ~ 5 km a.s.l. on 5 April, in the hours following a sudden increase in explosivity, producing one of the tallest eruption columns recorded at Piton de la Fournaise. PlumeTraj allowed us to discriminate each day's SO2, which otherwise would have led to a mass overestimate due to the plumes remaining visible for more than 24 h. The eruption exhibited a remarkable decoupling and anti-correlation between the intensity of the LFT signal and that of the magma and gas emission rates. LFT intensity peaked during the first phase with low magma and SO2 emissions, but quickly decreased during the second phase, replaced by unusually strong HFT. We conclude that the observation of strong HFT is associated with higher intensity of eruption, degassing, and greater height of neutral buoyancy of the plume, which may provide an alert to the presence of greater hazards produced by higher intensity eruptive activity. This might be particularly useful when direct visual observation is prevented by meteorological conditions. This eruption shows the importance of combining multiple data sets when monitoring volcanoes. Combining gas and seismic data sets allowed for a much more accurate assessment of the eruption than either could have done alone. Supplementary Information: The online version contains supplementary material available at 10.1007/s00445-023-01628-1.

Paroxysmal eruptions tracked by variations of helium isotopes: inferences from Piton de la Fournaise (La Réunion island).

Helium (He) with its isotopes (3He, 4He) is a key tracer enabling the Earth's mantle and dynamics to be characterized. Enrichment in primordial helium (3He) has been detected in volcanic gases of numerous magmatic systems in different geodynamic settings. Despite past use to monitor volcano-tectonic unrest, temporal 3He/4He variability in volcanic emissions is still poorly constrained. Here, we investigate noble gas chemistry of Piton de la Fournaise hotspot volcano, where temporal fluctuations of 3He/4He in response to the eruptive activity have never been studied. We compare the 3He/4He signature of volcanic gases and fluid inclusions and we highlight analogous evolution of the 3He/4He signature in both during the last decades of eruptive activity (1990-2017), even during the same eruption. We show that the maximum enrichment in 3He is found in magmatic fluids that fed the most voluminous eruptions which culminated in caldera collapse events. We argue that this enrichment in 3He mostly reflects a greater contribution of magmatic fluids from a primitive component of the mantle plume. These results emphasize that He isotopes may provide warnings of increases in deep magmatic contributions that potentially herald paroxysmal eruptions, as documented here at Piton de la Fournaise (2007) and also at Kilauea (2018).

Very- and ultra-long-period seismic signals prior to and during caldera formation on La Réunion Island.

Early detection of the onset of a caldera collapse can provide crucial information to understand their formation and thus to minimize risks for the nearby population and visitors. Here, we analyse the 2007 caldera collapse of Piton de la Fournaise on La Réunion Island recorded by a broadband seismic station. We show that this instrument recorded ultra-long period (ULP) signals with frequencies in the range (0.003-0.01 Hz) accompanied by very-long period (VLP) signals (between 0.02 and 0.50 Hz) prior to and during the caldera formation suggesting it is possible to detect the beginning of the collapse at depth and anticipate its surface formation. Interestingly, VLP wave packets with a similar duration of 20 s are identified prior to and during the caldera formation. We propose that these events could result from repeating piston-like successive collapses occurring through a ring-fault structure surrounding a magma reservoir from the following arguments: the source mechanism from the main collapse, the observations of slow source processes as well as observations from the field and the characteristic ring-fault seismicity.

Control of source fertility on the eruptive activity of Piton de la Fournaise volcano, La Réunion.

The eruptive activity of basaltic hotspot volcanoes displays major fluctuations on times scales of years to decades. Theses fluctuations are thought to reflect changes in the rate of mantle melt supply. However, the crustal filter generally masks the mantle processes involved. Here, we show that the cyclic and generally increasing activity of the Piton de la Fournaise volcano (La Réunion) since the mid 20th century is tightly linked to the fertility of its source, as recorded by 87Sr/86Sr and incompatible trace elements ratios of lavas. We identify a twofold control of source fertility on eruptive activity: melt extraction from fertile, incompatible element-enriched veins initiates decadal-scale eruptive sequences, so that vein distribution in the plume source directly controls the cyclic activity. Indirectly, reactive flow of enriched melts increases mantle porosity and promotes melts extraction from the peridotite matrix. This process is thought to have caused a fourfold increase in magma supply between 1998 and 2014 at Piton de la Fournaise, and could also explain magma surges at other frequently active hotspot volcanoes, such as Kilauea, Hawaii. The short-term eruptive activity of hotspot volcanoes appears to be ultimately linked to the distribution and size of lithological heterogeneities in mantle plumes.

Suicidality and aggressive behaviour.

Psychiatrists have always maintained that there is a relationship between aggressive behaviour and suicide in depressed patients. However, this relationship is based on inconsistent and undocumented hypotheses, not on reliable clinical experimental data. The present study was designed to investigate the relationship between aggressive behaviour assessed by means of the Buss and Durkee Hostility Inventory (BDHI), and suicide in a sample of 134 depressed out-patients. The group with a higher level of suicidal behaviour was of younger age. The association between depressive subtypes (major depression, recurrent; major depression, single episode; bipolar disorder, depressive episode; dysthymia) and suicidality was found to be statistically significant. In contrast, there was no correlation between depressive subtypes and aggressive behaviour. The relationship between suicide and guilt as measured by the BDHI suggests that, in depression, suicidal behaviour becomes part of a symptom pattern in which aggression does not appear to be the main component. The suicide dimension arises when the cognitive sphere is involved. In fact, in depression, suicide is included among the cognitive disturbances, together with guilt, paranoid and obsessive-compulsive symptoms, depersonalization/derealization and agitation.

Imipramine binding as a predictor of fluoxetine response in depressed patients.

We evaluated platelet 3H-imipramine (3H-IMI) binding parameters (Bmax and Kd) at baseline (t0) and 2 months after (t1) treatment with fluoxetine in a group of outpatients affected by a major depressive episode, according to DSM-IIIR criteria. The possible relationships between biological parameters and the Hamilton Rating Scale for Depression (HRSD) total score were examined. The results confirmed previous reports that depressed patients possessed a lower density (Bmax) of platelet 3H-IMI binding sites than healthy controls, but the Bmax tended to decrease with fluoxetine. In addition, we observed a negative correlation between Bmax values at t0 and the HRSD total scores at t1 indicating that the patients who responded better to fluoxetine were those with a lower Bmax at t0. Future studies will substantiate this preliminary observation on the possible usefulness of platelet 3H-IMI binding as a predictor of pharmacological response.

Psychological stress and body temperature changes in humans.

We investigated the possible changes in body temperature, heart frequency, and blood pressure in 22 residents sitting for the yearly exam at the Specialty School of Psychiatry at Pisa University. All subjects were then evaluated 2 or 3 weeks later, in calm situations. In a subgroup, a specific plasmatic diazepam binding inhibitor (BBIA), previously described, was also measured. The results showed that all subjects underwent significant stress-related changes in the parameters studied, which suggest the involvement of different mechanisms in preexam stress.

Personality features and platelet 3H-imipramine binding.

In an attempt to provide further information on the functions of the serotonergic system in humans, we investigated the possible correlation between a peripheral serotonergic marker, such as platelet 3H-imipramine binding, and the Minnesota Multiphasic Personality Inventory (MMPI) items and scales in a group of 20 healthy subjects. The results showed the presence of significant positive correlation between the maximum binding capacity, a measure of the number of 3H-imipramine sites, and 17 MMPI items suggestive of personality features of self-certainty, feeling of well-being and sense of reality.

Interaction between the serotonin and dopamine systems in humans: preliminary findings.

The availability of peripheral tools, such as platelet [3H]-imipramine binding and electroretinogram b-wave amplitude, for investigating serotonin and dopamine systems respectively, prompted us to explore the possible relationships between these two systems in a group of 8 healthy drug-free volunteers. The results showed a significant correlation between the peripheral parameters of serotonin and dopamine systems and underline the importance of studying different neurotransmitters at the same time in humans.

Cyclization under mild conditions of anthraniloyl- and N-methyl-anthraniloyl dipeptides.

Anthraniloyl- and N-methyl-anthraniloyl dipeptides containing C-terminal L and D proline residues have been synthesized and subjected to cyclization reaction under mild conditions. The influence of substituents and of the chirality of the residues on the output of the reaction is discussed.