Characterization of moderate ash-and-gas explosions at Santiaguito volcano, Guatemala, from infrasound waveform inversion and thermal infrared measurements.

The rapid discharge of gas and rock fragments during volcanic eruptions generates acoustic infrasound. Here we present results from the inversion of infrasound signals associated with small and moderate gas-and-ash explosions at Santiaguito volcano, Guatemala, to retrieve the time history of mass eruption rate at the vent. Acoustic waveform inversion is complemented by analyses of thermal infrared imagery to constrain the volume and rise dynamics of the eruption plume. Finally, we combine results from the two methods in order to assess the bulk density of the erupted mixture, constrain the timing of the transition from a momentum-driven jet to a buoyant plume, and to evaluate the relative volume fractions of ash and gas during the initial thrust phase. Our results demonstrate that eruptive plumes associated with small-to-moderate size explosions at Santiaguito only carry minor fractions of ash, suggesting that these events may not involve extensive magma fragmentation in the conduit.

Seismogenic lavas and explosive eruption forecasting.

Volcanic dome-building episodes commonly exhibit acceleration in both effusive discharge rate and seismicity before explosive eruptions. This should enable the application of material failure forecasting methods to eruption forecasting. To date, such methods have been based exclusively on the seismicity of the country rock. It is clear, however, that the rheology and deformation rate of the lava ultimately dictate eruption style. The highly crystalline lavas involved in these eruptions are pseudoplastic fluids that exhibit a strong component of shear thinning as their deformation accelerates across the ductile to brittle transition. Thus, understanding the nature of the ductile-brittle transition in dome lavas may well hold the key to an accurate description of dome growth and stability. Here we present the results of rheological experiments with continuous microseismic monitoring, which reveal that dome lavas are seismogenic and that the character of the seismicity changes markedly across the ductile-brittle transition until complete brittle failure occurs at high strain rates. We conclude that magma seismicity, combined with failure forecasting methods, could potentially be applied successfully to dome-building eruptions for volcanic forecasting.

Phase partitioning during fragmentation revealed by QEMSCAN Particle Mineralogical Analysis of volcanic ash.

Volcanic ash particle properties depend upon their genetic fragmentation processes. Here, we introduce QEMSCAN Particle Mineralogical Analysis (PMA) to quantify the phase distribution in ash samples collected during activity at Santiaguito, Guatemala and assess the fragmentation mechanisms. Volcanic ash from a vulcanian explosion and from a pyroclastic density current resulting from a dome collapse were selected. The ash particles resulting from both fragmentation modes are dense and blocky, typical of open-vent dome volcanoes and have a componentry consistent with their andesitic composition. We use image analysis to compare the fraction of each phase at particle boundaries compared to the total particle fraction. Our results show that the explosion-derived ash has an even distribution of plagioclase and glass, but boundaries enriched in pyroxene and amphibole. In contrast, the ash generated during dome collapse has an increased fraction of glass and decreased fraction of plagioclase at particle boundaries, suggesting that fractures preferentially propagate through glass during abrasion and milling in pyroclastic flows. This study presents QEMSCAN PMA as a new resource to identify generation mechanisms of volcanic ash, which is pertinent to volcanology, aviation, respiratory health and environmental hazards, and highlights the need for further experimental constraints on the fragmentation mechanism fingerprint.

High-load, high-temperature deformation apparatus for synthetic and natural silicate melts.

A unique high-load, high-temperature uniaxial press was developed to measure the rheology of silicate melts and magmatic suspensions at temperature up to 1050 degrees C. This new apparatus is designed to operate at constant stresses (up to 300 kN) or constant strain rates (approximately 10(-7) to 10(0) s(-1)) and further allows us to carry on experiments on samples with high viscosities (approximately 10(8) to 10(12) Pa s). The rheological instrument represents an advance in that it accommodates homogeneously heated samples (+/-2 degrees C) of voluminous sizes (up to 790 cm(3)) which permit the insertion of thermocouples to monitor temperature distribution evolutions during measurements. At last this setup allows for accurate measurements of viscosity of natural multiphase materials at strain rates and temperatures common to natural systems. The apparatus aspires to precisely (1) describe the onset of non-Newtonian behavior and its evolution with increasing strain rate until the point of rupture in the brittle regime, (2) constrain the effect of crystals and bubbles on the viscosity, and (3) record heating dissipated through viscous deformation. Here, we present a series of measurements on NIST standard material SRM 717a to calibrate the instrument. We couple the viscosity determined via Gent's equation with certified viscosity data of the standard material to calibrate this state-of-the-art apparatus. This work shows that we can resolve the viscosity of voluminous melt sample within 0.06 logarithmic unit and furthermore present the detection of minor viscous dissipation for a high-temperature, high strain rate experiment.

The permeability of fractured rocks in pressurised volcanic and geothermal systems.

The connectivity of rocks' porous structure and the presence of fractures influence the transfer of fluids in the Earth's crust. Here, we employed laboratory experiments to measure the influence of macro-fractures and effective pressure on the permeability of volcanic rocks with a wide range of initial porosities (1-41 vol. %) comprised of both vesicles and micro-cracks. We used a hand-held permeameter and hydrostatic cell to measure the permeability of intact rock cores at effective pressures up to 30 MPa; we then induced a macro-fracture to each sample using Brazilian tensile tests and measured the permeability of these macro-fractured rocks again. We show that intact rock permeability increases non-linearly with increasing porosity and decreases with increasing effective pressure due to compactional closure of micro-fractures. Imparting a macro-fracture both increases the permeability of rocks and their sensitivity to effective pressure. The magnitude of permeability increase induced by the macro-fracture is more significant for dense rocks. We finally provide a general equation to estimate the permeability of intact and fractured rocks, forming a basis to constrain fluid flow in volcanic and geothermal systems.

Crystal plasticity as an indicator of the viscous-brittle transition in magmas.

Understanding the flow of multi-phase (melt, crystals and bubbles) magmas is of great importance for interpreting eruption dynamics. Here we report the first observation of crystal plasticity, identified using electron backscatter diffraction, in plagioclase in andesite dome lavas from Volcán de Colima, Mexico. The same lavas, deformed experimentally at volcanic conduit temperature and load conditions, exhibit a further, systematic plastic response in the crystalline fraction, observable as a lattice misorientation. At higher stress, and higher crystal fraction, the amount of strain accommodated by crystal plasticity is larger. Crystal plastic distortion is highest in the intact segments of broken crystals, which have exceeded their plastic limit. We infer that crystal plasticity precludes failure and can punctuate the viscous-brittle transition in crystal-bearing magmas at certain shallow magmatic conditions. Since crystal plasticity varies systematically with imposed conditions, this raises the possibility that it may be used as a strain marker in well-constrained systems.

Fracture and compaction of andesite in a volcanic edifice.

The failure mode of lava-dilatant or compactant-depends on the physical attributes of the lava, primarily the porosity and pore size, and the conditions under which it deforms. The failure mode for edifice host rock has attendant implications for the structural stability of the edifice and the efficiency of the sidewall outgassing of the volcanic conduit. In this contribution, we present a systematic experimental study on the failure mode of edifice-forming andesitic rocks (porosity from 7 to 25 %) from Volcán de Colima, Mexico. The experiments show that, at shallow depths (<1 km), both low- and high-porosity lavas dilate and fail by shear fracturing. However, deeper in the edifice (>1 km), while low-porosity (<10 %) lava remains dilatant, the failure of high-porosity lava is compactant and driven by cataclastic pore collapse. Although inelastic compaction is typically characterised by the absence of strain localisation, we observe compactive localisation features in our porous andesite lavas manifest as subplanar surfaces of collapsed pores. In terms of volcano stability, faulting in the upper edifice could destabilise the volcano, leading to an increased risk of flank or large-scale dome collapse, while compactant deformation deeper in the edifice may emerge as a viable mechanism driving volcano subsidence, spreading and destabilisation. The failure mode influences the evolution of rock physical properties: permeability measurements demonstrate that a throughgoing tensile fracture increases sample permeability (i.e. equivalent permeability) by about a factor of two, and that inelastic compaction to an axial strain of 4.5 % reduces sample permeability by an order of magnitude. The implication of these data is that sidewall outgassing may therefore be efficient in the shallow edifice, where rock can fracture, but may be impeded deeper in the edifice due to compaction. The explosive potential of a volcano may therefore be subject to increase over time if the progressive compaction and permeability reduction in the lower edifice cannot be offset by the formation of permeable fracture pathways in the upper edifice. The mode of failure of the edifice host rock is therefore likely to be an important factor controlling lateral outgassing and thus eruption style (effusive versus explosive) at stratovolcanoes.

Elevated plasma levels of neuropeptide Y in patients with panic disorder.

OBJECTIVE: Neuropeptide Y is a pancreatic polypeptide closely associated with noradrenergic activity both in the central and peripheral nervous systems. The objective of this study was to assess plasma neuropeptide Y-like immunoreactivity in panic disorder. METHOD: Radioimmunoassays were performed in 12 patients with DSM-III-R panic disorder and two groups of normal comparison subjects (N = 22 and N = 16). RESULTS: Markedly higher plasma neuropeptide Y-like immunoreactivity was found in patients with panic disorder. CONCLUSIONS: Higher plasma neuropeptide Y-like immunoreactivity suggests that this peptide may be implicated in the etiology or expression of symptoms of panic disorder.

Sertraline treatment of generalized social phobia: a 20-week, double-blind, placebo-controlled study.

OBJECTIVE: The authors evaluated the efficacy, safety, and tolerability of sertraline, a selective serotonin reuptake inhibitor, in the treatment of generalized social phobia. METHOD: Adult outpatients with generalized social phobia (N=204) from 10 Canadian centers were randomly assigned to receive sertraline or placebo in a 2:1 ratio for a 20-week double-blind study following a 1-week, single-blind, placebo run-in. The initial dose of sertraline was 50 mg/day with increases of 50 mg/day every 3 weeks permitted after the fourth week of treatment (dosing was flexible up to a maximum of 200 mg/day). Primary efficacy assessments were the percentage of patients rated much or very much improved on the Clinical Global Impression (CGI) improvement item and the mean changes from baseline to study endpoint in total score on the social phobia subscale of the Marks Fear Questionnaire and total score on the Brief Social Phobia Scale. RESULTS: In intent-to-treat endpoint analyses of 203 of the patients, significantly more of the 134 patients given sertraline (N=71 [53%]) than of the 69 patients receiving placebo (N=20 [29%]) were considered responders according to their CGI improvement scores at the end of treatment. The mean reductions in the social phobia subscale of the Marks Fear Questionnaire and in the total score on the Brief Social Phobia Scale were 32.6% and 34.3% in the sertraline group and 10.8% and 18.6% in the placebo group, respectively. Analysis of covariance showed superiority of sertraline over placebo on all primary and secondary efficacy measures. Sertraline was well tolerated: 103 (76%) of the 135 sertraline-treated patients and 54 (78%) of the 69 placebo-treated patients completed the study. CONCLUSIONS: Sertraline is an effective treatment for patients with generalized social phobia.

Mixed anxiety and depression: diagnostic issues.

Mixed anxiety and depression (MAD) is a new diagnostic category introduced in the ICD-10 classification for patients seen mainly in primary care settings. These patients are defined as those suffering from symptoms of anxiety and depression of limited and equal intensity accompanied by at least some autonomic features, who do not qualify for specific diagnosis of anxiety or depressive disorders and are independent of stressful life events. The validity of this clinical entity is presently under investigation in the DSM-IV-MAD field trial. Cases of mixed anxiety and depression, however, are not limited to those meeting the criteria of this new "subsyndromal" category. Many patients fulfilling criteria for either depressive or anxiety disorders may also respectively present symptoms, syndromes, or a diagnosis of anxiety or depression. It is still not known whether anxious and depressive symptoms are two different expressions of the same psychopathologic underlying process. Tyrer's recent description of a "general neurotic syndrome" is an attempt to reunify syndromes separated in our present classifications. In this comprehensive approach, anxiety, depression, or MAD states are associated at different times with specific personality features and considered as expressing different levels of overreactivity to various stressful situations. This hypothesis would explain the close relationship existing between these two categories of symptoms and the common efficacy of some psychopharmacologic agents for both anxiety and depressive disorders.

Mixed anxiety and depression: from theory to practice.

The 10th International Classification of Disease (ICD-10) introduced the concept of mixed anxiety-depression to define patients presenting both anxiety and depressive symptoms of limited number and/or intensity, not sufficiently severe to fulfill criteria for a specific diagnosis of depressive or anxiety disorder. Epidemiologic surveys have shown that these patients may display significant levels of functional impairment, have unexplained somatic symptoms and a high use of nonpsychiatric medical care, have long-lasting symptoms, and are at risk for more severe psychiatric disorders. A DSM-IV field trial concluded that patients with affective-symptoms not meeting thresholds for DSM-III-R disorders were at least as common as patients with anxiety or mood disorders, and that their symptoms were associated with significant distress or impairment. Although some of these patients present residual symptoms from previous psychiatric episodes and may request treatment specific to these conditions, it is not known if those without a psychiatric history could benefit from pharmacologic or psychological treatments usually used in mild outpatient cases.

CCK4-induced panic in healthy subjects I: psychological and cardiovascular effects.

Sixteen healthy subjects participated in a crossover, double blind, and placebo-controlled study, designed to assess simultaneously the psychological and cardiovascular effects of cholecystokinin tetrapeptide (CCK4). Following an i.v. injection of 25 microg of CCK4, 44 percent of subjects experienced symptoms that fulfilled the DSM-IV criteria for a panic attack while no one panicked with placebo. CCK4 induced a significantly greater number and higher intensity of panic-like symptoms than placebo. A significant increase in state anxiety was observed in the period after CCK4 injection; this increase was significantly larger than the non-specific anxious reaction to placebo. CCK4 also affected cardiovascular signs. Both heart rate and mean blood pressure significantly increased after administration of CCK4. Again, these increases were significantly higher than those seen after placebo injection. We conclude that, in healthy subjects, CCK4 induces panic-like reaction characterized by a number of somatic, cognitive and emotional symptoms, which are accompanied by increases in heart rate and blood pressure.

CCK4-induced panic in healthy subjects II: neurochemical correlates.

Cholecystokinin tetrapeptide (CCK4) induces symptoms similar to those of panic attack. The present study investigated the effects of CCK4 administration on catecholaminergic system. In this double blind, randomised, crossover experiment, 16 healthy subjects received injections of either 25 microg of CCK4 or placebo on two separate occasions. Platelet and plasma catecholamine concentrations were assessed before the administration and compared to post-injection values. The results clearly show that both plasma and platelet concentrations of catecholamines are significantly affected by CCK4. Plasma norepinephrine (NE) and epinephrine (EPI) raised significantly above baseline in the immediate post-CCK4 period, while in plasma dopamine (DA), the significant increases were delayed. In the platelets, significant post-CCK4 increases of NE and EPI concentrations were observed with a delay of several minutes. In summary, we have demonstrated that, in healthy subjects, CCK4 increases peripheral concentrations of catecholamines in both plasma and platelets, with the most consistent changes occurring in platelet NE and plasma EPI concentrations.

The treatment of negative symptoms: a clinical and methodological study.

The primary objective of this study was to evaluate the efficacy, safety and tolerability of remoxipride (controlled release) versus haloperidol in patients with negative symptoms. The study comprised a multicentre, randomised, double-blind, parallel-group clinical trial. Two hundred and five patients were randomised to either remoxipride or haloperidol. Patients eligible for this study were aged 18-65 years, met the DSM-III-R diagnosis for chronic schizophrenia and the Positive and Negative Symptoms Scale (PANSS) criteria for predominant negative symptoms. There was a statistically significant reduction in the PANSS scores of at least 20% from baseline to last rating for 39 remoxipride (49.4%) and 45 haloperidol (47.6%) treated patients. There were no statistical differences found between the two treatment groups with respect to improvement of negative symptoms and adverse events. The PANSS data suggest that both remoxipride and haloperidol improve the cluster of negative symptoms concerned with social functioning. In addition, the design of the study provides a methodology that is appropriate to the study of primary negative symptoms in schizophrenia.

Severe obsessive-compulsive syndrome in a 10 year old: a 3 year follow-up.

Obsessive-Compulsive Disorder is rare in children but when present, its very nature is so pervasive and so complex that the therapy must be specially tailored to fit the distinct character of the young patient. We report the course and treatment of one case; then we discuss the interplay of implicit as well as explicit factors in the active process of alleviating dysfunctional behavior.

Clinical phobias and avoidant personality disorder among alcoholics admitted to an alcoholism rehabilitation setting.

One hundred seventy-three abstinent patients were screened for phobias and avoidant personality disorder. Ninety-six patients were interviewed and diagnosed by two independent assessors who were in agreement on 74% of the diagnoses. In DSM-III terms, over half of the sample (51.4%) met criteria for agoraphobia (8.5%), social phobia (7.8%) and avoidant personality disorder (35.1%). More than 70% of the patients in each diagnostic category were men. For the vast majority of the patients in the sample the disorder preceded the abuse of alcohol which was used by at least 40% of them to relieve their distress in the past. For many it had still a moderating effect on distress at the present but appeared to be mainly used out of "psychological dependence".

The treatment of avoidant personality disorder by social skills training in the clinic or in real-life settings.

Twenty-eight outpatients who met DSM-III diagnostic criteria for avoidant personality disorder completed 14 one and a half hour sessions of social skills training in the clinic only or a combination of four sessions in the clinic, four sessions in real-life and six follow-up sessions in the clinic. Subjects were assessed before treatment began, after four sessions, at the end of treatment and at three month follow-up points. Training in real-life did not enhance social skills training; no significant difference between the groups at any assessment points was found. In both groups improvement in time was significant and clinically worthwhile. The treatment effects were maintained up to the three month follow-up, where available. Social skills training appears to be a useful and promising intervention for avoidant personality disorder but its long term impact remains to be investigated.