Notes on the 1902 eruption of Santa María volcano,Guatemala

The first historic activity of Santa María volcano, Guatemala constituted one of the ten largest historic eruptions in the world, producing 5.5 km³ of debris. In hindsight, the six-month period before the October 1902 eruption was one of extremely abnormal seismicity in all of western Guatemala. The pyroclastis from the eruption were scattered widely over Western Guatemala and Southern Mexico and also caused world-wide atmospheric effects. The volcanics produced were of andesitic-dacitic composition, but there was wide variation from place to place in the sampled material — a fact apparently chiefly attributable to atmospheric-fractionation. There was apparently a change in chemistry of ash during the two-day eruption as well, the first, most voluminous ash was pumicious and white; later ash was finer, denser, darker, and slightly less silicious. The kinetic energy/thermal energy partition is determined to be similar to the value derived for Krakatoa,E _k/E _th ? 5.0 %. The thermal energy of the eruption was estimated at 4.2×10²⁵ ergs. The explosion crater left on Santa María’s southwest flank after the eruption had a volume equal to less than 0.5 km³, a small fraction of the volume of material erupted. The two-day 1902 blast has greatly overshadowed subsequent activity; extrusion of the Santiaguito dome, which has occurred since 1922 in the explosion crater, has produced about 0.7 km³ of dacite lava and 1.6×10²⁵ ergs of thermal energy in 48 years of activity.     

Soufrière of guadeloupe 1976–1977 eruption — mass and energy transfer and volcanic health hazards

The Soufrière volcano in Guadeloupe island delivered a phreatic eruption that commenced on July 8th, 1976 and lasted until March 1st, 1977. This eruption was similar to the 1797, 1798, 1809 and 1956 outbreaks. Phreatic activity ejected blocks derived from the fissure walls and fine pyroclasts produced by hydrothermal alteration of the old dome’s rocks. Field observations and measurements allowed the present authors to calculate the mass and energy transfer of steam and ashes: 10⁷ tons of water (very low considering that on the mountain summit the annual precipitation is 10 tons m)²,10⁶ m³ of ashes. The most important energy transfers was thermal: about 5 × 10²⁰ ergs for each phreatic eruption. The total kinetic energy output was 2 × 10¹⁹ ergs for a total thermal energy output of 64 × 10²⁰ ergs. The gases and fine pyroclasts did pollute the atmosphere, waters and soils and consequently affected the population living on the slopes of the volcano.     

Prediction and characteristics of the 1975 eruption of Tolbachik volcano,Kamchatka

According to a long-term prediction. Tolbachik volcano was expected to erupt with a 0.7 probability, some time in the period 1964–1978. An eruption of Tolbachik commenced at 21.45 GMT on July 5, 1975. It took place on the southwestern Hank of the volcano at an altitude of 880 m a.s.l. about 18 km from the central crater. An earthquake swarm preceded it. The place and time of eruption were predicted three days belore it began on the basis of epicenter locations and characteristics of recorded seismic activity. During the period July 5–28 gases and incandescent magma were continuously ejected to a height of 2,000 m above ground level. Ash clouds rose to a height of 6 to 8 km, with a train of ash extending over a horizontal distance of 300 km. The velocity of jets from the crater was about 200 m/see. During the first days of the eruption the quantity of materials erupted and the eruption power amounted to 1.25 · 10⁵ kg/see and 2.1 · 10¹¹W, respectively. The vertical growth of the scoria cone was consistent with the lawH=2.15³√vt, where the time and height are expressed in seconds and meters, respectively. The mouth of the volcano conduit was estimated to be 12 m in diameter. Lava began to erupt at 22^h23^m on July 28. During the period July 5–31 about 3 · 10¹¹ kg of magmatic material, consisting of ash, scoria and lava, was erupted onto the earth’s surface. The energy released over the period of eruption accounted for 5 · 10¹⁷ J.     

Observations of eruption clouds from Sakura-zima volcano,Kyushu, Japan from Skylab 4

Hasselblad and Nikon stereographic photographs taken from Skylab between 9 June 1973 and 1 February 1974 give synoptic plan views of several entire eruption clouds emanating from Sakura-zima volcano in Kagoshima Bay, Kyushu, Japan. Analytical plots of these stereographic pairs, studied in combination with meteorological data, indicate that the eruption clouds did not penetrate the tropopause and thus did not create a stratospheric dust veil of long residence time. A horizontal eddy diffusivity of the order of 10⁶ cm² s^?1 and a vertical eddy diffusivity of the order of 10⁵ cm² s^?1 were calculated from the observed plume dimensions and from available meteorological data. These observations are the first, direct evidence that explosive eruption at an estimated energy level of about 10¹⁸ ergs per paroxysm may be too small under atmospheric conditions similar to those prevailing over Sakura-zima for volcanic effluents to penetrate low-level tropospheric temperature inversions and, consequently, the tropopause over northern middle latitudes. Maximum elevation of the volcanic clouds was determined to be 3.4 km. The cumulative thermal energy release in the rise of volcanic plumes for 385 observed explosive eruptions was estimated to be 10²⁰ to 10²¹ ergs (10¹³ to 10¹⁴ J), but the entire thermal energy release associated with pyroclastic activity may be of the order of 2.5 × 10²² ergs (2.5 × 10¹⁵ J).Estimation of the kinetic energy component of explosive eruptions via satellite observation and meteorological consideration of eruption clouds is thus useful in volcanology as an alternative technique to confirm the kinetic energy estimates made by ground-based geological and geophysical methods, and to aid in construction of physical models of potential and historical tephra-fallout sectors with implications for volcano-hazard prediction.     

Eruption of Piip Crater (Kamchatka)

In autumn of 1966 on the northern slope of Kliuchevskoy volcano a chain of new adventive craters broke out at the height of about 2200 m. Eighty-four hours before the beginning of the eruption a swarm of preliminary volcanic earthquakes had appeared. The number of preliminary shocks was 457 with total energy of 4 × 10¹⁷ erg. With the beginning of the lava flow the earthquakes stopped and a continuous volcanic tremor appeared. The total energy of volcanic tremor amounts to 10¹⁶ erg. During the eruption numerous explosive earthquakes with the energy of 10¹⁵–10¹⁶ erg were recorded and besides the microbarograph of the Volcanostation recorded 393 explosions with an energy more than 10¹³ erg and their total energy was equal to 10¹⁷ erg. All together it has been formed 8 explosive craters and the lowest 9th crater was effusive. The slag cone was formed round this effusive crater, the lava effusion of basaltic-andesite composition (52,5% SiO₂) tooke place from the lava boccas at the cone base and from the crater. The lava flow covered a distance of 10 km along the valley of the Sopochnoy river and descended to a height of about 800 m. The lava flow velocity at the outflow reached 800 m/hr, the lava temperature was 1050°C. The effused lava volume amounts to 0.1 km³. The eruption stopped on December 25–26, 1966.     

Ejecta velocities,magma chamber pressure and kinetic energy associated with the 1968 eruption of arenal volcano

During the initial explosive phase of the eruption of Arenal volcano small projectiles were thrown a maximum distance of 5 km. Considering the effect of atmospheric drag these projectiles must have had initial velocities of at least 600 m/sec. For this velocity, the gas pressure in the magma chamber must have reached at least 4700 bars and the kinetic energy of the initial explosion is estimated as 2.4 ± 1.2 × 10^a ergs. Had the effect of aerodynamic braking been ignored in making these calculations, as has always been done in the past, the calculated initial velocity would have been 220 m/sec; chamber pressure and kinetic energy estimates would thus be substantially lower. Clearly, velocities of ejecta, chamber pressures and kinetic energies for many explosive volcanic events have been seriously underestimated in the recent past, as has been the ability of overlying materials to contain, in certain cases, tremendous overpressures for short periods of time. A projectile with an initial velocity of 600 m/sec would have a maximum range of more than 200 km on the moon. Thus, the presence of far-reaching secondary crater fields on the moon cannot, at this time, be considered evidence for an impact origin of the parent crater. 600 m/sec is not the upper limit for initial velocities of volcanic ejecta. There is some indication that such velocities could reach values greater than 2 km/sec, suggesting that volcanic as well as impact mechanisms may be able to impart escape velocity to lunar materials.     

The distribution of tephra deposits and reconstructing the parameters of 1973 eruption on Tyatya Volcano,Kunashir I., Kuril Islands

We studied the distribution of tephra deposits discharged by the basaltic (52–54% SiO₂) explosive eruption of 1973 on Tyatya Volcano (Kunashir I., Kuril Islands). We made maps showing lines of equal tephra thickness (isopachs) and lines of maximum size of pyroclastic particles (isopleths). These data were used to find the parameters of explosive activity using the standard techniques for each of the two phases of this eruption separately. The first, phreatomagmatic, phase discharged 0.008 km³ of tephra during the generation of maars on the volcano’s northern slope. The tephra mostly consisted of fragmented host rocks with admixtures of fragments of low vesiculated juvenile basalt. The phase lasted 20 hours, the rate of pyroclastic discharge was 2 × 10⁵ kg/s; the eruptive plume reached heights of 4–6 km with wind speeds within 10 m/s. The second, magmatic, phase discharged 0.07 km³ of tephra during the generation of the Otvazhnyi scoria cone on the volcano’s southeastern slope. The tephra mostly consisted of juvenile basaltic scoria. The highly explosive Plinian part of this phase lasted 36 hours, the rate of pyroclastic discharge was 8 × 10⁵ kg/s; the eruptive plume reached heights of 6–8 km with wind speeds of 10–20 m/s. The total tephra volume discharged by the eruption was approximately 0.08 km³; the total amount of ejected pyroclastic material (including the resulting monogenic edifices) was 0.11 km³; the volume of erupted magma was 0.05 km³ (the conversion was based on 2800 kg/m³ density); the volcanic explosivity index, or VEI, was 3. The production rate of the Tyatya plumbing system is estimated as 3 × 10⁵ m³ magma per annum.     

Stratigraphy, chemistry, and eruptive dynamics of the 12.4 ka plinian eruption of Apoyeque volcano, Managua, Nicaragua

Apoyeque volcano, located 9 km northwest of Managua city, erupted explosively at 12.4 ka. The Plinian eruption deposited a widespread pumice fall deposit known as the Upper Apoyeque Tephra (UAq). The UAq is massive, reversely graded, and consists of white juvenile pumice (~78 vol.%), a variety of cognate lithics and accidental altered lithics. The whole-rock pumice composition is rhyodacitic (SiO₂?=?66.9–68.5 wt.%) with a mineral paragenesis of plagioclase, orthopyroxene, clinopyroxene, amphibole, titanomagnetite, and ilmenite in a rhyolitic glass groundmass (SiO₂?=?74.4?±?0.6 wt.%). The deposit’s dispersal axis is to the south, with the deposit covering a minimum area of 877 km² within the 50 cm isopach and has a total volume of 3 km³ (dense rock equivalent, 1.15 km³). The eruption column reached a maximum height of ca.28 km. The eruption ejected a total mass of 3?×?10¹² kg at an average rate of 2?×?10⁸ kg/s, and based on available models, we infer duration of almost 4 h. Petrographic and geochemical characteristics suggest that the eruption was triggered by magma mixing.     

The prediction of large explosions of andesitic volcanoes

During the large explosions of the Bezymianny (1956), Shiveluch (1964) and Mount St. Helens (1980) volcanoes, 4.8·10¹², 3.0·10¹² and 8.2·10¹² kg of resurgent and magmatic material were ejected respectively. The eruptions were preceded and accompanied by significant crustal deformations and by a great number of volcanic earthquakes. In all three cases, earthquakes with an energy of E = 10⁹ J occurred 8–11 days before the eruption; their foci were at a distance of less than 5 km from the floor of the active crater and the power of earthquake swarms increased continuously and monotonously until the beginning of the eruption. The data obtained on deformations, earthquakes and volcanic activity may be used for the prediction of the place, time, energy and hazards of large explosions of andesitic volcanoes.     

The Pomici di Avellino eruption of Somma-Vesuvius (3.9 ka bp). Part I: stratigraphy, compositional variability and eruptive dynamics

The stratigraphic succession of the Pomici di Avellino Plinian eruption from Somma-Vesuvius has been studied through field and laboratory data in order to reconstruct the eruption dynamics. This eruption is particularly important in the Somma-Vesuvius eruptive history because (1) its vent was offset with respect to the present day Vesuvius cone; (2) it was characterised by a distinct opening phase; (3) breccia-like very proximal fall deposits are preserved close to the vent and (4) the pyroclastic density currents generated during the final phreatomagmatic phase are among the most widespread and voluminous in the entire history of the volcano. The stratigraphic succession is, here, divided into deposits of three main eruptive phases (opening, magmatic Plinian and phreatomagmatic), which contain five eruption units. Short-lived sustained columns occurred twice during the opening phase (H_t of 13 and 21.5 km, respectively) and dispersed thin fall deposits and small pyroclastic density currents onto the volcano slopes. The magmatic Plinian phase produced the main volume of erupted deposits, emplacing white and grey fall deposits which were dispersed to the northeast. Peak column heights reached 23 and 31 km during the withdrawal of the white and the grey magmas, respectively. Only one small pyroclastic density current was emplaced during the main Plinian phase. In contrast, the final phreatomagmatic phase was characterised by extensive generation of pyroclastic density currents, with fallout deposits very subordinate and limited to the volcano slopes. Assessed bulk erupted volumes are 21 × 10⁶ m³ for the opening phase, 1.3–1.5 km³ for the main Plinian phase and about 1 km³ for the final phreatomagmatic phase, yielding a total volume of about 2.5 km³. Pumice fragments are porphyritic with sanidine and clinopyroxene as the main mineral phases but also contain peculiar mineral phases like scapolite, nepheline and garnet. Bulk composition varies from phonolite (white magma) to tephri-phonolite (grey magma).     

Volume,energy and cyclicity of eruptions of Arenal volcano,Costa Rica

The 1968–73 (and continuing) eruption of Arenal Volcano, Costa Rica, a small 1633 m strato-volcano with long periods of repose, defines an eruptive cycle which is typical of Arenal’s pre-historic eruptions. An intense, short explosive phase (July 29–31, 1968) grades into an effusive phase, and is followed by a block lava flow. The eruptive rocks become increasingly less differentiated with time in a given cycle, ranging from andesite to basaltic andesite. Nuées ardentes are a characteristic of the initial explosions, and are caused by fall-back ejecta on slopes around the main crater — an explosion crater in the 1968 eruption — which coalesce into hot avalanches and descend major drainage channels. Total volume of pyroclastic flows was small, about 1.8 ± 0.5 × 10ⁿ m³, in the July 29–31 explosions, and are block and ash flows, with much accidental material. Overpressures, ranging up to perhaps 5 kilobars just prior to major explosions, were estimated from velocities of large ejected blocks, which had velocities of up to 600 m/sec. Total kinetic energy and volume of ejecta of all explosions are an estimated 3 × 10²² ergs and 0.03 km³, respectively. The block lava flow, emitted from Sept., 1968 to 1973 (and continuing) has a volume greater than 0.06 km³, and covers 2.7 km² at thicknesses ranging from 15 to over 100 m. The total volumes of the explosive and effusive phases for the 1968–73 eruption are about 0.05 km³ and 0.06 km³, respectively. The last eruption of Arenal occurred about 1500 AD. based on radiocarbon dating and archaeological means, and was about twice as voluminous as the current one (0.17 km³ versus 0.09 km³). The total thermal energies for this pre-historic eruption and the current one are 8 × 10²³ and 18 × 10²³, respectively. The total volume of Arenal’s cone is about 6 km³ from 1633 m (summit) to 500 m, and, estimates of age based on the average rate of cone growth from these two eruptions, suggest an age between 20,000 to 200,000 years.     

The May 1915 eruptions of Lassen Peak, II: May 22 volcanic blast effects, sedimentology and stratigraphy of deposits, and characteristics of the blast cloud

The May 22, 1915 eruptions of Lassen Peak involved a volcanic blast and the emplacement of three geographically and temporally distinct lahar deposits. The volcanic blast occurred when a Vulcanian explosion at the summit unroofed a shallow magma source, generating an eruption cloud that rose to an estimated height of 9 km above sea level. The blast cloud was probably caused by the collapse of a small portion of the eruption column; absence of a flank vent associated with these eruptions argues against it originating as an explosion that has been directed by vent geometry or location. The volcanic blast devasted 7 km² of the northeast flank of the volcano, and emplaced a deposit of juvenile tephra and accidental lithic and mineral fragments. Decrease in blast deposit thickness and median grain size with increasing distance from the vent suggests that the blast cloud lost transport competence as it crossed the devastated area. Scanning electron microscope examination of pyroclasts from the blast deposit indicates that the blast cloud was a dry, turbulent suspension that emplaced a thin deposit which cooled rapidly after deposition. Lahar deposits were emplaced primarily in Lost Creek, with minor lahars flowing down gullies on the west, northwest and north flanks of the volcano. The initial lahar was apparently triggered early in the eruption when the blast cloud melted the residual snowpack as it moved down the northeast flank of the peak. The event that triggered the later lahars is enigmatic; the presence of approximately five times more juvenile dacite bombs on the surface of the later lahars suggests that they may have been triggered by a change in eruption style or dynamics.     

Deposits of the 30 March 1956 directed blast at Bezymianny volcano,Kamchatka, Russia

 On 30 March 1956 a catastrophic directed blast took place at Bezymianny volcano. It was caused by the failure of 0.5 km³ portion of the volcanic edifice. The blast was generated by decompression of intra-crater dome and cryptodome that had formed during the preclimactic stage of the eruption. A violent pyroclastic surge formed as a result of the blast and spread in an easterly direction effecting an area of 500 km² on the lower flank of the volcano. The thickness of the deposits, although variable, decreases with distance from the volcano from 2.5 m to 4 cm. The volume of the deposit is calculated to be 0.2–0.4 km³. On average, the deposits are 84% juvenile material (andesite), of which 55% is dense andesite and 29% vesicular andesite. On a plot of sorting vs median diameter (Inman coefficients) the deposits occupy the area between the fall and flow fields. In the proximal zone (less than 19 km from the volcano) three layers can be distinguished in the deposits. The lower one (layer A) is distributed all over the proximal area, is very poorly sorted, enriched in fragments of dense juvenile andesite and contains an admixture of soil and uncharred plant remains. The middle layer (layer B) is distributed in patches tens to hundreds of metres across on the surface of layer A. Layer B is relatively well sorted as a result of a very low content of fine fractions, and it contains rare charred plant remains. The uppermost layer (layer C) forms still smaller patches on the surface of layer B. Layer C is characterized by intermediate sorting, is enriched in vesicular juvenile andesitic fragments, and contains a high percentage of the fine fraction and very rare plant remains which are thoroughly charred. Maximum clast size decreases from layer A to layer C. The absence of internal cross bedding is a characteristic of all three layers. In the distal zone (more than 19 km from the volcano) stratigraphy changes abruptly. Deposit here consists of one layer 26 to 4 cm in thickness, is composed of wavy laminated sand with a touch of gravel, is well sorted and contains uncharred plant remains. The Bezymianny blast deposits are not analogous with known types of pyroclastic surges, with the exception of the directed blast deposits of the Mount St.Helens eruption of 18 May 1980. The peculiarities of deposits from these two eruptions allow them to be separated into a special type: blast surge. This type of surge is formed when failure of volcanic edifice relieves the pressure from an inter-crater dome and/or cryptodome. A model is proposed to explain the peculiarities of the formation, transportation and emplacement of the Bezymianny blast surge deposits. Received: 19 December 1994 / Accepted: 12 December 1995     

Constraining tephra dispersion and deposition from three subplinian explosions in 2011 at Shinmoedake volcano,Kyushu, Japan

Constraining physical parameters of tephra dispersion and deposition from explosive volcanic eruptions is a significant challenge, because of both the complexity of the relationship between tephra distribution and distance from the vent and the difficulties associated with direct and comprehensive real-time observations. Three andesitic subplinian explosions in January 2011 at Shinmoedake volcano, Japan, are used as a case study to validate selected empirical and theoretical models using observations and field data. Tephra volumes are estimated using relationships between dispersal area and tephra thickness or mass/area. A new cubic B-spline interpolation method is also examined. Magma discharge rate is estimated using theoretical plume models incorporating the effect of wind. Results are consistent with observed plume heights (6.4–7.3 km above the vent) and eruption durations. Estimated tephra volumes were 15–34?×?10⁶ m³ for explosions on the afternoon of 26 January and morning of 27 January, and 5.0–7.6?×?10⁶ m³ for the afternoon of 27 January; magma discharge rates were in the range 1–2?×?10⁶ kg/s for all three explosions. Clast dispersal models estimated plume height at 7.1?±?1 km above the vent for each explosion. The three subplinian explosions occurred with approximately 12-h reposes and had similar mass discharge rates and plume heights but decreasing erupted magma volumes and durations.     

Magma and hydrothermally driven sector collapses: The 3100 and 11,500 y. B.P. eruptions of la Grande Decouverte (la Soufrière) volcano, Guadeloupe, French West Indies

We recently reported (Boudon et al., 1984) on an eruption similar to that of May 18, 1980 at Mount St. Helens, that took place about 3100 years ago at la Soufrière, Guadeloupe. During the course of detailed geological mapping of the deposits of this event, older debris flow and blast deposits were recognized in the northern sector of the mapped area. Uncarbonized wood fragments in the debris flow have yielded ages ca. 11,500 y. B.P. The deposits extend from an amphitheater crater westward to the caribbean shore about 10 km downslope from the volcano. The deposits and crater structure suggest that they are the result of catastrophic flank failure like the event 3100 years ago. Unlike the latter activity, however, no magmatic component is found in the deposits.     

The Klyuchevskoi Eruptions of 2015–2016

This paper deals with the summit eruptions of 2015–2016, as well as with the 2016 subterminal eruption of Klyuchevskoi. We estimate the dimensions of the depression that was produced by a landfall in the southeastern trough of the volcano. We estimated the volume and area of landfall deposits. The observed volumes of landfalls during the terminal eruptions of 1944?1945, 1985, and 2016 can vary within 0.006?0.140 km³. The theoretical volumes can reach 4?8 km³. We discuss the leading factors that cause landfalls on Klyuchevskoi. These include irreversible creep at depth, the influence of cracks and fissuring in the volcanic cone, as well as the constant intrusive activity of the volcano. Geodetic measurements revealed that the rates of sliding for several individual patches on the slopes varied between 6.7 cm/yr and 19.4 cm/yr. Video and photographic observations were used to estimate the thermal power of stable steam–gas and ash jets, volume of pyroclastics, and the volume of the erupted lava. The thermal power of the steam–gas jets for 2015 was approximately 122 × 10⁶ kW, that of the gas–ash jets was 5.9 × 10⁶ kW. The volume of discharged pyroclastic material was V = 0.00007 km³ for 2015 and V = 0.0003 km³ for 2016.     

The 1972 Eruption of Kartala volcano,grande comore

A summit eruption of Kartala commenced on September 8th, 1972 and finished on October 5th, 1972. In the course of this eruption, approximately 5×10⁶ m³ of alkali olivine basalt was erupted from a N-S fissure system within and adjacent to the caldera. Aa flows were partly ponded within the caldera, almost filling the 1918 Choungou Chagnoumeni crater pit, and partly spilled NW down the flanks of the volcano. The lavas are of uniform composition, almost identical to those erupted in 1965 and closely resembling the majority of flows erupted during the last 115 years. One-atmosphere melting experiments support petrographic and chemical evidence that the lavas are coctetic, with coprecipitation of olivine, augite and plagioclase. The lavas were crupted at, or close to, their liquidus temperature, determined at approximately 1170°C. Whereas eruptions of Kartala in the nineteenth century were distributed widely along a fissure system approximately 45 km long by 7 km wide, the eruptions since 1918 have been confined to the vicinity of the summit caldera.     

Volcano-seismic crisis in Montserrat,West Indies, 1966–67

The Soufriere Hills volcano in the south-eastern part of Montserrat erupted pyroclast flows as recently as A. D. 1646 ± 54 years and must therefore be considered dormant, not extinct. The highly destructive nature of pyroclast flow eruptions makes it imperative that such activity should be predicted and, if the threat of eruption becomes sufficiently large, the population should be moved to a sale distance from the volcano. Sharp increases in seismic and solfataric activity occurred in 1966 and these events indicated the abnormally high risk of an eruption in the near future. A network of four short period seismographs was established in the island in May 1966 and between this date and the end of 1967, 723 local earthquakes were recorded, of which 32 were reported felt in the island. Hypocentres were determined for 189 of these earthquakes, and most of these lay in a WNW to ESE belt beneath the Soufriere Hills, at depths of less than 15 km. The average rate of seismic energy release decreased with time throughout the series but there was a strong seasonal variation with maxima in May and November–December of each year. The average depth of the earthquakes decreased from 5.2 km in April and May 1966 to a minimum of 2.8 km from July to September 1966. After September the mean focal depths increased again and by the end of the crisis in November 1967 the mean depth was 9.7 km. Measurements carried out using water-tube tiltmeters showed that the region 2–3 km south-east of the Soufriere Hills was doming upwards until January 1967, then subsided between January–March 1967 and finally rose again at a slower rate between March and September 1967. Heat flow from Galway’s Soufriere which was 3 × 10⁵ cal/sec in 1954 increased to a maximum of 2 × 10⁵ cal/sec in October 1966, then declined to 5 × 10⁵ cal/sec in September 1967. The earthquake series was not the aftershock sequence of any major tectonic earthquake, and only two hypocentres were determined at depths greater than 15 km. It is concluded that magma was intruded into the upper crust beneath the Soufriere Hills volcano and that the earthquakes and other phenomena resulted from the upward migration of this magma.     

A weak phreatic eruption of June 2010 on Ekarma Volcano, Kuril Islands as a possible precursor of a future large magmatic eruption

We provide data concerning a weak phreatic eruption of Ekarma Volcano on Ekarma Island, in the Kurils, in June 2010. The ash plumes did not rise higher than 3 km above sea level. A preliminary estimate of the volume of erupted resurgent material (mostly tephra) is on order 2 × 10⁵ m³. Reconstruction of the volcano??s history and the dynamics of its eruptive activity for the last 4500?C5000 years suggests that a larger eruption can occur during the next few decades that will discharge juvenile pyroclastics and/or lava.     

Amplified hazard of small-volume monogenetic eruptions due to environmental controls, Orakei Basin, Auckland Volcanic Field, New Zealand

Orakei maar and tuff ring in the Auckland Volcanic Field is an example of a basaltic volcano in which the style and impacts of the eruption of a small volume of magma were modulated by a fine balance between magma flux and groundwater availability. These conditions were optimised by the pre-85?ka eruption being hosted in a zone of fractured and variably permeable Plio-Pleistocene mudstones and sandstones. Orakei maar represents an end-member in the spectrum of short-lived basaltic volcanoes, where substrate conditions rather than the magmatic volatile content was the dominant factor controlling explosivity and eruption styles. The eruption excavated a crater ?80?m deep that was subsequently filled by slumped crater wall material, followed by lacustrine and marine sediments. The explosion crater may have been less than 800?m in diameter, but wall collapse and wave erosion has left a 1,000-m-diameter roughly circular basin. A tuff ring around part of the maar comprises dominantly base surge deposits, along with subordinate fall units. Grain size, texture and shape characteristics indicate a strong influence of magma–water and magma–mud interactions that controlled explosivity throughout the eruption, but also an ongoing secondary role of magmatic gas-driven expansion and fragmentation. The tuff contains >70?% of material recycled from the underlying Plio-Pliestocene sediments, which is strongly predominant in the >2 ? fraction. The magmatic clasts are evolved alkali basalt, consistent with the eruption of a very small batch of magma. The environmental impact of this eruption was disproportionally large, when considering the low volume of magma involved (DRE?<?0.003?km³). Hence, this eruption exemplifies one of the worst-case scenarios for an eruption within the densely populated Auckland City, destroying an area of ~3?km² by crater formation and base surge impact. An equivalent scenario for the same magma conditions without groundwater interaction would yield a scoria/spatter cone with a diameter of 400–550?m, destroying less than a tenth of the area affected by the Orakei event.