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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.

While the eruptive record of Mount Etna is reasonably complete for the past 400 years, the activity of the early and late 1960s, which took place at the summit, is poorly documented in the scientific literature. From 1955 to 1971, the Central and Northeast Craters were the sites of long-lived mild Strombolian and effusive activity, and numerous brief episodes of vigorous eruptive activity, which led to repeated overflows of lava onto the external flanks of the volcano. A reconstruction of the sequence of the more important of these events based on research in largely obscure and nearly inaccessible sources permits a better understanding of the eruption dynamics and rough estimates of erupted volumes and of the changes to the morphology of the summit area. During the first half of 1964, the activity culminated in a series of highly dynamic events at the Central Crater including the opening of a fissure on the E flank of the central summit cone, lava fountains, voluminous tephra emission, prolonged strong activity with continuous lava overflows, and growth of large pyroclastic intracrater cones. Among the most notable processes during this eruption was the breaching of a section of the crater wall, which was caused by lateral pressure of lava ponding within the crater. Comparison with the apparently similar summit activity of 1999 allows us to state that (a) lava overflows from large pit craters at the summit are often accompanied by breaching of the crater walls, which represents a significant hazard to nearby observers, and that (b) eruptive activity in 1999 was much more complex and voluminous than in 1964. For 1960s standards however, the 1964 activity was the most important summit eruption in terms of intensity and output rates for about 100 years, causing profound changes to the summit morphology and obliterating definitively the former Central Crater.

The orientation of crustal seismic anisotropy changed at least twice by up to 80° because of volcanic eruptions at Ruapehu Volcano, New Zealand. These changes provide the basis for a new monitoring technique and possibly for future midterm eruption forecasting at volcanoes. The fast anisotropic direction was measured during three seismometer deployments in 1994, 1998, and 2002, providing an in situ measurement of the stress in the crust under the volcano. The stress direction changed because of an eruption in 1995–1996. Our 2002 measurements revealed a partial return to the pre-eruption stress state. These changes were probably caused by repeated filling and depressurizing of a magmatic dike system.

The 1998 eruption of Volcan Cerro Azul in the Galapagos Islands produced two intra-caldera vents and a flank vent that erupted more than 1.0×108 m3 of lava. Lava compositions changed notably during the 5-week eruption, and contemporaneous eruptions in the caldera and on the flank produced different compositions. Lavas erupted from the flank vent range from 6.3 to 14.1% MgO, nearly the entire range of MgO contents previously reported from the volcano. On-site monitoring of eruptive activity is linked with petrogenetic processes such that geochemical variations are evaluated in a temporal context. Lavas from the 1998 eruption record two petrogenetic stages characterized by progressively more mafic lavas as the eruption proceeded. Crystal compositions, whole rock major and trace element compositions, and isotope ratios indicate that early lavas are the product of mixing between 1998 magma and remnant magma of the 1979 eruption. Intra-caldera lavas and later lavas have no 1979 signature, but were produced by the 1998 magma incorporating olivine and clinopyroxene xenocrysts. Thus, early magma petrogenesis is characterized by mixing with the 1979 magma, followed by the magma progressively entraining wehrlite cumulate mush.

Effusion rate and degassing data collected at Mt. Etna volcano (Italy) in 2001 show variations occurring on time scales of hours to months. We use both long- and short-term data sets spanning January to August to identify this variation. The long data sets comprise a satellite- and ground-based time series of effusion rates, and the latter include field-based effusion rate and degassing data collected May 29–31. The satellite-derived effusion rates for January through August reveal four volumetric pulses that are characterized by increasing mean effusion rate values and lead up to the 2001 flank eruption. Peak effusion rates during these 23–57 day pulses were 1.2 m3 s−1 in Pulse 1 (1 Jan–4 Mar), 1.1 m3 s−1 in Pulse 2 (5 Mar–21 Apr), 4.2 m3 s−1 in Pulse 3 (24 Apr–18 Jun), 8.8 m3 s−1 in Pulse 4 (23 Jun–16 Jul), and 22.2 m3 s−1 during the flank eruption (17 Jul–9 Aug). Rank-order analysis of the satellite data shows that effusion rate values during the 2001 flank eruption define a statistically different trend than Etna's persistent activity from Jan 1 to Jul 17. Data prior to the flank eruption obey a power-law relationship that may define an effusion rate threshold of ∼3–5 m3 s−1 for Etna's typical persistent activity. Our short-term data coincide with the satellite-derived peak effusion period of Pulse 3. Degassing (at-vent puff frequency) shows a general increase from May 29 to 31, with hour-long variations in both puff frequency and lava flow velocity (effusion rate). We identify five 3–14 h degassing periods that contain 26 shorter (19–126 min-long) oscillations. This variation shows some positive correlation with effusion rate measurements during the same time period. If a relationship between puff frequency and effusion rate is valid, we propose that their short-term variation is the result of changes in the supply rate of magma to the near-vent conduit system. Therefore, these short-term data provide some evidence that the clear weeks- to months-long variation in Etna's effusive activity (January–August 2001) was overprinted by a minutes- to hour-scale oscillation in shallow supply.

describe the reactivation and the successive evolution of the shallow plumbing system of Mt. Etna between the end of the largest flank eruption of the last three centuries (1991 -1993) and the subterminal eruption from South-East Crater (SEC), which occurred between February and mid-November 1999. Our analysis is based on observations of the volcanic activity and petrological studies of the erupted volcanics. Bulk rock, mineral and glass compositions have been determined for more than 80 samples erupted from the four summit craters between October 1995 and February 1999. These data allow us to recognise significant compositional variations among the products of different craters. In particular, volcanics produced between 1995 and 1999 by Bocca Nuova (BN), Voragine (VOR) and North-East Crater (NEC) show limited compositional variations and are similar to those observed during recent eruptions (e.g., 1991-93). More primitive magmas have been produced during the more vigorous fire fountains episodes. On the contrary, the South-East Crater produced slightly more differentiated volcanics than those of the other summit craters following its reactivation (November 1996) until the end of 1998. Whole rock compositions of products from this crater show low CaO/Al 2 O 3 , whereas interstitial glasses have lower MgO and higher alkali contents than those from the other craters. However, since the beginning of 1999, and just before the start of the subterminal eruption from SEC, the volcanics erupted from this crater progressively changed in composition, becoming similar to those of the other craters. This trend indicates that within the conduits of the summit craters, distinct thermal and fluid-dynamical regimes can evolve, controlling the cooling and crystallisation of Etna magmas.

The Rotoiti eruption from the Taupo Volcanic Zone (TVZ ) in northern New Zealand produced voluminous pyroclastic deposits. The ferromagnesian mineral assemblage in these dominantly consists of cummingtonite þ hornblende þ orthopyroxene with uniform magnesium/iron ratios; a second assemblage of biotite þ hornblende þ orthopyroxene, also with uniform Fe/Mg ratios, appears midway through the eruption sequence and, thereafter, increases in abundance. These contrasting mineral assemblages, together with pumice clast and groundmass glass compositions, provide evidence for mingling of two discrete magmas. Similarities in the chemical characteristics of the two magmas suggest that they developed from a similar source. The eruption initially tapped relatively homogeneous magma that was erupted throughout most of this phase of activity. The middle stages of the eruption included some mixed magma. The final stages of the eruption were dominated by a second magma composition, which was probably injected into the bottom of the main magma body as the eruption proceeded. The source that fed the eruption was complex, and discrete magma bodies existed and evolved separately prior to the eruption. We conclude that eruptions in the TVZ are fed from a diffuse upper-crustal zone of partially interconnected, and at times physically separate, magma bodies rather than from centralized and necessarily large long-lived magma chambers.

The 2002–03 Mt Etna flank eruption began on 26 October 2002 and finished on 28 January 2003, after three months of continuous explosive activity and discontinuous lava flow output. The eruption involved the opening of eruptive fissures on the NE and S flanks of the volcano, with lava flow output and fire fountaining until 5 November. After this date, the eruption continued exclusively on the S flank, with continuous explosive activity and lava flows active between 13 November and 28 January 2003. Multi-disciplinary data collected during the eruption (petrology, analyses of ash components, gas geochemistry, field surveys, thermal mapping and structural surveys) allowed us to analyse the dynamics of the eruption. The eruption was triggered either by (i) accumulation and eventual ascent of magma from depth or (ii) depressurisation of the edifice due to spreading of the eastern flank of the volcano. The extraordinary explosivity makes the 2002–03 eruption a unique event in the last 300 years, comparable only with La Montagnola 1763 and the 2001 Lower Vents eruptions. A notable feature of the eruption was also the simultaneous effusion of lavas with different composition and emplacement features. Magma erupted from the NE fissure represented the partially degassed magma fraction normally residing within the central conduits and the shallow plumbing system. The magma that erupted from the S fissure was the relatively undegassed, volatile-rich, buoyant fraction which drained the deep feeding system, bypassing the central conduits. This is typical of most Etnean eccentric eruptions. We believe that there is a high probability that Mount Etna has entered a new eruptive phase, with magma being supplied to a deep reservoir independent from the central conduit, that could periodically produce sufficient overpressure to propagate a dyke to the surface and generate further flank eruptions.

Using near simultaneously acquired Landsat 7 Enhanced Thematic Mapper Plus (ETM+) and Earth Observing-1 Advanced Land Imager (ALI) data we assess the relative radiant responses over active lava flows from the Mt. Etna July/August 2001 flank eruption. By assessing the extent of saturation between the two instruments and using the dual-band method of extracting sub pixel thermal information, we show that the ALI represents an improvement over the ETM+ in the present ability to assess temperatures of hot active lava flows for a number of reasons. (1) The extra spectral channels provided by ALI compliment the current SWIR channels on ETM+ by providing a greater number of paired channel combinations for input into the dual-band method. Thus, dual-band temperature solutions can be determined for a greater range of lava flow types than previously possible using the two paired channel combinations available with the ETM+. (2) The ALI instrument is less susceptible than ETM+ to saturation within the SWIR, especially when using channels 5, 5p and 4p at wavelengths of 1.65, 1.25 and 0.87 μm respectively. (3) The greater radiometric sensitivity of the ALI 12 bit electronics coupled with a significantly higher signal to noise ratio aid in obtaining successful dual-band solutions.

In this work we present seismological and ground deformation evidence for the phase preparing the July 18 to August 9, 2001 flank eruption at Etna. The analysis performed, through data from the permanent seismic and ground deformation networks, highlighted a strong relationship between seismic strain release at depth and surface deformation. This joint analysis provided strong constraints on the magma rising mechanisms. We show that in the last ten years, after the 1991–1993 eruption, an overall accumulation of tension has affected the volcano. Then we investigate the months preceding the 2001 eruption. In particular, we analyse the strong seismic swarm on April 20–24, 2001, comprising more than 200 events (Mmax= 3.6) with prevalent dextral shear fault mechanisms in the western flank. The swarm showed a ca. NE-SW earthquake alignment which, in agreement with previous cases, can be interpreted as the response of the medium to an intrusive process along the approximately NNW-SSE volcano-genetic trend. These mechanisms, leading to the July 18 to August 9, 2001 flank eruption, are analogous to ones observed some months before the 1991–1993 flank eruption and, more recently, in January 1998 before the February-November 1999 summit eruption.

This paper details the observations taken from a reconnaissance trip to Mt. Etna, Italy during the 2002 flank eruption, and utilizes those observations to identify potential hazards in New Zealand. It also makes recommendations for preparation and response to those hazards. The various types of hazards posed by Etna are primarily lava flows, ashfall and earthquakes. Lava flows caused intense damage in proximal areas, including forests, roads and the destruction of ski lifts and several buildings. Ashfall affected a much larger area, and was thus responsible for most of the damage economically. While earthquakes were not severe by New Zealand standards, the unreinforced masonry structures that predominate on Etna did not cope well with the seismic activity that accompanied the eruption. Several lessons taken from this eruption are applicable to New Zealand, both in effects of basaltic and more silicic types of volcanism.

The simultaneous solution of the Planck equation (the so-called “dual-band” technique) for two shortwave infrared Landsat Thematic Mapper (TM) bands allows an estimate of the fractional area of the hottest part of an active flow and the temperature of the cooler crust. Here, the dual-band method has been applied to a time series of Mount Etna eruptions. The frequency distribution of the fractional area of the hottest component reveals specific differences between summit and flank lava flows. The shape of the density function shows a trend consistent with a Gaussian distribution and suggests a relationship between the moments of the distribution and the emplacement environment. Because flow composition of Etnean lavas generally remains constant during the duration of their emplacement, it appears that the shape of any particular frequency distribution is probably related to fluid mechanical aspects of flow emplacement that affect flow velocity and flow heat loss and thus the rate of formation of the surface crust. These factors include the influence of topographical features such as changes in slope gradient, changes in volume effusion rate, and progressive downflow increases in bulk or effective viscosity. A form of the general theoretical solution for the ‘dual-band’ system, which illustrates the relationship between radiance in TM bands 5 and 7, corresponding to hot fractional area and crust temperature, is presented. Generally speaking, it appears that for a given flow at any point in time, larger fractional areas of exposed hot material are correlated with higher temperatures and that, while the overall shape of that distribution is common for the flows studied, its amplitude and slope reflect individual flow rheological regimes.

The 13-day-long Gjalp eruption within the Vatnajokull ice cap in October 1996 provided important data on ice–volcano interaction in a thick temperate glacier. The eruption produced 0.8 km3 of mainly volcanic glass with a basaltic icelandite composition (equivalent to 0.45 km3 of magma). Ice thickness above the 6-km-long volcanic fissure was initially 550–750 m. The eruption was mainly subglacial forming a 150–500 m high ridge; only 2–4% of the volcanic material was erupted subaerially. Monitoring of the formation of ice cauldrons above the vents provided data on ice melting, heat flux and indirectly on eruption rate. The heat flux was 5–6×105 W m-2 in the first 4 days. This high heat flux can only be explained by fragmentation of magma into volcanic glass. The pattern of ice melting during and after the eruption indicates that the efficiency of instantaneous heat exchange between magma and ice at the eruption site was 50–60%. If this is characteristic for magma fragmentation in subglacial eruptions, volcanic material and meltwater will in most cases take up more space than the ice melted in the eruption. Water accumulation would therefore cause buildup of basal water pressure and lead to rapid release of the meltwater. Continuous drainage of meltwater is therefore the most likely scenario in subglacial eruptions under temperate glaciers. Deformation and fracturing of ice played a significant role in the eruption and modified the subglacial water pressure. It is found that water pressure at a vent under a subsiding cauldron is substantially less than it would be during static loading by the overlying ice, since the load is partly compensated for by shear forces in the rapidly deforming ice. In addition to intensive crevassing due to subsidence at Gjalp, a long and straight crevasse formed over the southernmost part of the volcanic fissure on the first day of the eruption. It is suggested that the feeder dyke may have overshot the bedrock–ice interface, caused high deformation rates and fractured the ice up to the surface. The crevasse later modified the flow of meltwater, explaining surface flow of water past the highest part of the edifice. The dominance of magma fragmentation in the Gjalp eruption suggests that initial ice thickness greater than 600–700 m is required if effusive eruption of pillow lava is to be the main style of activity, at least in similar eruptions of high initial magma discharge.

The July–August 2001 eruption of Mt. Etna stimulated widespread public and media interest, caused significant damage to tourist facilities, and for several days threatened the town of Nicolosi on the S flank of the volcano. Seven eruptive fissures were active, five on the S flank between 3,050 and 2,100 m altitude, and two on the NE flank between 3,080 and 2,600 m elevation. All produced lava flows over various periods during the eruption, the most voluminous of which reached a length of 6.9 km. Mineralogically, the 2001 lavas fall into two distinct groups, indicating that magma was supplied through two different and largely independent pathways, one extending laterally from the central conduit system through radial fissures, the other being a vertically ascending eccentric dike. Furthermore, one of the eccentric vents, at 2,570 m elevation, was the site of vigorous phreatomagmatic activity as the dike cut through a shallow aquifer, during both the initial and closing stages of the eruption. For 6 days the magma column feeding this vent was more or less effectively sealed from the aquifer, permitting powerful explosive and effusive magmatic activity. While the eruption was characterized by a highly dynamic evolution, complex interactions between some of the eruptive fissures, and changing eruptive styles, its total volume (~25×106 m3 of lava and 5–10×106 m3 of pyroclastics) was relatively small in comparison with other recent eruptions of Etna. Effusion rates were calculated on a daily basis and reached peaks of 14–16 m3 s-1, while the average effusion rate at all fissures was about 11 m3 s-1, which is not exceptionally high. The eruption showed a number of peculiar features, but none of these (except the contemporaneous lateral and eccentric activity) represented a significant deviation from Etna's eruptive behavior in the long term. However, the 2001 eruption could be but the first in a series of flank eruptions, some of which might be more voluminous and hazardous. Placed in a long-term context, the eruption confirms a distinct trend, initiated during the past 50 years, toward higher production rates and more frequent eruptions, which might bring Etna back to similar levels of activity as during the early to mid seventeenth century.

Mount Etna is among the few volcanoes on Earth that erupt nearly continuously, but its activity (in terms of output rate and flank eruption frequency) undergoes significant fluctuations in time. Such fluctuations do not occur randomly, but represent various stages of cycles on a scale of decades and centuries. Recurrent patterns are particularly evident since 1865, with four complete cycles and a fifth one initiated in 1993. Each cycle consists of three phases, beginning with low-level activity followed by nearly continuous summit activity and culminating with a series of flank eruptions, the last commonly being the most voluminous. A distinct increase in the output rate of Etna, along with more frequent and voluminous summit and flank eruptions since 1950, may be interpreted as part of a longer cycle that began after a large eruption in 1669 and has not yet reached its culminating phase. If that trend continues, the activity of Etna might become similar to that of the 17th century, when flank eruptions were more voluminous than they have been since; however, it is difficult to assess when this will take place.

Large ocean island volcanoes frequently develop productive rift zones located close to unstable flanks and sites of older major sector collapses. Flank deformation is often caused by slip along a decollement within or underneath the volcanic edifice. We studied how such a stressed volcanic flank may bias the rift zone development. The influence of basal lubrication and lateral flank creep on rift development and rift migration is still poorly constrained by field evidence; here our analog experiments provide new insights. We injected colored water into gelatin cones and found systematic orientations of hydro-fractures (dikes) propagating through the cones. At the base of the cone, diverse friction conditions were simulated. By variation of the basal creep conditions we modeled radial dike swarms, collinear rift zones and three-armed rift systems. It is illustrated that a single outward-creeping flank is sufficient to modify the entire rift architecture of a volcano. The experiments highlight the general unsteadiness of dike swarms and that the distribution and alteration of weak substratum may become a major player in shaping a volcano's architecture.

Analyses of Fe‐Ti oxides help constrain models of magma storage region processes for the Soufriere Hills Volcano, Montserrat (W.I.), and provide clear evidence of the nature of transient heating events in the magma storage region. To constrain timescales of magma heating and remobilization, the TiO2 zoning patterns in a time series of natural titanomagnetites were compared with those produced in controlled phase equilibrium experiments on the andesite. Most samples of andesite erupted from 1995 to 2002 contain titanomagnetite crystals with uniform core compositions (TiO278 wt %). Many crystals are characterized by rimward increases in TiO2, interpreted to be Ti diffusion gradients caused by heating of the andesite by invading basaltic magma. Some andesites erupted during periods of the highest observed mass eruption rate, however, contain titanomagnetite with uniformly low TiO2 contents from core to rim. The observation that no Ti diffusion gradients, and no elevated core TiO2 contents, occur in the vast majority of titanomagnetite grains in magma batches that were erupted more than 2 years after the onset of the present eruption strongly suggests, first, that heating of the batches of andesite occurred just before eruption, and, second, that injection of basaltic magma has continued throughout the eruption. Heat, but little mass, may be transferred from the invading basalt to the andesite in the magma storage region by injection of dikes or formation of sills. Ponding of basaltic magma at the base of a pre-existing andesitic magma storage region is the simplest explanation consistent with observations. The Fe‐Ti oxide data strongly suggest that an internal conduit within the andesitic magma storage region carries magma from the zone of heating to the overlying conduit, which carries the magma through the upper arc crust. In this model, the magma chamber is being emptied from the bottom, at the contact between pre-existing andesite and newly intruded basalt.

Merapi Volcano (Central Java, Indonesia) has been frequently active during Middle to Late Holocene time producing basalts and basaltic andesites of medium-K composition in earlier stages of activity and high-K magmas from ∼1900 14C yr BP to the present. Radiocarbon dating of pyroclastic deposits indicates an almost continuous activity with periods of high eruption rates alternating with shorter time spans of distinctly reduced eruptive frequency since the first appearance of high-K volcanic rocks. Geochemical data of 28 well-dated, prehistoric pyroclastic flows of the Merapi high-K series indicate systematic cyclic variations. These medium-term compositional variations result from a complex interplay of several magmatic processes, which ultimately control the periodicity and frequency of eruptions at Merapi. Low eruption rates and the absence of new influxes of primitive magma from depth allow the generation of basaltic andesite magma (56–57 wt% SiO2) in a small-volume magma reservoir through fractional crystallisation from parental mafic magma (52–53 wt% SiO2) in periods of low eruptive frequency. Magmas of intermediate composition erupted during these stages provide evidence for periodic withdrawal of magma from a steadily fractionating magma chamber. Subsequent periods are characterised by high eruption rates that coincide with shifts of whole-rock compositions from basaltic andesite to basalt. This compositional variation is interpreted to originate from influxes of primitive magma into a continuously active magma chamber, triggering the eruption of evolved magma after periods of low eruptive frequency. Batches of primitive magma eventually mix with residual magma in the magmatic reservoir to decrease whole-rock SiO2 contents. Supply of primitive magma at Merapi appears to be sufficiently frequent that andesites or more differentiated rock types were not generated during the past ∼2000 years of activity. Cyclic variations also occurred during the recent eruptive period since AD 1883. The most recent eruptive episode of Merapi is characterised by essentially uniform magma compositions that may imply the existence of a continuously active magma reservoir, maintained in a quasi-steady state by magma recharge. The whole-rock compositions at the upper limit of the total SiO2 range of the Merapi suite could also indicate the beginning of another period of high eruption rates and shifts towards more mafic compositions.

Volcanoes are not random phenomena, but owe their existence, location, morphology, and eruptive styles to tectonic plate motions. Volcanic landforms vary widely in size and morphology from the stereotypical towering glacier-clad stratovolcano. They range from small spatter cones to massive shield volcanoes several thousand cubic kilometers in volume or broad volcanic depressions, cinder cones being the most common volcanic construct. Their eruptions likewise span many orders of magnitude in volume. Evaluation of eruption magnitudes and frequencies contrasts the vast majority of mild-to-moderate eruptions (∼80% with volcanic explosivity index, or VEI ≤2) with the more infrequent larger, higher-impact events (5% with VEI ≥4). Increased risk from population growth in proximity to volcanoes has been mitigated by enhanced monitoring and hazard-reduction efforts.

The eruptive activity of Etna volcano is well known in detail due to the integration of numerous geological and historical investigations. The study of historical sources of the volcano’s activity started in the sixteenth century and has been reported in several catalogues of the eruptions published mainly in the eighteenth and nineteenth centuries. We have found a new document written in 1643 by the Fiscal Prosecutor of the High Court for the viceroy of Sicily in which he reported earthquakes occurring in the small town of Troina. The document also describes an eruption taking place in the Bronte region of Etna between 18 and 28 of July that was previously unknown in current historical catalogues, even those compiled by recent historiographical studies. This eruption clearly produced the volcanic products outcropping in the upper NW flank, shown on the new geological map of Etna as the Val di Cannizzola lava flow. The July 1643 eruption was a brief event with the emission of a roughly 2.7-km-long lava flow of very low volume (3–4 × 106 m3). It occurred in a period characterised instead by long-lasting and high-lava-volume eruptions that preceded the large and destructive 1669 eruption, the main event that has occurred on Etna in historical time.

International audience; The little known Tutupaca volcano (17° 01′ S, 70° 21′ W), located at the southern end of the Peruvian arc, is a dacitic dome complex that experienced a large explosive eruption during historical times. Based on historic chronicles and our radiometric data, this eruption occurred 218 ± 14 aBP, probably between 1787 and 1802 AD. This eruption was characterised by a large sector collapse that triggered a small debris avalanche (

Basaltic volcanic fields consist of one or more volcanoes within a defined area that is separate from other volcanic areas and that has an internally consistent tectonic/structural setting. Most of the volcanoes are monogenetic, each having only a single eruptive episode lasting from weeks to decades before becoming extinct, and are of small volume (typically around 1 km3 or less). These volcanoes share many eruptive processes with larger, polygenetic volcanoes of basaltic composition, including Strombolian, Hawaiian, and phreatomagmatic explosive activity and effusion of lava flows. They form a range of landforms including lava fields, scoria cones, small shields, maars, tuff cones, and tuff rings depending upon the dominance of magmatic volatiles versus phreatomagmatic explosions in driving eruptions, and upon the magma volume flux and processes within the shallow crust. Basaltic volcanic fields typically contain volcano alignments that may be related to crustal structures, and clusters of high spatial vent density that are likely related to variability in the upper mantle magma sources. Hazard assessment is complicated by the many factors that affect the timing and locations of successive eruptions within a volcanic field. Recent research on magma sources and ascent for monogenetic volcanoes suggests an important role for compositional heterogeneity in the upper mantle, and that volatile fluxes during eruptions can be of similar magnitude as at larger polygenetic volcanoes.

Shishaldin Volcano erupted repeatedly during April and May 1999, with major eruptive events on 19 April and 23 April. Tephra deposits >20 cm thick were distributed across the southern flanks and hyperconcentrated debris flows ran down the northern slope. All analyzed clasts were basaltic in composition, with abundant (~29 vol%) phenocrysts of plagioclase, olivine, and magnetite. Glass-inclusion analyses indicate low volatile contents ( 900 to 58 ppm, respectively). Comparisons of sulfur contents in glass inclusions and groundmass glasses suggest significant degassing occurred even prior to eruption. Trace-element studies suggest that the magma reservoir below Shishaldin may not be a closed, long-lived chamber, and U–Th–Ra isotopic analyses indicate short crustal residence times (on the order of at most a few thousand years) for the 1999 products. Comparison of the deposits from this eruption with other similarly sized eruptions suggests the 19 April explosive event should be classified as a sub-Plinian basaltic eruption. Such eruptions are rare. The 19 April explosive event was the largest at Shishaldin during the last 175 years. However, the petrology, chemistry and deposit thickness and distribution resemble those of at least 11 scoria deposits in the last 9,000 years, suggesting that this type of eruption is common for Shishaldin.

Shishaldin Volcano, in the central Aleutian volcanic arc, became seismically restless during the summer of 1998. Increasing unrest was monitored using a newly installed seismic network, weather satellites, and rare local visual observations. The unrest culminated in large eruptions on 19 April and 22–23 April 1999. The opening phase of the 19 April eruption produced a sub-Plinian column that rose to 16 km before rapidly dissipating. About 80 min into the 19 April event we infer that the eruption style transitioned to vigorous Strombolian fountaining. Exceptionally vigorous seismic tremor heralded the 23 April eruption, which produced a large thermal anomaly observable by satellite, but only a modest, 6-km-high plume. There are no ground-based visual observations of this eruption; however we infer that there was renewed, vigorous Strombolian fountaining. Smaller low-level ash-rich plumes were produced through the end of May 1999. The lava that erupted was evolved basalt with about 49% SiO2. Subsequent field investigations have been unable to find a distinction between deposits from each of the two major eruptive episodes.

Ngauruhoe cone, in southern Taupo Volcanic Zone, New Zealand, has grown rapidly over the last 2,500 years in an alternation of effusive, strombolian, vulcanian, and sub-plinian eruptions of andesitic magma. At times growth has been 'staccato' in fashion as evidenced in the historical record. Each historical eruption typically lasted days to months, alternating with repose periods of years to decades. Major historic eruptions occurred in 1870 1949 1954–1955 and 1973–1975, encompassing wide variations in eruptive style over short timescales. The early period of cone building appears to have been dominated by a more continuous form of activity characterised by a series of numerous frequent explosive eruptions, with associated lava flows. The 2.2-km3 cone has grown in a piecemeal sectorial manner reflecting constant modification to the morphology of the summit, which has funnelled eruption products to specific sectors of the cone. Eruption rates can be calculated on several different timescales. Discharge rates averaged over individual eruptive pulses vary by two orders of magnitude (2.7–280 m3 s–1), reflecting variations in high level magma ascent rates and processes such as degassing, which are, in turn, reflected in contrasting eruptive styles. Lower rates (e.g. 0.65 m3 s–1) are obtained by averaging the discharge over an entire eruption lasting several months and may correspond to the ascent rate of magma batch(es) feeding the eruption. The long-term growth rate of Ngauruhoe is 0.9 km3 ky–1. This is an average rate reflecting the long-term deep supply rate of magma to crustal reservoirs. By looking at eruption rates on these different timescales we are better able to constrain processes occurring at various depths within the plumbing system. There are few detailed studies of the growth patterns of young volcanic cones, but such data are essential in understanding the dynamics of andesitic systems. More than 60 lavas and pyroclastic units mapped on different sectors of Ngauruhoe cone have been correlated by flow chronology and their distinctive compositions into five groups. Although the cone has grown rapidly, Ngauruhoe shows little evidence for the existence of large crustal magma reservoirs and long-lived magma batches. Instead, abrupt and non-systematic changes in magma chemistry and isotopic composition between and within the five groups indicate that the volcano has an open-system, multi-process, multi-directional character and erupts small (

Lava dome eruptions commonly display fairly regular alternations between periods of high activity and periods of low or no activity. The time scale for these alternations is typically months to several years. Here we develop a generic model of magma discharge through a conduit from an open-system magma chamber with continuous replenishment. The model takes account of the principal controls on flow, namely the replenishment rate, magma chamber size, elastic deformation of the chamber walls, conduit resistance, and variations of magma viscosity, which are controlled by degassing during ascent and kinetics of crystallization. The analysis indicates a rich diversity of behavior with periodic patterns similar to those observed. Magma chamber size can be estimated from the period with longer periods implying larger chambers. Many features observed in volcanic eruptions such as alternations between periodic behaviors and continuous discharge, sharp changes in discharge rate, and transitions from effusive to catastrophic explosive eruption can be understood in terms of the non-linear dynamics of conduit flows from open-system magma chambers. The dynamics of lava dome growth at Mount St. Helens (1980–1987) and Santiaguito (1922–2000) was analyzed with the help of the model. The best-fit models give magma chamber volumes of ∼0.6 km3 for Mount St. Helens and ∼65 km3 for Santiaguito. The larger magma chamber volume is the major factor in explaining why Santiaguito is a long-lived eruption with a longer periodicity of pulsations in comparison with Mount St. Helens.

Seismicity preceding the September-October 1989 flank eruption at Mt. Etna volcano has been analysed by means of the fractal two-point correlation dimension D c relative to epicentres distribution and the scaling exponent D inferred from the seismic b-value. Time evolution of D c and D preceding the eruption onset revealed: a general decrease of D c and increase of D (9-4 months prior the eruption onset), intermittent rates of D c increase and D decrease (4 to 1 month), steady high values of D c and low values of D (1 month) and sharp decreases of D c and D marking the eruption onset. Results allowed to constrain the increment of seismic damage by recognising negative (mechanical hardening) and positive (mechanical softening) feedback prior the eruption onset.

During the 1995 to 1998 phase of dome growth at Soufriere Hills Volcano on Montserrat, we documented instability of the steep southern rim of English9s Crater, known as Galway9s Wall. The horseshoe-shaped English9s Crater provided good evidence for previous sector collapses, and assessments undertaken in late 1996 anticipated the possibility of a partial sector collapse and a SW-directed explosion, hazards previously unrecognized on Montserrat. A change from predominantly endogenous to exogenous growth of the lava dome at the end of 1996 eased the stress on the southern sector. However, rapid dome growth in November and December 1997 led to severe reloading and eventual sector failure at the base of the buried Galway9s Wall and in the adjacent hot-spring area. This failure resulted in the debris avalanche and lateral blast of 26 December 1997. Similar sector collapses at a number of small volcanoes in the Caribbean, as well as worldwide, are evidence that edifice instability develops commonly in dome-forming eruptions. The hazards from a sector collapse and a consequent lateral blast are extreme, and monitoring operations and disaster planning at such volcanoes should focus on these, as well as on the more common hazards of conventional pyroclastic flows associated with dome growth.

International audience; The eighteenth/nineteenth century ‘craters of elevation’ theory required magma to uplift strata, doming the surface and creating a central down-fallen ‘crater’ or graben. Exponents of craters of elevation attempted to apply it to explain the origin of all volcanoes, and rapidly the contemporary competing ‘craters of eruption’ theory replaced it as the paradigm for volcano construction. Several historic examples have shown that intrusions can cause uplift, termed bulges and can create features like those proposed for craters of elevation (e.g. at Usu 1944, Bezymianny 1955 and Mt. St. Helens 1980). Work on sedimentary basins that have had igneous activity has shown that intrusions create ‘forced folds’ that uplift and deform strata in a similar way to that originally proposed for craters of elevation. In view of the above, we investigate large-scale intrusion-related topographic changes at two sites where the craters of elevation theory was developed: the monogenetic volcanoes of the Chaîne des Puys, France and the Teide stratovolcano, Tenerife. We combine observations of such features with examples of forced folding to integrate the two fields of research. Our observations in the Chaîne des Puys show that: (1) the Petit Puy de Dôme has a bulge of up to 150-m uplift. The uplift has a central depressed area (a graben), a dense network of normal faults, basal thrusts and an aborted landslide. (2) The Grosmanaux volcano is a forced fold created by uplift of a previously flat-lying area, and has dense faulting and a graben on the resultant topographic bulge. It was the site also of a major vulcanian eruption from the associated Kilian crater. (3) The Gouttes volcano was uplifted by an intrusion like the Petit Puy de Dôme, but then collapsed to generate a landslide and lateral blast. (4) Excavation in the Lemptégy Volcano exposes intra-eruption intrusions with associated uplift, providing examples in cross-section of the internal deformation likely to be found inside other Chaîne des Puys uplifted bulges. On Teide, a bulge near the summit shows similar structures and surface tilting as seen on the Petit Puy de Dôme and this bulging may have formed during the eruption of the Lavas Negras, the most recent activity on the summit area. Fault scarps on Teide also expose small cryptodomes, like those seen at Lemptégy. These examples, coupled with field studies on eroded intrusions, data on forced folds in basins and analogue models, show how large-scale topographic remodelling and structural change can be created by intrusions. These can rapidly and significantly change the volcanic edifice. A crater of elevation bulge, or forced fold that is stabilised by the cooling of the intrusion, will remain an important structural element in a volcano. This process starts even at the small scale of monogenetic volcanoes, and could occur through the lifetime of any growing stratovolcano. Such activity may be commonplace, but may be masked by concomitant eruption or removed by subsequent collapse. Monitoring and hazard strategies should be ready to deal with such large-scale events that will seriously modify the eruptive activity and stability of a volcano within days or weeks.

The 2013 eruption of Pavlof Volcano, Alaska began on 13 May and ended 49 days later on 1 July. The eruption was characterized by persistent lava fountaining from a vent just north of the summit, intermittent strombolian explosions, and ash, gas, and aerosol plumes that reached as high as 8 km above sea level and on several occasions extended as much as 500 km downwind of the volcano. During the first several days of the eruption, accumulations of spatter near the vent periodically collapsed to form small pyroclastic avalanches that eroded and melted snow and ice to form lahars on the lower north flank of the volcano. Continued lava fountaining led to the production of clastogenic lava flows that extended to the base of the volcano, about 3–4 km beyond the vent. The generation of fountain-fed lava flows was a dominant process during the 2013 eruption; however, episodic collapse of spatter accumulations and formation of hot spatter-rich granular avalanches was a more efficient process for melting snow and ice and initiating lahars. The lahars and ash plumes generated during the eruption did not pose any serious hazards for the area. However, numerous local airline flights were cancelled or rerouted, and trace amounts of ash fall occurred at all of the local communities surrounding the volcano, including Cold Bay, Nelson Lagoon, Sand Point, and King Cove.

Effusive eruptions are explained as the mechanism by which volcanoes restore the equilibrium perturbed by magma rising in a chamber deep in the crust. Seismic, ground deformation and topographic measurements are compared with effusion rate during the 2007 Stromboli eruption, drawing an eruptive scenario that shifts our attention from the interior of the crust to the surface. The eruption is modelled as a gravity-driven drainage of magma stored in the volcanic edifice with a minor contribution of magma supplied at a steady rate from a deep reservoir. Here we show that the discharge rate can be predicted by the contraction of the volcano edifice and that the very-long-period seismicity migrates downwards, tracking the residual volume of magma in the shallow reservoir. Gravity-driven magma discharge dynamics explain the initially high discharge rates observed during eruptive crises and greatly influence our ability to predict the evolution of effusive eruptions.

The detection and understanding of the movement of magma at very shallow levels remains one of the most fascinating challenges of modern volcanology, because such information allows us to identify and circumscribe the most probable location where future eruptive vents will open. Unfortunately, it is rarely possible to observe any detail of the internal structure of the feeder system of recent eruptions; in only very few cases, geological observations in dissected volcanoes can help us imagine how magma moved and evolved inside the feeder system. In this paper, we describe the 1809 eruption of Mt. Etna, Italy, which represents one historical and rare case in which it is possible to closely observe the internal structure of the feeder system. This is possible thanks to the presence of two large pit craters located in the middle of the eruptive fracture field that allow studying a section of the shallow feeder system. Along the walls of one of these craters, we analyzed well–exposed cross sections of the uppermost 15–20 m of the feeder system and related volcanic products. Here, we describe the structure, morphology and lithology of this portion of the 1809 feeder system, including the host rock which conditioned the propagation of the dyke, and compare the results with other recent eruptions. Finally, we propose a dynamic model of the magma behavior inside a laterally–propagating feeder dyke, demonstrating how this dynamic triggered important changes in the eruptive style (from effusive/Strombolian to phreatomagmatic) during the same eruption. This is therefore an exceptional case to understand how basaltic magmas move during the propagation of an eruptive fissure, which furnishes fundamental elements for the modeling of superficial intrusive processes. Our results are also useful for hazard assessment related to the development of flank eruptions, potentially the most hazardous type of eruption from basaltic volcanoes in densely urbanized areas.

INTRODUCTION Scientists are asked to describe and understand the complex behavior of natural processes. This is often done in difficult conditions, with instruments detecting specific indicators and providing limited datasets to satisfy knowledge and imagination. Despite these limitations, many studies have been able to provide unprecedented understanding of different processes in nature, albeit often under specific (i.e., simplified) conditions. A progressively more quantitative approach has been often obtained exploiting the latest technological improvements available. The study of volcanic, or more generally, magmatic processes well exemplifies these conditions and progression (Figure 1). Qualitative reports of how volcanoes erupt date back to thousands of years, as the description of the 79 AD Vesuvio eruption from Pliny the Younger; however, most of our qualitative and quantitative understanding of the volcano factory and its various indicators has been definitely achieved in the frame of the technological boost of the last decades. Certainly, the tremendous improvement of the monitoring system of active and erupting volcanoes has allowed detecting many changes in the geophysical, geodetic and geochemical behavior before, during and after eruptions (e.g., Lowenstern et al., 2006; Sigmundsson et al., 2010; Chiodini et al., 2012). As a result, a significant amount of data has been collected on a reasonable amount of active volcanoes worldwide, and it is in general possible to assign some physical or chemical meaning to many detected changes. This knowledge is also crucial to define when a volcano enters a phase of deviation from its baseline, or unrest, which may culminate in an eruption and to forecast any impending eruption. The understanding of the processes occurring within volcanoes, ultimately leading to the geophysical, geodetic and geochemical changes detected at the surface, is supported by analytical, numerical, and experimental models (e.g., Cayol et al., 2000; Gudmundsson, 2006; Caricchi et al., 2007; Ruch et al., 2012). Modeling has reached a relatively sophisticated stage, allowing understanding otherwise inaccessible and/or long-lasting 2D and, to a lesser extent, 3D processes. Similarly crucial to understand the mean to longerterm behavior of volcanoes are many field and petrological-geochemical studies, supported by dating techniques (e.g., Gravley et al., 2007; Thordarson and Larsen, 2007; Collins et al., 2009; Wilson and Charlier, 2009; Corsaro et al., 2013). In particular, field studies prove fundamental in reconstructing the eruptive history of a volcano, including the eruption location, type, size and frequency; petrological and geochemical studies provide an invaluable amount of information on the processes and times characterizing the formation of the magma, its rise and emplacement within the crust, including mixing, mingling, crustal assimilation, and fractionation. These approaches have allowed reaching a dramatic advancement in our understanding of volcanoes. An overview of the major improvements in volcanology in the last decades is beyond the scope of this contribution. For facts, one can refer to the comprehensive, detailed and essential overview of Cashman and Sparks (2013). This includes many of the important studies on the emplacement (formation of magma chambers), rise (eruption triggers, dike propagation), and eruption of magma (conduit construction and evolution, magma rheology and fragmentation, eruptive styles). The described amount of research underlines the impressive efforts made by the volcanological community in considering and analyzing the several complex evolutionary stages of a magma within the volcano factory, from its generation to its eruption. Even though the reached level of knowledge may not unravel the many questions behind the volcano factory, it certainly provides a robust platform to test hypotheses and plan more advanced and sophisticated studies. Indeed, despite the important achievements, modern volcanology still has to fully define and understand several major processes, involving different topics and approaches, and resulting in likewise challenges for the future. Here the first-order processes, or challenges for volcanology, are summarized in an ideal journey from the deepest to the shallowest portions of the volcano factory (Figure 2). Many of these processes may be unraveled not only by observations on volcanoes on Earth, but also on extraterrestrial volcanoes, including those on Venus, Mars and Io. While studies on terrestrial volcanism provide the key to understand also extraterrestrial volcanism, it is likewise expectable that observations on adequately imaged volcanic edifices from Mars and Venus allow to better define volcanic processes on Earth.

In the last decades, the increasing availability of comprehensive geodetic datasets has allowed for more detailed constraints on subsurface magma storage and conduits at several active volcanoes worldwide. Here, by using a large dataset of geodetic measurements collected between early January 2001 and August 2001, we identified at least six different deformation stages that allow us to quantify the surface deformation patterns before, during and after the 2001 Mt. Etna volcanic eruption. Our results are largely in agreement with previous works (e.g. the presence of a deep inflating source and a shallow dike located beneath the north-western and upper southern flanks of the volcano, respectively). However, we provide (1) finer resolution of the temporal activity of these magmatic sources, leading to (2) new evidence related to the evolution of the magmatic system and the mechanical response of the western flank, in particular during the pre-eruptive phase. Results and analysis show a clear change in the ground deformation pattern of the volcano in response to the 20–24 April 2001 seismic swarm that occurred beneath the western flank, evolving from a volcano-wide inflation to a slight deflation of the summit area. We suggest that the source responsible for the volcano-wide inflation, beginning in the fall of 2000, experienced a drastic reduction in the inflation rate in response to this seismic swarm. Moreover, we provide evidence for the presence of a new inflating source located beneath the upper southern flank at a depth of ~ 7.0 km bsl that triggered both the occurrence of the 20–24 April 2001 seismic swarm and led to the rapid ascent of magma upward to the surface after 12 July (the Lower Vents system was fed by fresh magma rising from this source). The presence of this inflating source is inferred by (1) seismological and volcanological observations coming from the 2001 eruption and (2) seismological constraints coming from a previous similar episode that occurred at Etna during the 1993–1998 period. Furthermore, both shallow deflations observed after the 20–24 April 2001 seismic swarm and during the first day of the eruption also could be due to the deflation of two adjacent portions of the same shallow (~ 2 km bsl) reservoir. Such reservoirs would feed the activity that occurred at the South-East Crater after January 2001 and the activity of the Upper Vents system during the July–August eruption, in agreement with petrochemical observations. Through an updated revision of the available data, we shed some light on the relevance of pre-eruptive activity patterns, an important element for an effective volcano monitoring., The CGPS group is kindly acknowledged for providing raw data. Pablo J. González thanks the support of a Banting Postdoctoral Fellowship by the Canadian Government.

The properties and processes that control the size, duration, and style of eruption of rhyolite magma are poorly constrained because of a paucity of direct observations. Here, we investigate the small-volume, nonexplosive end-member. In particular, we determine the pre-eruptive storage conditions and eruption dynamics of Douglas Knob, a 0.011-km3 obsidian dome that erupted from a 500-m-long fissure in the Yellowstone volcanic system. To determine pre-eruptive storage conditions, we analyzed compositions of phenocrysts, matrix glass, and quartz-hosted glass inclusions by electron microprobe and Fourier-transform infrared analyses. The pre-eruptive melt is a high-silica rhyolite (∼75 wt.% SiO2) and was stored at 760 ± 30 °C and 50 ± 25 MPa prior to eruption, assuming vapor saturation at depth. To investigate emplacement dynamics and kinematics, we measured number densities and orientations of microlites at various locations across the lava dome. Microlites in samples closest to the inferred fissure vent are the most aligned. Alignment does not increase with distance traveled away from the vent, suggesting microlites record conduit processes. Strains of

Galileo data and numerical modeling were used to investigate the summer 1997 eruption at Pillan Patera on Io. This event, now defined as 'Pillanian' eruption style, included a high-temperature (greater than 1600 C), possibly ultrabasic, 140-km-high plume eruption that deposited dark, orthopyroxene-rich pyroclastic material over greater than 125,000 sq km, followed by emplacement of dark flow-like material over greater than 3100 sq km to the north of the caldera. We estimate that the high-temperature, energetic episode of this eruption had a duration of 52- 167 days between May and September 1997, with peak eruption temperatures around June 28, 1997. Galileo 20 m/pixel images of part of the Pillan flow field show a widespread, rough, pitted surface that is unlike any flow surface we have seen before. We suggest that th.s surface may have resulted from (1) a fractured lava crust formed during rapid, low-viscosity lava surging, perhaps including turbulent flow emplacement; (2) disruption of the lava flow by explosive interaction with a volatile-rich substrate: or (3) a combination of 1 and 2 with or without accumulation of pyroclastic materials on the surface. Well-developed flow lobes are observed, suggesting that this is a relatively distal part of the flow field. Shadow measurements at flow margins indicate a thickness of approx. 8-10 m. We have modeled the emplacement of putative ultrabasic flows from the summer 1997 Pillan eruption using constraints from new Galileo data. Results suggest that either laminar sheet flows or turbulent channelized flows could have traveled 50-150 km on a flat. unobstructed surface, which is consistent with the estimated length of the Pillan flow field (approx. 60 km). Our modeling suggests low thermal erosion rates (less than 0.1 m/d), and that the formation of deep (greater than 20 m) erosion channels was unlikely, especially distal to the source. We calculate a volumetric flow rate of approx. 2-7 x l0(exp 3) cu m/s, which is greater than those for typical Mauna Loa/Kilauea flows but comparable to those for the (1783) Laki eruption and the inferred flow rates of the Roza flows in the Columbia River flood basalts. The differences in ultrabasic eruption styles on Earth and Io appear to be controlled by the different eruption environments: Plumes at sites of ultrabasic eruptions on Io suggest strong magma-volatile: interactions on a low-gravity body lacking an atmosphere, whereas the geology at sites of komatiite eruptions on Earth suggest mostly submarine emplacement of thick flows with a pronounced lack of subaerial explosive activity.

The first direct evidence that patterns of basaltic eruptive activity may be very similar on Io and Earth was seen on November 26, 1999, when the solid-state imaging system on board the Galileo spacecraft obtained high-resolution images of a fissure eruption taking place in one of the calderas of the Tvashtar Catena complex. We analyzed the dynamics of the fissure eruption from the morphology of the lava fountains and pyroclastic deposits and derived an estimate of the eruption rate. Our best estimate of the volume eruption rate per unit length of fissure lies in the range 0.7 to 7 m3 s−1 m−1, and multiplying this rate by the fissure length of ∼25 km yields a total volume eruption rate of magma of ∼2 × 104 to 2 × 105 m3 s−1. The upper end of the inferred eruption rate is very close to the upper end of the range of eruption rates observed or inferred for fissure eruptions on Earth. Theoretical models of the possible dike systems feeding the fissure show that for eruptions of positively buoyant magma, the elastic properties of rocks are such that a magma flux of 6 to 7 m3 s−1 m−1 is the largest value that can ever be realized in such eruptions, this limiting value being independent of planetary gravity and thus the same on all silicate bodies. The eruption rate inferred for Tvashtar can also be achieved by a negatively buoyant magma, but in that case the source depth cannot be much greater than a few tens of kilometers. We find that some eruptive events are consistent with the effusion of magmas which are buoyant relative to the crust, whereas others appear to involve magmas which are not. This implies that the distribution of crustal volatiles is laterally very inhomogeneous. Our analyses suggest that the depths from which magmas make their final ascent to the surface of Io are generally of order tens, rather than hundreds, of kilometers.

The Plinian fall deposit of the Minoan eruption (Santorini, Greece) and its interlayered ash flow beds show textural, componentry and chemical trends indicative of their temporal evolution and conditions that lead to the ash-flow emplacement. The deposits have been sampled in detail at a selected locality, and the following features have been analyzed: (i) maximum clast size; (ii) grain size distribution; (iii) componentry; (iv) lithic types; (v) pumice morphology; (vi) pumice types; and (vii) pumice crystal abundance. Stratigraphic variations of these features are assumed to record changes that occurred during the eruption, including changes in eruptive plume height, nature and relative efficiency of the magma fragmentation process, conduit stability, and magma flow in the conduit. Based upon the inferred temporal changes, we propose the following eruption reconstruction. The sustained Plinian column activity reached its climax (in terms of mass eruption rate and plume altitude) soon after the beginning of the eruption, and subsequently began to gradually subside. As a result of eruption waning, the conduit walls began to collapse, causing an increase in the shear stress in the flowing vesicular magma and an increase in the efficiency of the magma fragmentation process. Eventually the conduit closed or became too narrow to support a high-standing eruption column, leading to ash flow eruption as a result of the collapse of what was left of the eruptive plume, and/or directly from emission of an overpressured jet. Subsequent conduit pressure increases led to conduit re-opening and a Plinian column with associated pumice fallout began anew. The eruptive magma fragmentation process is proposed to have been of a brittle nature and linked to the shear stress generated by conduit wall friction. Fragmentation efficiency is recorded by grain size distributions and free crystal contents of the deposits.

Mars Orbiter Camera image (5.23 m/pixel) and topographic data from the Mars Orbiter Laser Altimeter data are used to analyze a channel on the upper northern flank of the Elysium Mons volcano, Mars. We show that this channel is best explained as the product of the thermal erosion of the preexisting surface by a high-speed, turbulent lava flow fed from a fissure eruption. We deduce the volume eruption rate (∼3400–13,000 m3/s dense rock equivalent), the total volume of erupted lava (∼29–39 km dense rock equivalent), and the duration of the activity (40–130 days). Perhaps significantly, the erupted lava volume is essentially identical, given the uncertainties in the analysis, to the volume of the observed caldera (∼31 km3), which has implications for volume-limited eruptions on Mars and potentially for the unusual steep upper slopes of the volcano. The eruption that produced the channel appears to have been typical for Elysium Mons and implies that the other lava channels on the upper flank of the volcano may also have taken ∼1–4 months to have formed.

This paper documents a phreatomagmatic flank eruption that occurred 18 700 ± 100 a BP, on the lower north-eastern slope of Etna during the Ellittico volcano activity, which produced fall and surge deposits. This type of eruption is connected to a sedimentary basement ridge at Etna. The interaction between the rising magma and the shallow groundwater hosted in the volcanic pile overlying the impermeable sediments resulted in phreatomagmatic instead of strombolian activity. Three eruptive phases are distinguished based on field and analytical data: (i) an explosive phreatomagmatic opening, (ii) a main phase producing coarse lithic-rich fallout and a strombolian deposit, and (iii) the final pulsating surge-forming phase. The discovery of this phreatomagmatic flank eruption, which occurred at lower altitude, raises important issues for previous hazard assessments at Etna.

Mt Etna is cut by numerous fractures (fissures and faults) of very different origin and orientation. They have been used to define the activity and the tectonic setting of the volcano. After a discussion of the proposed tectonic models for Etna, an examination of the fractures, which are linked to the high flank eruptions, was carried out based on the geological and geophysical studies of the recent eruptions (1983, 1989, 1991-93). All of these surface breaks are of strictly volcanic origin; they open and advance very slowly, in relation to the propagation of the dyke, as well as its width and depth from the volcano surface. If the dyke summit is not too far from the surface (about 200-300 m), fissures and normal faults, arranged in a graben, appear. When the dyke intersects the slope of the volcano, a flank eruption follows. Therefore, these fractures do not have a tectonic or volcano-tectonic origin: they do not cut the entire volcanic edifice, and thus cannot be used to define the rift-zones nor to characterise the tectonic regime controlling the functioning of Etna. They give information on the dyke orientation on the slopes of the volcanic edifice and cannot be used as significative markers of extension [Frazzetta and Villari, 1981; Kieffer 1983a and b; Monaco et al., 1997]. The simultaneous opening of radial fractures, according to various azimuths, is frequent and clearly indicates that, in these cases, the regional stress field is not implicated. But high on Etna, the concentration of flank eruptions, on the eastern side, and the orientation change of the fractures (fig. 6), when they travel away from the summit, have been repeatedly indicated. The repetition of flank eruptions and the azimuth changes can be explained, simply, by the closeness of the Valle del Bove [Murray, 1994], which induces a decrease of the confinement pressure. The dyke emplacements of the summit eruptions cause an eastward displacement of the higher part of Etna. Marine geophysical data indicate that this volcano is, however, not the site of a large scale lateral spreading to the Ionian sea. Consequently, an eastward detachment is present only on the superior part of the volcano (figs. 1B and 7C). In fact, an up to 100 m high and oversteepened east-facing scarp, between the towns of Vena and Presa, extends towards the south for some kilometers [Lanzafame et al., 2000]. It is made up of volcanic rocks affected by strong brecciation. Inverse faults are found in front of the scarp. The base of this one is found at the level of the pre-Etnean clays, which would have helped the displacement of the volcanics. The studies on the tectonic setting in which Etna is located has called the attention of numerous researchers. From the earliest studies, the presence of numerous normal faults has supported the idea that this volcano, as many others, is active in an extensional regime. The most recent geological and geophysical data show a more complex situation. Deep under Etna (more than 10 km), a compressive field (sigma 1 N-S) is present according to focal mechanisms [Cardaci et al.; 1990; Ferrucci et al., 1993; Cocina et al., 1997]. More superficially, instead, extension is usual. The importance of the weight of the volcanic edifice, in the spatial (horizontal and vertical) modification of the compressive stress field, must still be clarified. It is very clear, in any case, that Etna cannot be explained by an extensional regime or kinematics in extension [Monaco et al., 1997] using normal faults, which form during the flank eruptions.

Deception Island is the most active volcano in the Antarctic Peninsula region. It is a large basalt–andesite shield volcano with a 10 km-wide restless caldera (Port Foster) and a complicated history of pre- and post-caldera eruptions. There has been no modern volcanological investigation of the entire island and it remains a largely unknown volcanic hazard. The pre-caldera period on the island began with the low-energy eruption of tephras from multiple centres (Fumarole Bay Formation), possibly by subaqueous fire fountaining during shoaling and likely initial emergence of the volcano. It was followed by subaerial effusive to weakly pyroclastic (Strombolian/Hawaiian) activity that constructed a small basaltic shield (Basaltic Shield Formation), and a large eruption that vented about 30 km3 of magma (Outer Coast Tuff Formation). The latter eruption may have been triggered by an influx of compositionally different magma into the main chamber feeding the volcano, and the evidence suggests that it was associated with a significant involvement with water (seawater?). The eruption was followed by caldera collapse, and there have been several small incremental caldera “collapses” subsequently. Post-caldera eruptions were all small-volume and predominantly phreatomagmatic (Baily Head and Pendulum Cove formations), but magmatic eruptions constructed several small lava deltas around the coast and also produced a local carapace of scoria and thin lavas, particularly around the caldera rim (Stonethrow Ridge Formation). Although the caldera is presently resurging, interpretation of the eruptive history of the island suggests that future eruptions are likely to be small in volume and will have only a limited regional impact.

The morphology and structure of the submarine flanks of the Canary Islands were mapped using the GLORIA long-range side-scan sonar system, bathymetric multibeam systems, and sediment echosounders. Twelve young (

The 2000 eruption of Miyakejima volcano started with a submarine eruption of basaltic andesite on the morning of June 27, which occurred following earthquake swarms during the previous night. The main phase of the summit eruption began, being associated by a sudden subsidence of the summit area on July 8. Continuous collapsing of the summit area that had continued until midAugust, resulted in the formation of a caldera with the volume of about 0.6 km3. Phreatic (or phreatomagmatic) eruptions took places during the growth of the caldera, although the total volume of eruptives was about 11 million m3. which is smaller by one magnitude than the caldera volume. Eruptives are enriched with hydrothermally altered materials such as smectite and kaolinite.The manner of the first collapse suggests the existence of a large open space under the summit just before the subsidence. Judging from geophysical observation results, the open space may have ascended in the manner of stoping. Successive formation of open spaces at deeper levels is likely to have caused the continuous collapse of the summit area. These open spaces may have been generated by magma's migration from under Miyakejima to the west. The migration is considered to have continued by August 18.It is likely that an inflow of underground water to the open spaces generated a hydrothermal system, where the open spaces acted as a sort of pressure cooker that built up overpressure of eruptions. The hydrothermal system was broken by the largest eruption on August 18, and the eruption column rose about 15 km above the summit. A boiling-over type of eruption occurred on August 29, whereby sufficient overpressure of steam was not built up, resulting in the generation of low-temperature ash cloud surges moving very slowly.

The volumes and estimated total lifetimes of the Tharsis shield volcanoes on Mars imply that they were built with an average magma supply rate within a factor of 2–3 of ∼0.05 m3 s−1. The morphologies and positions of the summit calderas of these volcanoes, specifically the overlapping relationships between the calderas, are evidence that multiple magma reservoirs existed within them, centered on distinctly different locations at various times. The requirement that the magma in an older reservoir must have cooled below its solidus temperature in order to change the local stresses in such a way that a new reservoir grew at a different location argues for long time gaps (probably tens of Myr) during which the supply rate of magma from the mantle was much smaller than at other times. Conversely, the need to offset conductive cooling to the surface once an active magma reservoir was established implies that the magma supply rate was large, ∼1–10 m3 s−1, for times of order 0.1 Myr. An initial pulse involving rates of more than 150 m3 s−1 acting for at least a few weeks was needed to initiate each new reservoir. The lengths of numerous long lava flows on the flanks of the Tharsis Montes imply that lava must have been erupted at rates of ∼100–300 m3 s−1 for periods of a few years to a few tens of years. The volumes of many of these flows exceed the amounts of magma that could be released from overpressured magma reservoirs of the sizes implied by the dimensions of the summit calderas with the surrounding rocks behaving elastically. A maintained high magma supply rate from the mantle (leading to buffered eruption conditions) is almost certainly required for such flows, whereas inelastic caldera collapse events (unbuffered eruption conditions) can explain the emplacement of other flows. Taken together, the various lines of evidence suggest that the Tharsis volcanoes were built episodically with active phases lasting less than 1 Myr alternating with ∼100 Myr quiet phases. We comment on the implications of these issues for the episodicity of the generation of magma in the mantle and for the mode of transport of the magma in dikes or diapirs.

During late September 1996, a major eruption took place at the NW part of the Vatnajokull glacier in central Iceland. The eruption was preceded by intense seismic activity, which began with a M w =5.6 earthquake two days previously. Two very active volcanic systems, Bardarbunga and Grimsvotn, are situated in that area underneath the permanent ice cap. The volcanoseismic phenomena associated with the eruption were recorded on both temporary (HOTSPOT) and permanent (SIL) seismic networks, covering most parts of the country. The recorded events were categorised, according to their waveform shape and frequency content, into three groups: (1) low-frequency events; (2) mixed-frequency events; and (3) volcanic tremor. The large earthquake at Bardarbunga volcano, which initiated the seismic activity before the eruption, was located inside the caldera and had the characteristics of a non-double couple event. The epicentres of the earthquake swarm that followed it initially delineated the caldera rim and then migrated towards Grimsvotn, possibly indicating lateral movements of magma from a shallow chamber beneath Bardarbunga. The eruption affected an area much larger than that between these two volcanoes, since seismic activity was also observed at distances 20 km away, at the Tindafjallajokull volcanic system. The spectral analysis of tremor, recorded at the nearest station to the eruption site, revealed its existence before the onset of the eruption in five narrow frequency bands (0.5–0.7, 1.6, 2.2, 2.8, 3.2 Hz) representing fundamental frequencies with their half- and quarter-subharmonics. This pattern continued until the last day of the eruption. It is believed that the eruption was caused by a dyke injection that had been going on beneath the Vatnajokull area for a period of 10 years.

A continuous Global Positioning System (GPS) network on Kilauea Volcano captured the most recent fissure eruption in Kilauea's East Rift Zone (ERZ) in unprecedented spatial and temporal detail. The short eruption drained the lava pond at Pueu Oeo, leading to a two month long pause in its on-going eruption. Models of the GPS data indicate that the intrusion's bottom edge extended to only 2.4 km. Continuous GPS data reveal rift opening 8 hours prior to the eruption. Absence of precursory summit inflation rules out magma storage overpressurization as the eruption's cause. We infer that stresses in the shallow rift created by the continued deep rift dilation and slip on the south flank decollement caused the rift intrusion.

High-resolution bathymetric mapping has shown that submarine flat-topped volcanic cones, morphologically similar to ones on the deep sea floor and near mid-ocean ridges, are common on or near submarine rift zones of Kilauea, Kohala (or Mauna Kea), Mahukona, and Haleakala volcanoes. Four flat-topped cones on Kohala were explored and sampled with the Pisces V submersible in October 1998. Samples show that flat-topped cones on rift zones are constructed of tholeiitic basalt erupted during the shield stage. Similarly shaped flat-topped cones on the northwest submarine flank of Ni'ihau are apparently formed of alkalic basalt erupted during the rejuvenated stage. Submarine postshield-stage eruptions on Hilo Ridge, Mahukona, Hana Ridge, and offshore Ni'ihau form pointed cones of alkalic basalt and hawaiite. The shield stage flat-topped cones have steep (∼25°) sides, remarkably flat horizontal tops, basal diameters of 1–3 km, and heights

One of the greatest remaining problems in modern volcanology is the process by which volcanic eruptions are triggered. It is generally accepted that eruptions are preceded by magma intrusion [Sigurdsson and Sparks, 1978]. The degree of interaction between previously ponded magma in a chamber and newly intruded magma determines the nature and rate of eruption and also the chemistry of erupted lavas and shallow dykes. Here, we investigate the physics of this interaction. Volcano monitoring at its most effective is a synergy between basic science and risk assessment, while hazard mitigation depends on reliable interpretation of eruption precursors. The simple and much used Mogi model relates ground deformation (?h) to changes in magma chamber volume. Gravity changes (?g) combined with ground deformation provide information on magma chamber mass changes. Our new models predict how the ?g/?h gradient will evolve as a volcano develops from a state of dormancy through unrest into a state of explosive activity. Thus by simultaneous measurement of deformation and gravity at a few key stations, magma chamber processes can be identified prior to the onset of conventional eruption precursors.