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Ninety-eight Quaternary volcanoes have been identified in the Ecuadorian Andes and the Galápagos Islands, from them, nine experienced at least one eruption in the last twenty years. Additionally, about 35 % of the Ecuadorian population live in areas that could be affected by future volcanic eruptions. The Instituto Geofísico of the Escuela Politécnica Nacional (IG-EPN) monitors and evaluates Ecuador’s volcanic hazards: nineteen volcanic hazard maps and hundreds of related articles have been published as a result of its research. The monitoring networks include eighteen volcanoes, with more than 266 stations, which also form the basis for early warning systems at several volcanoes. Volcanic activity is widely communicated by the IG-EPN through periodic information published in different media (website and social networks). Ecuadorian volcanoes will erupt in the future and, therefore, the IGEPN continuously updates its monitoring and hazard assessment practices and improves communication channels and protocols to successfully fulfil its responsibilities. Noventa y ocho volcanes cuaternarios han sido identificados en los Andes ecuatorianos y Galápagos de los cuales nueve han experimentado erupciones al menos una vez en los últimos veinte años. Adicionalmente, alrededor del 35 % de la población ecuatoriana vive en zonas que podrían ser afectadas durante futuras erupciones. El Instituto Geofísico de la Escuela Politécnica Nacional (IG-EPN) monitorea y evalúa la amenaza volcánica del país y, como resultado de sus investigaciones, diecinueve mapas de amenaza volcánica y centenares de artículos científicos han sido publicados. Las redes de vigilancia comprenden dieciocho volcanes e incluyen más de 266 estaciones, que son parte también de los sistemas de alerta temprana. La actividad volcánica es comunicada amplia y periódicamente por el IG-EPN a través diferentes medios (página web y redes sociales). Comprendiendo que futuras erupciones ocurrirán en Ecuador, el IG-EPN continúa actualizando sus prácticas de vigilancia y evaluación de la amenaza, y mejorando sus protocolos de comunicación para cumplir exitosamente sus responsabilidades.

The 1982 and 2015 eruptions are the first at Wolf volcano, Galápagos Archipelago, with eyewitness accounts and satellite imagery. Both eruptions are characterized by a rapid, intense initial phase and multiple eruptive vents leading to the formation of large ‘a‘ā lava fields with scarce pāhoehoe deposits, mostly associated with the waning phases. The 1982 eruption started on 28 August from an intra-caldera vent that produced high lava fountaining, but also occurred from a radial fissure on the SE flank. This eruption lasted for at least 9 days and generated approximately 70E+6 m3 of lava. The 2015 eruption started on 25 May from a circumferential fissure that also produced high lava fountaining and deposited reticulite scoria on the flanks of the volcano. For the first time since monitoring Galápagos eruptions, we observed cryptotephra from the 2015 eruption reaching and depositing in mainland Ecuador, 1400 km away from the source. Lava from the 2015 circumferential vents covered large areas on the SE and E flanks. On 13 June 2015 the eruption switched to an intra-caldera vent that was active until 30 June, which produced lava flows that covered most of the caldera floor. This eruption lasted 36 days and produced ~116E+6 m3 of lava, making it one of the largest eruptions in the Galápagos since the eruption of Sierra Negra in 1979. The combination of ground-based geophysical surveillance, remote sensing, eyewitness accounts, and detailed field work allows us, for the first time, to constrain the eruptive dynamics of this remote volcano with a day-by-day time resolution. In particular, our approach allows quantification of eruption rates, which represents critical information for understanding volcanic systems and for hazard assessment. First order rheological calculations further enable us to constrain the eruption dynamics and emplacement of the lava fields.

International audience; Sangay is one of the most active volcanoes in Ecuador, as it has been almost continuously erupting at least since the seventeenth century. However, because of its remote location and low associated risk to human population, little is known about its eruptions. Here we summarize Sangay's volcanic activity from January 2001 to May 2020, based on ground-based data, satellite-derived observations and chemical analysis of its erupted products. During the analyzed period, Sangay's activity changed from continuous to episodic, as revealed by seismic, thermal and ash emission data. We identified three main eruptive periods: the first, from 2001 to 2013, extruded a cumulative volume of 100 ± 50 million m3 of lava through long-lived activity; the second emitted 54 ± 27 million m3 in four short-lived episodes, which occurred once every year from 2015 to 2018; and finally, a third period since 2019, which has continuous but fluctuating intensity, and shows a significant increase in the extruded lava volume (172 ± 86 million m3 until May 31, 2020). Our results show a marked change in the eruption frequency and a significant increase in average discharge rate over time, although surface activity remained similar, with lava flows, small explosions and ash venting. We propose that three magmatic processes acted to explain the observed changes: between 2001 and 2013 the long-living low-intensity eruptions were promoted by buoyancy, while since 2019 similar but more intense activity was triggered by mass injections. In contrast, the episodic activity in between probably resulted from volatile exsolution due to crystallization (second boiling). Transitions between these three regimes are presumably the result of varying mass inflow rates. Our results provide insights into eruptive style transitions commonly observed at volcanoes of intermediate composition, such as Sangay, over a timescale of several years.

This research focuses on the main export product of Ecuador which is organic banana produced by the alliance of associated producers in El Guabo canton called "ASOGUABO". The Motoragsa oganization Cía. Ltd. intends the massification of Drones for the fumigation process, considering as main axes the economic, social and environmental ones. The type of research was non-experimental, mixed and with emphasis on the qualitative approach. As a result, the urgent need to do business with producers is established by promoting schools of new arts, languages and technologies. Drone imports will be based on certified qualities such as ISO 9001, ensuring a long-term business with the stock of spare parts and ready to give training talks for proper after-sales service

Currently, it is fairly widespread to use smartphones or tablets on field surveys to collect and geolocate damage data. However, geolocation is not a straight forward process and may give inaccurate results such as, for example when the size of the object to be surveyed is relatively small or the coverage of the satellite constellation (e.g. GPS) is inadequate due to obstacles and shadows present in urban areas. Moreover, the pressure that surveyors and technicians suffer during and after the impact of a natural hazard may make the whole geolocation process even more difficult. In this paper, we describe a methodology to overcome the issues of inaccurate records in five damage data surveys collected after the 7.8 magnitude earthquake that struck the coast of Ecuador in April 2016, together with the three administrative sources used to interpret the damage. We started off by homogenizing the various states of damage as charted in field and aerial surveys, including satellite imagery. We then resolved geolocation inaccuracies by using a set of algorithms that take into account the spatial context and the size of the building. These algorithms also flag the quality of the sources to ultimately compute a figure of the spatial distribution of the damage suffered by residential buildings, together with harm done to productive and social infrastructure. Without these preliminary proceedings, the geolocation inaccuracies of the damage data surveys would not have allowed for adequate and detailed risk assessment.

As part of the Acoustic Surveillance for Hazardous Eruptions project, two infrasound arrays were installed in northern and central Ecuador. The RIOE and LITE arrays were operational between 2006 and 2013, recording thousands of infrasound signals originating from eruptions of Tungurahua, El Reventador, and Sangay. We use Progressive Multi-Channel Correlation array processing together with hierarchical clustering to identify and associate impulsive infrasound signals with each volcano. Infrasound detections correspond to quasi-continuous activity of Sangay between mid 2006 and mid 2012, at least thirteen periods of activity of Tungurahua between 2006 and mid 2012, and strong signals from El Reventador in early 2008. We validate our detections using satellite observations from the MODIS (Moderate Resolution Imaging Spectroradiometer) volcano detection algorithm (MODVOLC) and independent eruption catalogs. For Sangay, we find a good agreement between our infrasound detections and MODVOLC triggers, whereas for El Reventador the agreement is fair. We attribute the fair correspondence at El Reventador to the low-temporal resolution of MODIS data and frequent cloud cover in the region that reduce satellite observational capability. Finally, our study highlights the benefits of infrasound arrays for monitoring volcanoes in Ecuador at regional distances, while further investigating the processes that limit volcanic infrasound detection.

After eight years of quiescence, Fernandina volcano experienced two short-lived eruptions, on 4 September 2017 and 16 June 2018. The eruptions were characterized by very short periods of unrest that started a few hours before the initiation of the eruptive activity. On the other hand, Sierra Negra volcano (Isabela Island) began a new eruptive period on 26 June 2018, after almost one year of persistent unrest characterized by an increase in the magnitude and number of seismic events and more than 5 meters of uplift since its last eruption in 2005. The Sierra Negra and Fernandina eruptions were located in remote zones where access is extremely complex. Thus, satellite images complement the continuous monitoring data of the Instituto Geofísico (IG-EPN) with remote observations and allow rapid response mapping in order to identify the areas affected by the lava flows. Finally, the aim of this Report is to encourage other scientists to investigate the behaviors of both pre-eruptive and eruptive periods registered during these eruptions.

The ongoing eruptive cycle of Tungurahua volcano (Ecuador) since 1999 has been characterized by over 15 paroxysmal phases interrupted by periods of relative calm. Those phases included Strombolians, Vulcanians and one Subplinian eruptions and they generated tephra fallouts, pyroclastic density currents (PDCs) and lava flows. The 01 February 2014 eruption occurred after 75 days of quiescence. Two days before the eruption, a gradual increase of seismicity associated with sporadic weak ash emissions occured. Between 13:30 and 16:30 UTC of the 01 February, a swarm of volcano tectonic and long period earthquakes was detected and announced the possibility of an eruption within hours or days. After a few hours without surface manifestations, two short-lived Vulcanian explosions triggered the paroxysmal phase at 22:39 UTC which lasted 40 min and produced an eruptive column 13.4 km in height sustained during about 9 min. The activity evolved at 23:36 UTC into sporadic Strombolian explosions with discrete ash emissions and continued for several weeks. Both tephra fall and PDCs were studied for their dispersal, sedimentology, volume and eruption source parameters. Tephra was distributed around 240° to the S-SW of the volcano, and the bulk deposit volume is estimated to be 1.53 ± 0.35 × 10−2 km3 (4.76 ± 2.23 × 106 m3 DRE; VEI 3). PDCs descended by 9 ravines of the N-NW flanks. It was one of Tungurahua’s largest eruptions, after the August 2006 Subplinian event. The Vulcanian eruptive mechanism is interpreted to be related to a steady magma ascent and the rise in over-pressure in a blocked conduit (plug) and/or a depressurized solidification front. The transition to Strombolian style is well documented from the tephra fall componentry. In any of the interpretative scenari, the short-lived precursors for such a major event as well as the unusual tephra dispersion pattern urge for renewed hazard considerations at Tungurahua.

In the last year, two Galápagos volcanoes had shown eruptive activity. The three observed eruptions produced multiple lava flows along eruptive fissures and vents covering several square kilometers. After eight years of quiescence, La Cumbre volcano, Fernandina Island experienced two short-lived eruptions, on 4 September 2017 and 16 June 2018. The eruptions were characterized by very short periods of unrest that started a few hours before the initiation of the eruptive activity. On the other hand, Sierra Negra volcano, Isabela Island, began a new eruptive period on 26 June, after almost one year of persistent unrest characterized by an increase in the magnitude and number of seismic events and more than 5 meters of uplift since its last eruption in 2005. The Sierra Negra and La Cumbre eruptions were located in remote zones where access is extremely complex. Thus, satellite images allowed us to: 1) complement the continuous monitoring data of the Instituto Geofísico (IG-EPN) with remote observations such as the appearance and distribution of the eruptive plumes and the evolution of the thermal anomalies along the ongoing eruptions; and 2) do a rapid response mapping in order to identify the areas affected by the lava flows, which threaten the native flora and fauna of the islands.

Following 84 years of repose, Tungurahua volcano, Ecuador initiated its present eruptive episode in October 1999, but its PDC activity only began in July 2006. A period of highly energetic Vulcanian eruptions started in 2012, those of 14 July 2013, 18 October 2013, and 1 February 2014 being the most important. These eruptions were well-monitored by a 5-station broadband seismic and acoustic array. Repeated repose intervals of ~ 3.5 months between Vulcanian events (VEI ~ 2) suggest that gases in the ascending juvenile magma experienced sequential pressurization cycles, as magma of preceding eruptive events solidified to form plugs that sealed the conduit. Every 34 months plug failure occurred, abrupt decompression followed, and the resulting Vulcanian explosions are associated with the highest seismic and acoustic energies ever registered anywhere. Small to moderate-sized PDC flows associated with the explosions and fountain collapses were generated and traveled ≤ 7 km down the steep N, NW, and W flanks of Tungurahua's cone at velocities of 11 to 18 m/s, although a small lateral blast and its PDC were clocked at 33 m/s descending the N flank. The explosive fragmentation of the plugs (a dense microcrystalline andesite) and the juvenile magma (a vesiculated glassy andesite) comprise the principal rock fragments of the PDC deposits. Each deposit typically consisting of two layers; a thin upper layer of large segregated and abraded clasts with few fines and a thicker lower layer that is fines-rich with few large clasts. Many deposits were studied and photographed within a few days of their formation, which are presented.

Sumaco Volcano is located in the rear-arc of Ecuador and produces phonolitic alkaline lavas hosting a unique assemblage of minerals including hauyne and titanaugite. The most mafic lavas are picrobasalts that contain titanaugite as the primary mineral phase; the most evolved tephri-phonolite lavas contain titanaugite + anorthoclase + hauyne. Titanaugite forms at middle to deep crustal pressures, whereas hauyne is only stable at shallow depths in highly oxidizing conditions. The Sumaco mineral assemblages and geochemistry indicate that fractionation of the titanaugite- and hauyne-bearing assemblage took place over a range of pressures from 5 to 25 kbar (14–75 km), with at least 50% of differentiation taking place at shallow crustal levels. Minerals record multiple cycles of recharge and mixing accompanied by an increase in fO2 and sulfur concentration during differentiation. Mantle-like Sr and Nd isotope values (87Sr/86Sr = 0.70406–0.70423; 143Nd/144Nd = 0.512880–0.512913) indicate minimal crustal assimilation. Sumaco’s unique geochemical composition is not observed in the nearby volcanoes Antisana, Pan de Azucar or El Reventador suggesting that its unique magma source is confined to this volcano. The high temperature and sulfate-saturated conditions at shallow depths suggest that magma ascends rapidly to a shallow reservoir where the majority of crystallization and recharge takes place prior to eruption. An important conclusion of this research is that Sumaco does not represent typical rear-arc subduction processes, and caution should be used when using Sumaco as an end-member to evaluate across-arc processes in the Northern Volcanic Zone.

Cotopaxi volcano, Ecuador, experienced notable restlessness in 2015 that was a major deviation from its normal background activity. Starting in April and continuing through November 2015 strong seismic activity, infrasound registry, hikes in SO2 degassing and flank deformation with small displacements were some of the geophysical anomalies that were registered. Obvious superficial changes, such as small hydromagmatic eruptions, emission of vapor and ash columns, thermal hotspots around the crater and in nearby orifices and exacerbated glacier melting were also observed. Our contribution provides an overview of the 2015 Cotopaxi unrest by presenting the patterns of geophysical data and the sequence of events produced by the volcano. Cotopaxi’s last important VEI 4 eruption was in 1877. Then it had devastating effects because of the transit of huge lahars down 3 major drainages. Comparatively, the 2015 activity never surpassed a magnitude VEI 2 and principally produced limited hydromagmatic explosions and semi-continuous low energy emissions and light ashfalls. Given the potential of major destruction from a large Cotopaxi eruption it is important to understand the geophysical fingerprints that characterized the 2015 episode with an eye to identifying onset of future restless periods. Overall, the monitoring activities, the data interpretation, formulation of reasonable eruptive scenarios, and finally, the preparation of a stream of constant information being relayed to concerned authorities and the public, was a real test of the IGEPN’s capacity to deal with a complicated eruption situation whose outcome was not apparent at the beginning, but which concluded in a very small eruptive episode.

Estimates of lava volume, and thus effusion rate, are critical for assessing volcanic hazard and are a priority for volcano observatories with responsibility for monitoring. The choice of specific methods used to approximate lava volume depends on both volcanological and practical considerations; in particular, whether field measurements are possible and how often they can be repeated. Volcán El Reventador (Ecuador) is inaccessible, and field measurements can only be made infrequently at a few locations in its caldera. We present both planimetric field and topographic satellite radar-based measurements of lava flow thicknesses and volumes for activity at El Reventador between 2002 and 2009. Lava volumes estimates range from 75 ± 24 × 106 m3 (based on field measurements of flow thickness) to 90 ± 37 × 106 m3 (from satellite radar retrieval of flow thickness), corresponding to time-averaged effusion rates of 9 ± 4 m3/s and 7 ± 2 m3/s, respectively. Detailed flow mapping from aerial imagery demonstrate that lava effusion rate was at its peak at the start of each eruption phase and decreased over time. Measurements of lava thickness made from a small set of Synthetic Aperture Radar (SAR) interferograms allowed the retrieval of the shape of the compound lava flow field and show that in 2009 it was subsiding by up to 6 cm/year. Satellite radar measurements thus have the potential to be a valuable supplement to ground-based monitoring at El Reventador and other inaccessible volcanoes.

International audience; Pyroclastic density currents (PDCs) from Tungurahua volcano, Ecuador, recurrently rush down the northern Vazcún valley and threaten the small tourist city of Baños located on its mouth. Estimating PDC hazards, i.e. PDC return rate and extent, is difficult in Baños and Vazcún because data from the literature are rare and debated, while geological exposures are few and vegetated. To improve our awareness of PDC hazards in the Baños area, we examined historical documents, conducted new geological research in the Vazcún valley, and obtained additional 14C data. We highlight complex radiocarbon results that may lead to difficulties when interpreting the PDC chronology, and offer recommendations to improve sampling strategies for 14C age determinations of PDC deposits. Overall, our results show that the 1640, 1773, and 1886 PDC-forming eruptions are recorded in the valley, while products of the 1918 and 2006 events were likely removed. Through considering recorded/unrecorded bias in the reconstruction of past PDC emplacement in Vazcún, we calculate a minimal average return rate of 18 PDC-forming events for pre-Columbian and historical eruptions since the devastating 3 ka BP eruption, which translates into a maximum average return rate of 150–200 years in the valley. However, the archives suggest that most PDCs did not affected the now-urbanized Baños area (e.g. 1918, 2006) and we estimate that the city is impacted on average every 350–500 years, a duration that is likely perceived as fairly long for people living in the area. The Baños case-study thus raises questions on how to communicate on uncertain threats and impacts, and how to improve alert messages in a town where economic incomes are essentially based on tourist activities. To better address these issues we plan in future works to focus on cognitive perception of risk and volcanic hazard judgment by populations of Baños and nearby rural communities.

Since 2000, a network of volunteers known as vigías has been engaged in community-based volcano monitoring, which involves local citizens in the collection of scientific data, around volcán Tungurahua, Ecuador. This paper provides the first detailed description and analysis of this well-established initiative, drawing implications for volcanic risk reduction elsewhere. Based on 32 semi-structured interviews and other qualitative data collected in June and July 2013 with institutional actors and with vigías themselves, the paper documents the origins and development of the network, identifies factors that have sustained it, and analyses the ways in which it contributes to disaster risk reduction. Importantly, the case highlights how this community-based network performs multiple functions in reducing volcanic risk. The vigías network functions simultaneously as a source of observational data for scientists; as a communication channel for increasing community awareness, understanding of hazard processes and for enhancing preparedness; and as an early warning system for civil protection. Less tangible benefits with nonetheless material consequences include enhanced social capital – through the relationships and capabilities that are fostered – and improved trust between partners. Establishing trust-based relationships between citizens, the vigías, scientists and civil protection authorities is one important factor in the effectiveness and resilience of the network. Other factors discussed in the paper that have contributed to the longevity of the network include the motivations of the vigías, a clear and regular communication protocol, persistent volcanic activity, the efforts of key individuals, and examples of successful risk reduction attributable to the activities of the network. Lessons that can be learned about the potential of community-based monitoring for disaster risk reduction in other contexts are identified, including what the case tells us about the conditions that can affect the effectiveness of such initiatives and their resilience to changing circumstances.

The deposits of the pyroclastic density currents from the August 2006 eruption of Tungurahua show three facies associations depending on the topographic setting: the massive, proximal cross-stratified, and distal cross-stratified facies. (1) The massive facies is confined to valleys on the slopes of the volcano. It contains clasts of >1 m diameter to fine ash material, is massive, and interpreted as deposited from dense pyroclastic flows. Its surface can exhibit lobes and levees covered with disk- shaped and vesicular large clasts. These fragile large clasts must have rafted at the surface of the flows all along the path in order to be preserved, and thus imply a sharp density boundary near the surface of these flows. (2) The proximal cross-stratified facies is exposed on valley overbanks on the upper part of the volcano and contains both massive coarse-grained layers and cross- stratified ash and lapilli bedsets. It is interpreted as deposited from (a) dense pyroclastic flows that overflowed the gentle ridges of valleys of the upper part of the volcano and (b) dilute pyroclastic density currents created from the dense flows by the entrainment of air on the steep upper flanks. (3) The distal cross- stratified facies outcrops as spatially limited, isolated, and wedge-shaped bodies of cross-stratified ash deposits located downstream of cliffs on valleys overbanks. It contains numerous aggrading dune bedforms, whose crest orientations reveal paren- tal flow directions. A downstream decrease in the size of the dune bedforms, together with a downstream fining trend in the grain size distribution are observed on a 100-m scale. This facies is interpreted to have been deposited from dilute pyroclastic density currents with basal tractional boundary layers. We sug- gest that the parental flows were produced from the dense flows by entrainment of air at cliffs, and that these diluted currents might rapidly deposit through “pneumatic jumps”. Three modes are present in the grain size distribution of all samples indepen- dently of the facies, which further supports the interpretation that all three facies derive from the same initial flows. This study emphasizes the influence of topography on small volume pyro- clastic density currents, and the importance of flow transforma- tion and flow-stripping processes.

Long-lasting andesitic eruptions sometimes include strong short-lived explosive events, which can pose significant hazards in populated regions. The origin and dynamics of such violent eruptions remain poorly known and may involve a combination of different factors. Tungurahua volcano, Ecuador, reawakens in 1999 and is an example of such an open-vent system that experienced a strong and deadly andesitic pyroclastic flow-forming event in August 2006. Inspection of the deposits suggested that the event could have been triggered by magma mixing (coexistence of both silicic pumices and andesitic scoria in the tephra), magma-water interaction (presence of xenolithic clasts) or deep andesitic magma reinjection (based on mineral chemistry). Here we investigate these options by performing a high-resolution mass budget analysis of the scoria fall deposit. This is achieved by analysing componentry compositions and their mass distribution pattern in the layer, which allow us to document and integrate exponential and power laws mass decay rates over wide areas. The results yield a total mass for the tephra layer of similar to 2 x 10(10) kg. The pumice mass fraction is far too small (

Repeated ash fall events have occurred during the 1999-ongoing eruption of Tungurahua volcano, Ecuador, notably during the late 1999 and August 2001 eruptive phases. While the eruptive styles were similar, these two phases had different impacts on nearby rural and urban Andean populations: ash falls in late 1999 had limited effects on human health and farming, whereas the 2001 phase resulted in medical problems, death of animals in livestock, and damages to houses and crops. Here we investigate the origin of this difference by estimating the size of the August 2001 event (VEI, magnitude, intensity), and by comparing monitoring information of the 1999 and 2001 phases (duration, explosion rate, column height, SO2 output rate). The results show that both phases ranked at VEI 3, although the longer 1999 phase was likely larger than the 2001 phase. Mass magnitude (M) and intensity (I) indexes calculated for the 2001 phase reach M approximate to 2.7 and I approximate to 6.5 when based on ash fall layer data, but increase to M approximate to 3.2 and I approximate to 7.0 when ballistic products are included. We investigated the influence of rain fall and wind flow regimes on ash dispersion, sedimentation and remobilization. The analysis indicates that the harmful effect of the 2001 phase resulted from unfavorable conditions that combined volcanological and seasonal origins, including: a) a low elevation of the ash plume above rural regions owed to a usually bent-over column, b) ash sedimentation in a narrow area west of the volcano under sub-steady wind directions, c) anticipated ash settling by frequent rain flushing of low intensity, and d) formation of a wet cohesive ash coating on buildings and harvests. Conversely, the stronger 1999 phase injected a large amount of ash at higher elevation in the dry season; the ash was widely disseminated across the whole Ecuadorian territory and beyond, and was frequently removed by rain and winds. In summary, our study illustrates the influences of eruption size and weather conditions on the impact of volcanic activity in a tropical setting and puts emphasis on the necessity to merge volcanological and meteorological monitoring duties for hazard assessment and alert level definition, in order to mitigate the effect of ash falls in the Andes and elsewhere.

[1] The lowermost section of a Vulcanian or Plinian volcanic eruption column may be thought of as a momentum-driven, turbulent, free-shear jet flow. We propose that large-amplitude and long-duration infrasonic (

More than 100 separate incidents of interactions between aircraft and volcanic ash were documented between 1973 and 2003. Incidents on international flight paths over remote areas have resulted in engine failures and significant damage and expense to commercial airlines. To protect aircraft from volcanic ash, pilots need rapid and reliable notification of ash- generating events. A global infrasound array network, consisting of the International Monitoring System (IMS) and other national networks, has demonstrated a capability for remote detection of Vulcanian to Plinian eruptions that can inject ash into commercial aircraft cruise altitudes (approximately 12 kilometers) near the tropopause. The identification of recurring sound signatures associated with high- altitude ash injection implies that acoustic remote sensing can improve the reliability and reduce the latency of these notifications.

[1] An important objective in volcanology is the quantification of eruption intensity through the study of elastic energy propagated into the atmosphere and ground. To better understand the relation between elastic wave radiation and eruptive activity we deployed seismic, acoustic, and video instrumentation at the active Tungurahua Volcano (Ecuador) in Nov.–Dec. of 2004. Our data show that plume expansion scales very poorly with both seismic and acoustic trace energy and only the initial amplitude of the acoustic signal is perhaps correlated with initial plume rise speeds. In general, the eventual size of Tungurahua eruption plumes does not appear to be controlled by elevated material accelerations within the conduit, which are primary influences on elastic energy radiation. This result has vital implications for volcano observatories, which are interested in using seismic and acoustic trace amplitudes as proxies for eruption magnitudes.

Successful mitigation of a possible volcanic disaster depends upon the early detection of renewed volcanic activity. With considerable optimism, volcano observatories instrument dangerous volcanoes, with the hope of an early recognition of the reactivation of a volcano. Reventador volcano's November 3, 2002 eruption came with little warning and had a tremendous socio-economic impact. Reventador volcano, a young andesitic cone in the Eastern Cordillera of Ecuador, has had, at least, 16 eruptions between 1541 and 2002. These eruptions were characterized by small pyroclastic flows, blocky lava flows, debris flows, and limited ash falls. With the exception of a M=4 earthquake near the volcano one month earlier, only seismic activity related to the eruption onset was registered. Following only 7 hours of seismic tremor, the paroxysmal eruption began at 0912 h on November 3, 2002 with a sustained column that ascended to 17 km and five pyroclastic flows, that traveled as much as 9 km to the east. By mid-afternoon ash falls of 1-10 mm thickness began blanketing the Interandean Valley near Quito. The economic impact was significant, including severe damage to the principal petroleum pipelines, closure of schools, businesses, and Quito's airport for 10 days. It is important to conclude that for those volcanoes that are characterized by low silica, volatile-rich, fluid magmas, magma ascent can be aseismic, rapid, and without much warning. This event should serve as a clear reminder to scientists, civil defense, and authorities of the rapid onset of the eruptions of some volcanoes Erupciones volcánicas con poco aviso: el caso de la erupción sorpresiva del 3 de Noviembre del 2002 del Volcán Reventador. La mitigación exitosa de un posible desastre volcánico depende de la detección oportuna de la reactivación de un volcán. Con mucho optimismo, los observatorios volcánicos efectúan un monitoreo de volcanes peligrosos, en espera de reconocer tempranamente el inicio de nueva actividad. La erupción del volcán Reventador, el día 3 de Noviembre de 2002, comenzó con poco aviso. El volcán Reventador es un volcán joven andesítico de la Cordillera Oriental del Ecuador que ha tenido, al menos, 16 erupciones desde 1541. Dichas erupciones fueron caracterizadas por flujos piroclásticos y lávicos, flujos de escombros y caída limitada de ceniza. Con la excepción de un fuerte sismo cerca del volcán un mes antes, se registró solamente la sismicidad que comenzó el proceso eruptivo. Luego de 7 horas de 'tremor' sísmico, la erupción paroxismal empezó a las 0912 h de ese día con una columna sostenida que ascendió a los 17 km y con cinco flujos piroclásticos que viajaron hasta 9 km al este. Antes de las 1500 h empezó a caer ceniza en el Valle Interandino cerca de Quito, formando una película de 1 a 10 mm de espesor. El impacto económico fue grande, pues resultó en graves daños a los oleoductos y el cierre de colegios y negocios y del aeropuerto de Quito durante 10 días. Hay que concluir que en aquellos volcanes que aportan magmas de bajo contenido de sílice, ricos en gases y muy fluidos, el ascenso del magma en el conducto puede ser asísmico, rápido y sin aviso. Así, esta erupción es muy útil para recordarle a los científicos, la defensa civil y a las autoridades que algunos volcanes pueden reactivarse con erupciones violentas, sin mayor aviso

Continuous monitoring of Cotopaxi volcano from January 1989 to September 1997 shows that it is subject to a steady shallow Long Period (LP) activity. LP events are concentrated in a column with a diameter of about 3 km and a height of about 12 km, between an elevation of 4 km and 8 km depth. They do not occur in swarms, nor have there been periods of complete calm. High frequency volcano-tectonic (VT) events are mostly located on the northeastern side of the LP column, with the maximum activity of both types of events coinciding in depth. LP activity cannot be related to unrest of the volcano. The most likely explanation for the continuous occurrence of LP events beneath Cotopaxi is that they are produced by the interaction of glacier thaw water and hot material at shallow depths. The relative spatial distribution of both type of events in two adjacent zones suggest that VT and LP activities are interconnected.