The “Mera” lahar deposit in the upper Amazon basin: Transformation of a late Pleistocene collapse at Huisla volcano, central Ecuador

Over the last years, project work in teams has become commonplace in organizations. Studies have indicated that the motivational climate in which teams operate is highly relevant in determining employee behavior. This study investigates the effect of motivational climates, as defined by goal setting theory, on collaboration in project teams. In a survey among 173 senior project members from different organizations, we found that congruence between performance and mastery climates is positively and significantly related to collaboration behavior in teams. Furthermore, we highlight the moderating role of prosocial motivation in the relationship between (in)congruence in motivational climates and collaboration. Specifically, we find that under conditions of low prosocial motivation, a focus on either a mastery or a performance climate is preferable to adopting a congruence between these two climates, at least in terms of collaboration in teams

Cambios en los dinamismos eruptivos durante las erupciones de larga duración: el caso de las erupciones del 2006 del volcán Tungurahua (Ecuador)

El seguimiento de los potenciales cambios en los dinamismos eruptivos que ocurren durante las erupciones de larga duración representa un gran reto para la vulcanología actual y constituye una etapa crucial del monitoreo volcánico y de la evaluación de la amenaza. En muchos volcanes, los períodos eruptivos son largos (del orden de varios años), tiempo durante el cual los volcanes presentan una actividad intermitente, sin llegar a experimentar erupciones explosivas importantes, como por ejemplo en el volcán Ubinas (Perú) que se reactivó en el 2006 y cuya actividad se extendió hasta el 2008 (Rivera et al., 2010). En otros casos, el tiempo entre el inicio de la erupción y el paroxismo eruptivo puede ser relativamente largo, del orden de meses o años. Este fue el caso del volcán Tungurahua (Ecuador) que se reactivó en 1999, y cuyo paroxismo se produjo 7 años después de iniciada la actividad eruptiva. La población que vive bajo la amenaza volcánica en el caso de erupciones de larga duración tiende a acostumbrarse a las nuevas condiciones impuestas por el volcán, lo cual puede comprometer seriamente su capacidad de reacción ante los cambios en el tipo de actividad eruptiva. Por tal motivo, es primordial tener un mejor entendimiento de las causas por las cuales ciertos volcanes se mantienen con niveles de actividad bajo a moderadamente explosivos, mientras que otros sufren una evolución hacia una actividad altamente explosiva. Los estudios integrales (geofísica, petrología, cronología eruptiva) realizados en el volcán Tungurahua, permiten aportar ciertos elementos de respuesta a ésta interrogante

Aquatic community response to volcanic eruptions on the Ecuadorian Andean flank: evidence from the palaeoecological record

Aquatic ecosystems in the tropical Andes are under increasing pressure from human modification of the landscape (deforestation and dams) and climatic change (increase of extreme events and 1.5 °C on average temperatures are projected for AD 2100). However, the resilience of these ecosystems to perturbations is poorly understood. Here we use a multi-proxy palaeoecological approach to assess the response of aquatic ecosystems to a major mechanism for natural disturbance, volcanic ash deposition. Specifically, we present data from two Neotropical lakes located on the eastern Andean flank of Ecuador. Laguna Pindo (1°27.132′S–78°04.847′W) is a tectonically formed closed basin surrounded by a dense mid-elevation forest, whereas Laguna Baños (0°19.328′S–78°09.175′W) is a glacially formed lake with an inflow and outflow in high Andean Páramo grasslands. In each lake we examined the dynamics of chironomids and other aquatic and semi-aquatic organisms to explore the effect of thick (> 5 cm) volcanic deposits on the aquatic communities in these two systems with different catchment features. In both lakes past volcanic ash deposition was evident from four large tephras dated to c.850 cal year BP (Pindo), and 4600, 3600 and 1500 cal year BP (Baños). Examination of the chironomid and aquatic assemblages before and after the ash depositions revealed no shift in composition at Pindo, but a major change at Baños occurred after the last event around 1500 cal year BP. Chironomids at Baños changed from an assemblage dominated by Pseudochironomus and Polypedilum nubifer-type to Cricotopus/Paratrichocladius type-II, and such a dominance lasted for approximately 380 years. We suggest that, despite potential changes in the water chemistry, the major effect on the chironomid community resulted from the thickness of the tephra being deposited, which acted to shallow the water body beyond a depth threshold. Changes in the aquatic flora and fauna at the base of the trophic chain can promote cascade effects that may deteriorate the ecosystem, especially when already influenced by human activities, such as deforestation and dams, which is frequent in the high Andes

Understanding cyclic seismicity and ground deformation patterns at volcanoes: intriguing lessons from Tungurahua volcano, Ecuador

Cyclic seismicity and ground deformation patterns are observed on many volcanoes worldwide where seismic swarms and the tilt of the volcanic flanks provide sensitive tools to assess the state of volcanic activity. Ground deformation at active volcanoes is often interpreted as pressure changes in a magmatic reservoir, and tilt is simply translated accordingly into inflation and deflation of such a reservoir. Tilt data recorded by an instrument in the summit area of Tungurahua volcano in Ecuador, however, show an intriguing and unexpected behaviour on several occasions: prior to a Vulcanian explosion when a pressurisation of the system would be expected, the tilt signal declines significantly, hence indicating depressurisation. At the same time, seismicity increases drastically. Envisaging that such a pattern could carry the potential to forecast Vulcanian explosions on Tungurahua, we use numerical modelling and reproduce the observed tilt patterns in both space and time. We demonstrate that the tilt signal can be more easily explained as caused by shear stress due to viscous flow resistance, rather than by pressurization of the magmatic plumbing system. In general, our numerical models prove that if magma shear viscosity and ascent rate are high enough, the resulting shear stress is sufficient to generate a tilt signal as observed on Tungurahua. Furthermore, we address the interdependence of tilt and seismicity through shear stress partitioning and suggest that a joint interpretation of tilt and seismicity can shed new light on the eruption potential of silicic volcanoes

Landscape-scale drivers of glacial ecosystem change in the montane forests of the eastern Andean flank, Ecuador

Understanding the impact of landscape-scale disturbance events during the last glacial period is vital in accu- rately reconstructing the ecosystem dynamics of montane environments. Here, a sedimentary succession from the tropical montane cloud forest of the eastern Andean flank of Ecuador provides evidence of the role of non- climate drivers of vegetation change (volcanic events, fire regime and herbivory) during the late-Pleistocene. Multiproxy analysis (pollen, non-pollen palynomorphs, charcoal, geochemistry and carbon content) of the se- diments, radiocarbon dated to ca. 45–42 ka, provide a snap shot of the depositional environment, vegetation community and non-climate drivers of ecosystem dynamics. The geomorphology of the Vinillos study area, along with the organic‐carbon content, and aquatic remains suggest deposition took place near a valley floor in a swamp or shallow water environment. The pollen assemblage initially composed primarily of herbaceous types (Poaceae-Asteraceae-Solanaceae) is replaced by assemblages characterised by Andean forest taxa, (first Melastomataceae-Weinmannia-Ilex, and later, Alnus-Hedyosmum-Myrica). The pollen assemblages have no modern analogues in the tropical montane cloud forest of Ecuador. High micro-charcoal and rare macro-charcoal abundances co-occur with volcanic tephra deposits suggesting transportation from extra-local regions and that volcanic eruptions were an important source of ignition in the wider glacial landscape. The presence of the coprophilous fungi Sporormiella reveals the occurrence of herbivores in the glacial montane forest landscape. Pollen analysis indicates a stable regional vegetation community, with changes in vegetation population co- varying with large volcanic tephra deposits suggesting that the structure of glacial vegetation at Vinillos was driven by volcanic activity

WHAT’S CAUSING ASYMMETRIC DEFORMATION AT TUNGURAHUA VOLCANO, ECUADOR?

IAVCE

A pre-Columbian obsidian trade from secondary fluvial sources supported by new geochemical data from the Alto Coca Reserve and Sumaco sites (Napo Province, Ecuador)

none6New obsidian samples (fragments of pebbles and flakes), mixed with ceramic sherds, were found in 10–25 cm cm deep excavations in the Alto Coca Reserve (Napo Province, Ecuador) upon a flat platform on a ridgetop when digging postholes and drainage ditches. Charcoal associated with both obsidian and pottery fragments, attesting to a possible settlement and human pathways (i.e. coluncos), were dated between 1040 and 1210 AD by the AMS radiocarbon (14C) method. Representative samples of obsidian found in the Alto Coca Reserve were analyzed by INAA (major elements) and ICP-OES-MS (trace elements), together with four additional obsidian samples collected from the Sumaco Volcano area, located at the same longitude but ca. 45 km to the south. The Sumaco site (dated by radiocarbon between 1398 and 1451 AD) was preliminary investigated by Santi et al. (in J Archaeol Sci 37:1753–1760. https:// doi: 10. 1016/j. jas. 2010. 01. 034, 2010). Major and trace elements analyses of all the samples closely match with obsidian pebbles collected by Knight et al. (in J Archaeol Sci 38:1069–1079. https:// doi. org/ 10. 1016/j. jas. 2010. 12. 002, 2011) along the Cosanga River and its tributaries, in the eastern piedmont of the Cordillera Real. In particular, they correspond to the secondary fluvial sources of obsidian named “Cosanga A” and “Cosanga B” (as defined by the literature; e.g. Knight et al. in J Archaeol Sci 38:1069–1079. https:// doi. org/ 10. 1016/j. jas. 2010. 12. 002, 2011) most likely deriving from erosional processes of primary sources involving the obsidian-bearing deposits of the Las Caucheras area (5–10 km to the east and north-east of the Cosanga town) where several rhyolite eruptive centers (mostly domes) are related to the youngest activity of the Aliso Volcano. The extensive outcrops of the Andean highlands primary sources of obsidian from the well-known pre-Columbian mines at Sierra de Guamaní, located at the crest of the Eastern Cordillera, are not correlated at all with the investigated samples. The geochemical signatures of the obsidian from the Alto Coca Reserve and Sumaco area therefore support a pre-Columbian exploitation of the secondary fluvial sources of obsidian, along the Cosanga-Quijos Valleys, where obsidian pebbles were collected and brought eastward, towards the Amazonian area.restrictedSanti, Patrizia; Thurber, Mark; Taussi, Marco; Oddone, Massimo; Mothes, Patricia A.; Renzulli, AlbertoSanti, Patrizia; Thurber, Mark; Taussi, Marco; Oddone, Massimo; Mothes, Patricia A.; Renzulli, Albert

Impact of tephra falls on Andean communities: The influences of eruption size and weather conditions during the 1999–2001 activity of Tungurahua volcano, Ecuador

International audienceRepeated 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 ≈ 2.7 and I ≈ 6.5 when based on ash fall layer data, but increase to M ≈ 3.2 and I ≈ 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

Estimating rates of decompression from textures of erupted ash particles produced by 1999-2006 eruptions of Tungurahua volcano, Ecuador

International audiencePersistent low- to moderate-level eruptive activity of andesitic volcanoes is difficult to monitor because small changes in magma supply rates may cause abrupt transitions in eruptive style. As direct measurement of magma supply is not possible, robust techniques for indirect measurements must be developed. Here we demonstrate that crystal textures of ash particles from 1999 to 2006 Vulcanian and Strombolian eruptions of Tungurahua volcano, Ecuador, provide quantitative information about the dynamics of magma ascent and eruption that is difficult to obtain from other monitoring approaches. We show that the crystallinity of erupted ash particles is controlled by the magma supply rate (MSR); ash erupted during periods of high magma supply is substantially less crystalline than during periods of low magma supply. This correlation is most easily explained by efficient degassing at very low pressures (<<50 MPa) and degassing-driven crystallization controlled by the time available prior to eruption. Our data also suggest that the observed transition from intermittent Vulcanian explosions at low MSR to more continuous periods of Strombolian eruptions and lava fountains at high MSR can be explained by the rise of bubbles through (Strombolian) or trapping of bubbles beneath (Vulcanian) vent-capping, variably viscous (and crystalline) magma