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Pritchard M.E.,Cornell University | Henderson S.T.,Cornell University | Jay J.A.,Cornell University | Soler V.,CSIC - Institute of Natural Products and Agrobiology | And 12 more authors.
Journal of Volcanology and Geothermal Research | Year: 2014

We record non-eruptive background seismicity at eight potentially active volcanoes and one geothermal area in Chile and Bolivia for the first time in order to set a baseline for future episodes of unrest. We also compare seismicity to coincident new regional observations of ground deformation from InSAR and satellite observed thermal anomalies from the ASTER instrument. We deploy small temporary seismometer networks (1 to 5 stations each) of short and intermediate period instruments for 3-27. months at the nine areas between the years 2004 and 2012 at: Parinacota, Guallatiri, Isluga, Irruputuncu, Olca-Paruma, Ollagüe, Sol de Mañana, Putana, and Láscar. Despite the lack of shallow earthquakes in the global catalogs at these volcanoes, we find that all have volcano-tectonic events with at least 27 earthquake swarms - the most active are Putana, Guallatiri and Ollagüe. We find two examples where changes in seismicity are likely related to either deformation (in 2009 at Putana) or an increase in temperature (in 2012 at Isluga). Further, we document for the first time ground deformation at a Pliocene volcano called Sillajhuay, located in the Holocene volcano gap (i.e., 70. km from the nearest active volcano Isluga). We find that the four deforming volcanoes between 18 and 24°S are seismically active, but that seismic activity does not imply measurable ground deformation. Similarly, the seismically active volcanoes have satellite thermal hotspots, but there is no correlation between relative amounts of seismic activity and hotspot temperature. Because several of the volcanoes show variations in seismic activity, temperature, and deformation over the course of a few years unrelated to eruptions, decadal and longer observations are needed to constrain background activity in the central Andes. © 2014 Elsevier B.V. Source

Lopez T.,University of Alaska Fairbanks | Thomas H.E.,Nicarnica Aviation | Prata A.J.,Nicarnica Aviation | Amigo A.,Volcano Hazards Program | And 2 more authors.
Journal of Volcanology and Geothermal Research | Year: 2015

Measurements of volcanic emissions (ash and SO2) from small-sized eruptions at three geographically dispersed volcanoes are presented from a novel, multichannel, uncooled imaging infrared camera. Infrared instruments and cameras have been used previously at volcanoes to study lava bodies and to assess plume dynamics using high temperature sources. Here we use spectrally resolved narrowband (~0.5-1μm bandwidth) imagery to retrieve SO2 and ash slant column densities (gm-2) and emission rates or fluxes from infrared thermal imagery at close to ambient atmospheric temperatures. The relatively fast sampling (0.1-0.5Hz) of the multispectral imagery and the fast sampling (~1Hz) of single channel temperature data permit analysis of some aspects of plume dynamics. Estimations of SO2 and ash mass fluxes, and total slant column densities of SO2 and fine ash in individual small explosions from Stromboli (Italy) and Karymsky (Russia), and total SO2 slant column densities and fluxes from Láscar (Chile) volcanoes, are provided. We evaluate the temporal evolution of fine ash particle sizes in ash-rich explosions at Stromboli and Karymsky and use these observations to infer the presence of at least two distinct fine ash modes, with mean radii of <10μm and >10μm. The camera and techniques detailed here provide a tool to quickly and remotely estimate fluxes of fine ash and SO2 gas and characterize eruption size. © 2015 Elsevier B.V. Source

Lara L.E.,Volcano Hazards Program | Orozco G.,Volcano Hazards Program | Pina-Gauthier M.,Compania Minera Las Cenizas
Tectonophysics | Year: 2012

On January 19th 1835 a strong Strombolian flank eruption at Osorno (41.1°S) volcano was observed by Ch. Darwin, who was at the Chiloé Island at that time. One month later, a large M 8.5 thrust earthquake took place in central Chile with an epicentral area located ca. 480. km far away from Osorno volcano and a rupture zone that extended from ca. 35°S to 39°S, fairly similar to rupture zone of the Maule 2010 Mw 8.8 earthquake for what is the predecessor. Despite the dates, both have been considered as a typical earthquake-eruption pair and a case-study of remote tectonic triggering. In order to distinguish between remote and local (intraarc) tectonic control we perform a structural analysis of the 1835 fissure vents and cone alignments comparing the resulting geometry with that expected from both the active regional transpression along the arc and the coseismic strain pattern related with such a remote megathrust earthquake.Although the cone loading effect cannot be neglected, the asymmetric pattern of fissures and cone alignments with a prevailing NE-striking SHmax suggest a dominant arc tectonics control. In turn, volumetric expansion modeled with the inferred remote earthquake parameters is minimal at the Osorno volcano. Thus, the 1835 thrust earthquake would have not had a direct effect on the magma ascent and the final eruptive morphology. This case-study could serve as a threshold for the expected remote triggering related with megathrust earthquakes in the Andean subduction zone where statistically based models suggest possible effects even up to 700. km from the epicentral area. © 2011 Elsevier B.V. Source

Sepulveda P.,University of Chile | Le Roux J.P.,University of Chile | Le Roux J.P.,University of Los Andes, Chile | Lara L.E.,Volcano Hazards Program | And 3 more authors.
Biogeosciences | Year: 2015

Hotspot oceanic islands typically experience subsidence due to several processes related to migration of the oceanic plate away from the mantle plume and surface flexural loading. However, many other processes can interrupt subsidence, some of which may be associated with catastrophic events. A study of the biostratigraphy and sedimentology of Holocene deposits on Robinson Crusoe Island (RCI) on the Juan Fernández Ridge (JFR) indicated that dramatic uplift has occurred since 8000 years BP, at a rate of about 8.5mm yr-1. This is evidenced by supratidal flats with tepee structures and sand layers containing marine gastropods (mostly Nerita sp.) that are now exposed ca. 70 m a.s.l. The active hotspot is located 280 km further west and the last volcanic activity on RCI occurred at ca. 800 000 years BP. Long-term subsidence is evidenced by deep submerged marine abrasion terraces at RCI. As no direct evidence was found for the existence of a compensating bulge generated by the present hotspot upon which RCI would be situated, it must be concluded that subsidence in the wake of the mantle plume beneath the migrating plate was interrupted by very rapid uplift, but on a scale that did not fully compensate for the previous subsidence. This can be attributed to large-scale landslides followed by isostatic rebound, although this is only vaguely reflected in the low-resolution bathymetry of the area. To determine if this mechanism produced the uplift, a detailed bathymetric survey of the area will be required. If such a survey confirms this hypothesis, it may have implications for the short-term dynamics of vertical variations of oceanic edifices and their related effects on ecosystems and human population. © Author(s) 2015. Source

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