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Montgomery-Brown E.K.,California Volcano Observatory | Wicks C.W.,Earthquake Science Center | Cervelli P.F.,California Volcano Observatory | Langbein J.O.,Earthquake Science Center | And 4 more authors.
Geophysical Research Letters | Year: 2015

Slow inflation began at Long Valley Caldera in late 2011, coinciding with renewed swarm seismicity. Ongoing deformation is concentrated within the caldera. We analyze this deformation using a combination of GPS and InSAR (TerraSAR-X) data processed with a persistent scatterer technique. The extension rate of the dome-crossing baseline during this episode (CA99 to KRAC) is 1cm/yr, similar to past inflation episodes (1990-1995 and 2002-2003), and about a tenth of the peak rate observed during the 1997 unrest. The current deformation is well modeled by the inflation of a prolate spheroidal magma reservoir â7km beneath the resurgent dome, with a volume change of â6×106m3/yr from 2011.7 through the end of 2014. The current data cannot resolve a second source, which was required to model the 1997 episode. This source appears to be in the same region as previous inflation episodes, suggesting a persistent reservoir. Key Points Uplift at Long Valley began in late 2011 Well modeled by inflation of â7km deep prolate ellipsoid Source colocated with previous sources, suggesting persistent reservoir. © 2015. American Geophysical Union. All Rights Reserved.

Pallister J.S.,Cascades Volcano Observatory | Diefenbach A.K.,Cascades Volcano Observatory | Burton W.C.,12201 Sunrise Valley Drive | Munoz J.,Servicio Nacional de Geologia y Mineria | And 4 more authors.
Andean Geology | Year: 2013

We use geologic field mapping and sampling, photogrammetric analysis of oblique aerial photographs, and digital elevation models to document the 2008-2009 eruptive sequence at Chaitén Volcano and to estimate volumes and effusion rates for the lava dome. We also present geochemical and petrologic data that contribute to understanding the source of the rhyolite and its unusually rapid effusion rates. The eruption consisted of five major phases: 1. An explosive phase (1-11 May 2008); 2. A transitional phase (11-31 May 2008) in which low-altitude tephra columns and simultaneous lava extrusion took place; 3. An exogenous lava flow phase (June-September 2008); 4. A spine extrusion and endogenous growth phase (October 2008-February 2009); and 5. A mainly endogenous growth phase that began after the collapse of a prominent Peléean spine on 19 February 2009 and continued until the end of the eruption (late 2009 or possibly earliest 2010). The 2008-2009 rhyolite lava dome has a total volume of approximately 0.8 km3. The effusion rate averaged 66 m3s-1 during the first two weeks and averaged 45 m3s-1 for the first four months of the eruption, during which 0.5 km3 of rhyolite lava was erupted. These are among the highest rates measured world-wide for historical eruptions of silicic lava. Chaitén's 2008-2009 lava is phenocryst-poor obsidian and microcrystalline rhyolite with 75.3±0.3% SiO2. The lava was erupted at relatively high temperature and is remarkably similar in composition and petrography to Chaitén's pre-historic rhyolite. The rhyolite's normative composition plots close to that of low pressure (100-200 MPa) minimum melts in the granite system, consistent with estimates of approximately 5 to 10 km source depths based on phase equilibria and geodetic studies. Calcic plagioclase, magnesian orthopyroxene and aluminous amphibole among the sparse phenocrysts suggest derivation of the rhyolite by melt extraction from a more mafic magmatic mush. High temperature and relatively low viscosity enabled rapid magma ascent and high effusion rates during the dome-forming phases of the 2008-2009 eruption.

News Article | April 20, 2016

At nighttime, ominous lightning flashes above erupting volcanoes light up the sky like a living nightmare. Now, scientists are closer to understanding volcanic lightning, which stems from both ash and ice, two new studies reveal. Unraveling the origin of volcanic lightning has been difficult. In thunderstorms, the culprits are colliding ice crystals, which generate enough of an electric charge to trigger lightning. But ash clouds are less predictable and harder to study than supercells (thunderstorms), so scientists are still trying to figure out what sets off volcanic lightning. For instance, it seems absurd to blame ice for lightning in a volcanic inferno. Two new studies reveal different reasons for lightning above erupting volcanoes. One cause is static electricity, from particles rubbing together in dense ash clouds near the ground. The other source of lightning happens near the stratosphere, high above the Earth's surface, where jockeying ice crystals unleash powerful jolts. [Images: Grimsvotn Volcano Puts on Lightning Show] At Sakurajima volcano in Japan, ash particles are responsible for lightning that strikes near the ground, researchers led by Corrado Cimarelli, a volcanologist at Ludwig Maximilian University in Munich, Germany, reported Feb. 23 in the journal Geophysical Research Letters. For that study, the scientists recorded video of volcanic lightning at Sakurajima, one of the world's most active volcanoes. By comparing the video to infrasound and electromagnetic data, the researchers discovered thick clouds of ash give rise to static electricity. The particles rub together and the resulting charge buildup generates lightning strikes. (This is called triboelectricity.) Ice also plays a role in volcanic lightning, a separate study found. Researchers tracked the location of lightning strikes during an April 2015 eruption of Calbuco volcano in Chile. In this case, the bolts were breaking some 60 miles (about 100 kilometers) from the eruption, and at near-stratospheric heights of about 12 miles (20 km) above Earth's surface. The scientists think ice formed in the top of the thinning ash cloud — which was also carrying water vapor — producing lightning like a thundercloud does. The study was published April 12 in Geophysical Research Letters. These discoveries could have important implications for volcano monitoring. Because larger eruptions trigger more lightning, "simply seeing that lightning is associated with an eruption tells you that there are potential aviation issues," said Alexa Van Eaton, lead author of the Calbuco study and a volcanologist at the U.S. Geological Survey Cascades Volcano Observatory in Vancouver, Washington. During the March eruption of Alaska's Pavlof volcano, Van Eaton and her colleagues used the World Wide Lightning Location network to monitor the volcano's ash cloud, she said. The ash from Pavlof and other southwest Alaska volcanoes can drift into international and local flight paths. Van Eaton ultimately hopes to use lightning flashes to gauge the power of volcanic eruptions remotely. "Lightning is telling us things that other geophysical monitoring techniques can't see," van Eaton told Live Science. Bigger eruptions trigger more lightning, van Eaton said. "Simply seeing that lightning is associated with an eruption tells you that there are potential aviation issues, and it informs the way you respond to a volcano," she said. Both studies also bring scientists closer solving the mystery of volcanic lighting. "It's surprising that there are really different processes inside a volcanic eruption plume system that generate electrification," van Eaton said. "It opens a world of questions that we didn't even know existed." Copyright 2016 LiveScience, a Purch company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

Denlinger R.P.,Cascades Volcano Observatory | Moran S.C.,U.S. Geological Survey
Journal of Geophysical Research: Solid Earth | Year: 2014

On 2 October 2004, a significant noneruptive tremor episode occurred during the buildup to the 2004-2008 eruption of Mount St. Helens (Washington). This episode was remarkable both because no explosion followed, and because seismicity abruptly stopped following the episode. This sequence motivated us to consider a model for volcanic tremor that does not involve energetic gas release from magma but does involve movement of conduit magma through extension on its way toward the surface. We found that the tremor signal was composed entirely of Love and Rayleigh waves and that its spectral bandwidth increased and decreased with signal amplitude, with broader bandwidth signals containing both higher and lower frequencies. Our modeling results demonstrate that the forces giving rise to this tremor were largely normal to conduit walls, generating hybrid head waves along conduit walls that are coupled to internally reflected waves. Together these form a crucial part of conduit resonance, giving tremor wavefields that are largely a function of waveguide geometry and velocity. We find that the mechanism of tremor generation fundamentally masks the nature of the seismogenic source giving rise to resonance. Thus multiple models can be invoked to explain volcanic tremor, requiring that information from other sources (such as visual observations, geodesy, geology, and gas geochemistry) be used to constrain source models. With concurrent GPS and field data supporting rapid rise of magma, we infer that tremor resulted from drag of nearly solid magma along rough conduit walls as magma was forced toward the surface.

Gerlach T.,Cascades Volcano Observatory
Eos | Year: 2011

Which emits more carbon dioxide (CO 2): Earth's volcanoes or human activities? Research findings indicate unequivocally that the answer to this frequently asked question is human activities. However, most people, including some Earth scientists working in fields outside volcanology, are surprised by this answer. The climate change debate has revived and reinforced the belief, widespread among climate skeptics, that volcanoes emit more CO 2 than human activities [Gerlach, 2010; Plimer, 2009]. In fact, present-day volcanoes emit relatively modest amounts of CO 2, about as much annually as states like Florida, Michigan, and Ohio.

Major J.J.,Cascades Volcano Observatory | Lara L.E.,Servicio Nacional de Geologia y Mineria
Andean Geology | Year: 2013

Chaitén Volcano erupted unexpectedly in May 2008 in one of the largest eruptions globally since the 1990s. It was the largest rhyolite eruption since the great eruption of Katmai Volcano in 1912, and the first rhyolite eruption to have at least some of its aspects monitored. The eruption consisted of an approximately 2-week-long explosive phase that generated as much as 1 km3 bulk volume tephra (~0.3 km3 dense rock equivalent) followed by an approximately 20-month-long effusive phase that erupted about 0.8 km3 of high-silica rhyolite lava that formed a new dome within the volcano's caldera. Prior to its eruption, little was known about the eruptive history of the volcano or the hazards it posed to society. This edition of Andean Geology contains a selection of papers that discuss new insights on the eruptive history of Chaitén Volcano, and the broad impacts of and new insights obtained from analyses of the 2008-2009 eruption. Here, we summarize the geographic, tectonic, and climatic setting of Chaitén Volcano and the pre-2008 state of knowledge of its eruptive history to provide context for the papers in this edition, and we provide a revised chronology of the 2008-2009 eruption.

Lara L.E.,Servicio Nacional de Geologia y Mineria | Moreno R.,Adolfo Ibáñez University | Amigo A.,Servicio Nacional de Geologia y Mineria | Hoblitt R.P.,Cascades Volcano Observatory | Pierson T.C.,Cascades Volcano Observatory
Andean Geology | Year: 2013

Prior to May 2008, it was thought that the last eruption of Chaitén Volcano occurred more than 5,000 years ago, a rather long quiescent period for a volcano in such an active arc segment. However, increasingly more Holocene eruptions are being identified. This article presents both geological and historical evidence for late Holocene eruptive activity in the 17th century (AD 1625-1658), which included an explosive rhyolitic eruption that produced pumice ash fallout east of the volcano and caused channel aggradation in the Chaitén River. The extents of tephra fall and channel aggradation were similar to those of May 2008. Fine ash, pumice and obsidian fragments in the pre-2008 deposits are unequivocally derived from Chaitén Volcano. This finding has important implications for hazards assessment in the area and suggests the eruptive frequency and magnitude should be more thoroughly studied.

Lehto H.L.,University of South Florida | Roman D.C.,University of South Florida | Moran S.C.,Cascades Volcano Observatory
Journal of Volcanology and Geothermal Research | Year: 2010

The 2004-2008 eruption of Mount St. Helens (MSH), Washington, was preceded by a swarm of shallow volcano-tectonic earthquakes (VTs) that began on September 23, 2004. We calculated locations and fault-plane solutions (FPS) for shallow VTs recorded during a background period (January 1999 to July 2004) and during the early vent-clearing phase (September 23 to 29, 2004) of the 2004-2008 eruption. FPS show normal and strike-slip faulting during the background period and on September 23; strike-slip and reverse faulting on September 24; and a mixture of strike-slip, reverse, and normal faulting on September 25-29. The orientation of σ 1 beneath MSH, as estimated from stress tensor inversions, was found to be sub-horizontal for all periods and oriented NE-SW during the background period, NW-SE on September 24, and NE-SW on September 25-29. We suggest that the ephemeral ~90° change in σ 1 orientation was due to intrusion and inflation of a NE-SW-oriented dike in the shallow crust prior to the eruption onset. © 2010 Elsevier B.V.

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