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Available geophysical and geologic data provide a simplified model of the current magmatic plumbing system of Mount St. Helens (MSH). This model and new geochemical data are the basis for the revised hazards assessment presented here. The assessment is weighted by the style of eruptions and the chemistry of magmas erupted during the past 500 years, the interval for which the most detailed stratigraphic and geochemical data are available. This interval includes the Kalama (A. D. 1480-1770s?), Goat Rocks (A.D. 1800-1857), and current eruptive periods. In each of these periods, silica content decreased, then increased. The Kalama is a large amplitude chemical cycle (SiO2: 57%-67%), produced by mixing of arc dacite,...
Categories: Publication; Types: Citation; Tags: Bulletin of Volcanology
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In or around 1790 a.d. an explosive eruption took place in the summit caldera of Kilauea shield volcano. A group of Hawaiian warriors close to the caldera at the time were killed by the effects of the explosions. The stratigraphy of pyroclastic deposits surrounding Kilauea (i.e., the Keanakakoi Ash Member) suggests that the explosions referred to in the historic record were the culmination of a prolonged hydrovolcanic eruption consisting of three main phases. The first phase was phreatomagmatic and generated well-bedded, fine fallout ash rich in glassy, variably vesiculated, juvenile magmatic and dense, lithic pyroclasts. The ash was mainly dispersed to the southwest of the caldera by the northeasterly trade winds....
Categories: Publication; Types: Citation; Tags: Bulletin of Volcanology
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Broadband seismic data collected on Ruapehu volcano, New Zealand, in 1994 and 1998 show that the 1995-1996 eruptions of Ruapehu resulted in a significant change in the frequency content of tremor and volcanic earthquakes at the volcano. The pre-eruption volcanic seismicity was characterized by several independent dominant frequencies, with a 2 Hz spectral peak dominating the strongest tremor and volcanic earthquakes and higher frequencies forming the background signal. The post-eruption volcanic seismicity was dominated by a 0.8-1.4 Hz spectral peak not seen before the eruptions. The 2 Hz and higher frequency signals remained, but were subordinate to the 0.8-1.4 Hz energy. That the dominant frequencies of volcanic...
Categories: Publication; Types: Citation; Tags: Bulletin of Volcanology
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Personnel from the U.S. Geological Survey's Cascades Volcano Observatory conducted first-order, class-II leveling surveys near Lassen Peak, California, in 1991 and at Newberry Volcano, Oregon, in 1985, 1986, and 1994. Near Lassen Peak no significant vertical displacements had occurred along either of two traverses, 33 and 44 km long, since second-order surveys in 1932 and 1934. At Newberry, however, the 1994 survey suggests that the volcano's summit area had risen as much as 97??22 mm with respect to a third-order survey in 1931. The 1931 and 1994 surveys measured a 37-km-long, east-west traverse across the entire volcano. The 1985 and 1986 surveys, on the other hand, measured only a 9-km-long traverse across the...
Categories: Publication; Types: Citation; Tags: Bulletin of Volcanology
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Structural reappraisal of several classic rheomorphic ignimbrites in Colorado, Idaho, the Canary Islands and Italy has, for the first time, revealed abundant oblique folds, curvilinear folds and sheathfolds which formed during emplacement. Like their equivalents in tectonic shear-zones, the sheathfold axes lie sub-parallel to a pervasive elongation lineation, and appear as eye structures on rock surfaces normal to the transport direction. With the recognition of sheathfolds, ignimbrites previously inferred to have undergone complex rheomorphic deformation histories are re-interpreted as recording a single, progressive deformation event. In some examples, the trends of sheathfolds and related lineations change with...
Categories: Publication; Types: Citation; Tags: Bulletin of Volcanology
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The Pu'u 'Ō'ō-Kūpaianaha eruption on the east rift zone of Kīlauea began in January 1983. The first 9 years of the eruption were divided between the Pu'u 'Ō'ō (1983–1986) and Kūpaianaha (1986–1992) vents, each characterized by regular, predictable patterns of activity that endured for years. In 1990 a series of pauses in the activity disturbed the equilibrium of the eruption, and in 1991, the output from Kūpaianaha steadily declined and a short-lived fissure eruption broke out between Kūpaianaha and Pu'u 'Ō'ō. In February 1992 the Kūpaianaha vent died, and, 10 days later, eruptive episode 50 began as a fissure opened on the uprift flank of the Pu'u 'Ō'ō cone. For the next year, the eruption was marked by instability...
Categories: Publication; Types: Citation; Tags: Bulletin of Volcanology
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The three-day eruption at Novarupta in 1912 consisted of three discrete episodes. Episode I began with plinian dispersal of rhyolitic fallout (Layer A) and contemporaneous emplacement of rhyolitic ignimbrites and associated proximal veneers. The plinian column was sustained throughout most of the interval of ash flow generation, in spite of progressive increases in the proportions of dacitic and andesitic ejecta at the expense of rhyolite. Accordingly, plinian Layer B, which fell in unbroken continuity with purely rhyolitic Layer A, is zoned from >99% to ???15% rhyolite and accumulated synchronously with emplacement of the correspondingly zoned ash flow sequence in Mageik Creek and the Valley of Ten Thousand Smokes...
Categories: Publication; Types: Citation; Tags: Bulletin of Volcanology
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The vesicularity, permeability, and structure of pumice clasts provide insight into conditions of vesiculation and fragmentation during Plinian fall and pyroclastic flow-producing phases of the ~7,700 cal. year B.P. climactic eruption of Mount Mazama (Crater Lake), Oregon. We show that bulk properties (vesicularity and permeability) can be correlated with internal textures and that the clast structure can be related to inferred changes in eruption conditions. The vesicularity of all pumice clasts is 75–88%, with >90% interconnected pore volume. However, pumice clasts from the Plinian fall deposits exhibit a wider vesicularity range and higher volume percentage of interconnected vesicles than do clasts from pyroclastic-flow...
Categories: Publication; Types: Citation; Tags: Bulletin of Volcanology
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Various parameters of the internal structure of a debris-avalanche deposit from ancestral Mount Shasta (size and percentage of block facies in each exposure, number and width of jigsaw cracks, and number of rounded clasts in matrix facies) were measured in order to study flow and emplacement mechanisms. Three types of coherent blocks were identified: blocks of massive or brecciated lava flows or domes, blocks of layered volcaniclastic deposits, and blocks of accidental material, typically from sedimentary units underlying Shasta Valley. The mean maximum dimension of the three largest blocks of layered volcaniclastic material is 220 m, and that of the lava blocks, 110 m. This difference may reflect plastic deformation...
Categories: Publication; Types: Citation; Tags: Bulletin of Volcanology
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We investigated the distribution of Cl, F, Li, and Be in pumices, obsidians, and crystallized dome rocks at Chaitén volcano in 2008–2009 in order to explore the behavior of these elements during explosive and effusive volcanic activity. Electron and ion microprobe analyses of matrix and inclusion glasses from pumice, obsidian, and microlite-rich dome rock indicate that Cl and other elements were lost primarily during crystallization of the rhyolitic dome after it had approached the surface. Glass in pumice and microlite-free obsidian has 888 ± 121 ppm Cl, whereas residual glass in evolved microlite-rich dome rock generally retains less Cl (as low as <100 ppm). Estimated Cl losses were likely >0.7 Mt Cl, with a potential...
Categories: Publication; Types: Citation; Tags: Bulletin of Volcanology
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Historical eruptions have produced lahars and floods by perturbing snow and ice at more than 40 volcanoes worldwide. Most of these volcanoes are located at latitudes higher than 35°; those at lower latitudes reach altitudes generally above 4000 m. Volcanic events can perturb mantles of snow and ice in at least five ways: (1) scouring and melting by flowing pyroclastic debris or blasts of hot gases and pyroclastic debris, (2) surficial melting by lava flows, (3) basal melting of glacial ice or snow by subglacial eruptions or geothermal activity, (4) ejection of water by eruptions through a crater lake, and (5) deposition of tephra fall. Historical records of volcanic eruptions at snow-clad volcanoes show the following:...
Categories: Publication; Types: Citation; Tags: Bulletin of Volcanology
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The first eruptive activity at Kīlauea Volcano’s summit in 25 years began in March 2008 with the opening of a 35-m-wide vent in Halema‘uma‘u crater. The new activity has produced prominent very-long-period (VLP) signals corresponding with two new behaviors: episodic tremor bursts and small explosive events, both of which represent degassing events from the top of the lava column. Previous work has shown that VLP seismicity has long been present at Kīlauea’s summit, and is sourced approximately 1 km below Halema‘uma‘u. By integrating video observations, infrasound and seismic data, we show that the onset of the large VLP signals occurs within several seconds of the onset of the degassing events. This timing indicates...
Categories: Publication; Types: Citation; Tags: Bulletin of Volcanology
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Leveling surveys in 1923, 1976, and each year from 1983 to 1993 have shown that the east-central part of the Yellowstone caldera, near the base of the Sour Creek resurgent dome, rose at an average rate of 14??1 mm/year from 1923 to 1976 and 22??1 mm/year from 1976 to 1984. In contrast, no detectable movement occurred in the same area from 1984 to 1985 (-2??5 mm/year), and from 1985 to 1993 the area subsided at an average rate of 19??1 mm/year. We conclude that uplift from 1923 to 1984 was caused by: (1) pressurization of the deep hydrothermal system by fluids released from a crystallizing body of rhyolite magma beneath the caldera, then trapped beneath a self-sealed zone near the base of the hydrothermal system;...
Categories: Publication; Types: Citation; Tags: Bulletin of Volcanology
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Emplacement of a giant submarine slide complex, offshore of South Kona, Hawaii Island, was investigated in 2001 by visual observation and in-situ sampling on the bench scarp and a megablock, during two dives utilizing the Remotely Operated Vehicle (ROV) Kaiko and its mother ship R/V Kairei. Topography of the bench scarp and megablocks were defined in 3-D perspective, using high-resolution digital bathymetric data acquired during the cruise. Compositions of 34 rock samples provide constraints on the landslide source regions and emplacement mechanisms. The bench scarp consists mainly of highly fractured, vesiculated, and oxidized a-a lavas that slumped from the subaerial flank of ancestral Mauna Loa. The megablock...
Categories: Publication; Types: Citation; Tags: Bulletin of Volcanology
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The results from two different types of gas measurement, telemetered in situ monitoring of reducing gases on the dome and airborne measurements of sulfur dioxide emission rates in the plume by correlation spectrometry, suggest that the combination of these two methods is particularly effective in detecting periods of enhanced degassing that intermittently punctuate the normal background leakage of gaseous effluent from Mount St Helens to the atmosphere. Gas events were recorded before lava extrusion for each of the four dome-building episodes at Mount St Helens since mid-1984. For two of the episodes, precursory reducing gas peaks were detected, whereas during three of the episodes, COSPEC measurements recorded...
Categories: Publication; Types: Citation; Tags: Bulletin of Volcanology
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Lava lakes experience filling, circulation, and often drainage depending upon the style of activity and location of the vent. Features formed by these processes have proved difficult to document due to dangerous conditions during the eruption, inaccessibility, and destruction of features during lake drainage. Kilauea Iki lava lake, Kilauea, Hawai'i, preserves many such features, because lava ponded in a pre-existing crater adjacent to the vent and eventually filled to the level of, and interacted with, the vent and lava fountains. During repeated episodes, a cyclic pattern of lake filling to above vent level, followed by draining back to vent level, preserved features associated with both filling and draining. Field...
Categories: Publication; Types: Citation; Tags: Bulletin of Volcanology
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Outflow sheets of the Hiko tuff and the Racer Canyon tuff, which together extend over approximately 16000 km2 around the Caliente caldera complex in southeastern Nevada, have long been considered to be products of simultaneous or near-simultaneous eruptions from inset calderas in the west and east ends, respectively, of the caldera complex. New high-precision 40Ar/39Ar geochronology and paleomagnetic data demonstrate that emplacement of the uppermost part of the Racer Canyon tuff at 18.33??0.03 Ma was nearly synchronous with emplacement of the single outflow cooling unit of the much larger overlying Hiko tuff at 18.32??0.04 Ma. Based on comparison with the geomagnetic polarity time scale derived from the sea-floor...
Categories: Publication; Types: Citation; Tags: Bulletin of Volcanology
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Seismicity is one of the most commonly monitored phenomena used to determine the state of a volcano and for the prediction of volcanic eruptions. Although several real-time earthquake-detection and data acquisition systems exist, few continuously measure seismic amplitude in circumstances where individual events are difficult to recognize or where volcanic tremor is prevalent. Analog seismic records provide a quick visual overview of activity; however, continuous rapid quantitative analysis to define the intensity of seismic activity for the purpose of predicing volcanic eruptions is not always possible because of clipping that results from the limited dynamic range of analog recorders. At the Cascades Volcano Observatory,...
Categories: Publication; Types: Citation; Tags: Bulletin of Volcanology
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The postglacial eruption rate for the Mount Adams volcanic field is ∼0.1 km3/k.y., four to seven times smaller than the average rate for the past 520 k.y. Ten vents have been active since the last main deglaciation ∼15 ka. Seven high flank vents (at 2100-2600 m) and the central summit vent of the 3742-m stratocone produced varied andesites, and two peripheral vents (at 2100 and 1200 m) produced mildly alkalic basalt. Eruptive ages of most of these units are bracketed with respect to regional tephra layers from Mount Mazama and Mount St. Helens. The basaltic lavas and scoria cones north and south of Mount Adams and a 13-km-long andesitic lava flow on its east flank are of early postglacial age. The three most extensive...
Categories: Publication; Types: Citation; Tags: Bulletin of Volcanology


map background search result map search result map Degassing of Cl, F, Li and Be during extrusion and crystallization of the rhyolite dome at Volcán Chaitén, Chile during 2008 and 2009 Degassing of Cl, F, Li and Be during extrusion and crystallization of the rhyolite dome at Volcán Chaitén, Chile during 2008 and 2009