Search USGS⌕ Search

Geology topics

Research about Augustine Volcano

Source-linked reports with geographic coverage including Augustine Volcano.

13 recordsLinked to original sources
USGS2022

Earthquakes indicated stress field change during the 2006 unrest of Augustine Volcano, Alaska

To examine controls on the local stress field at Augustine Volcano, Alaska, before its 2006 eruption, we calculated fault plane solutions for volcano-tectonic earthquakes from 2002 to 2006. The P-axis orientation was first aligned to the regional maximum compression (NW) and then rotated by about 90° (perpendicular to the dike alignment) after the onset of surface deformation in mid-August 2005. Using 3D finite element models, we systematically evaluated the effects of tectonic stresses, volcanic edifice densities, and dike overpressures on the local stress field orientation. Combining data and models to generate “phase diagrams” of different stress controls by these competing effects, we argue that moderate tectonic stress of 2–3 MPa at 600 m above sea level slightly exceeded the edifice loading before the precursory deformation and was then overprinted by a local stress field from dike opening with an overpressure of ~15 MPa.

Alaska↗
USGS2021

Eruption of compositionally heterogeneous andesites from a complex storage region during the 2006 eruption of Augustine Volcano

Despite the common occurrence of heterogeneous andesitic eruptions, few studies have investigated the compositional effects on microlite crystallization and vesiculation in co-erupted natural samples. In 2006, Augustine Volcano erupted compositionally heterogeneous andesites that range from 56.4 to 63.3 wt% SiO 2 and include two endmember lithologic groups: low-silica andesite (LSA) and high-silica andesite (HSA). Textural and compositional differences between LSA and HSA end members are explored for two discrete, sequential vulcanian explosions from January 17 (event 9) and 27 (event 10), 2006. Groundmass glass compositions of pyroclasts within LSA and HSA compositional suites are not colinear and do not correlate with plagioclase microlite crystallinities, indicating eruption from multiple isolated shallow magma reservoirs with various pressure-temperature pathways. HSA pyroclasts have lower crystallinities, 0.02–0.24, than most LSA pyroclasts, 0.16–0.39, demonstrating the influence of composition on crystallinity. Additionally, microlite textural and groundmass glass compositional differences exist between consecutive vulcanian explosions. The event 9 deposits have a typical bimodal density distribution and groundmass glass compositions range from 65 to 78 wt% SiO 2 . Plagioclase microlite number densities (MN V ) are 10 4.6–6.4 mm −3 and crystallinities are 0.02 to 0.28, similar to products from other andesitic vulcanian eruptions. Deposits from the early phase of event 10 have a bimodal density distribution and contain a high proportion of LSA pyroclasts, similar to event 9. Groundmass glass compositions range from 72 to 79 wt% SiO 2 and plagioclase MN V are 10 5.9–6.3 mm −3 , forming narrower ranges compared to event 9. A transition occurred during the later phase of event 10 to a unimodal density distribution, a more homogeneous groundmass glass composition, 75–78 wt% SiO 2 , a higher proportion of HSA pyroclasts, and the highest MN V of 10 5.9–6.7 mm −3 . We interpret this shift to reflect eruption from reservoir depths around 4–6 km and the cessation of pre-eruptive magma staging in the upper conduit, transitioning the eruption to continuous and effusive phases. Attention to heterogeneous andesitic erupted products reveals additional details about heterogeneous shallow magma storage, variable upper conduit magma staging, and a range of pressure-temperature paths prior to fragmentation.

Alaska↗
USGS2020

Phase equilibrium of a high-SiO2, andesite at fO2 = RRO: Implications for Augustine volcano and other high-fO2 arc andesites

Understanding the impact of magmatic plumbing systems on explosive volcanic activity is important for hazard management. This study describes phase equilibria experiments using a high-silica andesite (HSA; SiO 2 = 62.5 wt%) from the 2006 eruption of Augustine Volcano, Alaska. Experiments were conducted under H 2 O saturated conditions, f 0 2 "> f 0 2 f02 = RRO (Re–ReO 2 or ~ Ni–NiO + 2), at pressures of 50–200 MPa ( P Total = P H2O ), and at temperatures of 800–1060 ° C. Run durations varied from 23 to 539 h, inversely scaled with temperature. The natural Augustine HSA phase assemblage (plagioclase, two pyroxenes, Fe–Ti oxides, magnesio-hornblende) was reproduced at 860–880 ° C and 120–200 MPa. Comparing experimental and natural glass and plagioclase compositions further refined those conditions to ~ 870 °C and 120–170 MPa. Crystallization of euhedral quartz was accompanied by biotite and small amounts of cummingtonite at T ≤ 850 °C. The relatively high temperature appearance of these typically low- T phases indicates that higher f 0 2 "> f 0 2 f02 could enhance their stability. The storage conditions estimated from our experiments compare well with previous magma plumbing system models for Augustine from geophysical and petrological data. The refined experimental pressure range suggests a storage depth of 4.6–6.6 km, assuming a crustal density of 2650 kg/m 3 . The strong petrological and geochemical similarities between the products of the 2006, 1986, and 1976 eruptions suggest that the Augustine magmatic system had generally consistent crystallization conditions for the HSA lithology during that > 30-year time interval. The experimental results broad implications for understanding higher f 0 2 "> f 0 2 magmas at andesitic arc volcanoes.

Alaska↗
USGS2014

Cogenetic late Pleistocene rhyolite and cumulate diorites from Augustine Volcano revealed by SIMS 238U-230Th dating of zircon, and implications for silicic magma generation by extraction from mush

Augustine Volcano, a frequently active andesitic island stratocone, erupted a late Pleistocene rhyolite pumice fall that is temporally linked through zircon geochronology to cumulate dioritic blocks brought to the surface in Augustine's 2006 eruption. Zircon from the rhyolite yield a 238 U- 230 Th age of ∼25 ka for their unpolished rims, and their interiors yield a bimodal age populations at ∼26 ka and a minority at ∼41 ka. Zircon from dioritic blocks, ripped from Augustine's shallow magmatic plumbing system and ejected during the 2006 eruption, have interiors defining a ∼26 ka age population that is indistinguishable from that for the rhyolite; unpolished rims on the dioritic zircon are dominantly younger (≤12 ka) indicating subsequent crystallization. Zircon from rhyolite and diorite overlap in U, Hf, Ti, and REE concentrations although diorites also contain a second population of high-U, high temperature grains. Andesites that brought dioritic blocks to the surface in 2006 contain zircon with young (≤9 ka) rims and a scattering of older ages, but few zircon that crystallized during the 26 ka interval. Both the Pleistocene-age rhyolite and the 2006 dioritic inclusions plot along a whole-rock compositional trend distinct from mid-Holocene–present andesites and dacites, and the diorites, rhyolite, and two early Holocene dacites define linear unmixing trends often oblique to the main andesite array and consistent with melt (rhyolite) extraction from a mush (dacites), leaving behind a cumulate amphibole-bearing residue (diorites). Rare zircon antecrysts up to ∼300 ka from all rock types indicate that a Quaternary center has been present longer than preserved surficial deposits.

Alaska↗
USGS2013

Pre-eruptive magmatic conditions at Augustine Volcano, Alaska, 2006: Evidence from amphibole geochemistry and textures

Variations in the geochemistry and texture of amphibole phenocrysts erupted from Augustine Volcano in 2006 provide new insights into pre- and syn-eruptive magma storage and mixing. Amphiboles are rare but present in all magma compositions (low- to high-silica andesites) from the 3 month long eruption. Unzoned magnesiohornblende in the high- and low-silica andesites exhibit limited compositional variability, relatively high SiO 2 (up to 49·7 wt %), and relatively low Al 2 O 3 (< 11·1 wt %). Intermediate-silica andesites and quenched mafic enclaves contain amphiboles that vary in composition (e.g. SiO 2 40·8–48·9 wt %, Al 2 O 3 6·52–15·2 wt %) and classification (magnesiohornblende–magnesiohastingsite–tschermakite). Compositional variation in amphibole is primarily controlled by temperature-dependent substitutions. Both high- and low-silica andesites represent remnant magmas that were stored in the shallow crust at 4–8 km depth, remaining distinct owing to a complex subsurface plumbing system. Intermediate-silica andesites and quenched mafic inclusions represent pre-eruptive hybrids of resident high- and low-silica andesite magmas and an intruding basalt. Amphiboles in explosive phase high-silica andesites are largely euhedral and unreacted, consistent with the high magma flux rates from depth during this phase (up to 13 800 m 3 s –1 ). Phenocrysts from the other lithologies have reaction rims that range from 1 to >1000 μm in thickness. Reaction rim microlite sizes correlate with reaction rim thicknesses. Reaction rims <50 μm thick contain microlites 1–10 μm in length whereas reaction rims >80 μm thick contain microlites 10–100 μm in length. Differentiating between heating- and decompression-induced amphibole reaction rim formation is problematic because of a lack of experimental constraints. We attempt a new approach to assessing reaction rim formation, based on a kinetic theory of crystal nucleation and growth, in which the differences in reaction rim textures represent different degrees of amphibole disequilibrium. Large crystals and low number densities suggest relatively lower levels of disequilibrium resulting in growth-dominated crystallization. Smaller crystals and larger number densities are indicative of higher nucleation rates and a high driving force.

Alaska↗
USGS2011

The Augustine magmatic system as revealed by seismic tomography and relocated earthquake hypocenters from 1994 through 2009

We incorporate 14 years of earthquake data from the Alaska Volcano Observatory with data from a 1975 controlled‐source seismic experiment to obtain the three‐dimensional P and S wave velocity structure and the first high‐precision earthquake locations at Augustine Volcano to be calculated in a fully three‐dimensional velocity model. Velocity tomography shows two main features beneath Augustine: a narrow, high‐velocity column beneath the summit, extending from ∼2 km depth to the surface, and elevated velocities on the south flank. Our relocation results allow a thorough analysis of the spatio‐temoral patterns of seismicity and the relationship to the magmatic and eruptive activity. Background seismicity is centered beneath the summit at an average depth of 0.6 km above sea level. In the weeks leading to the January 2006 eruption of Augustine, seismicity focused on a NW‐SE line along the trend of an inflating dike. A series of drumbeat earthquakes occurred in the early weeks of the eruption, indicating further magma transport through the same dike system. During the six months following the onset of the eruption, the otherwise quiescent region 1 to 5 km below sea level centered beneath the summit became seismically active with two groups of earthquakes, differentiated by frequency content. The deep longer‐period earthquakes occurred during the eruption and are interpreted as resulting from the movement of magma toward the summit, and the post‐eruptive shorter‐period earthquakes may be due to the relaxation of an emptied magma tube. The seismicity subsequently returned to its normal background rates and patterns.

Alaska↗
USGS2010

Seismic observations of Augustine Volcano, 1970-2007

Seismicity at Augustine Volcano in south-central Alaska was monitored continuously between 1970 and 2007. Seismic instrumentation on the volcano has varied from one to two short-period instruments in the early 1970s to a complex network comprising 8 to 10 short-period, 6 broadband, and 1 strong-motion instrument in 2006. Since seismic monitoring began, the volcano has erupted four times; a relatively minor eruption in 1971 and three major eruptions in 1976, 1986, and 2006. Each of the major eruptions was preceded by 9 to 10 months of escalating volcano-tectonic (VT) earthquake activity that began near sea level. The major eruptions are characterized seismically by explosive eruptions, rock avalanches, lahars, and periods of small repetitive low-frequency seismic events often called drumbeats that are associated with periods of lava effusion, and they all followed a similar pattern, beginning with an explosive onset that was followed by several months of discontinuous effusive activity. Earthquake hypocenters were observed to move upward from near sea level toward the volcano&rsquo;s summit over a roughly 9-month period before the 1976 and 1986 eruptions. The 1976 eruption was preceded by a small number of earthquakes that ranged in depth from 2 to 5 km below sea level. Earthquakes in this depth range were also observed following the 2006 eruption. The evolution of earthquake hypocenters associated with the three major eruptions, in conjunction with other supporting geophysical and geological observations, suggests that the Augustine magmatic system consists of a deeper magma source area at about 3.5 to 5 km below sea level and a shallower system of cracks near sea level where volatiles and magma may temporally reside as they ascend to the surface. The strong similarity in seismicity and character of the 1976, 1986, and 2006 eruptions suggests that the processes responsible for magma generation, rise, and eruption at Augustine Volcano have been roughly constant since the early 1970s.

Alaska↗
USGS2009

Volcanic processes and geology of Augustine Volcano, Alaska

Augustine Island (volcano) in lower Cook Inlet, Alaska, has erupted repeatedly in late-Holocene and historical times. Eruptions typically beget high-energy volcanic processes. Most notable are bouldery debris avalanches containing immense angular clasts shed from summit domes. Coarse deposits of these avalanches form much of Augustine's lower flanks. A new geologic map at 1:25,000 scale depicts these deposits, these processes. We correlate deposits by tephra layers calibrated by many radiocarbon dates.Augustine Volcano began erupting on the flank of a small island of Jurassic clastic-sedimentary rock before the late Wisconsin glaciation (late Pleistocene). The oldest known effusions ranged from olivine basalt explosively propelled by steam, to highly explosive magmatic eruptions of dacite or rhyodacite shed as pumice flows. Late Wisconsin piedmont glaciers issuing from the mountainous western mainland surrounded the island while dacitic eruptive debris swept down the south volcano flank.Evidence is scant for eruptions between the late Wisconsin and about 2,200 yr B.P. On a few south-flank inliers, thick stratigraphically low pumiceous pyroclastic-flow and fall deposits probably represent this period from which we have no radiocarbon dates on Augustine Island. Eruptions between about 5,350 and 2,200 yr B.P. we know with certainty by distal tephras. On Shuyak Island 100 km southeast of Augustine, two distal fall ashes of Augustinian chemical provenance (microprobe analysis of glass) date respectively between about 5,330 and 5,020 yr B.P. and between about 3,620 and 3,360 yr B.P. An Augustine ash along Kamishak Creek 70 km southwest of Augustine dates between about 3,850 and 3,660 yr B.P. A probably Augustinian ash lying within peat near Homer dates to about 2,275 yr B.P.From before 2,200 yr B.P. to the present, Augustine eruptive products abundantly mantle the island. During this period, numerous coarse debris avalanches swept beyond Augustine's coast, most recently in A.D. 1883. The decapitated summit after the 1883 eruption, replaced by andesite domes of six eruptions since, shows a general process: collapse of steep summit domes, then the summit regrown by later dome eruptions. The island's stratigraphy is based on six or seven coarse-pumice tephra "marker beds." In upward succession they are layers G (2,100 yr B.P.), I (1,700 yr B.P.), H (1,400 yr B.P.), C (1,200-1,000 yr B.P.), M (750 yr B.P.), and B (390 yr B.P.).A coarse, hummocky debris-avalanche deposit older than about 2,100 yr B.P.-or perhaps a stack of three of them-lies along the east coast, the oldest exposed such bouldery diamicts on Augustine Island. Two large debris avalanches swept east and southeast into the sea between about 2,100 and 1,800 yr B.P. A large debris avalanche shed east and east-northeast into the sea between 1,700 and 14,00 yr B.P.Between about 1,400 and 1,100 yr B.P. debris avalanches swept into the sea on the volcano's south, southwest, and north-northwest. Pumiceous pyroclastic fans spread to the southeast and southwest, lithic pyroclastic flows and lahars (?) to the south and southeast. Pyroclastic flows, pyroclastic surges, and lahars swept down the west and south flanks between about 1,000 and 750 yr B.P.A debris avalanche swept into the sea on the west, and a small one on the south-southeast, between about 750 and 400 yr B.P. Large lithic pyroclastic flows shed to the southeast; smaller ones descended existing swales on the southwest and south.Between about 400 yr B.P. and historical time (late 1770s), three debris avalanches swept into the sea on the west-northwest, north-northwest, and north flanks. One of them (West Island) was large and fast: most of it rode to sea far beyond a former sea cliff, and its surface includes geomorphic evidence of having initiating a tsunami. Augustine's only conspicuous lava flow erupted on the north flank.During this prehistoric period numerous domes grew at the volcano's summit, remnants of which form the east and south sides of the present summit-dome complex. Three domes grew below the summit area on the upper south and northwest flanks. In between large eruptions that deposited coarse pumiceous fall beds, many smaller eruptions emplaced beds of sand-sized ash on the volcano flanks.During the past 750 years, beach and back-beach eolian dunes accreted at the southwest coast, forming a ribbed coastwise topography. Lesser dunes grew at the backs of beaches in coves on other flanks.An eruption in 1883 shed a debris avalanche swiftly into the sea on the north-northeast, followed by pyroclastic flows and surges. Eruptions in 1935 and 1963-64 grew summit domes that spilled over the southwest and south flanks and shed coarse rubbly lithic pyroclastic flows down those flanks. Eruptions and 1976 and 1986 grew domes that draped down the north flank and shed voluminous pyroclastic flows to the northeast through north-northwest flanks, when smaller pyroclastic flows and (or) lahars swept down other flanks. A small dome-building eruption in January-March 2006 after this report was all but complete we treat only fleetingly. The largest debris avalanches sweep into the sea at Augustine's coast at speeds inferred between 60 and 80 m/s. Augustine is capable of initiating damaging tsunami to lower Cook Inlet, but geologic evidence for them on the mainland is sporadic and sparse.

Alaska↗
USGS2008

Deformation of the Augustine Volcano, Alaska, 1992-2005, measured by ERS and ENVISAT SAR interferometry

The Augustine Volcano is a conical-shaped, active stratovolcano located on an island of the same name in Cook Inlet, about 290 km southwest of Anchorage, Alaska. Augustine has experienced seven significant explosive eruptions - in 1812, 1883, 1908, 1935, 1963, 1976, 1986, and in January 2006. To measure the ground surface deformation of the Augustine Volcano before the 2006 eruption, we applied satellite radar interferometry using Synthetic Aperture Radar (SAR) images from three descending and three ascending satellite tracks acquired by European Remote Sensing Satellite (ERS) 1 and 2 and the Environment Satellite (ENVISAT). Multiple interferograms were stacked to reduce artifacts caused by atmospheric conditions, and we used a singular value decomposition method to retrieve the temporal deformation history from several points on the island. Interferograms during 1992 and 2005 show a subsidence of about 1-3 cm/year, caused by the contraction of pyroclastic flow deposits from the 1986 eruption. Subsidence has decreased exponentially with time. Multiple interferograms between 1992 and 2005 show no significant inflation around the volcano before the 2006 eruption. The lack of a pre-eruption deformation signal suggests that the deformation signal from 1992 to August 2005 must have been very small and may have been obscured by atmospheric delay artifacts.

Alaska↗
USGS2007

SAR measurements of surface displacements at Augustine Volcano, Alaska from 1992 to 2005

Augustine volcano is an active stratovolcano located at the southwest of Anchorage, Alaska. Augustine volcano had experienced seven significantly explosive eruptions in 1812, 1883, 1908, 1935, 1963, 1976, and 1986, and a minor eruption in January 2006. We measured the surface displacements of the volcano by radar interferometry and GPS before and after the eruption in 2006. ERS-1/2, RADARSAT-1 and ENVISAT SAR data were used for the study. Multiple interferograms were stacked to reduce artifacts caused by different atmospheric conditions. Least square (LS) method was used to reduce atmospheric artifacts. Singular value decomposition (SVD) method was applied for retrieval of time sequential deformations. Satellite radar interferometry helps to understand the surface displacements system of Augustine volcano.

Alaska↗
USGS2006

Local infrasound observations of large ash explosions at Augustine Volcano, Alaska, during January 11–28, 2006

We present and interpret acoustic waveforms associated with a sequence of large explosion events that occurred during the initial stages of the 2006 eruption of Augustine Volcano, Alaska. During January 11–28, 2006, 13 large explosion events created ash-rich plumes that reached up to 14 km a.s.l., and generated atmospheric pressure waves that were recorded on scale by a microphone located at a distance of 3.2 km from the active vent. The variety of recorded waveforms included sharp N-shaped waves with durations of a few seconds, impulsive signals followed by complex codas, and extended signals with emergent character and durations up to minutes. Peak amplitudes varied between 14 and 105 Pa; inferred acoustic energies ranged between 2×10 8 and 4×10 9 J. A simple N-shaped short-duration signal recorded on January 11, 2006 was associated with the vent-opening blast that marked the beginning of the explosive eruption sequence. During the following days, waveforms with impulsive onsets and extended codas accompanied the eruptive activity, which was characterized by explosion events that generated large ash clouds and pyroclastic flows along the flanks of the volcano. Continuous acoustic waveforms that lacked a clear onset were more common during this period. On January 28, 2006, the occurrence of four large explosion events marked the end of this explosive eruption phase at Augustine Volcano. After a transitional period of about two days, characterized by many small discrete bursts, the eruption changed into a stage of more sustained and less explosive activity accompanied by the renewed growth of a summit lava dome.

Alaska↗
USGS2006

Thickness distribution of a cooling pyroclastic flow deposit on Augustine Volcano, Alaska: Optimization using InSAR, FEMs, and an adaptive mesh algorithm

Interferometric synthetic aperture radar (InSAR) imagery documents the consistent subsidence, during the interval 1992–1999, of a pyroclastic flow deposit (PFD) emplaced during the 1986 eruption of Augustine Volcano, Alaska. We construct finite element models (FEMs) that simulate thermoelastic contraction of the PFD to account for the observed subsidence. Three-dimensional problem domains of the FEMs include a thermoelastic PFD embedded in an elastic substrate. The thickness of the PFD is initially determined from the difference between post- and pre-eruption digital elevation models (DEMs). The initial excess temperature of the PFD at the time of deposition, 640 °C, is estimated from FEM predictions and an InSAR image via standard least-squares inverse methods. Although the FEM predicts the major features of the observed transient deformation, systematic prediction errors (RMSE = 2.2 cm) are most likely associated with errors in the a priori PFD thickness distribution estimated from the DEM differences. We combine an InSAR image, FEMs, and an adaptive mesh algorithm to iteratively optimize the geometry of the PFD with respect to a minimized misfit between the predicted thermoelastic deformation and observed deformation. Prediction errors from an FEM, which includes an optimized PFD geometry and the initial excess PFD temperature estimated from the least-squares analysis, are sub-millimeter (RMSE = 0.3 mm). The average thickness (9.3 m), maximum thickness (126 m), and volume (2.1 × 10 7 m 3 ) of the PFD, estimated using the adaptive mesh algorithm, are about twice as large as the respective estimations for the a priori PFD geometry. Sensitivity analyses suggest unrealistic PFD thickness distributions are required for initial excess PFD temperatures outside of the range 500–800 °C.

Alaska↗