Geology topics

Kristi L. Wallace

Publications and source records attributed to Kristi L. Wallace.

At least 55 records · Page 3Linked to original sources

USGS2017

The 2014 eruptions of Pavlof Volcano, Alaska

Pavlof Volcano is one of the most frequently active volcanoes in the Aleutian Island arc, having erupted more than 40 times since observations were first recorded in the early 1800s . The volcano is located on the Alaska Peninsula (lat 55.4173° N, long 161.8937° W), near Izembek National Wildlife Refuge. The towns and villages closest to the volcano are Cold Bay, Nelson Lagoon, Sand Point, and King Cove, which are all within 90 kilometers (km) of the volcano (fig. 1). Pavlof is a symmetrically shaped stratocone that is 2,518 meters (m) high, and has about 2,300 m of relief. The volcano supports a cover of glacial ice and perennial snow roughly 2 to 4 cubic kilometers (km 3 ) in volume, which is mantled by variable amounts of tephra fall, rockfall debris, and pyroclastic-flow deposits produced during historical eruptions. Typical Pavlof eruptions are characterized by moderate amounts of ash emission, lava fountaining, spatter-fed lava flows, explosions, and the accumulation of unstable mounds of spatter on the upper flanks of the volcano. The accumulation and subsequent collapse of spatter piles on the upper flanks of the volcano creates hot granular avalanches, which erode and melt snow and ice, and thereby generate watery debris-flow and hyperconcentrated-flow lahars. Seismic instruments were first installed on Pavlof Volcano in the early 1970s, and since then eruptive episodes have been better characterized and specific processes have been documented with greater certainty. The application of remote sensing techniques, including the use of infrasound data, has also aided the study of more recent eruptions. Although Pavlof Volcano is located in a remote part of Alaska, it is visible from Cold Bay, Sand Point, and Nelson Lagoon, making distal observations of eruptive activity possible, weather permitting. A busy air-travel corridor that is utilized by a numerous transcontinental and regional air carriers passes near Pavlof Volcano. The frequency of air travel across the region results in a relatively large number of airborne observations of eruptive activity. During the 2014 Pavlof eruptions, the Alaska Volcano Observatory received observations and photographs from pilots and local observers, which aided evaluation of the eruptive activity and the areas affected by eruptive products. This report outlines the chronology of events associated with the 2014 eruptive activity at Pavlof Volcano, provides documentation of the style and character of the eruptive episodes, and reports briefly on the eruptive products and impacts. The principal observations are described and portrayed on maps and photographs, and the 2014 eruptive activity is compared to historical eruptions.

Alaska↗

USGS2017

2015 Volcanic activity in Alaska—Summary of events and response of the Alaska Volcano Observatory

The Alaska Volcano Observatory (AVO) responded to eruptions, volcanic unrest or suspected unrest, and seismic events at 14 volcanic centers in Alaska during 2015. The most notable volcanic activity consisted of continuing intermittent ash eruptions from Cleveland and Shishaldin volcanoes in the Aleutian Islands. Two eruptive episodes, at Veniaminof and Pavlof, on the Alaska Peninsula ended in 2015. During 2015, AVO re-established the seismograph network at Aniakchak, installed six new broadband seismometers throughout the Aleutian Islands, and added a Multiple component Gas Analyzer System (MultiGAS) station on Augustine.

Alaska↗

USGS2017

Reducing risk where tectonic plates collide—U.S. Geological Survey subduction zone science plan

The U.S. Geological Survey (USGS) serves the Nation by providing reliable scientific information and tools to build resilience in communities exposed to subduction zone earthquakes, tsunamis, landslides, and volcanic eruptions. Improving the application of USGS science to successfully reduce risk from these events relies on whole community efforts, with continuing partnerships among scientists and stakeholders, including researchers from universities, other government labs and private industry, land-use planners, engineers, policy-makers, emergency managers and responders, business owners, insurance providers, the media, and the general public. Motivated by recent technological advances and increased awareness of our growing vulnerability to subduction-zone hazards, the USGS is uniquely positioned to take a major step forward in the science it conducts and products it provides, building on its tradition of using long-term monitoring and research to develop effective products for hazard mitigation. This science plan provides a blueprint both for prioritizing USGS science activities and for delineating USGS interests and potential participation in subduction zone science supported by its partners. The activities in this plan address many USGS stakeholder needs: High-fidelity tools and user-tailored information that facilitate increasingly more targeted, neighborhood-scale decisions to mitigate risks more cost-effectively and ensure post-event operability. Such tools may include maps, tables, and simulated earthquake ground-motion records conveying shaking intensity and frequency. These facilitate the prioritization of retrofitting of vulnerable infrastructure; Information to guide local land-use and response planning to minimize development in likely hazardous zones (for example, databases, maps, and scenario documents to guide evacuation route planning in communities near volcanoes, along coastlines vulnerable to tsunamis, and built on landslide-prone terrain); New tools to assess the potential for cascading hazards, such as landslides, tsunamis, coastal changes, and flooding caused by earthquakes or volcanic eruptions; Geospatial models of permanent, widespread land- and sea-level changes that may occur in the immediate aftermath of great ( M ≥8.0) subduction zone earthquakes; Strong partnerships between scientists and public safety providers for effective decision making during periods of elevated hazard and risk; Accurate forecasts of far-reaching hazards (for example, ash clouds, tsunamis) to avert catastrophes and unnecessary disruptions in air and sea transportation; Aftershock forecasts to guide decisions about when and where to re-enter, repair, or rebuild buildings and infrastructure, for all types of subduction zone earthquakes.

Circular↗

USGS2016

Late Pleistocene and Holocene tephrostratigraphy of interior Alaska and Yukon: Key beds and chronologies over the past 30,000 years

The Aleutian Arc-Alaska Peninsula and Wrangell volcanic field are the main source areas for tephra deposits found across Alaska and northern Canada, and increasingly, tephra from these eruptions have been found further afield in North America, Greenland, and Europe. However, there have been no broad scale reviews of the Late Pleistocene and Holocene tephrostratigraphy for this region since the 1980s, and this lack of data is hindering progress in identifying these tephra both locally and regionally. To address this gap and the variable quality of associated geochemical and chronological data, we undertake a detailed review of the latest Pleistocene to Holocene tephra found in interior Alaska and Yukon. This paper discusses nineteen tephra that have distributions beyond southwest Alaska and that have the potential to become, or already are, important regional markers. This includes three ‘modern’ events from the 20th century, ten with limited data availability but potentially broad distributions, and six that are widely reported in interior Alaska and Yukon. Each tephra is assessed in terms of chronology, geochemistry and distribution, with new Bayesian age estimates and geochemical data when possible. This includes new major-element geochemical data for Crater Peak 1992, Redoubt 1989–90, and two andesitic tephra from St Michael Island (Tephra D), as well as revised age estimates for Dawson tephra, Oshetna, Hayes set H, Aniakchak CFE II, and the White River Ashes, northern and eastern lobes.

Quaternary Science Reviews↗

USGS2015

Hail formation triggers rapid ash aggregation in volcanic plumes

During explosive eruptions, airborne particles collide and stick together, accelerating the fallout of volcanic ash and climate-forcing aerosols. This aggregation process remains a major source of uncertainty both in ash dispersal forecasting and interpretation of eruptions from the geological record. Here we illuminate the mechanisms and timescales of particle aggregation from a well-characterized ‘wet’ eruption. The 2009 eruption of Redoubt Volcano in Alaska incorporated water from the surface (in this case, a glacier), which is a common occurrence during explosive volcanism worldwide. Observations from C-band weather radar, fall deposits, and numerical modeling demonstrate that volcanic hail formed rapidly in the eruption plume, leading to mixed-phase aggregation of ~95% of the fine ash and stripping much of the cloud out of the atmosphere within 30 minutes. Based on these findings, we propose a mechanism of hail-like aggregation that contributes to the anomalously rapid fallout of fine ash and the occurrence of concentrically-layered aggregates in volcanic deposits.

Alaska↗

USGS2015

'Is Ash Falling?', an online ashfall reporting tool in support of improved ashfall warnings and investigations of ashfall processes

The primary volcano hazard in Alaska is airborne ash, which endangers aircraft flying the busy North Pacific air routes and consequently affects global commerce. Downwind ashfall is also a significant threat to commerce, transportation and day-to-day activities in nearby Alaska communities. A web-enabled database, "Is Ash Falling?" has been developed to collect ashfall observations and encourage sample collections from the public during eruptions, enabling volcano observatory staff to concentrate on eruption response. Knowing the locations of filed ashfall reports improves public ashfall warnings and forecasts by providing on-the-ground checks for ash dispersion and fallout computer models and satellite imagery interpretation. Reports of ashfall are shared with emergency management agencies and the wider public. These reports also give scientists a more complete record of the amount, duration and other conditions of ashfall.

Journal of Applied Volcanology↗

USGS2014

Significance of a near-source tephra-stratigraphic sequence to the eruptive history of Hayes Volcano, south-central Alaska

Bluffs along the Hayes River valley, 31 km northeast and 40 km downstream from Hayes Volcano, reveal volcanic deposits that shed new light on its eruptive history. Three thick (>10 cm) and five thin (<10 cm) tephra-fall deposits are dacitic in whole rock composition and contain high proportions of amphibole to pyroxene and minor biotite and broadly correlate to Hayes tephra set H defined by earlier investigators. Two basal ages for the tephra-fall sequence of 3,690±30 and 3,750±30 14 C yr B.P. are also consistent with the Hayes tephra set H timeframe. Distinguishing among Hayes tephra set H units is critical because the set is an important time-stratigraphic marker in south-central Alaska and this section provides a new reference section for Hayes tephra set H. Analysis of Fe-Ti oxide grains in the tephras shows promise for identifying individual Hayes deposits. Beneath the dacitic tephra sequence lies an older, poorly sorted tephra (tephra A) that contains dacite and rhyolite lapilli and whose basal age is 4,450±30 14 C yr B.P. Immediately below the tephra-fall sequence (Unit III) lies a series of mass-flow deposits that are rich in rhyodacitic clasts (Unit II). Below Unit II and possibly coeval with it, is a 20–30 m thick pumiceous pyroclastic-flow deposit (Unit I) that extends to the valley floor. Here informally named the Hayes River ignimbrite, this deposit contains pumice clasts of rhyolite with quartz, sanidine, plagioclase, and biotite phenocrysts, an assemblage that is unique among known Quaternary volcanic products of Hayes and other Alaskan volcanoes. Units I, II, and tephra A of Unit III represent at least two previously unrecognized eruptions of Hayes Volcano that occurred prior to ~3,700 yr B.P. No compositionally equivalent distal tephra deposits correlative with Hayes Volcano rhyodacites or rhyolites have yet been identified, perhaps indicating that some of these deposits are pre-Holocene, and were largely removed by glacial ice during the last ice age. More field and analytical work is needed to further refine the eruptive history of Hayes Volcano.

Alaska↗

USGS2013

Early and late Holocene glacial fluctuations and tephrostratigraphy, Cabin Lake, Alaska

Marked changes in sediment types deposited in Cabin Lake, near Cordova, Alaska, represent environmental shifts during the early and late Holocene, including fluctuations in the terminal position of Sheridan Glacier. Cabin Lake is situated to receive meltwater during periods when the outwash plain of the advancing Sheridan Glacier had aggraded. A brief early Holocene advance from 11.2 to 11.0 cal ka is represented by glacial rock flour near the base of the sediment core. Non-glacial lake conditions were restored for about 1000 years before the water level in Cabin Lake lowered and the core site became a fen. The fen indicates drier-than-present conditions leading up to the Holocene thermal maximum. An unconformity spanning 5400 years during the mid-Holocene is overlain by peat until 1110 CE when meltwater from Sheridan Glacier returned to the basin. Three intervals of an advanced Sheridan Glacier are recorded in the Cabin Lake sediments during the late Holocene: 1110–1180, 1260–1540 and 1610–1780 CE. The sedimentary sequence also contains the first five reported tephra deposits from the Copper River delta region, and their geochemical signatures suggest that the sources are the Cook Inlet volcanoes Redoubt, Augustine and Crater Peak, and possibly Mt Churchill in the Wrangell Volcanic field.

Alaska↗

USGS2013

Andesites of the 2009 eruption of Redoubt Volcano, Alaska

Crystal-rich andesites that erupted from Redoubt Volcano in 2009 range from 57.5 to 62.5 wt.% SiO 2 and have phenocryst and phenocryst-melt relations consistent with staging in the upper crust. Early explosive products are low-silica andesites (LSA, < 58 wt.% SiO 2 ) that ascended from deeper crustal levels during or before the 6 months of precursory activity, but a broad subsequent succession to more evolved and cooler products, and predominantly effusive dome growth, are interpreted to result from progressive mobilization and mixing with differentiated magmas tapped from pre-2009 Redoubt intrusions at ~ 3–6 km depth. Initial explosions on March 23–28 ejected predominantly LSA with a uniform phenocryst assemblage of high-Al amphibole, ~ An 70 plagioclase, ortho- and clinopyroxene, FeTi oxides (890 to 960 °C), and traces of magmatic sulfide. Melt in the dominant microlite-poor LSA was compositionally uniform dacite (67–68 wt.% SiO 2 ) but ranged to rhyolite with greater microlite growth. Minor amounts of intermediate- to high-silica andesite (ISA, HSA; 59–62.5 wt.% SiO 2 ) also erupted during the early explosions and most carried rhyolitic melt (72–74 wt.% SiO 2 ). A lava dome grew following the initial tephra-producing events but was destroyed by an explosion on April 4. Ejecta from the April 4 explosion consists entirely of ISA and HSA, as does a subsequent lava dome that grew April 4–July 1; LSA was absent. Andesites from the April 4 event and from the final dome had pre-eruptive temperatures of 725–840 °C (FeTi oxides) and highly evolved matrix liquids (77–80 wt.% SiO 2 ), including in rare microlite-free pyroclasts. ISA has mixed populations of phenocrysts suggesting it is a hybrid between HSA and LSA. The last lavas from the 2009 eruption, effused May 1–July 1, are distinctly depleted in P 2 O 5 , consistent with low temperatures and high degrees of crystallization including apatite. Plagioclase–melt hygrometry and comparison to phase equilibrium experiments are consistent with pre-eruptive storage of all three magma types at 100–160 MPa (4–6 km depth), if they were close to H 2 O-saturation, coincident with the locus of shallow syn-eruptive seismicity. Deeper storage would be indicated if the magmas were CO 2 -rich. Relatively coarse-grained clinopyroxene-rich reaction rims on many LSA amphibole phenocrysts may result from slow ascent to, or storage at, depths shallow enough for the onset of appreciable H 2 O exsolution, consistent with pre-eruptive staging in the uppermost crust. We interpret that the 2009 LSA ascended from depth during the 8 or more months prior to the first eruption, but that the magma stalled and accumulated in the upper crust where its phenocryst rim and melt compositions were established. Ascent of LSA through stagnant mushy intrusions residual from earlier Redoubt activity mobilized differentiated magma pockets and interstitial liquids represented by HSA, and as LSA–HSA hybrids represented by ISA, that fed the subsequently erupted lava domes.

Alaska↗

USGS2013

Injection, transport, and deposition of tephra during event 5 at Redoubt Volcano, 23 March, 2009

Among the events of the 2009 eruption at Redoubt Volcano, Alaska, event 5 was the best documented by radar, satellite imagery, and deposit mapping. We use the new Eulerian tephra transport model Ash3d to simulate transport and deposition of event 5 tephra at distances up to 350 km. The eruption, which started at about 1230 UTC on 23 March, 2009, sent a plume from the vent elevation (estimated at 2.3 ± 0.1 km above sea level or a.s.l.) to about 16 ± 2 km above sea level in 5 min. The plume was a few kilometers higher than would be expected for the estimated average mass eruption rate and atmospheric conditions, possibly due to release of most of the eruptive mass in the first half of the 20-minute event. The eruption injected tephra into a wind field of high shear, with weak easterly winds below ~ 3 km elevation, strong southerly winds at 6–10 km and weak westerlies above ~ 16 km. Model simulations in this wind field predicted development of a northward-migrating inverted “v”-shaped cloud with a southwest-trending arm at a few kilometers elevation, which was not visible in IR satellite images due to cloud cover, and a southeast-trending arm at > 10 km elevation that was clearly visible. Simulations also predicted a deposit distribution that strongly depended on plume height: a plume height below 15 km predicted ash deposits that were located west of those mapped, whereas good agreement was reached with a modeled plume height of 15–18 km. Field sampling of the deposit found it to contain abundant tephra aggregates, which accelerated the removal of tephra from the atmosphere. We were able to reasonably approximate the effect of aggregation on the deposit mass distribution by two methods: (1) adjusting the grain-size distribution, taking the erupted mass < = 0.063 mm in diameter and distributing it evenly into bins of coarser size; and (2) moving 80–90% of the mass < = 0.063 mm into a single particle bin ranging in size from 0.25 to 1 mm. These methods produced an area inside the 100 g m − 2 isomass lines that was within a few tens of percent of mapped area; however they under-predicted deposit mass at very proximal (< 50 km) and very distal (> 250 km) locations. Modeled grain-size distributions at sample locations are also generally coarser than observed. The mismatch may result from a combination of limitations in field sampling, approximations inherent in the model, errors in the numerical wind field, and aggregation of particles larger than 0.063 mm.

Alaska↗

USGS2013

Character, mass, distribution, and origin of tephra-fall deposits from the 2009 eruption of Redoubt Volcano, Alaska: highlighting the significance of particle aggregation

The 2009 eruption of Redoubt Volcano included 20 tephra-producing explosions between March 15, 2009 and April 4, 2009 (UTC). Next-Generation radar (NEXRAD) data show that plumes reached heights between 4.6 km and 19 km asl and were distributed downwind along nearly all azimuths of the volcano. Explosions lasted between < 1 and 31 min based on the signal duration at a distal seismic station (86 km). From Moderate Resolution Imaging Spectroradiometer (MODIS) imagery and field data, we estimate that over 80,000 km 2 received at least minor ash fall (> 0.8 mm thick), including communities along the Kenai Peninsula (80–100 km) and the city of Anchorage (170 km). Trace ash (< 0.8 mm) was reported as far as Fairbanks, 550 km NNE of the volcano. We estimate the total mass of tephra-fall deposits at 54.6 × 10 9 kg with a total DRE volume of 20.6 × 106 m 3 . On March 15, a small (4.6 km asl) phreatic explosion containing minor, non-juvenile ash, erupted through the summit ice cap. The first five magmatic explosions (events 1–5) occurred within a 6-hour period on March 23. Plumes rose to heights between 5.5 km and 14.9 km asl during 2- to 20-minute-duration explosions, and were dispersed mainly along a NNE trajectory. Trace ash fall was reported as far as Fairbanks. Owing to a shift in wind direction and heavy snowfall during these events, field discrimination among many of these layers was possible. All deposits comprise a volumetrically significant amount of particle aggregates, yet only event 5 deposits contain coarse clasts including glacier ice. The most voluminous tephra fall was deposited on March 24 (event 6) from a 15 minute explosion that sent a plume to 18.3 km asl, and dispersed tephra to the WNW. Within 10 km of the vent, this deposit contains 1–11 cm pumice clasts in a matrix of 1–2 mm aggregate lapilli. A small dome was presumably emplaced between March 23 and March 26 and was subsequently destroyed during 1–14 minute magmatic explosions of events 7–8 (March 26) that sent plumes between 8.2 km and 19 km asl. Ash fell along a broad swath to the ESE, covering communities along the Kenai Peninsula with up to 1 mm of ash. Proximal deposits are largely composed of aggregate lapilli of 1–2 mm with very little coarse juvenile material. Events 9–18 (March 27) sent plumes between 5.2 km and 15.5 km asl during < 1–11-minute-long explosions. Ash clouds dispersed along trajectories to the NE, ENE and N and event 17 deposited up to 1 mm of ash on upper Kenai Peninsula and Anchorage. A moderate-size dome was emplaced between March 29 and April 4 and was subsequently destroyed during event 19 on April 4 which lasted 31 min and sent ash to 15.2 km asl. The proximal deposit is principally composed of dense dome rock, unlike earlier events, indicating that event 19 was likely caused by dome failure. The cloud dispersed to the SE along a narrow trajectory and up to 1–2 mm of ash fell on the lower Kenai Peninsula. Particle size data showing a preponderance of fine ash, even in the most proximal locations, along with the abundance of aggregate lapilli documented in most samples, confirms that particle aggregation played a significant role in the 2009 eruption and induced premature fallout of fine ash.

Alaska↗

USGS2013

Constructing a reference tephrochronology for Augustine Volcano, Alaska

Augustine Volcano is the most historically active volcano in Alaska's populous Cook Inlet region. Past on-island work on pre-historic tephra deposits mainly focused on using tephra layers as markers to help distinguish among prevalent debris-avalanche deposits on the island (Waitt and Beget, 2009, USGS Prof Paper 1762), or as source material for petrogenetic studies. No comprehensive reference study of tephra fall from Augustine Volcano previously existed. Numerous workers have identified Holocene-age tephra layers in the region surrounding Augustine Island, but without well-characterized reference deposits, correlation back to the source volcano is difficult. The purpose of this detailed tephra study is to provide a record of eruption frequency and magnitude, as well as to elucidate physical and chemical characteristics for use as reference standards for comparison with regionally distributed Augustine tephra layers. Whole rock major- and trace-element geochemistry, deposit componentry, and field context are used to correlate tephra units on the island where deposits are coarse grained. Major-element glass geochemistry was collected for use in correlating to unknown regional tephra. Due to the small size of the volcanic island (9 by 11 km in diameter) and frequent eruptive activity, on-island exposures of tephra deposits older than a couple thousand years are sparse, and the lettered Tephras B, M, C, H, I, and G of Waitt and Beget (2009) range in age from 370-2200 yrs B.P. There are, however, a few exposures on the south side of the volcano, within about 2 km of the vent, where stratigraphic sections that extend back to the late Pleistocene glaciation include coarse pumice-fall deposits. We have linked the letter-named tephras from the coast to these higher exposures on the south side using physical and chemical characteristics of the deposits. In addition, these exposures preserve at least 5 older major post-glacial eruptions of Augustine. These ultra-proximal sites, along with an off-island section 20 km to the west, provide the first continuous tephrochronology for Augustine that extends from the earliest to latest Holocene. Because examined pumice-fall exposures are limited to a narrow azimuth on the south side of the volcano, the on-island record is likely an incomplete catalog of major eruptions. It is possible however, that the coarse-grained near vent exposures (within 2 km) represent large eruptions that blanketed the entire island in tephra and are representative of the entire Holocene record. The major Holocene tephra units exposed on-island are composed of coarse-grained (cm-scale) pumice ranging in color from white to cream (variably oxidized), and light to medium gray as well as banded varieties. Accidental lithic assembles are highly variable and often unique for individual eruptions. Pumices range from 60-66 wt % SiO2 in whole-rock composition and are distinguishable using trace and minor element abundances and field context. Glass geochemistry is often distinguishable between tephras, but more overlap exists among deposits and presents challenges for correlating to regional tephras.

Alaska↗

USGS2011

The reawakening of Alaska's Augustine volcano

Augustine volcano, in south central Alaska, ended a 20-year period of repose on 11 January 2006 with 13 explosive eruptions in 20 days. Explosive activity shifted to a quieter effusion of lava in early February, forming a new summit lava dome and two short, blocky lava flows by late March (Figure 1). The eruption was heralded by eight months of increasing seismicity, deformation, gas emission, and small phreatic eruptions, the latter consisting of explosions of steam and debris caused by heating and expansion of groundwater due to an underlying heat source.

Alaska↗

USGS2010

Aviation response to a widely dispersed volcanic ash and gas cloud from the August 2008 eruption of Kasatochi, Alaska, USA

The extensive volcanic cloud from Kasatochi's 2008 eruption caused widespread disruptions to aviation operations along Pacific oceanic, Canadian, and U.S. air routes. Based on aviation hazard warnings issued by the National Oceanic and Atmospheric Administration, U.S. Geological Survey, the Federal Aviation Administration, and Meteorological Service of Canada, air carriers largely avoided the volcanic cloud over a 5 day period by route modifications and flight cancellations. Comparison of time coincident GOES thermal infrared (TIR) data for ash detection with Ozone Monitoring Instrument (OMI) ultraviolet data for SO 2 detection shows congruent areas of ash and gas in the volcanic cloud in the 2 days following onset of ash production. After about 2.5 days, the area of SO 2 detected by OMI was more extensive than the area of ash indicated by TIR data, indicating significant ash depletion by fall out had occurred. Pilot reports of visible haze at cruise altitudes over Canada and the northern United States suggested that SO 2 gas had converted to sulfate aerosols. Uncertain about the hazard potential of the aging cloud, airlines coped by flying over, under, or around the observed haze layer. Samples from a nondamaging aircraft encounter with Kasatochi's nearly 3 day old cloud contained volcanic silicate particles, confirming that some fine ash is present in predominantly gas clouds. The aircraft's exposure to ash was insufficient to cause engine damage; however, slightly damaging encounters with volcanic clouds from eruptions of Reventador in 2002 and Hekla in 2000 indicate the possibility of lingering hazards associated with old and/or diffuse volcanic clouds.

Alaska↗

USGS2010

An improved proximal tephrochronology for Redoubt Volcano, Alaska

Sediment cores from lakes in volcanically active regions can be used to reconstruct the frequency of tephra-fall events. We studied sediment cores from two lakes within 25 km of the summit of Redoubt Volcano, western Cook Inlet, to develop a robust age model for the Holocene tephrochronology, and to assess the extent to which the tephrostratigraphies were correlative between the two nearby lakes. Visually distinct tephra layers were correlated among cores from Bear and Cub lakes, located within 17 km of each other, to construct a composite age model, which incorporates two Pu-activity profiles and 27 radiocarbon ages, and extends the record back to 11,540 cal a BP. The age model was used to interpolate the ages and quantify the uncertainties of ages for all tephras at least 1 mm thick. Between − 55 and 3850 a BP, 31 tephras were deposited in Bear Lake and 41 tephras in Cub Lake. Bear Lake contains an additional 38 tephras deposited between 11,540 and 3850 a BP. During the period of overlap, (− 55 to 3850 a BP), 24 tephras are of significantly different ages, including nine from Bear Lake and 17 from Cub Lake. The presence of these unique tephras indicates that ejecta plumes erupted from Redoubt Volcano can be highly directional, and that sediment cores from more than one lake are needed for a comprehensive reconstruction of tephra-fall events. Unlike distal lakes in south Alaska, where geomorphic and limnological factors dominate the quality of the tephrostratigraphic record, the variability in tephra-fall trajectory near a Redoubt Volcano appears to be a major control on the number of tephras contained in the sediment of proximal lakes.

Alaska↗

USGS2010

Public outreach and communications of the Alaska Volcano Observatory during the 2005-2006 eruption of Augustine Volcano: Chapter 27 in The 2006 eruption of Augustine Volcano, Alaska

The 2005-6 eruption of Augustine Volcano in the Cook Inlet region, Alaska, greatly increased public desire for volcano hazard information, as this eruption was the most significant in Cook Inlet since 1992. In response to this heightened concern, the Alaska Volcano Observatory (AVO) increased ongoing efforts to deliver specific eruption-focused information to communities nearest to the volcano, created a public communications strategy to assist staff with managing requests, and used the recently upgraded AVO Web site as a primary information-delivery path. During the eruption, AVO responded to a minimum of ~1,700 individual requests for information from the media, the public, and other organizations with responsibilities associated with volcanic activity in Alaska; requests were received both as phone calls to the observatory and e-mail stemming from the AVO Web site. Staff also delivered approximately two dozen Augustine-specific presentations and gave nearly three dozen tours of the AVO Anchorage Operations Center in Anchorage. This intensity of public interaction was markedly higher than during noneruptive periods. During the Augustine unrest and eruption, AVO also refined its internal communication procedures, instituted and maintained up-to-date and concise talking points concerning the most recent and relevant volcanic activity and hazards, and created a media management plan to assist staff in working with members of the media. These items aided staff in maintaining a consistent message concerning the eruption, potential hazards, and our response activities. The AVO Web site, with its accompanying database, is the backbone of AVO's external and internal communications. This was the first Cook Inlet volcanic eruption with a public expectation of real-time access to data, updates, and hazards information over the Internet. In March 2005, AVO improved the Web site from individual static pages to a dynamic, database-driven site. This new system provided quick and straightforward access to the latest information for (1) staff within the observatory, (2) emergency managers from State and local governments and organizations, (3) the media, and (4) the public. From mid-December 2005 through April 2006, the AVO Web site served more than 45 million Web pages and about 5.5 terabytes of data.

Alaska↗

USGS2010

Timing, distribution, and character of tephra fall from the 2005-2006 eruption of Augustine Volcano: Chaper 9 in The 2006 eruption of Augustine Volcano

The 2005–6 eruption of Augustine Volcano produced tephra-fall deposits during each of four eruptive phases. Late in the precursory phase (December 2005), small phreatic explosions produced small-volume, localized, mostly nonjuvenile tephra. The greatest volume of tephra was produced during the explosive phase (January 11–28, 2006) when 13 discrete Vulcanian explosions generated ash plumes between 4 and 14 km above mean sea level (asl). A succession of juvenile tephra with compositions from low-silica to high-silica andesite is consistent with the eruption of two distinct magmas, represented also by a low-silica andesite lava dome (January 13–16) followed by a high-silica andesite lave dome (January 17–27). On-island deposits of lapilli to coarse ash originated from discrete vent explosions, whereas fine-grained, massive deposits were elutriated from pyroclastic flows and rock falls. During the continuous phase (January 28–February 10, 2006), steady growth and subsequent collapses of a high-silica andesite lava dome caused continuous low-level ash emissions and resulting fine elutriate ash deposits. The emplacement of a summit lava dome and lava flows of low-silica andesite during the effusive phase (March 3–16, 2006) resulted in localized, fine-grained elutriated ash deposits from small block-and-ash flows off the steep-sided lava flows. Mixing of two end-member magmas (low-silica and highsilica andesite) is evidenced by the overall similarities between tephra-fall and contemporaneous lava-dome and flow lithologies and by the chemical heterogeneity of matrix glass compositions of coarse lapilli and glass shards in the ash-size fraction throughout the 2005–6 eruption. A total mass of 2.2×10 10 kg of tephra fell (bulk volume of 2.2×10 7 m 3 and DRE volume of 8.5×10 6 m 3 ) during the explosive phase, as calculated by extrapolation of mass data from a single Vulcanian blast on January 17. Total tephra-fall volume for the 2005–6 eruption is about an order of magnitude smaller than other historical eruptions from Augustine Volcano. Ash plumes of short duration and small volume caused no more than minor amounts (≤1 mm) of ash to fall on villages and towns in the lower Cook Inlet region, and thus little hazard was posed to local communities. The bulk of the ash fell into Cook Inlet. Monitoring by the Alaska Volcano Observatory during the eruption helped to prevent hazardous encounters of ash and aircraft.

Alaska↗

USGS2000

Historically active volcanoes in Alaska - a quick reference

Explore the source record for details and available documents.

Fact Sheet↗