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At least 1,783 records · Page 99Linked to original sources
USGS2017

Marine tephrochronology of the Mt. Edgecumbe volcanic field, southeast Alaska, USA

The Mt. Edgecumbe Volcanic Field (MEVF), located on Kruzof Island near Sitka Sound in southeast Alaska, experienced a large multiple-stage eruption during the last glacial maximum (LGM)-Holocene transition that generated a regionally extensive series of compositionally similar rhyolite tephra horizons and a single well-dated dacite (MEd) tephra. Marine sediment cores collected from adjacent basins to the MEVF contain both tephra-fall and pyroclastic flow deposits that consist primarily of rhyolitic tephra and a minor dacitic tephra unit. The recovered dacite tephra correlates with the MEd tephra, whereas many of the rhyolitic tephras correlate with published MEVF rhyolites. Correlations were based on age constraints and major oxide compositions of glass shards. In addition to LGM-Holocene macroscopic tephra units, four marine cryptotephras were also identified. Three of these units appear to be derived from mid-Holocene MEVF activity, while the youngest cryptotephra corresponds well with the White River Ash eruption at not, vert, similar 1147 cal yr BP. Furthermore, the sedimentology of the Sitka Sound marine core EW0408-40JC and high-resolution SWATH bathymetry both suggest that extensive pyroclastic flow deposits associated with the activity that generated the MEd tephra underlie Sitka Sound, and that any future MEVF activity may pose significant risk to local population centers.

Alaska↗
USGS2003

Geochronology and eruptive history of the Katmai volcanic cluster, Alaska Peninsula

In the Katmai district of the Alaska Peninsula, K–Ar and 40 Ar/ 39 Ar ages have been determined for a dozen andesite–dacite stratocones on the arc front and for 11 rear-arc volcanoes, 10 of which are monogenetic. Tied to mapping and stratigraphic studies, our dating emphasized proximal basal lavas that rest on basement rocks, in order to estimate ages of inception of each polygenetic cone. Oldest among arc-front cones is Alagogshak Volcano (690–43 ka), succeeded in the Holocene by the active Mount Martin cone. Mount Mageik consists of four overlapping subedifices, basal lavas of which give ages of 93, 71, and 59 ka, and Holocene. The three small prehistoric cones of Trident Volcano yield ages of 143, 101–58, and 44 ka. Falling Mountain and Mount Cerberus, dacite domes near the 1912 Novarupta vent, are related compositionally to the Trident group and give ages of 70 ka and 114 ka. Mount Katmai, which underwent caldera collapse in 1912, consists of two subedifices that overlapped in space and time, and is the only arc-front center here to include basalt and rhyolite; one cone began by 90 ka, the other by 47 ka. Snowy Mountain also consists of two contiguous cones, which started around 200 and 171 ka, respectively, the younger remaining active into the Holocene. Devils Desk, the only mafic cone on the arc front, was short-lived at about 245 ka. In the rear-arc, (1) Mount Griggs produced mafic-to-silicic andesite in several episodes between 292 ka and the Holocene; (2) the Savonoski River cluster includes a Pliocene dacite dome and five small mafic cones (390–88 ka); (3) Gertrude Creek cone (49.8% SiO 2 ) yields an age of 500 ka; and (4) the Saddlehorn Creek cluster includes five Pliocene basalt-to-andesite remnants. Eruptive volumes were reconstructed, permitting estimates of average eruption rates for edifice lifetimes. Since the mid Pleistocene, total volume erupted along the arc front here is 210±47 km 3 and in the rear-arc 39±6 km 3 , of which Mount Griggs alone accounts for 35±5 km 3 . Most productive has been Mount Katmai at 70±18 km 3 , yielding a rate of ∼1 km 3 /kyr, followed by Mount Mageik (0.33 km 3 /kyr) and Mount Griggs (0.3 km 3 /kyr since 50 ka).

Alaska↗
USGS2002

Linking the pacific decadal oscillation to seasonal stream discharge patterns in Southeast Alaska

This study identified and examined differences in Southeast Alaskan streamflow patterns between the two most recent modes of the Pacific decadal oscillation (PDO). Identifying relationships between the PDO and specific regional phenomena is important for understanding climate variability, interpreting historical hydrological variability, and improving water-resources forecasting. Stream discharge data from six watersheds in Southeast Alaska were divided into cold-PDO (1947-1976) and warm-PDO (1977-1998) subsets. For all watersheds, the average annual streamflows during cold-PDO years were not significantly different from warm-PDO years. Monthly and seasonal discharges, however, did differ significantly between the two subsets, with the warm-PDO winter flows being typically higher than the cold-PDO winter flows and the warm-PDO summer flows being typically lower than the cold-PDO flows. These results were consistent with and driven by observed temperature and snowfall patterns for the region. During warm-PDO winters, precipitation fell as rain and ran-off immediately, causing higher than normal winter streamflow. During cold-PDO winters, precipitation was stored as snow and ran off during the summer snowmelt, creating greater summer streamflows. The Mendenhall River was unique in that it experienced higher flows for all seasons during the warm-PDO relative to the cold-PDO. The large amount of Mendenhall River discharge caused by glacial melt during warm-PDO summers offset any flow reduction caused by lack of snow accumulation during warm-PDO winters. The effect of the PDO on Southeast Alaskan watersheds differs from other regions of the Pacific Coast of North America in that monthly/seasonal discharge patterns changed dramatically with the switch in PDO modes but annual discharge did not. ?? 2002 Elsevier Science B.V. All rights reserved.

Journal of Hydrology↗
USGS1997

Evaluation of conditions along the grounding line of temperate marine glaciers: An example from Muir Inlet, Glacier Bay, Alaska

In the marine environment, stability of the glacier terminus and the location of subglacial streams are the dominant controls on the distribution of grounding-line deposits within morainal banks. A morainal bank complex in Muir Inlet, Glacier Bay, SE Alaska, is used to develop a model of terminus stability and location of subglacial streams along the grounding line of temperate marine glaciers. This model can be used to interpret former grounding-line conditions in other glacimarine settings from the facies architecture within morainal bank deposits. The Muir Inlet morainal bank complex was deposited between 1860 A.D. and 1899 A.D., and historical observations provide a record of terminus positions, glacial retreat rates and sedimentary sources. These data are used to reconstruct the depositional environment and to develop a correlation between sedimentary facies and conditions along the grounding line. Four seismic facies identified on the high-resolution seismic-reflection profiles are used to interpret sedimentary facies within the morainal bank complex. Terminus stability is interpreted from the distribution of sedimentary facies within three distinct submarine geomorphic features, a grounding-line fan; stratified ridges, and a field of push ridges. The grounding-line fan was deposited along a stable terminus and is represented on seismic-reflection profiles by two distinct seismic facies, a proximal and a distal fan facies. The proximal fan facies was deposited at the efflux of subglacial streams and indicates the location of former glacifluvial discharges into the sea. Stratified ridges formed as a result of the influence of a quasi-stable terminus on the distribution of sedimentary facies along the grounding line. A field of push ridges formed along the grounding line of an unstable terminus that completely reworked the grounding-line deposits through glacitectonic deformation. Between 1860 A.D. and 1899 A.D. (39 years), 8.96 x 108 m3 of sediment were deposited within the Muir Inlet morainal bank complex at an average annual sediment accumulation rate of 2.3 x 107 m3/a. This rate represents the annual sediment production capacity of the glacier when the Muir Inlet drainage basin is filled with glacial ice.

Marine Geology↗
USGS1997

Lithofacies and seismic-reflection interpretation of temperate glacimarine sedimentation in Tarr Inlet, Glacier Bay, Alaska

High-resolution seismic-reflection profiles of sediment fill within Tart Inlet of Glacier Bay, Alaska, show seismic facies changes with increasing distance from the glacial termini. Five types of seismic facies are recognized from analysis of Huntec and minisparker records, and seven lithofacies are determined from detailed sedimentologic study of gravity-, vibro- and box-cores, and bottom grab samples. Lithofacies and seismic facies associations, and fjord-floor morphology allow us to divide the fjord into three sedimentary environments: ice-proximal, iceberg-zone and ice-distal. The ice-proximal environment, characterized by a morainal-bank depositional system, can be subdivided into bank-back, bank-core and bank-front subenvironments, each of which is characterized by a different depositional subsystem. A bank-back subsystem shows chaotic seismic facies with a mounded surface, which we infer consists mainly of unsorted diamicton and poorly sorted coarse-grained sediments. A bank-core depositional subsystem is a mixture of diamicton, rubble, gravel, sand and mud. Seismic-reflection records of this subsystem are characterized by chaotic seismic facies with abundant hyperbolic diffractions and a hummocky surface. A bank-front depositional subsystem consists of mainly stratified and massive sand, and is characterized by internal hummocky facies on seismic-reflection records with significant surface relief and sediment gravity flow channels. The depositional system formed in the iceberg-zone environment consists of rhythmically laminated mud interbedded with thin beds of weakly stratified diamicton and stratified or massive sand and silt. On seismic-reflection profiles, this depositional system is characterized by discontinuously stratified facies with multiple channels on the surface in the proximal zone and a single channel on the largely flat sediment surface in the distal zone. The depositional system formed in the ice-distal environment consists of interbedded homogeneous or laminated mud and massive or stratified sand and coarse silt. This depositional system shows continuously stratified seismic facies with smooth and flat surfaces on minisparker records, and continuously stratified seismic facies which are interlayered with thin weakly stratified facies on Huntec records.

Marine Geology↗
USGS1997

Persistence rates and detection probabilities of oiled king eider carcasses on St Paul Island, Alaska

Following an oil spill off St Paul Island, Alaska in February 1996, persistence rates and detection probabilities of oiled king eider (Somateria spectabilis) carcasses were estimated using the Cormack-Jolly-Seber model. Carcass persistence rates varied by day, beach type and sex, while detection probabilities varied by day and beach type. Scavenging, wave action and weather influenced carcass persistence. The patterns of persistence differed on rock and sand beaches and female carcasses had a different persistence function than males. Weather, primarily snow storms, and degree of carcass scavenging, diminished carcass detectability. Detection probabilities on rock beaches were lower and more variable than on sand beaches. The combination of persistence rates and detection probabilities can be used to improve techniques of estimating total mortality.

Marine Pollution Bulletin↗
USGS1998

A drift experiment to assess the influence of wind on recovery of oiled seabirds on St Paul Island, Alaska

We used wooden blocks to estimate the proportion of oiled seabird carcasses that were likely to be recovered on beaches of St Paul Island, Alaska following a near-shore oil spill. We released a total of 302 blocks 6 km north of the island in 1997 at the site of a 17 II 1996 oil spill. We used a paired design and released half the blocks when the winds were onshore and released the second half when the winds were offshore. We systematically searched beaches after the second release to recover blocks. We recovered 93 of 152 (61%) blocks released when winds were onshore but only 1 of 150 (0.7%) blocks released when winds were offshore. Given that winds following the 1996 spill were offshore, we conclude that most birds killed at sea following the 1996 spill were likely not recovered on beaches.

Marine Pollution Bulletin↗
USGS1999

Benthic marine debris, with an emphasis on fishery-related items, surrounding Kodiak Island, Alaska, 1994-1996

Composition and abundance of benthic marine debris were investigated during three bottom trawl surveys in inlet and offshore locations surrounding Kodiak Island, Alaska, 1994-1996. Debris items were primarily plastic and metal regardless of trawl location. Plastic bait jars, fishing line, and crab pots were the most common fishery-related debris items and were encountered in large amounts in inlets (20-25 items km-2), but were less abundant outside of inlets (4.5-11 items km-2). Overall density of debris was also significantly greater in inlets than outside of inlets. Plastic debris densities in inlets ranged 22-31.5 items km-2, 7.8-18.8 items km-2 outside of inlets. Trawls in inlets contained almost as much metal debris as plastic debris. Density of metal debris ranged from 21.2 to 23.7 items km-2 in inlets, a maximum of 2.7 items km-2 outside of inlets. Inlets around the town of Kodiak had the highest densities of fishery-related and total benthic debris. Differences in benthic debris density between inlets and outside of inlets and differences by area may be due to differences in fishing activity and water circulation patterns. At the current reduced levels of fishing activity, however, yearly monitoring of benthic debris appears unnecessary. Copyright (C) 1999.

Marine Pollution Bulletin↗
USGS2000

Comparison of pigeon guillemot, Cepphus columba, blood parameters from oiled and unoiled areas of Alaska eight years after the Exxon Valdez oil spill

In 1997, we compared the haematological and plasma biochemical profiles among populations of pigeon guillemots, Cepphus columba, in areas oiled and not oiled by the 1989 Exxon Valdez oil spill (EVOS) that occurred in Prince William Sound (PWS), Alaska. Pigeon guillemot populations in PWS were injured by EVOS and have not returned to pre-spill levels. If oil contamination is limiting recovery of pigeon guillemots in PWS, then we expected that blood parameters of pigeon guillemots would differ between oiled and unoiled areas and that these differences would be consistent with either toxic responses or lower fitness. We collected blood samples from chicks at approximately 20 and 30 days after hatching. Physiological changes associated with chick growth were noted in several blood parameters. We found that only calcium and mean cell volume were significantly different between the chicks in oiled and unoiled areas. Despite these differences, blood biomarkers provided little evidence of continuing oil injury to pigeon guillemot chicks, eight years after the EVOS. Preliminary data from adults indicated elevated aspartate aminotransferase activity in the adults from the oiled area, which is consistent with hepatocellular injury. Because adults have greater opportunities for exposure to residual oil than nestlings, we recommend studies that fully evaluate the health of adults residing in oiled areas. (C) 2000 Elsevier Science Ltd.

Marine Pollution Bulletin↗
USGS2000

Cytochrome P450 1A induction in sea ducks inhabiting nearshore areas of Prince William Sound, Alaska

Following the Exxon-Valdez oil spill, hepatic rates of EROD activity and thus, P450 1A expression, were significantly higher in harlequin ducks ( Histrionicus histrionicus ) and Barrow’s goldeneyes ( Bucephala islandica ) from oiled areas of Prince William Sound, Alaska when compared to birds from unoiled sites. Polychlorinated biphenyl exposure did not account for areal differences in P450 1A induction in harlequin ducks. Background hydrocarbon levels in Prince William Sound were negligible prior to the 1989 oil spill, but remnant Exxon-Valdez oil was still present in nearshore habitats of the spill zone coincident with our study. We conclude that P450 1A induction in sea ducks from areas oiled during the Exxon-Valdez oil spill was likely due to exposure to residual oil. We speculate that biochemical and physiological changes in individuals chronically exposed to oil may be constraining population recovery of some sea duck species affected by the spill.

Alaska↗
USGS2017

Recurring middle Pleistocene outburst floods in east-central Alaska

Recurring glacial outburst floods from the Yukon-Tanana Upland are inferred from sediments exposed along the Yukon River near the mouth of Charley River in east-central Alaska. Deposits range from imbricate gravel and granules indicating flow locally extending up the Yukon valley, to more distal sediments consisting of at least 10 couplets of planar sands, granules, and climbing ripples with up-valley paleocurrent indicators overlain by massive silt. An interglacial organic silt, occurring within the sequence, indicates at least two flood events are associated with an earlier glaciation, and at least three flood events are associated with a later glaciation which postdates the organic silt. A minimum age for the floods is provided by a glass fission track age of 560,000 ?? 80,000 yr on the GI tephra, which occurs 8 m above the flood beds. A maximum age of 780,000 yr for the floods is based on normal magnetic polarity of the sediments. These age constraints allow us to correlate the flood events to the early-middle Pleistocene. And further, the outburst floods indicate extensive glaciation of the Yukon-Tanana Upland during the early-middle Pleistocene, likely representing the most extensive Pleistocene glaciation of the area. ?? 2003 University of Washington. Published by Elsevier Inc. All rights reserved.

Quaternary Research↗
USGS1999

PAH refractory index as a source discriminant of hydrocarbon input from crude oil and coal in Prince William Sound, Alaska

Geochemical correlation and differentiation of hydrocarbons from crude oils and coals is difficult. The complex mixture of the hydrocarbon constituents and the dynamic nature of these constituents in the environment as they weather contribute to this difficulty A new parameter, the polycyclic aromatic hydrocarbon (PAH) refractory index, is defined here to help in this correlation. The PAH refractory index is a ratio of two of the most refractory constituents of most crude oils, namely triaromatic steranes and monomethylchrysenes. These are among the most persistent compounds in oil after deposition in the environment and thus retain reliably the signature of the original petroleum input. This index is utilized in Prince William Sound (PWS) to differentiate three different oils, as well as to provide evidence that coal, not oil, is the dominant source of the PAHs which are prominent constituents of marine sediments from PWS and the Gulf of Alaska.Geochemical correlation and differentiation of hydrocarbons from crude oils and coals is difficult. The complex mixture of the hydrocarbon constituents and the dynamic nature of these constituents in the environment as they weather contribute to this difficulty. A new parameter, the polycyclic aromatic hydrocarbon (PAH) refractory index, is defined here to help in this correlation. The PAH refractory index is a ratio of two of the most refractory constituents of most crude oils, namely triaromatic steranes and monomethylchrysenes. These are among the most persistent compounds in oil after deposition in the environment and thus retain reliably the signature of the original petroleum input. This index is utilized in Prince William Sound (PWS) to differentiate three different oils, as well as to provide evidence that coal, not oil, is the dominant source of the PAHs which are prominent constituents of marine sediments from PWS and the Gulf of Alaska.

Conference Paper↗
USGS2001

Formation and failure of volcanic debris dams in the Chakachatna River valley associated with eruptions of the Spurr volcanic complex, Alaska

The formation of lahars and a debris avalanche during Holocene eruptions of the Spurr volcanic complex in south-central Alaska have led to the development of volcanic debris dams in the Chakachatna River valley. Debris dams composed of lahar and debris-avalanche deposits formed at least five times in the last 8000-10,000 years and most recently during eruptions of Crater Peak vent in 1953 and 1992. Water impounded by a large debris avalanche of early Holocene (?) age may have destabilized an upstream glacier-dammed lake causing a catastrophic flood on the Chakachatna River. A large alluvial fan just downstream of the debris-avalanche deposit is strewn with boulders and blocks and is probably the deposit generated by this flood. Application of a physically based dam-break model yields estimates of peak discharge (Qp) attained during failure of the debris-avalanche dam in the range 104 < Qp < 106 m3 s-1 for plausible breach erosion rates of 10-100 m h-1. Smaller, short-lived, lahar dams that formed during historical eruptions in 1953, and 1992, impounded smaller lakes in the upper Chakachatna River valley and peak flows attained during failure of these volcanic debris dams were in the range 103 < Qp < 104 m3 s-1 for plausible breach erosion rates. Volcanic debris dams have formed at other volcanoes in the Cook Inlet region, Aleutian arc, and Wrangell Mountains but apparently did not fail rapidly or result in large or catastrophic outflows. Steep valley topography and frequent eruptions at volcanoes in this region make for significant hazards associated with the formation and failure of volcanic debris dams. Published by Elsevier Science B.V.

Geomorphology↗
USGS2003

Depositional environments and processes in Upper Cretaceous nonmarine and marine sediments, Ocean Point dinosaur locality, North Slope, Alaska

A 178-m-thick stratigraphic section exposed along the lower Colville River in northern Alaska, near Ocean Point, represents the uppermost part of a 1500 m Upper Cretaceous stratigraphic section. Strata exposed at Ocean Point are assigned to the Prince Creek and Schrader Bluff formations. Three major depositional environments are identified consisting, in ascending order, of floodplain, interdistributary-bay, and shallow-marine shelf. Nonmarine strata, comprising the lower 140 m of this section, consist of fluvial distributaries, overbank sediments, tephra beds, organic-rich beds, and vertebrate remains. Tephras yield isotopic ages between 68 and 72.9 Ma, generally consistent with paleontologic ages of late Campanian-Maastrichtian determined from dinosaur remains, pollen, foraminifers, and ostracodes. Meandering low-energy rivers on a low-gradient, low-relief floodplain carried a suspended-sediment load. The rivers formed multistoried channel deposits (channels to 10 m deep) as well as solitary channel deposits (channels 2-5 m deep). Extensive overbank deposits resulting from episodic flooding formed fining-upward strata on the floodplain. The fining-upward strata are interbedded with tephra and beds of organic-rich sediment. Vertical-accretion deposits containing abundant roots indicate a sheet flood origin for many beds. Vertebrate and nonmarine invertebrate fossils along with plant debris were locally concentrated in the floodplain sediment. Deciduous conifers as well as abundant wetland plants, such as ferns, horsetails, and mosses, covered the coastal plain. Dinosaur skeletal remains have been found concentrated in floodplain sediments in organic-rich bone beds and as isolated bones in fluvial channel deposits in at least nine separate horizons within a 100-m-thick interval. Arenaceous foraminifers in some organic-rich beds and shallow fluvial distributaries indicate a lower coastal plain environment with marginal marine (bay) influence. Marginal marine strata representing interdistributary bay deposits overlie the nonmarine beds and comprise about 15 m of section. Extensive vegetated sand flats, shoals, and shallow channels overlain by shallow bay deposits (less than 7 m deep), containing storm-generated strata characterize the marginal marine beds. Abundant bioturbation and roots characterize the stratigraphic lowest bay deposits; bioturbated sediment, pelecypods, barnacles, and benthic microfossils are found in the overlying bay storm deposits. The sediments abruptly change upward from hummocky cross-stratified bay deposits to a muddy marsh deposit containing shallow organic-rich channels to prograding nonmarine to marginal marine beds. Transgressive, abundantly fossiliferous shallow-marine strata more than 13 m thick comprise the uppermost exposures at Ocean Point. The marine beds overlie nonmarine and bay strata and represent an environment dominated episodically by storms. The age of the marginal marine and marine beds is late Maastrichtian based on pollen. ?? 2003 Elsevier Ltd. All rights reserved.

Cretaceous Research↗
USGS1997

Distribution and stability of eelgrass beds at Izembek Lagoon, Alaska

Spatial change in eelgrass meadows, Zostera marina L., was assessed between 1978 and 1987 and between 1987 and 1995 at Izembek Lagoon, Alaska. Change in total extent was evaluated through a map to map comparison of data interpreted from a 1978 Landsat multi-spectral scanner image and 1987 black and white aerial photographs. A ground survey in 1995 was used to assess spatial change from 1987. Eelgrass beds were the predominant vegetation type in the lagoon, comprising 44-47% (15000-16000 ha) of the total area in 1978 and 1987. Izembek Lagoon contains the largest bed of seagrass along the Pacific Coast of North America and largest known single stand of eelgrass in the world. There was a high degree of overlap in the spatial distribution of eelgrass among years of change detection. The overall net change was a 6% gain between, 1978 and 1987 and a <1% gain between 1987 and 1995. The lack of significant change in eelgrass cover suggests that eelgrass meadows in Izembek Lagoon have been stable during the 17-year period of our study.

Alaska↗
USGS1999

Modeling bird mortality associated with the M/V Citrus oil spill off St. Paul Island, Alaska

We developed a model to estimate the number of bird carcasses that were likely deposited on the beaches of St. Paul Island, Alaska following the M/V Citrus oil spill in February 1996. Most of the islands beaches were searched on an irregular schedule, resulting in the recovery of 876 King Eider carcasses. A sub-sample of beaches were intensively studied to estimate daily persistence rate and detection probability [Fowler, A.C., Flint, P.L., 1997. Marine Pollution Bulletin]. Using these data, our model predicted that an additional 733±70 King Eider carcasses were not detected during our searches. Therefore, we estimate that at least 1609±70 King Eider carcasses occurred on beaches as a result of the spill. We lacked sufficient sample size to model losses for other species, thus we applied the estimated recovery rate for King Eiders (54%) to other species and estimate a total combined loss of 1765 birds. In addition, 165 birds were captured alive making the total estimated number of birds impacted by the M/V Citrus spill 1930. Given that oiled birds occurred in places on the island which could not be systematically searched combined with the fact that it was unlikely that oiled birds that died at sea would have been recovered during our searches [Flint, P.L., Fowler, A.C., 1998. Marine Pollution Bulletin], our estimate of total mortality associated with the spill should be considered a minimum.

Alaska↗
USGS2003

Coupled heat and fluid flow modeling of the Carboniferous Kuna Basin, Alaska: Implications for the genesis of the Red Dog Pb-Zn-Ag-Ba ore district

The Red Dog deposit is a giant 175 Mton (16% Zn, 5% Pb), shale-hosted Pb-Zn-Ag-Ba ore district situated in the Carboniferous Kuna Basin, Western Brooks Range, Alaska. These SEDEX-type ores are thought to have formed in calcareous turbidites and black mudstone at elevated sub-seafloor temperatures (120-150??C) within a hydrogeologic framework of submarine convection that was structurally organized by large normal faults. The theory for modeling brine migration and heat transport in the Kuna Basin is discussed with application to evaluating flow patterns and heat transport in faulted rift basins and the effects of buoyancy-driven free convection on reactive flow and ore genesis. Finite element simulations show that hydrothermal fluid was discharged into the Red Dog subbasin during a period of basin-wide crustal heat flow of 150-160 mW/m2. Basinal brines circulated to depths as great as 1-3 km along multiple normal faults flowed laterally through thick clastic aquifers acquiring metals and heat, and then rapidly ascended a single discharge fault zone at rates ??? 5 m/year to mix with seafloor sulfur and precipitate massive sulfide ores. ?? 2003 Elsevier Science B.V. All rights reserved.

Conference Paper↗
USGS2000

Record of late holocene debris avalanches and lahars at Iliamna Volcano, Alaska

Iliamna Volcano is a 3053-meter high, glaciated stratovolcano in the southern Cook Inlet region of Alaska and is one of seven volcanoes in this region that have erupted multiple times during the past 10,000 yr. Prior to our studies of Iliamna Volcano, little was known about the frequency, magnitude, and character of Holocene volcanic activity. Here we present geologic evidence of the most recent eruptive activity of the volcano and provide the first outline of Late Holocene debris-avalanche and lahar formation. Iliamna has had no documented historical eruptions but our recent field investigations indicate that the volcano has erupted at least twice in the last 300 yr. Clay-rich lahar deposits dated by radiocarbon to ???1300 and ???90 yr BP are present in two major valleys that head on the volcano. These deposits indicate that at least two large, possibly deep-seated, flank failures of the volcanic edifice have occurred in the last 1300 yr. Noncohesive lahar deposits likely associated with explosive pyroclastic eruptions date to 2400-1300,>1500,???300, and <305 yr BP. Debris-avalanche deposits from recent and historical small-volume slope failures of the hydrothermally altered volcanic edifice cover most of the major glaciers on the volcano. Although these deposits consist almost entirely of hydrothermally altered rock debris and snow and ice, none of the recently generated debris avalanches evolved to lahars. A clay-rich lahar deposit that formed <90??60 radiocarbon yr BP and entered the Johnson River Valley southeast of the volcano cannot be confidently related to an eruption of Iliamna Volcano, which has had no known historical eruptions. This deposit may record an unheralded debris avalanche and lahar. ?? 2000 Elsevier Science B.V. All rights reserved.

Journal of Volcanology and Geothermal Research↗