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At least 595 records · Page 33Linked to original sources
USGS2012

Studies by the U.S. Geological Survey in Alaska, 2011

The collection of papers that follow continues the series of U.S. Geological Survey (USGS) investigative reports in Alaska under the broad umbrella of the geologic sciences. This series represents new and sometimes-preliminary findings that are of interest to Earth scientists in academia, government, and industry; to land and resource managers; and to the general public. The reports presented in Studies by the U.S. Geological Survey in Alaska cover a broad spectrum of topics from various parts of the State, serving to emphasize the diversity of USGS efforts to meet the Nation's needs for Earth-science information in Alaska. This professional paper is one of a series of "online only" versions of Studies by the U.S. Geological Survey in Alaska , reflecting the current trend toward disseminating research results on the World Wide Web with rapid posting of completed reports.

Alaska↗
USGS2024

New U-Pb geochronology and geochemistry of Paleozoic metaigneous rocks from western Yukon and eastern Alaska, cross-border synthesis, and implications for tectonic models

The tectonic evolution of and relation between the Yukon-Tanana terrane and the Lake George assemblage, as well as other associated tectonic assemblages in western Yukon and eastern Alaska, have been debated for decades. The Yukon-Tanana terrane is widely considered to be an allochthonous rifted fragment derived from the Laurentian continental margin, whereas the Lake George assemblage and associated assemblages are currently interpreted to be part of the parautochthonous continental margin of western North America (Laurentia). To address these topics, we present 40 new U-Pb zircon ages and 20 new whole-rock geochemical analyses. We incorporate these data into a new compilation of available geological mapping for a large area that straddles the Alaska-Yukon border, together with 34 previously published U-Pb age determinations and an extensive geochemical database of metaigneous rocks from Late Devonian to Early Mississippian and middle to late Permian assemblages in this area. Magmatism in the Lake George assemblage and related assemblages occurred in two pulses from about 371 to 360 and from about 358 to 347 million years ago (Ma); geochemical discrimination diagrams indicate a large crustal component, possibly indicative of arc magmatism, for felsic metaigneous rocks and a range of tectonic environments for mafic rocks. Magmatism in the Fortymile River and related assemblages, and parts of the Nasina assemblage—all parts of the Yukon-Tanana terrane—are mainly Early Mississippian and span a crystallization age range from about 361 to 343 Ma; geochemical discrimination diagrams for these rocks indicate primarily arc geochemical signatures for both mafic and felsic rocks. Middle to late Permian crystallization ages (about 261–253 Ma) are indicated for felsic metaigneous rocks in the Klondike assemblage and some of the felsic metaigneous rocks in the Nasina assemblage. Based on our mapping, we propose the existence of a possible unconformity between the Mississippian and Permian felsic metavolcanic rocks within the Nasina assemblage that is marked by sporadic occurrences of stretched-pebble conglomerate. Our combined database supports the well-established model of a magmatic arc comprising the Fortymile River and Finlayson assemblages of the rifted Yukon-Tanana terrane continental fragment on which a middle to late Permian arc (Klondike assemblage) was later built. The assemblages of the Yukon-Tanana terrane were subsequently intruded by Late Triassic to Early Jurassic granitoids, presumably during reaccretion of the Yukon-Tanana terrane to the continental margin. Permian and Late Triassic to Early Jurassic intrusions have not been mapped in the now structurally lower plate Lake George assemblage; their absence is one of the lines of evidence that have been used to support the parautochthonous, rather than allochthonous, origin of the Lake George assemblage and related assemblages. Our new data, together with previously published ranges of igneous crystallization ages and geochemical tectonic signatures of the Late Devonian to Early Mississippian magmatic rocks in the Lake George assemblage and associated assemblages and in the Fortymile River, Nasina, and correlated assemblages of the Yukon-Tanana terrane, indicate that the currently accepted interpretation of the Lake George assemblage and associated rocks being part of parauthochthonous North America is not the only possible interpretation of this tectonic entity. Approximately half of the dated intrusive rocks in the Lake George assemblage are contemporaneous with the metaigneous rocks of the Yukon-Tanana terrane arc (<361 Ma). We speculate that our approximately 361 Ma U-Pb age for quartz syenite in part of the North American continental margin in south-central Yukon defines the beginning of rifting of the Laurentian margin. Although the currently favored model of prolonged middle Paleozoic subduction and extension in both the Yukon-Tanana terrane and parautochthonous North America allows for simultaneous middle Paleozoic magmatism on both sides of the Slide Mountain Ocean, we now propose an alternative hypothesis in which the Lake George assemblage represents a deeper part of the rifted Yukon-Tanana terrane arc. If this is the case, the absence of Permian and Late Triassic to Early Jurassic arc rocks in the Lake George assemblage could be explained either by the arcs of these ages not being wide enough to have affected the Lake George assemblage or by tectonic displacement of these arc rocks away from the Lake George assemblage. Our approximately 259 Ma U-Pb zircon age and geochemical analyses of metarhyolite in the Seventymile terrane in Alaska, which comprises remnants of the back-arc basin that separated the Yukon-Tanana terrane from the Laurentian continental margin, confirm the presence of a late middle Permian volcanic arc component to the terrane. Our approximately 319 Ma U-Pb zircon age from the Chicken assemblage (as redefined in this study) in eastern Alaska, combined with previously reported fossil ages and a U-Pb zircon age from this assemblage, indicate that it is a Late Mississippian to Early Pennsylvanian arc assemblage. We propose several other relatively young, locally developed arc assemblages outboard of the ancient continental margin of Laurentia that may correlate with the Chicken assemblage, but we consider its origin to remain an enigma.

Alaska↗
USGS1966

The Alaska earthquake, March 27, 1964: Field investigations and reconstruction effort

One of the greatest geotectonic events of our time occurred in southern Alaska late in the afternoon of March 27, 1964. Beneath a leaden sky, the chill of evening was just settling over the Alaskan countryside. Light snow was falling on some communities. It was Good Friday, schools were closed, and the business day was ending. Suddenly without warning half of Alaska was rocked and jarred by the most violent earthquake to occur in North America this century. The descriptive summary that follows is based on the work of many investigators. A large and still-growing scientific literature has accumulated since the earthquake, and this literature has been freely drawn upon here. In particular, the writers have relied upon the findings of their colleagues in the Geological Survey. Some of these findings have been published, but some are still being prepared for publication. Moreover, some field investigations are still in progress. This is the first in a series of six reports that the U.S. Geological Survey published on the results of a comprehensive geologic study that began, as a reconnaissance survey, within 24 hours after the March 27, 1964, Magnitude 9.2 Great Alaska Earthquake and extended, as detailed investigations, through several field seasons. The 1964 Great Alaska earthquake was the largest earthquake in the U.S. since 1700. Professional Paper 541, in 1 part, describes Field Investigations and Reconstruction Effort.

Alaska↗
USGS2011

Geologic map of Saint Lawrence Island, Alaska

Saint Lawrence Island is located in the northern Bering Sea, 190 km southwest of the tip of the Seward Peninsula, Alaska, and 75 km southeast of the Chukotsk Peninsula, Russia (see index map, map sheet). It lies on a broad, shallow-water continental shelf that extends from western Alaska to northeastern Russia. The island is situated on a northwest-trending structural uplift exposing rocks as old as Paleozoic above sea level. The submerged shelf between the Seward Peninsula and Saint Lawrence Island is covered mainly with Cenozoic deposits (Dundo and Egiazarov, 1982). Northeast of the island, the shelf is underlain by a large structural depression, the Norton Basin, which contains as much as 6.5 km of Cenozoic strata (Grim and McManus, 1970; Fisher and others, 1982). Sparse test-well data indicate that the Cenozoic strata are underlain by Paleozoic and Proterozoic rocks, similar to those exposed on the Seward Peninsula (Turner and others, 1983). Saint Lawrence Island is 160 km long in an east-west direction and from 15 km to 55 km wide in a north-south direction. The east end of the island consists largely of a wave-cut platform, which has been elevated as much as 30 m above sea level. Isolated upland areas composed largely of granitic plutons rise as much as 550 m above the wave-cut platform. The central part of the island is dominated by the Kookooligit Mountains, a large Quaternary shield volcano that extends over an area of 850 km 2 and rises to an elevation of 630 m. The west end of the island is composed of the Poovoot Range, a group of barren, rubble-covered hills as high as 450 m that extend from Boxer Bay on the southwest coast to Taphook Mountain on the north coast. The Poovoot Range is flanked on the southeast by the Putgut Plateau, a nearly flat, lake-dotted plain that stands 30?60 m above sea level. The west end of the island is marked by uplands underlain by the Sevuokuk pluton (unit Kg), a long narrow granite body that extends from Gambell on the north to near Boxer Bay on the south. Headlands having rugged cliffs or narrow, boulder-strewn beaches characterize the southwest coastline. The geologic map of Saint Lawrence Island was prepared from published and unpublished field investigations carried out between 1966 and 1971 by W.W. Patton, Jr., Bela Csejtey, Jr., T.P. Miller, J.T. Dutro, Jr., J.M. Hoare, and W.H. Condon (Patton and Csejtey, 1971, 1980) and data from Ormiston and Fehlmann (1969). Fossils collected during these investigations are reported in the Alaska Paleontological Database (www.alaskafossil.org), and mineral resource information is summarized in the online Alaska Resource Data File (Hudson, 1998).

Alaska↗
USGS2026

Geologic map of the Emmons Lake volcanic center, Alaska

Introduction The Emmons Lake volcanic center is a spatially clustered group of stratovolcanoes and calderas in the southwestern part of the Alaska Peninsula, Alaska. The volcanic center is characterized by several ice- and snow-clad stratovolcanoes located within and along the margins of a nested-caldera complex that includes Emmons Lake. A shieldlike ancestral edifice (ancestral Mount Emmons) is truncated by the caldera complex and forms a broad volcanic platform around the center. The main stratovolcanoes of the Emmons Lake volcanic center are Pavlof Sister, Pavlof Volcano, Little Pavlof, Double Crater, Mount Hague, and Mount Emmons. Several small unnamed cinder cones and vents also are located within Emmons Lake volcanic center and on the east flank of Pavlof Volcano. Many of these cones and vents have been the source of the young lava flows that mantle the floor of the caldera. Pavlof Volcano, in the northeastern part of the Emmons Lake volcanic center, is one of the most historically (that is, the past about 300 years) active volcanoes in Alaska, and eruptions from Pavlof Volcano pose the greatest hazards to the region. Volcanic rocks of the Emmons Lake volcanic center overlie continental and marine sedimentary rocks of chiefly Late Jurassic to early Tertiary age. The oldest rocks in the area are those of the Naknek Formation, consisting of volcaniclastic sandstone, siltstone, and conglomerate of Late Jurassic age. The southern part of the area includes rocks of the Belkofski Formation, a thick sequence of volcaniclastic sandstone, siltstone, and conglomerate of middle Tertiary age. Lava flows, volcanic breccia, and fluvial volcaniclastic rocks of late Miocene age, which unconformably overlie the Belkofski Formation south of the Emmons Lake volcanic center, are primarily exposed on the islands just south of the Alaska Peninsula. The Emmons Lake volcanic center was affected multiple times by glaciation associated with the glacier expansion that characterized the Quaternary. Glaciation has played a key role in shaping the present-day landscape, and much of the eruptive history of the Emmons Lake volcanic center has involved interactions with glacier ice. Thus, a brief review of the Quaternary glacial history of the area is provided to establish the physical context for Emmons Lake volcanic center eruptive activity.

Alaska↗
USGS2004

Water Quality and Streamflow of the Indian River, Sitka, Alaska, 2001-02

The Indian River Basin, located near Sitka Alaska, drains an area of 12.3 square miles. This watershed is an important natural resource of Sitka National Historic Park. At the present time, the watershed faces possible development on large tracts of private land upstream of the park that could affect the water quality of Indian River. Due to this concern, a study was conducted cooperatively with the National Park Service. The approach was to examine the water quality of the Indian River in the upper part of the watershed where no development has occurred and in the lower part of the basin where development has taken place. Measurements of pH, water temperature, and dissolved oxygen concentrations of the Indian River were within acceptable ranges for fish survival. The Indian River is calcium bicarbonate type water with a low buffering capacity. Concentrations of dissolved ions and nutrients generally were low and exhibited little variation between the two study sites. Analysis of bed sediment trace element concentrations at both sampling sites indicates the threshold effect concentration was exceeded for arsenic, chromium, copper, nickel, and zinc; while the probable effect concentration was exceeded by arsenic, chromium and nickel. However, due to relatively large amounts of organic carbon present in the bed sediments, the potential toxicity from trace elements is low. Discharge in the Indian River is typical of coastal southeast Alaska streams where low flows generally are in late winter and early spring and greater flows are during the wetter fall months. Alaska Department of Fish and Game has established instream flow reservations on the lower 2.5 miles of the Indian River. Discharge data indicate minimum flow requirements were not achieved during 236 days of the study period. Natural low flows are frequently below the flow reservations, but diversions resulted in flow reservations not being met a total of 140 days. Thirty-five algae species were identified from the sample collected at Indian River near Sitka while 24 species were identified from the sample collected at Indian River at Sitka. Most species of algae identified in the Indian River samples were diatoms and the majority were pinnate diatoms; however, green algae and (or) blue-green algae accounted for much of the algal biomass at the two sites. The trophic condition of the Indian River is oligotrophic, and algal productivity likely is limited by low concentrations of dissolved nitrogen. Few invertebrate taxa were collected relative to many high-quality streams in the contiguous United States, but the number of taxa in Indian River appears to be typical of Alaska streams. Ephemeroptera was the most abundant order sampled followed by Diptera.

Scientific Investigations Report↗
USGS2007

Geology and origin of epigenetic lode gold deposits, Tintina Gold Province, Alaska and Yukon

More than 50 million ounces of lode gold resources have been defined in the previous 15 years throughout accreted terranes of interior Alaska and in adjacent continental margin rocks of Yukon. The major deposits in this so-called Tintina Gold Province formed around 105 to 90 million years ago in east-central Alaska and Yukon, and around 70 million years ago in southwestern Alaska, late in the deformational history of their host rocks. All gold deposits studied to date formed from CO 2 -rich and 18 O-rich crustal fluids, most commonly of low salinity. The older group of ores includes the low-grade intrusion-related gold systems at Fort Knox near Fairbanks and those in Yukon, with fluids exsolved from fractionating melts at depths of 3 to 9 kilometers and forming a zoned sequence of auriferous mineralization styles extending outward to the surrounding metasedimentary country rocks. The causative plutons are products of potassic mafic magmas generated in the subcontinental lithospheric mantle that interacted with overlying lower to middle crust to generate the more felsic ore-related intrusions. In addition, the older ores include spatially associated, high-grade, shear-zonerelated orogenic gold deposits formed at the same depths from upward-migrating metamorphic fluids; the Pogo deposit is a relatively deep-seated example of such. The younger gold ores, restricted to southwestern Alaska, formed in unmetamorphosed sedimentary rocks of the Kuskokwim basin within 1 to 2 kilometers of the surface. Most of these deposits formed via fluid exsolution from shallowly emplaced, highly evolved igneous complexes generated mainly as mantle melts. However, the giant Donlin Creek orogenic gold deposit is a product of either metamorphic devolatilization deep in the basin or of a gold-bearing fluid released from a flysch-melt igneous body.

Alaska, Yukon↗
USGS2021

A comparison of Landsat 8 Operational Land Imager and Provisional Aquatic Reflectance science product, Sentinel–2B, and WorldView–3 imagery for empirical satellite-derived bathymetry, Unalakleet, Alaska

Satellite-derived bathymetry (SDB) based upon an empirical band ratio method is a cost-effective means for mapping nearshore bathymetry in coastal areas vulnerable to natural hazards. This is particularly important for the low-lying coastal community of Unalakleet, Alaska, that has been negatively affected not only by flooding, storm surge, and historically strong storms but also by high erosion rates stemming from the Unalakleet River and Norton Sound. The purpose of this study was to assess the viability of different satellite imagery, including Landsat 8 (L8) Operational Land Imager, Sentinel–2B, WorldView–3, and L8 Provisional Aquatic Reflectance science product, for deriving SDB for Unalakleet, Alaska. Correlations were performed between satellite imagery band ratios and topobathymetric (topobathy) light detection and ranging (lidar) and in situ single-beam sound navigation and ranging (sonar). The satellite imagery correlations with topobathy lidar did not yield as high of a linear relation with water depths as the satellite imagery correlations with the single-beam sonar. An extinction depth, where light no longer attenuates through the water column, was not identified because of the shallow depths within the topobathy lidar and single-beam sonar datasets. Although some single-beam soundings measured at 7 meters deep, the correlations with the SDB band ratios did not yield a strong linear relation. Satellite imagery band ratio correlations with Electronic Navigational Chart soundings did not yield a strong linear relation because of older source data. Less than optimal linear regressions were most likely due to the geography of Unalakleet, Alaska, a low-lying coastal community subject to high erosion rates from surrounding waters. This study is one of the first attempts to compare different satellite imagery band ratio correlations with topobathy lidar and in situ sonar to assess the viability for nearshore SDB for coastal Unalakleet, Alaska.

Alaska↗
USGS2025

Selected special conditions affecting peak streamflow and extreme floods in Alaska through water year 2022

The U.S. Geological Survey, in cooperation with the Alaska Department of Transportation and Public Facilities, inventoried selected special conditions for annual peak flows and identified extreme floods at streamgages in Alaska through water year 2022 to facilitate hydrologic analysis. Special conditions identified from U.S. Geological Survey gaging records and basin characteristics included regulation and diversion, urbanization, indeterminate drainage areas, drainage areas less than the minimum used in regional analyses, glacial lake outburst floods, other outburst floods, and snowmelt floods. For peak flows that occurred during calendar years 1980–2019, an atmospheric river dataset was used to identify atmospheric river presence or absence on the dates peak flows occurred. Extreme floods (defined as peak flows exceeding the 1-percent annual exceedance probability flood magnitude or an empirical measure of relative magnitude using Creager’s coefficient C) were identified and associated with flood-generating mechanisms using the other inventoried special conditions and other information. The gaging record contained glacial lake outburst floods at 15 streamgages and other types of outburst floods at 10 streamgages. Non-outburst peak flows in Alaska resulted from a mixture of rainfall and melt-based flood-generating mechanisms in all but the most rain-dominated seasonal flow regime. Melt-based flood-generating mechanisms included snowmelt, high-elevation snow and ice melt, or rain-on-snow events. Atmospheric rivers were common in Alaska and conterminous basins in Canada, occurring in that region on 67 percent of the days in the calendar year 1980–2019 period. Atmospheric rivers were more common on the days of peak flows and even more common on the days of non-outburst extreme floods. The percentage of days when an atmospheric river was present increased to 78 percent for the days of peak flows in that period and to 83 percent for the days of non-outburst extreme floods in that period. Of 149 extreme floods in the gaging record, 38 were generated by outburst floods. Of the non-outburst extreme floods, 72 percent were generated by rainfall and 26 percent were generated by melt-based processes or a combination of rainfall and melt-based processes. Flood-generating mechanisms could not be determined for the final 2 percent of the non-outburst extreme floods because the month and day of the peak flows were unknown and no other information was available. Secondary factors strongly associated with extreme floods included antecedent rain and streamflow conditions and warm storm conditions that produced rain instead of snow or generated snowmelt.

Alaska↗
USGS1957

Lead-alpha age determinations of granitic rocks from Alaska

Lead-alpha activity age determinations were made on zircon from seven granitic rocks of central and southeastern Alaska. The results of the age determinations indicate two periods of igneous intrusion, one about 95 million years ago, during the Cretaceous period, and another about 53 million years ago, during the early part of the Tertiary. The individual ages determined on zircon from 2 rocks from southeastern Alaska and 1 from east-central Alaska gave results of 90, 100, and 96 million years; those determined on 4 rocks from central Alaska gave results of 47, 56, 58, and 51 million years.

Alaska↗
USGS1952

Preliminary summary review of thorium-bearing mineral occurrences in Alaska

Thorium-bearing minerals are known at 47 localities in Alaska. At these localities the thorium occurs as a major constituent or in minor amounts as an impurity in one or more of the following 12 minerals: allanite, columbite, ellsworthite, eschynite, gummite, monazite, orangite, parisite, thorianite, thorite, xenotime, and zircon. In addition other minerals, such as biotite and sphene, are radioactive and may contain thorium. Several unidentified columbate minerals with uranium or thorium and uranium as major constituents have been recognized at some localities. The distribution, by type of deposit, of the 57 thorium occurrences is as follows: lode - 3, lode and placer - 1, granitic rock - 3, granitic rock and related placer - 14, and placer - 26. Of the four lode occurrences only the radioactive veins at Salmon Bay in southeastern Alaska and the contact metamorphic deposit in the Nixon Fork area of central Alaska warrant further consideration, although insufficient data are available to determine whether these two deposits have commercial possibilities. The remaining occurrences of thorium-bearing minerals in Alaska are limited to placer deposits and disseminations of accessory minerals in granitic rocks. In most of these occurrences the thorium-bearing minerals occur in only trace amounts and consequently warrent little further consideration. More data are needed to determine the possibilities of byproduct recovery of thorium-bearing minerals from several of the gold and tin placers.

Alaska↗
USGS2017

Analysis of a GRACE global mascon solution for Gulf of Alaska glaciers

We present a high-resolution Gravity Recovery and Climate Experiment (GRACE) mascon solution for Gulf of Alaska (GOA) glaciers and compare this with in situ glaciological, climate and other remote-sensing observations. Our GRACE solution yields a GOA glacier mass balance of –65 ± 11 Gt a –1 for the period December 2003 to December 2010, with summer balances driving the interannual variability. Between October/November 2003 and October 2009 we obtain a mass balance of –61 ± 11 Gt a –1 from GRACE, which compares well with –65 ± 12 Gt a –1 from ICESat based on hypsometric extrapolation of glacier elevation changes. We find that mean summer (June–August) air temperatures derived from both ground and lower-troposphere temperature records were good predictors of GRACE-derived summer mass balances, capturing 59% and 72% of the summer balance variability respectively. Large mass losses during 2009 were likely due to low early melt season surface albedos, measured by the Moderate Resolution Imaging Spectroradiometer (MODIS) and likely associated with the 31 March 2009 eruption of Mount Redoubt, southwestern Alaska. GRACE data compared well with in situ measurements at Wolverine Glacier (maritime Alaska), but poorly with those at Gulkana Glacier (interior Alaska). We conclude that, although GOA mass estimates from GRACE are robust over the entire domain, further constraints on subregional and seasonal estimates are necessary to improve fidelity to ground observations.

Alaska↗
USGS2020

Use of genetic mark-recapture to estimate breeding site fidelity and philopatry in a threatened sea duck population, Alaska-breeding Steller’s eiders

The Steller’s eider (Polysticta stelleri) is a sea duck that breeds in Arctic tundra regions of Russia and Alaska. The Alaska-breeding population is listed as threatened under the U.S. Endangered Species Act because of a perceived contraction of their breeding range in North America. Understanding demographic rates of the listed population is critical for determining and evaluating measures that can lead to an increase in abundance and thus, long-term viability. Specifically, estimates of return rates to breeding areas by adult females and natal areas by juvenile females are needed for planning effective recovery actions. We used a suite of polymorphic loci to genotype individuals and generated genetic profiles of nesting females and female offspring from nest materials collected from 1995 – 2016 in a ~170 km2 study area near Utqiaġvik, Alaska. We analyzed capture histories of genetically-identified individuals to estimate breeding site fidelity, temporary emigration, and natal site fidelity (philopatry). From a sample of 365 nests, we found that breeding site fidelity of adult females was high (0.91, SE 0.07) and temporary emigration also was high (0.77, SE 0.06) and variable across years (range 0.34 – 0.97). From egg shell remains of 124 hatched females, we observed nine recaptures as nesting adults, suggesting that philopatry was also high (range 0.6-1.0). Given the relatively high rates of adult female breeding site fidelity and female philopatry that we estimated, management actions that reduce mortality of adult females and increase annual productivity are likely to help maintain the population of a few hundred breeding Steller’s eiders on the Arctic Coastal Plain of Alaska.

Alaska↗
USGS1992

Puffins as samplers of juvenile pollock and other forage fish in the Gulf of Alaska

We sampled the nestling diets of tufted puffins (Fratercula cirrhata) and horned puffins (F. corniculata) in 3 years at colonies from the north-central Gulf of Alaska to the eastern Aleutian Islands, Alaska, USA. Overall, tufted puffins consumed (by weight) 41% sandlance (Ammodytes hexapterus), 22% capelin (Mallotus villosus), 19% walleye pollock (Theragra chalcogramma), 13% other fish, and 5% invertebrates, whereas horned puffins took 85% sandlance, 4% capelin, 2% pollock, 8% other fish, and <1 % invertebrates. All of the pollock consumed were young of the year, whereas 4 year-classes of capelin were present, from young of the year through spawning adults. Puffins took mostly first-year sandlance, but fish in their second year or older were also common at colonies near Kodiak, Alaska. The importance of juvenile pollock in the diet of tufted puffins varied geographically from little or no use in the north-central Gulf and Kodiak areas to moderate use (5 to 20%) in the Semidi and Shumagin Islands to heavy use (25 to 75%) in the Sandman Reefs and eastern Aleutians. An estimated 11 billion pollock were consumed by tufted puffins throughout the region in 1986. The proportion of pollock in puffin diets at the Semidi Islands was strongly correlated with independent estimates of cohort strength in 3 years. Puffins may thus provide a useful index of distribution and year class abundance of first-year pollock, a species that currently supports an important commercial fishery in the Gulf of Alaska.

Alaska↗
USGS2020

A 36-year record of rock avalanches in the Saint Elias Mountains of Alaska, with implications for future hazards

Glacial retreat and mountain-permafrost degradation resulting from rising global temperatures have the potential to impact the frequency and magnitude of landslides in glaciated environments. Several recent events, including the 2015 Taan Fiord rock avalanche, which triggered a tsunami with one of the highest wave runups ever recorded, have called attention to the hazards posed by landslides in regions like southern Alaska. In the Saint Elias Mountains, the presence of weak sedimentary and metamorphic rocks and active uplift resulting from the collision of the Yakutat and North American tectonic plates create landslide-prone conditions. To differentiate between the typical frequency of landsliding resulting from the geologic and tectonic setting of this region, and landslide processes that may be accelerated due to changes in climate, we used Landsat imagery to create an inventory of rock avalanches in a 3700 km2 area of the Saint Elias Mountains. During the period from 1984-2019, we identified 220 rock avalanches with a mean recurrence interval of 60 days. We compared our landslide inventory with a catalog of M ≥ 4 earthquakes to identify potential coseismic events, but only found three possible earthquake-triggered rock avalanches. We observed a distinct temporal cluster of 41 rock avalanches from 2013 through 2016 that correlated with above average air temperatures (including the three warmest years on record in Alaska, 2014-2016); this cluster was similar to a temporal cluster of recent rock avalanches in nearby Glacier Bay National Park and Preserve. The majority of rock avalanches initiated from bedrock ridges in probable permafrost zones, suggesting that ice loss due to permafrost degradation, as opposed to glacial thinning, could be a dominant factor contributing to rock-slope failures in the high elevation areas of the Saint Elias Mountains. Although earthquake-triggered landslides have episodically occurred in southern Alaska, evidence from our study suggests that area-normalized rates of non-coseismic rock avalanches were greater during the period from 1964 to 2019, and that the frequency of these events will continue to increase as the climate continues to warm. These findings highlight the need for hazard assessments in Alaska that address changes in landslide patterns related to climate change.

Alaska↗
USGS1997

Gas hydrate resources of northern Alaska

Large amounts of natural gas, composed mainly of methane, can occur in arctic sedimentary basins in the form of gas hydrates under appropriate temperature and pressure conditions. Gas hydrates are solids, composed of rigid cages of water molecules that trap molecules of gas. These substances are regarded as a potential unconventional source of natural gas because of their enormous gas-storage capacity. Most published gas hydrate resource estimates are highly simplified and based on limited geological data. The gas hydrate resource assessment for northern Alaska presented in this paper is based on a "play analysis" scheme, in which geological factors controlling the accumulation and preservation of gas hydrates are individually evaluated and risked for each hydrate play. This resource assessment identified two gas hydrate plays; the in-place gas resources within the gas hydrates of northern Alaska are estimated to range from 6.7 to 66.8 trillion cubic metres of gas (236 to 2,357 trillion cubic feet of gas), at the 0.50 and 0.05 probability levels respectively. The mean in-place hydrate resource estimate for northern Alaska is calculated to be 16.7 trillion cubic metres of gas (590 trillion cubic feet of gas). If this assessment is valid, the amount of natural gas stored as gas hydrates in northern Alaska could be almost seven times larger then the estimated total remaining recoverable conventional natural gas resources in the entire United States.

Alaska↗
USGS2011

Evaluation of long-term gas hydrate production testing locations on the Alaska North Slope

The results of short duration formation tests in northern Alaska and Canada have further documented the energy resource potential of gas hydrates and justified the need for long-term gas hydrate production testing. Additional data acquisition and long-term production testing could improve the understanding of the response of naturally-occurring gas hydrate to depressurization-induced or thermal-, chemical-, and/or mechanical-stimulated dissociation of gas hydrate into producible gas. The Eileen gas hydrate accumulation located in the Greater Prudhoe Bay area in northern Alaska has become a focal point for gas hydrate geologic and production studies. BP Exploration (Alaska) Incorporated and ConocoPhillips have each established research partnerships with U.S. Department of Energy to assess the production potential of gas hydrates in northern Alaska. A critical goal of these efforts is to identify the most suitable site for production testing. A total of seven potential locations in the Prudhoe Bay, Kuparuk, and Milne Point production units were identified and assessed relative to their suitability as a long-term gas hydrate production test site. The test site assessment criteria included the analysis of the geologic risk associated with encountering reservoirs for gas hydrate testing. The site selection process also dealt with the assessment of the operational/logistical risk associated with each of the potential test sites. From this review, a site in the Prudhoe Bay production unit was determined to be the best location for extended gas hydrate production testing. The work presented in this report identifies the key features of the potential test site in the Greater Prudhoe Bay area, and provides new information on the nature of gas hydrate occurrence and potential impact of production testing on existing infrastructure at the most favorable sites. These data were obtained from well log analysis, geological correlation and mapping, and numerical simulation.

Conference Paper↗
USGS2019

Serologic evidence for influenza A virus exposure in three loon species (Gavia spp.) breeding in Alaska

Limited information exists about exposure to influenza A viruses (IAVs) in many wild waterbird species, including loons. We analyzed serum samples from breeding adult Pacific ( Gavia pacifica ), Red-throated ( Gavia stellata ), and Yellow-billed ( Gavia adamsii ) loons sampled at three locations along the coast of Alaska, US from 2008 to 2017 to gain a better understanding of the potential role loons play in IAV ecology. We screened loon sera for IAV antibodies using three tests—blocking enzyme-linked immunosorbent assay (bELISA), agar gel immunodiffusion (AGID), and hemagglutination inhibition (HI)—and examined patterns in seroprevalence among species and sampling locations. We found evidence of IAV infection in all loon species and at all breeding locations, although concordance was imperfect among serological tests. Diagnostic tests yielded seroprevalence estimates of 24% (42/172) with bELISA, 8% (5/60) with AGID, and 6% (4/70) with HI. The IAV subtypes to which loon sera reacted using HI were consistent with those detected in waterfowl and gulls at other locations in Alaska, suggesting that loons may be exposed to IAV maintained in sympatric waterbirds. Our study provided evidence that loons inhabiting Alaska were exposed to IAV. However, given imperfect concordance among serologic tests, and relatively low seroprevalence as compared to other avian taxa exposed to IAV in Alaska, they make poor IAV surveillance targets.

Alaska↗