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At least 1,315 records · Page 73Linked to original sources
USGS2020

Prioritizing habitats based on abundance and distribution of molting waterfowl in the Teshekpuk Lake Special Area of the National Petroleum Reserve, Alaska

The National Petroleum Reserve in Alaska (NPR-A) encompasses more than 9.5 million hectares of federally managed land on the Arctic Coastal Plain of northern Alaska, where it supports a diversity of wildlife, including millions of migratory birds. Within the NPR-A, Teshekpuk Lake and the surrounding area provide important habitat for migratory birds, including large numbers of waterfowl and shorebirds that use the area for breeding and molting. This area has been designated by the Bureau of Land Management as the Teshekpuk Lake Special Area (TLSA) and is estimated to host 22 percent of the entire Pacific black brant ( Branta bernicla nigricans ) population as it undergoes flightless wing molt. Additionally, numerous other waterfowl species use the area for breeding and molting, including greater white-fronted geese ( Anser albifrons ), snow geese ( Chen caerulescens ), Canada geese ( Branta hutchinsii ), and tundra swans ( Cygnus columbianus ). A data-derived procedure was developed to define important habitats based on recent distributions of molting birds. That procedure was used to identify areas that could be prioritized for exclusion from oil and gas development within a pre-defined “Goose Molting Area” in the TLSA. This analysis was requested by the Bureau of Land Management to provide information for the development of alternative scenarios for an updated NPR-A, Integrated Activity Plan/Environmental Impact Statement. Habitat selections were based on the population densities of Pacific black brant and Canada geese and pre-defined thresholds for the minimum fraction of the population contained within selected areas. Selections were based on long-term records of population density combined with global-positioning system data to reveal small-scale patterns of habitat use. The highest population density of the Pacific black brant was found along the Beaufort Sea coast on the eastern edge of the study area, whereas Canada geese were somewhat more widely distributed. Depending on the selection criteria and width of protective buffers placed around selected habitat units, 52–85 percent of the Goose Molting Area was identified as high-priority habitat. The effectiveness of this approach to habitat protection assumes that buffers around selected habitat units are wide enough to provide adequate protection from disturbance related to oil and gas development. This assumption remained a key source of uncertainty that could be addressed through additional study of disturbance effects on molting waterfowl.

Alaska↗
USGS2021

Assessment of barrier island morphological change in northern Alaska

Arctic barriers islands are highly dynamic features influenced by a variety of oceanographic, geologic, and environmental factors. Many Alaskan barrier islands and spits serve as habitat and protection for native species, as well as shelter the coast from waves and storms that cause flooding and degradation of coastal villages. This study summarizes changes to barrier morphology in time and space along the North Slope coast of Alaska between the United States-Canadian border and Cape Beaufort from 1947 to 2020. Changes considered in this study include number of barriers, area and perimeter, shoreline length, barrier sinuosity and width, presence and number of relict terminus features, presence and coverage of tundra vegetation, barrier orientation, and elevation metrics. Wave conditions are also summarized and related to changes in barrier morphology. The results in this report help to better predict future barrier evolution and prevalence along Alaska’s coast by increasing our understanding of Arctic barrier development, migration and degradation.

Alaska↗
USGS2022

Abundance and distribution of sea otters (Enhydra lutris) in the southcentral Alaska stock, 2014, 2017, and 2019

The Southcentral Alaska (SCAK) sea otter ( Enhydra lutris ) stock is the northernmost stock of sea otters, a keystone predator known for structuring nearshore marine ecosystems. We conducted aerial surveys within the range of the SCAK sea otter stock to provide recent estimates of sea otter abundance and distribution. We defined three survey regions: (1) Eastern Cook Inlet (2017), (2) Outer Kenai Peninsula (2019), and (3) Prince William Sound (2014 and 2017). Combined, the three regional estimates yielded an overall abundance estimate of 21,617 sea otters (standard error [SE] = 2,190) with an average density of 1.96 sea otters per square kilometer (km 2 ; SE = 0.55). Sea otters were distributed unevenly across the survey regions and densities varied from 0.52 sea otters/km 2 (SE = 0.18) in the deep rock-walled glacial fjords along parts of the Outer Kenai Peninsula to nearly 20 sea otters/km 2 (SE = 6.70) in shallow soft-bottom communities such as those in Orca Inlet and Kachemak Bay. These survey results represent the best available contemporary information concerning the distribution, density, and abundance of sea otters across the range of the SCAK stock. Survey data files have been standardized and formatted in data releases associated with this report so that they can be queried and displayed with standard geographic information system and database management software. In addition to providing contemporary information on sea otter populations, this report details how an observer-based aerial survey method has been applied in Alaska over 2 decades.

Alaska↗
USGS2022

Systematic mapping of the ocean-continent transform plate boundary of the Queen Charlotte fault system, southeastern Alaska and western British Columbia—A preliminary bathymetric terrain model

In 2015, U.S. Geological Survey scientists in collaboration with scientists from other institutions began a study of the Queen Charlotte fault—the first systematic study of the fault in more than three decades. The primary goal of the study was to gain a better understanding of the earthquake, tsunami, and underwater-landslide hazards throughout southeastern Alaska, as well as gather data to develop geologic models that can be applied to similar plate boundaries around the globe, such as the San Andreas fault system in southern California, the Alpine fault in New Zealand, and the North Anatolian fault in Turkey. A bathymetric terrain model was compiled from six different multibeam surveys of the previously unmapped Queen Charlotte fault offshore of southeastern Alaska and Haida Gwaii archipelago.

Alaska, British Columbia↗
USGS2024

Using the horizontal-to-vertical spectral ratio method to estimate thickness of the Barry Arm landslide, Prince William Sound, Alaska

Conducting detailed investigations of large landslides is difficult, especially in the subsurface, largely due to environmental factors such as steep slopes, difficult access, and numerous objective hazards. These factors have made it challenging to accurately estimate the depth to the failure surface of the Barry Arm landslide, a large (roughly 10 8 cubic meters), deep-seated bedrock landslide in Prince William Sound, Alaska, recognized in 2019. The landslide has exhibited accelerated movement in recent years and poses a potential tsunamigenic hazard if rapid failure occurs. Failure surface depth, equivalent to landslide thickness, is a necessary metric for landslide-volume calculations and associated tsunami wave models. In this report, we used seismic noise recorded by a seismometer located on the Barry Arm landslide in Alaska to calculate the horizontal-to-vertical spectral ratio (HVSR) to investigate the site fundamental frequency ( f 0 ) and depth of the failure surface. To ensure that observed peak frequencies in the spectral ratio were related to the underlying stratigraphy (and not caused by other noise sources like nearby glaciers, topographic resonance, weather, or human activities), we also calculated HVSRs using earthquake signals, HVSRs at other seismic stations within a 2.5-kilometer radius, and a standard spectral ratio between the landslide station and other sites. We observed multiple peaks in the landslide HVSR curves at 1.5 hertz (Hz), 4–5 Hz, and 7–11 Hz. The frequencies of these peaks were consistent at the landslide site through time and across methods and were dissimilar to those identified at other seismic stations in the area, making it unlikely the peaks were caused by local noise. Directional HVSRs calculated at 15-degree intervals showed amplification of the higher frequency peaks in the direction parallel to slip, indicating two-dimensional site effects. We used the distinct frequency peaks in the seismic record to develop a 4-layer conceptual model of the landslide wherein the top of the deepest layer represents the primary failure surface, or the boundary between damaged (mobile) and undamaged material. We inverted Rayleigh wave ellipticity curves within this 4-layer configuration with constraints on S-wave velocity and layer thickness based on analogous material properties identified in the literature. This was necessary absent any site-specific subsurface S-wave velocity data. The best-fitting models indicate a mean slope-normal depth to the failure surface of 188 (±9) meters (m), with additional stratigraphic boundaries at 4 and 20 m below ground surface, potentially representing layered motion. These results agree with and improve upon ranges estimated by previous studies and can support future modeling and assessment efforts at Barry Arm.

Alaska↗
USGS1944

Chromite occurrences and a nickel prospect, Baranof Island, southeastern Alaska

This report presents the results of a brief geologic reconnaissance of some of the chromite-bearing sills between Red Bluff Bay and Silver Bay in central Baranof Island, southeastern Alaska (see figs. 1 and 2), and the results of a magnetic study of a chromite body in the ultrabasic rocks at Red Bluff Bay. Also included are the results of a brief examination of a nickel prospect near Sitka. The field work, upon which this report is largely based, was done by the authors in the early part of August 1943 as a part of a Geological Survey project to investigate some of the ultrabasic rocks of southeastern Alaska to determine the presence or absence in them of significant nickel-copper or chromium deposits. Previous studies of some of the chromite-bearing ultrabasic rocks of Baranof Island were made by Guild and Balsley during the summer of 1941.

Alaska↗
USGS1947

Preliminary report on the gypsum deposits near Iyoukeen Cove, Chicagof Island, southeastern Alaska

The only known gypsum deposits in Alaska are on northeastern Chichagof Island, southeastern Alaska, at Iyoukeen Cove (fig. 1). The area first developed and for a time worked by the Pacific Coast Gypsum Co. is approximately 1 mile upstream from the mouth of Gypsum Creek at an elevation of about 70 feet (fig. 2). The second deposit, known as the Gypsum-Camel property, is on tidewater 12 miles northeast of the mouth of Gypsum Creek (fig. 2). Iyoukeen Cove is about 35 air miles southwest of Juneau and is on both the mail-boat and the airline routes between Juneau and Sitka. The two deposits were examined by a Geological Survey party during the summer of 1946. Topographic and geologic maps were made of the vicinity of both deposits (figs. 2 and 3). Accessible underground workings at the Gypsum-Camel property also were mapped,

Alaska↗
USGS1948

Preliminary report on a lead-zinc occurrence at Berg Basin, Wrangell district, southeastern Alaska

A brief examinatin of lead-zinc occurrence at Berg Basin, Wrangell district, southeastern Alaska, was undertaken in 1947 as part of the U.S. Geological Survey's program of minerals investigations in Alaska. No lead-zinc ore body has yet been proved at Berg Basin, but because of recent interest in that area this preliminary report has been prepared for the purpose of making available immediately all data collected to date. A more complete report is in preparation.

Alaska↗
USGS1952

Pumice deposits in the Alaska Peninsula-Cook Inlet region

Three principal areas of pumice deposition have been found in the Alaska Peninsula-Cook Inlet region: Katmai National Monument, Augustine Island, and the Veniaminof-Aniakchak area. Vast quantities of pumice were deposited in Katmai National Monument resulting from the eruption of Mt. Katmai and related volcanic action in 1912. The principal deposits in the coastal areas of the Monument occur in the valley of the Katmai River and in the Amalik Bay-Kukak Bay area. Several areas of pumice deposition have been found on the south and west sides of Augustine Island, located 200 miles southwest of Anchorage. Mining was carried on by the Alaska Katmalite Corporation during the period 1946-1949, but no production has taken place since that time. Pumice deposits found in the Aniakchak-Veniaminof area have probably been derived from three principal sources: Aniakchak Crater, Mt. Veniaminof and Purple Crater. The limited data available indicate the deposits of chief interest occur in the valley of the Aniakchak River and in areas adjacent to Chignik Bay.

Alaska↗
USGS1952

Preliminary report on the Nelson and Radovan copper prospects, Nizina district, Alaska

Renewed copper exploration by Alaska Copper Mines, Incorporated, at the Nelson and Radovan prospects, Nizina district, Alaska, led the Geological Survey in 1951 to map in detail the Nelson fault block, and to re-examine the old workings. In addition, two new prospects were studied. The Nelson fault block is cut by many dominantly strike-slip faults of small displacement, and by bedding faults. Slickensided chalcocite shows post-mineral movement, and chalcocite veinlet in a filled solution cavity indicates that some of the chalcocite is secondary, perhaps very recent. Structural relations indicate two overthrust faults cut the block. The Radovan Greenstone prospect shows massive chalcocite, up to 3 feet wide, in a silicified, epidotized fault zone in the Nikolai greenstone. Ore indicated by surface exposures may amount to 450 tons of chalcocite. The Radovan Low-Contact prospect is on a continuation of the same fault approximately 3 miles southwest of the Greenstone prospect, and 150 feet above the contact of the Nikolai greenstone and the overlying Chitistone limestone. Limonite staining is widespread in bedding planes and small faults near the fault zone; mineralization in the fault zone consists of pyrite, chalcocite, bornite, malachite, realgar, orpiment and stibnite. The sulphides in the fault zone, plus the widespread silicification and epidotization indicate a strong zone of hydrothermal activity which merits extensive prospecting.

Open-File Report↗
USGS1952

Coal investigations in the Homer district, Kenai coal field, Alaska, in 1950 and 1951

This report presents the results of work done in the last three weeks of the 1950 field season and in all of the 1951 season, and supplements reports by Barnes (19149) and Cobb (1950, 1951). Barnes' report covers investigations of coal-bearing rocks of the Tertiary Kenai formation in a coastal belt between Bluff Point and the head of Kachemak Bay (pl. 2). Cobb's reports deal with similar rocks exposed along the coast between Bluff Point and the beach bluffs about 7 miles south of the village of Cohoe, and in the lower reaches of the Ninilchik River valley. The present report covers extensions of previous mapping in the valleys of Deep Creek and the Anchor River, and on high land between the area covered by Barnes' report and the Anchor River valley. The results of ground and aerial reconnaissance of most of the Homer district also are presented. The writer, assisted by F. J. Markewioz, carried on the field work which is the basis for this report, between August 13 mad September 6, 1950, and between May 10 and August 30, 1951. Field work included traverses along Deep Creek and the Anchor River, and between the southeast end of Tustumena Lake and the head of Kachemak Bay. It included also the detailed measurement and tracing of coal beds on the upland north and northwest of Homer, sampling of coal beds along the northwest shore of Kachemak Bay and the southeast shore of Cook Inlet, and both ground and aerial reconnaissance of the rest of the Homer district and adjoining areas. The writer is indebted to James W. Scott, Forester, U. S. Bureau of Land Management, Lomer, Alaska, who accompanied him on a traverse from Tustumena Lake to Kaohemak Bay and assisted at many other times during the 1950 and 1951 field seasons. Ralph Gaetano and Thomas Shelford of Homer were of great assistance in locating and reaching isolated outcrops of coal-bearing rooks. Daniel B. Krinsley, of the Alaska Terrain and Permafrost Section of the U. S. Geological Survey, has generously made available the results of many of his observations in remote parts of the Homer district which could not be visited by the writer.

Alaska↗
USGS1954

Geologic investigations of proposed power sites at Cooper, Grant, Ptarmigan and Crescent Lakes, Alaska

The Geological Survey, as part of its program of the classification of public lands with respect to mineral and water resources, is currently making a systematic study and evaluation of the potential water power sites in Alaska. This report describes the geologic conditions and their relation to possible plans for the development of water power at Cooper, Grant, Ptarmigan, and Crescent Lakes on the Kenai Peninsula near Seward, Alaska.

Alaska↗
USGS1955

Geochemical exploration for antimony in southeastern Alaska

Preliminary geochemical prospecting by the Geological Survey was carried out in 1952 in muskeg-covered ground at Caamano Point, Cleveland Peninsula, Alaska, in an effort to delimit areas of stibnite concentrations. It was conducted to aid, if possible, a prospecting project of the Defense Minerals Exploration. Samples were collected from soil and decomposed limestone-and-schist bedrock at depths ranging from 18 inches to 60 inches, by means of a pipe with an interior plunger. Initial sampling was followed by detailed sampling of the areas where the antimony content of the soils consistently averaged more than 300 ppm. These Areas of major soil concentrations were prospected by surface trenching and percussion drilling to depths of 20 feet which proved the existence of stibnite ore. Next a shaft and drifts made in the most favorable area proved disseminated stibnite ore to depths of 60 feet. This geochemical work of soil sampling to indicate hidden ore bodies in a typical Alaskan muskeg area is believed to be the first application in Alaska of such techniques in active ore exploration. The results show the economic feasibility of such exploration as a first step in extending the known boundaries of mineralized areas, and in directing initial exploration toward the most favorable areas of near-surface ore bodies. Data are presented to help establish values of soil content of antimony that may be considered as normal in this type of geologic terrain.

Alaska↗
USGS1955

Ground-water reconnaissance in five Eskimo villages in the lower Kuskokwim-Yukon River area, Alaska

In response to a request from the Sanitation and Engineering Section of the Alaska Department of Health, a reconnaissance of the possibility of obtaining ground-water supplies for the five villages in the lower Kuskokwim-Yukon River area was made by the Geological Survey early in June 1955. The five Eskimo villages--Kwethluk, Hooper Bay, Chevak, Tununak, and Kwigillingok--are in western Alaska between the lower reaches of the two rivers. (See sketch page two). As there has been no development of ground water in the area, this report is based on a brief investigation of the surficial geology and the topography.

Alaska↗
USGS1963

Placer tin deposits in central Alaska

Placer tin, in the form of cassiterite (Sn02) and (or) tinstone (fragments including cassiterite and some vein or rock material), is known or reported in deposits that have been prospected or mined for placer gold in four areas adjacent to the Yukon River in central Alaska, 120 to 240 miles west of Fairbanks. These areas are: the Morelock Creek area, on the north side of the Yukon River about 30 miles upstream from Tanana; the Moran Dome area, about 16 miles north of the Yukon River and 25 miles northwest of Tanana; the Mason Creek area, on the north side of the Yukon River about 36 miles west of Tanana; and the Ruby-Long area, on the south side of the Yukon River near Ruby and about 40 miles east of Galena. The only extensive placer mining in these areas has been in the Ruby-Long area. Other placer deposits including some cassiterite are known in central Alaska but are not discussed in this report. Bedrock in these areas is predominantly schist of various types with some associated greenstone and other metamorphic rocks. Some granite is exposed in the Moran Dome and Ruby-Long areas and in areas close to Morelock and Mason Creeks. Barren, milky quartz veins and veinlets transecting the metamorphic rocks are common. No cassiterite was found in the bedrock, and no bedrock source of the tin has been reported. In the Moran Dome and Mason Creek areas, and in part of the Ruby-Long area, tourmaline is present in the rocks of the tin-bearing drainage basins, and apparently absent elsewhere in these areas. The placer deposits are in both valley floor and bench alluvium, which are predominantly relatively thin, rarely exceeding a thickness of 30 feet. Most of the alluvium deposits are not perennially frozen. In the Morelock Creek area tin-bearing deposits are 5 to 5? miles above the mouth of the creek, and meager evidence indicates that cassiterite and gold are present in Morelock Creek valley and some of the tributaries both upstream and downstream from these deposits. The concentrates recovered in samples average about 57 percent tin, and the gold averages about 922 fine. Prospecting indicates that the placer tin deposits are small and of relatively low grade, and that the greater part of the value of the deposits is the gold. In the Moran Dome area the known tin-bearing deposits are in the valley floor and bench gravels along upper Tozimoran Creek. Much of the alluvium is unfrozen, but the deeper portions of the bench gravels and the gravels some distance from the streams are in part frozen. Tin-bearing samples have been obtained from prospect pits and drill holes at a number of sites on Tozimoran Creek between its head and the confluence with Slate Creek. Gold recovered from some of these samples has a fineness of 835. The presence of cassiterite and gold on Ash Creek has been confirmed by sampling. Cassiterite and gold reportedly occur on upper Melozimoran Creek, and several other stream valleys in this area may be tin bearing. In the Mason Creek area cassiterite has been reported in the valley floor and bench alluvial deposits on Mason Creek, but its presence could not be confirmed in the brief field examinations of creek and dump-pile gravel that were made. The limited number of pits and cuts available precluded a valid sampling without additional drilling, pitting, or trenching. In the Ruby-Long area the valleys of Midnight, Birch, and Big Creeks are known to have appreciable concentrations of cassiterite in the gold-bearing placer deposits. The alluvial deposits in the valleys of Ruby, Glacier, Flint, Trail, Long, Fifth of July, Short, Flat, Greenstone, and Monument Creeks contain some cassiterite, but sufficient information could not be obtained to make an evaluation of these occurrences. Cassiterite concentrates, reportedly ranging from 52 to 70.24 percent tin, have been recovered in connection with gold mining operations on Midnight, Birch, and Big Creeks.

Open-File Report↗
USGS1964

Reconnaissance geochemistry of stream sediments from three areas near Juneau, Alaska

Results of a preliminary inquiry into background metal content of stream sediments near Juneau, Alaska, and whether this background is related to geologic terrane indicate that stream sediments derived chiefly from metamorphic rocks show significantly higher modal nickel, zinc, and arsenic than do sediments derived mainly from sedimentary or igneous rocks. Metal-content data that are closely related to areal geology will be required before systematic geochemical prospecting by stream-sediment sampling in southeast Alaska will be very effective.

Alaska↗