Geology topics

Research about lower Cook Inlet

Source-linked reports with geographic coverage including lower Cook Inlet.

7 recordsLinked to original sources

USGS2021

Monitoring the recovery of seabirds and forage fish following a major ecosystem disruption in Lower Cook Inlet

Following the North Pacific marine heatwave of 2014-2016 and associated extreme die-off of seabirds in the winter of 2015-2016, we repeated historical marine bird and forage fish surveys around two seabird colonies (Gull Island, Chisik Island) in lower Cook Inlet during 2016-2019 in order to document immediate and lingering impacts of the heatwave on resident fish and seabird populations. At sea, we conducted acoustic/trawl surveys for fish in near-colony areas, while simultaneously counting seabirds on survey transects. At colonies, we monitored bird numbers on whole colony censuses and population plot counts and assessed annual reproductive success of Black-legged Kittiwakes ( Rissa tridactyla ) and Common Murres ( Uria aalge ). Our studies suggest that impacts of the heatwave on seabirds and their forage base were severe and extended for several years beyond the heatwave itself. Although fish biomass indices were greatest in 2016-2017, the forage community was largely dominated by juvenile fish with low nutritional value following a collapse of key species of forage fish during the marine heatwave. Lowest fish biomass was observed in 2018, coincident with a marked decline in the at-sea abundance of many seabirds around colonies. By 2019 there were signs of improvement in prey abundance and quality, and significant aggregations of pre-spawning capelin and large sand lance were observed in and around Kachemak Bay. In comparison with historical (1996-1999) bird colony surveys, kittiwake population counts decreased by more than 70% at Chisik Island, and by 8-29% at Gull Island. Similarly, murre counts decreased at Chisik Island by 72% and by more than 20% at Gull Island. Kittiwakes had complete reproductive failure at Chisik Island from 2016-2018, with minimal success in 2019. At Gull Island, kittiwakes also failed in 2016 and 2018 but had unusually high productivity in 2017 and 2019. Murres also had complete reproductive failures at Chisik Island in all four years and at Gull Island during 2016, 2017 and 2018. Murres finally fledged chicks in 2019, albeit at about half the normal rate. Finally, we also observed unusually high levels of predator disturbance (egg predation, flushing adults from plots) and unprecedented numbers of adult birds in poor body condition (“skinny murres”), particularly in 2018. Together, these results indicate that an extreme disruption of marine food webs occurred during and after the heatwave. Given the prolonged reproductive failures, continued monitoring is required to assess continuing impacts and recovery from the 2014-2016 heatwave. For example, murre chicks that would have been produced in 2016 should, after 4-5 years away, start recruiting to the colony in 2021, and thereby replace aged adults that would have died naturally in the past year(s). Without such natal recruitment for at least the next 3-4 years, we should document a continuing decline in bird numbers at the colonies.

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USGS1981

Submarine topography and physiography of lower Cook Inlet, Alaska

The submarine topography of lower Cook Inlet, Alaska, is complex because the bathymetric aspects and water depths change rapidly over short distances. The folded upper Tertiary subbottom was eroded during the first of five major Quaternary glacial advances over the inlet, and later fluvial, fluvioglacial, glacial, and marine erosional and depositional processes shaped the bottom to its present configuration. Most of lower Cook Inlet has a relative smooth topography showing small local highs and lows, and slopes with gradients generally ranging from less than a degree to locally about 5°. Around the southwestern Kenai Peninsula and the Barren and Kodiak Islands, strong faulting with vertical movement has added to the complexity of bottom topography. Less complex, nonfaulted areas occur near Kalgin Island and south Kachemak Bay and around Augustine Island. To facilitate description of lower Cook Inlet the estuarine body is divided into three large regions, northern and central, southern, and eastern; and these regions are divided into smaller physiographic areas on the basis of submarine topographic characteristics and 20-m depth zonations. Each area is named by combining the geographic name of a nearby place or feature on land with a common term for a marine physiographic feature -- trough, platform, ramp, slope, plateau. Local highs and deeps having lees than 5-m relief, which can be important to fisheries and specific research or economic studies, are not named, mentioned in text, or shown on the figures.

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USGS1981

Current meter observations within lower Cook Inlet, Alaska, 1978-1979 from the R/V Sea Sounder, Pacific-Arctic Branch, U.S. Geological Survey

The U.S. Geological Survey under contract to the U.S. Bureau of Land Management conducted geo-environmental hazard studies within lower Cook Inlet, Alaska from 1975 through 1979 (Bouma and Hampton, 1976; Bouma and others, 1977 a,b, 1978 ; Hampton and Bouma 1979). As part of this effort the U.S. Geological Survey research vessel, R/V SEA SOUNDER, conducted two cruises in 1978 and one cruise in 1979 (Table 1). A number of stations were occupied for various periods of time (Fig. 1) during which tidal current speed and direction data was recorded. Some 1978 data was obtained concurrently with bottom boundary layer experiments conducted with a large instrumented tripod system referred to as GEOPROBE (Cacchione and Drake, 1979).

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USGS1980

Identification of bedforms in lower Cook Inlet, Alaska

The seafloor of the central part of lower Cook Inlet, Alaska, is characterized by the presence of different sizes and types of bedforms. The bedforms in the sandy sediments include straight-crested to sinuous to lunate ripples, small, medium, and large sand waves, sand ridges, sand ribbons, and sand patches. In addition, rocky and pebbly seafloor has been identified. The water depth ranges from 25 to 120 m, and surface currents average 3.8 kt (2 m/s). Bottom currents have been measured at as much as 42 cm/s at 1 m above bottom. Underwater television observations have shown that the rate of sand transport is lower than expected because small amounts of clay and organic matter appear to inhibit remobilization. Only during the last 1 to 2 h of ebb and flood stages of spring tides, and during storms, does significant transport occur. Comparison of data from high-resolution seismic profiling systems, side-scan sonar, bottom television and camera, and bottom sampling shows that bottom and bedform interpretations based solely on sonographs can be in error. Measuring the length of ‘acoustic shadows’ on sonographs to obtain bedform heights gives dimensions that are too large by factors of 3–7. Bottom television investigations revealed that the troughs between small sand waves are flat and carpeted by shell fragments. Such coarse material has a high acoustic reflectance that is not related to slope or height and can lead to false interpretations on bedform dimensions. Our observations have shown that small sand waves commonly superimposed on larger ones are slightly higher than those present on flat hard bottom but are still less than calculated from acoustic shadows. Where the bottom is rather smooth or contains elevations small enough to be masked by bathymetric ‘noise’ caused by the pitching of the vessel, sonographs typically show either small sand waves, sand ribbons, sand patches, rocks, or smooth bottom. The smooth-bottom category can vary widely from ripples to gravelly or shelly or to small rocks with biological overgrowth as verified by television observations. Our observations have clearly demonstrated the need for an integrated multi-scale observation and sampling program in order to classify the bottom characteristics and to provide quantitative data for transport calculations.

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USGS1979

Clay mineralogy, fine-grained sediment dispersal, and inferred current patterns, lower Cook Inlet and Kodiak shelf, Alaska

Because lower Cook Inlet and Kodiak shelf are being explored and developed for their petroleum resources, it is essential for environmental reasons to understand the sediment dispersal routes and current patterns. The Susitna River flows into upper Cook Inlet and is the source of clay minerals in Holocene deposits found in western lower Cook Inlet. The Copper River, in the northern Gulf of Alaska, provides clay minerals to the Kodiak shelf and southeastern lower Cook Inlet. In addition, crosion of local bedrock outcrops on the shelf produces some clays that are deposited on the Kodiak shelf. Current patterns can be inferred from the clay-mineral distribution pattern. This is true even if the clay-size fraction is a minor sediment component, and in areas where coarse-grained relict deposits occur. Some potential dangers from offshore petroleum development include: (1) rapid and complete mixing of Cook Inlet waters, (2) adsorption of pollutants by clay deposited in quiet bays, and (3) ion-exchange and adsorption of chemical pollutants on clays that are part of the suspended sediment load in lower Cook Inlet.

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USGS1977

Geologic framework of lower Cook Inlet, Alaska

Lower Cook Inlet is located in south-central Alaska between lat 58°45' and 60°30' N. and between long 151° and 154° W. (fig. 1). Geographic features on the perimeter of the area are the Aleutian Range on the northwest, Kalgin Island on the northeast, the Kenai Peninsula on the east, the Barren Islands on the southeast, and the Kamishak Hills-Cape Douglas area on the south. Augustine Island, a prominent active composite volcano, is in the southwestern part of lower Cook Inlet. Lower Cook Inlet is part of a large bay that is nearly surrounded by mountains except where it opens southeastward into the Gulf of Alaska and southward into Shelikof Strait. In anticipation of oil and gas lease sales in lower Cook Inlet, the U.S. Geological Survey acquired geological and geophysical data to study the geologic framework and petroleum geology of this area. These data were included in the lower Cook Inlet environmental impact statements (Alaska Outer Continental Shelf Office, 1976a, b) and are being made available to other government agencies and the public.

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USGS1975

Hydrocarbon potential, geologic hazards, and the technology, time-frame and infrastructure for exploration and development of the lower Cook Inlet, Alaska; a preliminary assessment

The Lower Cook Inlet Outer Continental Shelf (OCS) contains 5600 km 2 of submerged land in less than 200 m of water 150 to 350 km southwest of Anchorage, Alaska. This area could contain from 0.3 to 1.4 billion barrels of oil and from 0.6 to 2.7 trillion cubic feet of natural gas depending upon the statistical confidence level indicated. The known geology of this submerged area, is extrapolated to the offshore from onshore data. The sedimentary rocks are as old as Triassic and as young as Pleistocene. The Mesozoic strata include volcanic rocks, volcanoclastic and marine clastic sediments. Tertiary, rocks from which the oil and gas in Upper Cook Inlet are produced, consist of nonmarine conglomerate, sandstone, siltstone and coal. The potential objective section for oil and gas in this OCS area ranges from Middle Jurassic through the Tertiary. The present structural configuration of this area is a northeast trending trough filled with Tertiary sediments. The trough is flanked by two major faults, the Bruin Bay fault on the northwest and the Border Ranges fault on the southeast. Between these faults is the OCS area containing anticlinal structures and faults which may be traps for hydrocarbons. Potential geologic hazards are present in this area. It is an area of intense tectonism expressed as seismic activity (earthquakes) and volcanic eruptions which produce many natural disturbances including tsunamis. This distribution of soft sediment and other submarine features which relate to geologic hazards are only generally known.

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