USGS Science⌕ Search

Geology topics

Research about Cook Inlet

Source-linked reports with geographic coverage including Cook Inlet.

23 records · Page 2Linked to original sources
USGS1999

Seasonal shorebird use of intertidal habitats in Cook Inlet, Alaska

Seasonal shorebird use of intertidal habitats of Cook Inlet, Alaska, was studied from February 1997 to February 1999 using aerial surveys as the principal method of assessment. On-ground studies were conducted to validate aerial survey results and to assess shorebird use of vegetated habitats, especially during the breeding season. Twenty-eight species of shorebirds were recorded using the area, ranging from all being present during spring to a single species present during winter. The annual pattern of use was characterized by the sudden occurrence and rapid increase in numbers of birds during early May and their abrupt departure in mid- to late-May. During this period, survey totals frequently exceeded 150,000 birds per day. Comparatively little use occurred during summer and autumn, but use was significant from late autumn to early spring when Rock Sandpipers ( Calidris ptilocnemis ) resided in the Inlet. A single species, the Western Sandpiper ( C. maun ), was by far the numerically dominant shorebird, accounting for three-fourths of all birds recorded. The Pacific flyway population of this species numbers 2-3 million birds of which we estimated 20-47% used Cook Inlet embayments, especially southern Redoubt Bay. Cook .Inlet also supported between 11 and 21% of the Pacific flyway population of Dunlin ( C. alpina pacifica ) and what may be the entire population (ca. 20,000 birds) of the nominate race of the Rock Sandpiper ( C. p. ptilocnemis ). Several areas along the west side of Cook Inlet proved to be extremely important to shorebirds. Southern Redoubt Bay supported 73% of all shorebirds during spring (average 32,000 per day) while Susitna Flats accounted for 82% of use during winter (8,400 per day). International criteria used to assess the conservation importance of particular wetland sites to shorebirds not only place Cook Inlet at the highest level of recognition but afford similar recognition to several individual embayments therein. The large human population and the extent of oil and natural gas production facilities occurring in the Cook Inlet region potentially pose serious risks to shorebirds and intertidal habitats.

Alaska↗
USGS1999

Biological effects of the 1997/98 ENSO in Cook Inlet, Alaska

We have been conducting detailed studies of the biology of seabirds in relation to oceanography and forage fish ecology in lower Cook Inlet, Alaska, since 1995. This fortuitously allowed us to document biological effects of the 1997/98 ENSO in this region. Anomalously warm sea surface temperatures (SSTs) were observed in the Gulf of Alaska (GOA) beginning in June of 1997, but not in Cook Inlet until September, 1997. Warm temperature anomalies at the surface and at depth persisted until May of 1998, when temperatures returned to average in the GOA and Cook Inlet. Thus, temperature anomalies occurred outside the core window of productivity (June–August) for forage fish and seabirds in both 1997 and 1998. Abundance or production of phytoplankton, zooplankton, fish, and seabirds in lower Cook Inlet varied among years, and overall appeared to be depressed in 1998. We observed a few biological anomalies that might be attributed to ENSO effects: (1) a significant die-off of Common Murres occurred in March–May of 1998, (2) murres and Black-legged Kittiwakes were physiologically stressed during the 1998 breeding season, (3) murres failed to reproduce at one colony in 1998, (4) kittiwake breeding success was lower than usual at colonies in 1998, and (5) phenology of breeding was later in 1998 for both murres and kittiwakes. We presume that seabird die-offs, reduced productivity and delayed phenology were linked to a reduction or delay in food availability, but the mechanism by which anomalously warm water temperatures in winter reduce forage fish availability during the summer breeding season for seabirds is not known.

Alaska↗
USGS1978

Geologic framework of lower Cook Inlet, Alaska

Three seismic reflectors are present throughout the lower Cook Inlet basin and can be correlated with onshore geologic features. The reflections come from unconformities at the base of the Tertiary sequence, at the base of Upper Cretaceous rocks, and near the base of Upper Jurassic strata. A contour map of the deepest horizon shows that Mesozoic rocks are formed into a northeast-trending syncline. Along the southeast flank of the basin, the northwest-dipping Mesozoic rocks are truncated at the base of Tertiary rocks. The Augustine-Seldovia arch trends across the basin axis between Augustine Island and Seldovia. Tertiary rocks thin onto the arch from the north and south. Numerous anticlines, smaller in structural relief and breadth than the Augustine-Seldovia arch, trend northeast parallel with the basin, and intersect the arch at oblique angles. The stratigraphic record shows four cycles of sedimentation and tectonism that are bounded by three regional unconformities in lower Cook Inlet and by four thrust faults and the modern Benioff zone in flysch rocks of the Kenai Peninsula and the Gulf of Alaska. The four cycles of sedimentation are, from oldest to youngest, the early Mesozoic, late Mesozoic, early Cenozoic, and late Cenozoic. Data on organic geochemistry of the rocks from one well suggest that Middle Jurassic strata may be a source of hydrocarbons. Seismic data show that structural traps are formed by northeast-trending anticlines and by structures formed at the intersections of these anticlines with the transbasin arch. Stratigraphic traps may be formed beneath the unconformity at the base of Tertiary strata and beneath unconformities within Mesozoic strata.

Alaska↗
USGS1967

Ground breakage and associated effects in the Cook Inlet area, Alaska, resulting from the March 27, 1964, earthquake

The great 1964 Alaska earthquake caused considerable ground breakage in the Cook Inlet area of south-central Alaska. The breakage occurred largely in thick deposits of unconsolidated sediments. The most important types of ground breakage were (1) fracturing or cracking and the extrusion of sand and gravel with ground water along fractures in various types of landforms, and (2) slumping and lateral extension of unconfined faces, particularly along delta fronts. The principal concentration of ground breakage within the area covered by this report was in a northeast-trending zone about 60 miles long and 6 miles wide in the northern part of the Kenai Lowland. The zone cut across diverse topography and stratigraphy. Cracks were as much as 30 feet across and 25 feet deep. Sand, gravel, and pieces of coal and lignite were extruded along many fissures. It is suggested that the disruption in this zone may be due to movement along a fault in the underlying Tertiary rocks. The outwash deltas of Tustumena and Skilak Lakes in the Kenai Lowland, of Eklutna Lake and Lake George in the Chugach Mountains, of Bradley Lake in the Kenai Mountains, and at the outlet of upper Beluga Lake at the base of the Alaska Range showed much slumping, as did the delta of the Susitna River. Parts of the flood plains of the Skilak River, Fox River, and Eagle River were extensively cracked. A few avalanches and slumps occurred along the coast of Cook Inlet in scattered localities. Some tidal flats were cracked. However, in view of the many thick sections of unconsolidated sediments and the abundance of steep slopes, the cracking was perhaps less than might have been expected. Observations along the coasts indicated changes in sea level which, although caused partly by compaction of unconsolidated sediments, may largely be attributed to crus1tal deformation accompanying the earthquake. Most of the Cook Inlet area was downwarped, although the northwest side of Cook Inlet may have been slightly unwarped. Maximum change in the Cook Inlet area was probably less than 6 feet. Little or no regional tilting was detected in the lake basins of Tustumena and Skilak Lakes.

Alaska↗