Search USGS⌕ Search

Geology topics

Research about Anchorage, Alaska

Source-linked reports with geographic coverage including Anchorage, Alaska.

49 records · Page 3Linked to original sources
USGS1974

Water-quality and geohydrologic data at two sanitary landfill sites near Anchorage, Alaska

Water-quality and geohydrologic data were collected at two sanitary landfill (solid-waste disposal) sites near Anchorage, Alaska. The study was undertaken by the U.S. Geological Survey in cooperation with the Greater Anchorage Area Borough and the U.S. Air Force. The purpose of the study was to evaluate the environmental effects of solid-waste disposal on the ground-water system and establish criteria for selecting future landfill sites. This report is a compilation of the data collected through August 1973.

Alaska↗
USGS1972

Reconnaissance bedrock geologic map of the Chugach Mountains near Anchorage, Alaska

The area between Knik and Turnagain Arms east of Anchorage is underlain mostly by rocks that are part of an extensive arcuate belt of thick Mesozoic marine deposits that extend through the Chugach-Kenai-Kodiak Mountains. The two main units in this belt are the Jurassic (?) and Cretaceous Valdez (?) Group composed of flysch deposits and the McHugh Complex composed of oceanic metavolcanic sequences tectonically mixed with metaclastic rocks derived from a continental magmatic arc. Deformation of the McHugh Complex is characterized by pervasive, closely spaced shear fractures and is melange-like in some areas. Deformation of the Valdez (?) Group is characterized by tight folding that was initiated before the sediments were completely lithified. The folds have steeply dipping axial surfaces that are overturned to the northwest in some areas and to the southeast in other areas. The Jurassic and(or) Cretaceous McHugh Complex is separated from the Valdez (?) Group by the Eagle River thrust fault. The Valdez (?) Group was probably deposited primarily on oceanic crust that was collapsed against the continental margin in latest Cretaceous to early Tertiary time. An accurate belt of upper Paleozoic to lower Mesozoic rocks to the north and west had been deformed, accreted to the continental margin, and intruded by plutons prior to the deposition of the Jurassic (?) and Cretaceous sediments. Rocks of the continental terrane that underlie the Wrangell and Talkeetna Mountains and the Alaska Range are locally exposed in the map area north and west of the Knik fault zone. Near the village of Eklutna, the junction between the two terranes is marked by an ophiolitic assemblage.

Alaska↗
USGS1968

Alaska Railroad Terminal Reserve, Anchorage, soil-stability study: Stability in the vicinity of boring lines 1 and 2

This report has been prepared in response to a request dated April 22, 1966, from the General Manager of The Alaska Railroad to the Director, U.S. Geological Survey, for an evaluation of the propriety of continued industrial expansion on land contained within The Alaska Railroad Terminal Reserve and nearby. It is based on field examination June 8-12, 1966, in company with Messrs. E. B. Eckel and E. G. Dobrovolny, field work September 19-October 3, 1966, and May 1-June 4, 1967, on discussions with the staff of The Alaska Railroad, my colleagues, and Professor H. B. Seed of the University of California, and on review of published and unpublished material pertinent to the area and its problems. During the fall of 1966 a detailed topographic map of the port area was prepared for The Alaska Railroad by Jay Whiteford and Associates. During late 1966 and early 1967 a drilling, sampling and soils testing program in an area of immediate interest along Boring Lines 1 and 2 was made by Adams, Corthell, Lee, Wince, and Associates (ACLW), a consultant engineering firm, under contract to The Alaska Railroad. Most of the basic data used in this report for stability analyses, such as the geometry of the ground surface and the physical properties of the materials, was derived from the Whiteford map and the ACLW investigations.

Alaska↗
USGS1967

Effect of the earthquake of March 27, 1964, on the Eklutna Hydroelectric Project, Anchorage, Alaska, with a section on television examination of earthquake damage to underground communication and electrical systems in Anchorage

The March 27, 1964, Alaska earthquake and its associated aftershocks caused damage requiring several million dollars worth of repair to the Eklwtna Hydroelectric Project, 34 miles northeast of Anchorage. Electric service from the Eklutna powerplant was interrupted during the early phase of the March 27 earthquake, built was restored (intermittently) until May 9,1964, when the plant was closed for inspection and repair. Water for Eklutna project is transported from Eklutna Lake to the powerplant at tidewater on Knik Arm of Cook Inlet by an underwater intake connected to a 4.46-mile tunnel penstock. The primary damage caused by the earthquake was 1at the intake structure in Eklutna Lake. No damage to the power tunnel was observed. The piles-supported powerplant and appurtenant structures, Anchorage and Palmer substations, and the transmission lines suffered minor dammage. Most damage occurred to facilities constructed on un-consolidated sediments and overburden which densified and subsided during the earthquake. Structures built on bedrock experienced little or no damage. Underground communication and electrical systems in Anchorage were examined with a small-diameter television camera to locate damaged areas requiring repair. Most of the damage was concentrated at or near valley slopes. Those parts of the systems within the major slide areas of the city were destroyed.

Alaska↗
USGS1966

Effects of the March 1964 Alaska earthquake on the hydrology of the Anchorage area, Alaska

The Anchorage hydrologic system was greatly affected by the seismic shock. Immediate but temporary effects included increased stream discharge, seiche action on lakes, and fluctuations in ground-water levels. Generally, ground-water levels were residually lowered after the initial period of fluctuation. This lowering is attributed either to changes in the discharge zones offshore or to a change in the permeability of the aquifers by seismically induced strain. Water supplies were disrupted temporarily by snowslides on streams and by sanding or turbidity in wells. Salt-water encroachment to wells on Fire Island seems to have increased. The approximate 3.7-foot lowering of land level and the diminished artesian head may permit further salt-water encroachment. Increased pore pressure in the Pleistocene Bootlegger Cove Clay led to liquefaction in silt and sand lenses that contributed to the disastrous bluff landslides. Measurements after the earthquake indicate that most pore pressures are declining, whereas some remain high or are increasing. Subsidence in the area was caused principally by tectonic readjustment, but differential compaction within the Bootlegger Cove Clay contributed to subsidences estimated to be as much as 0.6 foot beneath Anchorage.

Alaska↗
USGS1965

Water resources appraisal of the Anchorage area, Alaska

At the present, water use in the Anchorage area amounts to about 21 mgd (million gallons per day); of this amount ground water accounts for about 10 mgd. By 1980, 60 mgd may be required to meet the demand. The greatest potential problem is overpumping the ground-water reservoir resulting in excessive declines in water levels, which, in turn, might lead to salt-water intrusion. A well-laid plan for conjunctive use of surface and ground water seems to be the most promising means of supplying the expected need of 60 mgd, and of preventing saltwater intrusion of the aquifers. Total inflow into the Anchorage hydrologic system amounts to about 180 mgd. Of this amount Ship and South Fork Campbell Creeks contribute about 130 mgd, North Fork Campbell Creek and other streams contribute an estimated 24 mgd, and precipitation and ground-water inflow contribute an estimated 26 mgd. Of the total outflow, which must be equivalent to the inflow, Ship and Chester Creeks contribute about 94 mgd, Campbell Creek about 25 mgd, and ground-water pumpage contributes an assumed amount of approximately 10 mgd. The difference of 50 mgd between inflow and outflow presumably is accounted for; by submarine discharge beneath Cook Inlet and evapotranspiration. Surface and subsurface storage of excess stream discharge during periods of high flow can overcome the problem of water shortages during periods of greatest demand. Surface storage can be accomplished by construction of an additional dam on Ship Creek. Natural ground-water storage can be supplemented by spreading techniques to increase the amount of ground-water recharge. Additional recharge can be provided by returning air-conditioning water to the aquifer through recharge wells. Recharge along the coastline would be a means of maintaining a fresh-water barrier against salt-water intrusion. The area with the greatest potential for ground-water development is along Ship Creek east and north of Mountain View. The alluvial fan east of Mountain View seems favorable for installation of deep wells; and withdrawal of ground water in this area is not likely to result in salt-water intrusion. Similar favorable conditions exist in the alluvial fan areas of North and South Forks Campbell Creek. Infiltration galleries in alluvial deposits along Ship Creek are a relatively inexpensive and convenient means of withdrawing water. To plan for orderly and economical development of the Anchorage area's water resources, geologic and hydrologic studies are needed. An expanded network of stream-gaging stations and observation wells is needed. Deep wells near the coastline are needed to monitor any changes in chemical quality of ground water that would indicate impending salt-water intrusion. Borehole geophysical studies and pumping tests are needed to define the boundaries and hydraulic characteristics of the aquifers. The primary goal of these and other supplementing studies would be to provide the information needed to construct an electric-analog model of the Anchorage hydrologic system. Such a model would provide a means of assessing quantitatively alternative methods of water development.

Alaska↗
USGS1965

Effects of the earthquake of March 27, 1964, at Anchorage, Alaska

Anchorage, Alaska’s largest city, is about 80 miles west-northwest of the epicenter of the March 27 earthquake. Because of its size, Anchorage bore the brunt of property damage from the quake; it sustained greater losses than all the rest of Alaska combined. Damage was caused by direct seismic vibration, by ground cracks, and by landslides. Direct seismic vibration affected chiefly multistory buildings and buildings having large floor areas, probably because of the long period and large amplitude of the seismic waves reaching Anchorage. Most small buildings were spared. Ground cracks caused capricious damage throughout the Anchorage Lowland. Cracking was most prevalent near the heads or within landslides but was also widespread elsewhere. Landslides themselves caused the most devastating damage. Triggering of landslides by the earthquake was related to the physical-engineering properties of the Bootlegger Cove Clay, a glacial estuarine-marine deposit that underlies much of the Anchorage area. The Bootlegger Cove Clay contains zones of low shear strength, high water content, and high sensitivity that failed under the vibratory stress of the earthquake. Shear strength in sensitive zones ranged from less than 0.2 tsf to about 0.5 tsf; sensitivity ranged from about 10 to more than 40. Sensitive zones generally are centered about 10 to 20 feet above sea level, between zones of stiff insensitive clay. Many physical tests by the U.S. Army Corps of Engineers were directed toward analyzing the causes of failure in the Bootlegger Cove Clay and finding possible remedies. Strengths and sensitivities were measured directly in the field by means of vane shear apparatus. A4tterberg limits, natural water contents, triaxial shear, sensitivity, dynamic modulus, consolidation strength, and other properties were measured in the laboratory. Pulsating-load tests simulated earthquake loading. Most of the destructive landslides in the Anchorage area moved primarily by translation rather than by rotation. Thus, all the highly damaging slides were of a single structural dynamic family despite wide variations in size, appearance, and complexity. They slid on nearly horizontal slip surfaces after loss of strength in the Bootlegger Core Clay. Same failures are attributed to spontaneous liquefaction of sand layers. All translatory slides surmounted flat-topped bluffs bounded marginally by steep slopes facing lower ground. Destructive translatory slides occurred in the downtown area (Fourth Avenue slide and L Street slide), at Government Hill, and at Turnagain Heights. Less destructive slides occurred in many other places-mostly uninhabited or undeveloped areas. In most translatory slides, damage was greatest in graben areas at the head and in pressure-ridge areas at the toe. Many buildings inside the perimeters of slide blocks were little damaged despite horizontal translations of several feet. The large Turnagain Heights slide, however, was characterized by a complete disintegration and drastic lowering of the prequake land surface. Extensive damage back from the slide, moreover, was caused by countless tension cracks. An approximation of the depth of failure in the Bootlegger Cove Clay in the various slides may be obtained by using a geometric relationship herein called the "graben rule." Because the cross-sectional area of the graben at the head of the slide approximated the cross-sectional area of the space voided behind the slide block as the block moved outward, the depth of failure was equal to the area of the graben divided by the lateral displacement. This approximation supplements and accords with test data obtained from borings. The graben rule should apply to any translatory slide in which flowage of material from the zone of failure has not been excessive. Geologic evidence indicates that landslides similar to those triggered by the March 27 earthquake have occurred in the Anchorage area at various times in the past.

Alaska↗
USGS1951

Water utilization Ship Creek near Anchorage, Alaska

Ship Creek drains an area in the Chugach Mountains, flows westward through Anchorage, and empties into Knik Arm. It emerges from the mountains 10 miles east of Anchorage and above that point has a drainage area of 90 square miles. Stream flow records for the 4 year period, 1947 through 1950, show a mean flow of 156 second-feet with a variation from 114 second-feet for 1950 to 198 second-feet for 1949. The monthly distribution of flow has considerable variation with about one-fifth of the runoff in the 6 month period December to May, and about one-half the runoff in the 3 month period, June, July, and August. Storage is therefore required for regulation and most effective use of the streamflow. There is no natural storage in the basin. Storage possibilities and power developments are not favorable. Two possible sites are considered in this report, one at mile 1.0 and one at mile 3.5. Development at the former site would produce 3200 and 2300 KW for 50 percent and 90 percent of the time while development at the latter would produce 5000 and 4400 KW for 50 percent and 90 percent of the time. Ship Creek is not a glacier fed stream and thus is free from glacial silt and offers a good source of municipal and industrial water supply. The natural flow is sufficient to supply present demands and it is believed that with the development of storage demands created by any foreseeable expansion of Anchorage and the surrounding area can readily be met.

Alaska↗
USGS1947

Reconnaissance report on geology of Eklutna Lake dam site and conduit route near Anchorage, Alaska

Summary and Recommendations 1. Eklutna Lake and Eklutna Creek lie in a wide, deep, glaciated, trough-like valley. Downstream from the lake, this valley is partially filled with unconsolidated glacial and alluvial deposits. 2. Eklutna Lake dam site, located about 400 feet below the lake outlet, is suitable for a low dam of flexible, earth-embankment type. Adequate control of the stream can be obtained by raising the lake level about 50 feet to altitude 910 feet, which will provide hold-over storage from wet years to dry years. Such a structure will have a crest length of about 1,950 feet. A. Bedrock is probably 200 to 475 feet below stream bed at the proposed axis. The dam will rest on glacial deposits of till, clay, sand and gravel, and on deposits of lake-shore and alluvial fan gravels. B. Geologic conditions in the area of the right abutment, as yet imperfectly known, may make necessary a long, deep cutoff extending for an unknown distance beyond the north end of the dam. C. A foundation exploration program is recommended that includes deepening test pit No. 1 and drill hole No. 2, and drilling 11 new holes. It is suggested that one drill hold near the center of the valley be taken to bedrock to give a complete picture of the fill materials underlying the foundation. 3. Delivery of water from the forebay of the reservoir to the powerhouse eight miles downvalley by means of a conduit is regarded as infeasible because: difficult terrain of the route will require earthwork more extensive than the volume of the dam; the route is subject to land slides, and will require expensive maintenance; it is more or less completely exposed to adverse winter conditions that may engender icing conditions; and it is easily subject to sabotage. It is recommended that the water be taken to the powerhouse through a rock tunnel.

Alaska↗