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At least 289 records · Page 16Linked to original sources
USGS1984

Offset of Tertiary arcs on the Alaska Peninsula: A section in Geological Survey research, fiscal year 1981

Geologic mapping and potassium-argon dating by R. L. Detterman, F. H. Wilson, J. E. Case, and Nora Shew in the Ugashik and western part of the Karluk quadrangles have shown that the Eocene and Oligocene volcanic arc continues into these quadrangles from the south in the Chignik and Sutwik Island quadrangles. Surface exposures of the arc extend northward to approximately 57°30'N., or midway through the Ugashik quadrangle, but none are observed north of that point. Subsurface drill-hole data (Brockway and others, 1975) indicate continuation of the arc, possibly offset to the northwest of the northernmost known surface exposures. In the extreme northern part of the Ugashik and Karluk quadrangles, volcanic rocks again become important. These volcanic rocks are as yet undated; however, they may be related to the Katmai late Tertiary volcanic centers. Like the early Tertiary volcanic arc, the present-day Aleutian arc is also offset to the northwest in the northern part of the Ugashik and Karluk quadrangles. No major offset of the Mesozoic rocks is indicated through the offset zone; this fact suggests a change in the Tertiary tectonic regime in the area of the offset.

Alaska↗
USGS1997

Kinderhookian (Lower Mississippian) calcareous rocks of the Howard Pass quadrangle, western Brooks Range: A section in Geologic studies in Alaska by the U.S. Geological Survey, 1995

Calcareous rocks of Kinderhookian (early Early Mississippian) age are widely distributed across the Howard Pass quadrangle in the western Brooks Range. Most occur in the lower part of the Lisburne Group (herein called the Rough Mountain Creek unit) and the upper part of the Endicott Group (Kayak Shale) in two sequences (Key Creek and Aniuk River) of the Endicott Mountains allochthon. Kinderhookian strata are also found in the Kelly River allochthon (Utukok Formation?) and in sections of uncertain stratigraphic affinity and structural level spatially associated with mafic volcanic rocks. Predominant Kinderhookian lithologies in the Lisburne Group are skeletal supportstone (rich in pelmatozoans, bryozoans, and brachiopods) and lesser spiculite; skeletal supportstone and calcarenite are the chief calcareous rock types in the Kayak Shale. Conodont and brachiopod faunas indicate that all of the Rough Mountain Creek unit and much of the Kayak Shale in the study area are of late Kinderhookian age. Lithologic and paleontologic data suggest that Kinderhookian strata in the Howard Pass quadrangle were deposited largely in inner- and middle-shelf settings with normal marine salinity and locally high energy. Overall, calcareous beds in the Rough Mountain Creek unit accumulated in a wider range of environments, less subject to siliciclastic input, than did calcareous beds in the Kayak, and Kinderhookian beds of both units in the Key Creek sequence formed in less diverse, somewhat shallower environments than correlative rocks in the Aniuk River sequence. Lithofacies patterns and contact relations imply that decreased siliciclastic influx, perhaps accompanied by relative sea-level rise, initiated deposition of the Rough Mountain Creek unit; relative sea-level rise and concurrent circulatory restriction most likely ended its deposition. Kinderhookian calcareous rocks in the Howard Pass quadrangle have several implications for middle Paleozoic paleogeography of the western Brooks Range. First, sequences of the Endicott Mountains allochthon that contain the Rough Mountain Creek unit contrast sharply with other sequences included in this allochthon that contain thicker and younger Carboniferous platform carbonate successions. These differences in stratigraphic succession suggest significant shortening within the Endicott Mountains allochthon. Second, Kinderhookian calcareous rocks in the Howard Pass quadrangle may have been a secondary source for carbonate turbidites of the Rim Butte unit (Ipnavik allochthon).

Alaska↗
USGS2001

Quaternary geology, Cold Bay and False Pass quadrangles, Alaska Peninsula

Recent mapping and interpretation of Quaternary geologic features has improved our understanding of the interaction between volcanic, glacial, and tectonic activity in the Cold Bay and False Pass 1:250,000-scale quadrangles on the Alaska Peninsula. The glacial and volcanic record of the map area strongly suggests that continental-shelf glaciations and two massive volcanic centers were the dominant controls over landscape development during Pleistocene time. Ancestral Morzhovoi and Emmons Volcanoes were major impediments to flow of shelf glaciers during much of the Pleistocene. Our mapping suggests that the area around Emmons Volcano may have also been an important source area for glaciers during this period. Our data further indicate that Frosty Volcano developed late in the Pleistocene, having had no apparent impact on early Brooks Lake glacial advances but serving as a source area for later glacial advances during late Brooks Lake time. We also believe that major Holocene eruptions of Frosty Volcano have yielded multiple debris and ash flows resulting in the construction of a new south summit cone that filled an earlier crater. Frosty Volcano was the source area for multiple Holocene glacial advances, and its flanks preserve the best record of Neoglacial activity in the map area.

Alaska↗
USGS2001

Reconnaissance geology north of the Hoholitna River, Taylor Mountains D-1 1:63,360-scale quadrangle, southwestern Alaska: A section in Geological studies in Alaska by the U.S. Geological Survey, 1999

The lower Paleozoic (Silurian and Ordovician) carbonate stratal succession is divided into six unnamed stratigraphic units in the northern part of the Taylor Mountains D-1 1:63,360-scale quadrangle of southwestern Alaska. Several of these units have previously been recognized in the McGrath and Medfra quadrangles to the northeast in strata of the Nixon Fork subterrane of the Farewell terrane (Decker and others, 1994 ). These rocks occur along the south side of a prominent east-west-trending anticlinoria! axis exposed slightly to the north in the Sleetmute A-2 1:63,360-scale quadrangle. Rocks of the Nixon Fork subterrane are now thought to represent a continental margin sequence rifted from Siberia. The low thermal alteration indices exhibited by the rocks of this area have elicited interest for petroleum exploration. However, low total organic carbon (TOC) values from potential source rocks within this lower Paleozoic succession indicate low petroleum potential.

Alaska↗
USGS2001

Use of Landsat MSS and TM imagery to improve reconnaissance geologic mapping in the Ruby quadrangle, west-central Alaska: A section in Geological studies in Alaska by the U.S. Geological Survey, 1999

By using Multispectral Scanner (MSS) and Thematic Mapper (TM) satellite images, the spatial relation of units JMtu (mafic, ultramafic, and sedimentary rocks, undivided) and PzZrqs (pelitic and quartzitic schist) of Wilson and others (1998) from the northeastern portion of the Ruby 1:250,000-scale quadrangle geologic map was further defined. The MSS image was first analyzed using spectral signatures to separate and highlight pixels associated only with the units of interest. This approach was ineffective at separating the units from areas of the image with similar spectral signatures, but it did show that unit JMtu and associated areas consistently had a high brightness value, while unit PzZrqs and associated areas consistently had a low brightness value. Consequently, a new approach was developed using spectral enhancement to emphasize the differences between these high- and low- brightness areas. Once the TM image was obtained, the spectral signature separation and spectral enhancement approaches were again tested, but the results were similar to those found using the MSS image. By using the results from the spectral enhancement of the MSS image in combination with current ground-truth data, the locations of units JMtu and PzZrqs in the Ruby quadrangle were reinterpreted.

Alaska↗
USGS1902

Reconnaissance from Fort Hamlin to Kotzebue Sound, Alaska, by way of Dall, Kanuti, Allen, and Kowak Rivers

The reconnaissance described in the following pages was carried out in pursuance of a plan which has been followed for some years by the United States Geological Survey in the topographic and geologic exploration of the little-known parts of Alaska and in the collection of such information as will be of value not only to the scientific world, but to the prospector, the miner, and the trader. Capital disappears and years are wasted by prospectors who push out beyond the shifting frontier and pursue their search for gold where gold is not to be expected, and lives are being continually lost because the location and character of trails, drainage ways, and mountain ranges and passes are unknown, or because the knowledge which a few possess is not in a form available for the use of others.

Alaska↗
USGS1976

Geological Survey research 1976

This U.S. Geological Survey activities report includes a summary of recent (1976 fiscal year) scientific and economic results accompanied by a list of geologic and hydrologic investigations in progress and a report on the status of topographic mapping. The summary of results includes: (1) Mineral resources, Water resources, (2) Engineering geology and hydrology, (3) Regional geology, (4) Principles and processes, (5) Laboratory and field methods, (6) Topographic surveys and mapping, (7) Management of resources on public lands, (8) Land information and analysis, and (9) Investigations in other countries. Also included are lists of cooperating agencies and Geological Survey offices.

Professional Paper↗
USGS1976

Numerical simulation analysis of the interaction of lakes and ground water

Because the interrelationship of lakes and ground water is perhaps the least understood aspect of lake hydrology, vertical-section, steadystate, numerical-model simulations were run to evaluate the factors that control the interaction of lakes and ground water. The study is concerned only with lakes encircled by water-table mounds that are at a higher altitude than lake level. Simulations of one-lake and multiple-lake systems in vertical sections show that for many hydrogeologic settings, the line (divide) separating local from regional ground-water flow systems is continuous beneath individual lakes. If the divide is continuous, there exists a point along it at which the head is a minimum compared to all other points along the divide. This point of minimum head is always greater than the head represented by lake level, therefore in such a setting there can be no movement of lake water through the lake bed to the ground-water system. In a setting where the divide is not continuous, the lake loses water through part of its bed, but rarely in the littoral zone of the lake. Factors that strongly influence the position, shape, and continuity of the flow-system divide beneath lakes are height of the water table on the downslope side of the lake relative to lake level, position and hydraulic conductivity of aquifers within the ground-water reservoir, ratio of horizontal to vertical hydraulic conductivity of the groundwater system, and lake depth.

Professional Paper↗
USGS1976

The Guatemalan earthquake of February 4, 1976, a preliminary report

The Guatemalan earthquake of February 4, 1976, with a surface-wave magnitude of 7.5, was generated by left-lateral slippage on the Motagua fault and was felt over an area of at least 100,000 km2. This earthquake claimed more than 22,700 lives and injured more than 76,000 people. The preliminary estimate of losses is about $1,100,000,000.

Professional Paper↗
USGS1978

Effects of urbanization on streamflow and sediment transport in the Rock Creek and Anacostia River basins, Montgomery County, Maryland, 1962-74

Land use, precipitation, streamflow, and sediment discharge data were collected from nine small drainage basins in Montgomery County, Maryland, to evaluate runoff and sediment response to sediment-control practices in areas undergoing urban development. Drainage basins ranged in size from 0.35 to 21.1 sq mi and land use ranged from rural to 60 percent urban. Urbanization did not affect low and medium flows, but it did result in increased storm runoff and peak flows. Suspended sediment transported from one of the basins that underwent urban development, the 21.1 sq mi Anacostia River basin, averaged 15 ,400 tons/yr between 1962 and 1974. Bedload was estimated as 5 to 11 percent of the total load. Cropland, urban land, and construction sites were the major sources of sediment. Average annual sediment yields ranged from 065 to 4.3 tons/acre for cropland, 3.7 tons/acre for urban land, and 7 to 100 tons/acre for urban construction sites. The magnitude of the yields from construction sites was significantly affected by (1) the slope of the sites, (2) the proximity of stream channels, (3) buffer zones of natural vegetation, and (4) sediment-control measures. Sediment controls, particularly those enforced under a 1971 sediment-control ordinance, apparently decreased construction-site sediment yields by 60 to 80 percent.

Maryland↗
USGS1977

Large landslides, composed of megabreccia, interbedded in Miocene basin deposits, southeastern Arizona

The landslides in the Kearny and El Capitan Mountain quadrangles, Pinal and Gila Counties, Ariz., are tabular or lens like masses of megabreccia enclosed in Miocene basin deposits. The megabreccias within individual slide blocks are composed of pervasively brecciated Precambrian and younger formations that remain in normal stratigraphic sequence, indicating that each landslide moved as a fairly coherent mass. The megabreccias consist of fresh, mostly angular rock fragments in a comminuted matrix of the same composition as the fragments. The matrix ranges in amount from sparse to abundant. Where the matrix is sparse, the fragments fit tightly with little or no rotation. Locally fragments are rotated but not moved far; most units within a slide block are lithologically homogeneous. The Kearny landslides are conformably interbedded in steeply east-dipping playa and alluvial deposits. They form map units from a few tens of meters to nearly 4 km long and from less than 1 to 270 m wide. Narrow ridges expose sections through the landslides at about right angles to the direction of movement. The upper (proximal) ends have been eroded; the lower (distal) ends are buried. The El Capitan landslide dips very gently southward. Although partly dissected during erosion of the enclosing alluvial and lakebed deposits, its approximate original outline is still preserved. It forms a thin sheet, 5-15 m thick and at least 3.8 km long; the maximum outcrop width, near its distal end, is about 1.5 km. The Kearny landslides show little evidence of having exerted differential pressure on the underlying soft playa and alluvial deposits, and the contacts with the underlying sediments have little relief. The distal end of the El Capitan landslide, on the other hand, has considerable relief. As the landslide came to an abrupt stop, the end plowed into the underlying sediments, compressing them into fol9.s and forming sandstone dikes. The source of the El Capitan landslide is a well-defined amphitheater on the south side of El Capitan Mountain 1,500 to more than 3,000 m above and 1.5-3 km north of the proximal end of the landslide. The long distance traveled on a very gentle slope indicates that the El Capitan landslide had a very low coefficient of friction, similar to some modern and prehistoric avalanches. According to Shreve, they may have traveled on a thin lubricating layer of compressed air. The coefficient of friction of the Kearny landslides cannot be determined. However, the nonturbulent character of both the Kearny and El Capitan landslides indicates that they slid rather than flowed.

Professional Paper↗