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At least 91 records · Page 5Linked to original sources
USGS1961

Lava temperatures in the 1959 Kilauea eruption and cooling lake

The 1959 summit eruption of Kilauea Volcano, Hawaii, filled the crater of Kilauea Iki with a lake of lava 365 feet deep. Temperatures of the erupting basalt ranged between 1060° and 1190°C. Temperatures down a 12.7-foot-deep hole, drilled into the crust of the lake 5 months after cessation of eruptive activity, agree with calculated temperatures based on the heat equation. The cooling effect of rainfall is pronounced only in the upper 3½ feet of the crust.

Hawaii↗
USGS1962

Lava tree molds of the September 1961 eruption, Kilauea Volcano, Hawaii

Well-developed lava tree molds were formed during the September 1961 eruption along the east rift zone of Kilauea Volcano. The upright molds were produced where fluid lava, flowing through dense tropical forest, became chilled against the larger trees and tree ferns and later drained away. Where the lava ponded temporarily in a structural valley, tree molds more than 14 feet high mark the high level attained by the flow.

Hawaii↗
USGS1962

Mechanics of a small landslide block, Wattener Lizum, Austria

A small landslide block left a trail about 81 meters long on an 11½-degree slope in the Tuxer Voralpen, Austria. The movement is explained in terms of fluid pressure mechanics; hypothetically, the requisite pore pressure was caused by the loading of contiguous saturated segments of the slide path during rapid sliding.

Wattener Lizum↗
USGS1963

Reef Creek Detachment Fault, Northwestern Wyoming

he Reef Creek fault is in northwestern Wyoming, a few miles east of the northeast border of Yellowstone National Park. It lies within the area covered by the more extensive Heart Mountain fault. Like that fault, it is a décollement or detachment fault in which strata became detached along a basal shearing plane and moved laterally on a slightly inclined fault surface. At the most northwesterly exposures the Reef Creek fault parallels the bedding; southeastward it cuts upward across the bedding as a transgressive fault and becomes a fault in which the allochthonous blocks moved on the surface of the ground. The fault blocks consist chiefly of the Madison Limestone of Mississippian age and volcanic tuffs and breccias of the Cathedral Cliffs Formation of early or middle Eocene age. The Reef Creek fault blocks are scattered over a 7- by 14-mile area, but a considerable part of the scattering is due to “piggy-back” transportation on the Heart Mountain fault blocks. The Reef Creek fault is younger than the Cathedral Cliffs Formation and older than the middle Eocene early basic breccia. Consequently, the rocks transported by it were emplaced either in late early Eocene or in early middle Eocene time. Both the Reef Creek fault and the South Fork fault are older than the principal movement along the Heart Mountain fault. The movement of all three fault masses was southeastward, and the mechanics of their emplacement is believed to have been similar. Movement was due in part to gravity, but considering the low slope involved, gravity alone seems to be inadequate. The shaking motion of many earthquakes is suggested as a contributing force which acted in conjunction with the constant force of gravity.

Wyoming↗
USGS1963

Late Pleistocene glacial drainage in the Devils Lake Region, North Dakota

The Devils Lake region of northeastern North Dakota is covered with glacial drift deposited by the Leeds lobe of the Mankato Substage of the Wisconsin Stage of the Pleistocene and is underlain by Pierre Shale of Cretaceous age. Associated with the Sheyenne River, which flows through the southern part of the region in a deep trench, are many stream terraces, spillways, deposits of ice-contact stratified drift, and eroded ground-moraine areas. Six stages of drainage have been established to which these various features can be assigned. In the first two stages the features formed as melt water drained to the glacial James River south of the region and as the ice front stood at and later retreated from the site of the Heimdal moraine, a recessional moraine of the Leeds lobe. The later stages occurred after the valley of the Sheyenne River was free of ice and after glacial Lake Souris northwest of the region drained down the valley to glacial Lake Agassiz in the eastern part of the state. Features originating during the four later stages are largely related to the deposition of the North Viking moraine (another, more northern, recessional moraine of the Leeds lobe) and subsequent retreat of the ice from the moraine. Discharge from the local Devils and Stump lakes and from glacial Lake Souris also were of considerable importance in the genesis of many features.

North Dakota↗
USGS1964

Barchan-dune movement in Imperial Valley, California

The movement of 47 barchan dunes on the west side of Salton Sea, California, ranged from 325 to 925 feet over the 7 years between 1956 and 1963, an average of 82 feet per year. During the 15 years between 1941 and 1956, the movement of 34 of these dunes ranged between 350 and 1200 feet, an average of 50 feet per year. This difference in average movement during the two intervals is attributed primarily to increased sand supply. Movement ( D ) plotted against height of slip face ( H ) for the Salton dunes fits reasonably well with Finkel's reciprocal curve (1 /D = n + k H ) or with a law of the type D = Pe rH . Factors other than height affect the rate of movement, one of the more important being the state of the dune, whether growing or steady state. Barchan shape, whether fat or slim, may also influence the rate of movement of growing dunes. None of these dunes needs be more than 300 years old.

California↗
USGS1964

Oriented lakes and lineaments of northeastern Bolivia

Strongly oriented lineaments, defined by lake shores and stream and vegetation alignments, are distributed throughout more than 45,000 square miles of the Beni basin in northeastern Bolivia. The area in which these features occur is a flat, poorly drained, lake-studded plain. It is underlain by flat-lying, poorly consolidated, continental clastic sediments of Late Cenozoic age which, in turn, overlie crystalline basement. To the west the basin sediments abut abruptly against the folded and faulted Andean foothills and to the east they gradually overlap gently rolling crystalline outcrops of the Brazilian Shield. The main lineaments within the basin show preferred orientations perpendicular to each other in northwest-southeast and northeast-southwest directions. These two preferred directions of lineament orientation occur in sediments that extend from the margin of the Brazilian Shield westward 200 miles to where the basin sediments are 10,000 feet thick. Two poorly developed sets of lineaments that trend roughly north-south and east-west are also present within the basin. Most lakes are strongly rectilinear in outline with shores that commonly trend northwest-southeast and northeast-southwest. They range in size from about 1000 feet square to 5.4 by 12.4 miles. Only a few lakes have streams draining into or out of them. Those that have been studied on the ground are shallow with relatively flat bottoms and abrupt steep sides. The water surfaces are almost level with the surrounding flat terrain. The two major northwest-southeast and northeast-southwest trends are probably controlled by a regionally oriented system of longitudinal and cross fractures in the crystalline basement; the poorly developed north-south and east-west sets of lineaments may reflect basement “shear” fractures. The oriented lakes and many of the major northwest-southeast and northeast-southwest-trending lineaments occupy shallow surficial subsidences that appear to form by progressive downfaulting of basement blocks or differential compaction of uncon-solidated deposits over basement blocks. The minor north-south and east-west sets and some of the northwest-southeast and northeast-southwest-trending stream and vegetation lineaments may reflect individual fractures in the underlying basement rather than areal subsidence over basement blocks. The youthful appearance of some oriented features indicates that they are probably forming at the present. Because of the unique environment of the Beni basin, where alluvial deposits are accumulating over a relatively stable shield margin in an area of flat terrain and high water table, many of the subtle surficial depressions are clearly visible as lakes with orthogonally oriented shore lines. Lakes of comparable size, shape, and degree of orientation are known to occur elsewhere only in the Old Crow Plain area of Canada. It is postulated that prelithification fractures, such as those in the Beni basin, must play a significant role during compaction, jointing, faulting, and folding of sedimentary sequences. Criteria are needed to distinguish between fracture trends that are inherited from basement rocks, and those formed by postdepositional deformation.

GSA Bulletin↗
USGS1964

Potassium-argon dates of three pleistocene interglacial basalt flows from the Sierra Nevada, california

Potassium-argon dates of 90,000 ± 90,000 years and 60,000 ± 50,000 years on the basalt in Sawmill Canyon of the Sierra Nevada, California, that underlies a moraine correlated with the Tahoe Glaciation and overlies pre-Tahoe till show that the Tahoe is probably less than 100,000 years old. Pre-Tahoe basalt near Sonora Pass gives a date of 150,000 ± 30,000 years. These data support the correlation of the Tahoe with early Wisconsin. Tahoe Glaciation in the southernmost Sierra Nevada seems to have been no less extensive than pre-Tahoe glaciation. The basalt that forms the Devils Postpile, believed by Matthes (1960) to have been extruded between his El Portal (Sherwin?) and Wisconsin glaciations, gives a date of 940,000 ± 160,000 years.

California↗
USGS1965

On lantern slides

Before photography, look at the original from as many feet away as it is inches wide, and you will see it as it will look to the audience as a slide on the screen.

GSA Bulletin↗
USGS1965

Biota of a late glacial rocky mountain pond

The sediments of a late glacial sag pond in Huerfano Park, south-central Colorado, have yielded a varied biota consisting of vertebrates, terrestrial and fresh-water mollusks, sponges, and pollen. Wood from the sediments has a radiocarbon age of 9600 ± 200 years. The vertebrate fauna contains the tooth of a prairie dog and the remains of frog, salamander, snake, and fish—all characteristic of present-day montane lakes and ponds and their margins in Colorado. The mollusks are all living species, and the fauna is dominated by gastropods. With the exception of one form (Vitrina alaskana Dall), whose known range does not extend as far south as Huerfano Park, the fauna is not significantly different from the mollusks living in the area today. The sediments also contain an abundant and unusually diversified sponge fauna in which as many as six species may be represented. A pollen spectrum from the sediments is composed of arboreal pollen characteristic of the present-day Transition Zone flora which, in Colorado, grows on the upper edge of the Great Plains and all of the foothills belt. Vertical variation in the sediment types and the enclosed biota makes it possible to recreate the changing depositional environment and local climate throughout the life of the pond. The basal sediments, interbedded marl and clastic materials, are interpreted as indicating deposition during alternating wet and dry periods. A bed of nearly pure calcium carbonate marl, which reaches a thickness of 2 feet, forms the middle stratigraphic unit. It is highly fossiliferous and is thought to have been deposited during a warm dry period with relatively mild winters. The uppermost stratigraphic unit is a gray carbonaceous clay which filled the basin as vegetation encroached upon the lake and the lake itself was reduced to a marsh. Because of the radiocarbon age and the reconstruction of the climate based upon faunal and sedimentological changes, the lower two stratigraphic units are thought to correlate with the Lubbock Subpluvial, and the uppermost unit, the gray carbonaceous clay, with the early part of the Yellow House Interval as described in the Llano Estacado, New Mexico.

Colorado↗
USGS1965

Isotopic ages of minerals from granitic rocks of the central Sierra Nevada and Inyo Mountains, California

Potassium-argon ages of biotite and hornblende from specimens of 17 granitic plutons in the central Sierra Nevada and the western Inyo Mountains, California, range from 69 to 183 m. y. The Mount Givens, Lamarck. and Round Valley Peak Granodiorites and related younger and more felsic quartz monzonites represent a pulse of magma emplaced in the general time interval of 80-90 million years ago, during Cretaceous time. Mineral ages of granitic rocks that flank these plutons on both the east and the west have been reduced during the emplacement of the Cretaceous intrusive rocks and are minimum ages for the time of crystallization. The ages of hornblende from the Tinemaha Granodiorite (150 to 180 m. y.) may approach crystallization dates. In conjunction with ages for other intrusive rocks in the Sierra Nevada and adjacent desert ranges they strongly suggest a magmatic episode during the Early Jurassic.

California↗
USGS1965

Investigation of initial Sr87/Sr86 ratios in the Sierra Nevada Plutonic Province

One to three whole-rock samples from each of more than a dozen discrete plutonic intrusions in the east-central Sierra Nevada batholith have been analyzed for Sr 87 /Sr 86 and Rb/Sr ratios to obtain information on initial Sr 87 abundances. The initial Sr 87 /Sr 86 ratios in the rock magmas forming this province appear to have been in the range 0.7073 ± .0010 in the majority of cases. This range is definitely higher than that found for modern alkali-type and tholeiite-type basalt magmas of oceanic regions, which commonly range between 0.703 and 0.705. However, it is much lower than the average Sr 87 /Sr 86 ratios found in Precambrian sialic regions which range from 0.71 to 0.73. It seems clear therefore that the Sierra Nevada magmas were not derived solely either from the typical source regions of oceanic basalt or from the melting of ancient crustal sial. It is possible that these magmas represent a mixture of oceanic basalt and crustal sial, as would be the case of anatexis in a geosyncline containing much volcanic material of fairly recent origin and some terrigenous sialic detritus. They may instead be of mantle derivation with admixtures of crustal material assimilated during their rise. The whole-rock Rb-Sr age results derivec from the study indicate that the Lamarck and Mount Givens Granodiorites and the alaskite of Evolution Basin and porphyritic biotite granite of Dinkey Lakes form a younger group of intrusive rocks of 90 ± 10 m.y. Although the sampling was not designed for isochron age studies, it appears that most of the remaining rock units are considerably older.

GSA Bulletin↗
USGS1965

Role of fluid pressure in mechanics of overthrust faulting: Reply

Davis cites four areas of low-angle faulting in which he believes that high fluid pressures can have played no important part in the development and movement of the thrust plates, but it seems to us that the concept or some variant of it may help to explain the observed field relationships in the three out of these four areas with which we have had some first-hand experience. In the areas of the Heart Mountain thrust of Wyoming, the Muddy Mountain thrust of Nevada, and the structurally higher, crystalline thrust sheets of the Swiss Alps, field relationships which include evidence of dehydration reactions during metamorphism of evaporites and of pelitic rocks suggest that interstitial fluid pressures may have been high and thus have played an essential part in the development of the thrust faults. In the fourth area cited by Davis, that of his own studies in the Klamath Mountains of California, we have had no first-hand experience and thus are not competent to answer his criticisms.

GSA Bulletin↗
USGS1965

Eclogites and eclogites: Their differences and similarities

Eclogites are divisible into three groups based on mode of occurrence: Group A, inclusions in kimberlites, basalts, or layers in ultramafic rocks; Group B, bands or lenses within migmatite gneissic terrains; Group C, bands or lenses within alpine-type metamorphic rocks. The compositions range from olivine basalt for Group A to tholeiitic basalts for Group C. New analytical data on six eclogites from glaucophane schist terrains in California and New Caledonia now permit comparisons among the three eclogite types. The pyrope content of the garnets is distinctive for each group as follows: Group A, greater than 55 per cent py; Group B, 30–55 per cent py; Group C, less than 30 percent py. Pyroxenes coexisting with these garnets also reflect a compositional change related to their occurrence. The jadeite content progressively increases from Group A through Group B, whereas the diopside content decreases. A comparison of eclogites from different geologic occurrences but with similar bulk compositions demonstrates variation in Ca-Mg partition between coexisting garnet and pyroxene. The Ca/Mg ratio increases in garnet and decreases in pyroxene from Group A through Group B eclogites. This obvious difference in the Ca-Mg partition between coexisting garnet-pyroxene in eclogites of the same bulk composition indicates a broad range of pressure-temperature conditions obtained during crystallization. Experimental synthesis of eclogite-like material at high pressures and temperatures demonstrates that some eclogites may form in the earth's mantle, but naturally occurring Group C eclogites have coexisting garnet-pyroxene with distinct Ca/Mg ratios when compared to Group A or B eclogites of similar bulk composition. This difference in the Ca/Mg ratio must reflect the pressure-temperature conditions characterizing the glaucophane schist facies.

GSA Bulletin↗
USGS1965

Potassium-argon age and paleomagnetism of the Bishop Tuff, California

Duplicate potassium-argon age determinations on each of three samples from widely separated localities indicate that the age of the Bishop Tuff, California, is about 0.7 million years. Two of the samples are from the basal ash fall that preceded the ash flow eruptions; one of these two samples was collected within 1 m of the contact of the Bishop Tuff with the underlying Sherwin Till. The third sample is from near the present exposed surface of the Bishop Tuff. The minimum age of the Sherwin Till (Kansan?) is thus 0.7 million years. The samples used for previously published age determinations of about 1 million years were probably contaminated with older material. Paleomagnetic results from five widely separated localities indicate that the welded part of the Bishop Tuff became magnetized when the geomagnetic field was normal and that it may have cooled in several centuries or less. The Brunhes-Matuyama polarity epoch boundary is now uncertain in the range of 0.7 to 1.0 million years.

California↗
USGS1966

Tropical lakes, copropel, and oil shale

During a long-continued study of the lacustrine beds of the Eocene Green River Formation, I have tried to interpret past events from observation of present-day processes. After a search of some 40 years, four lakes have been found that are producing a kind of organic ooze judged to be a modern analogue of the precursors of rich oil shale. Two of the lakes are in central Africa and two are in Florida. All four are shallow. The ooze in all four is predominantly algal, entirely in the form of minute fecal pellets, and does not decay in warm, wet, oxidizing environments. Several of the most unusual, mummified microorganisms found in the oil shale of the Green River are illustrated as testament to the inference that the Eocene organic oozes also were resistant to decay. Studies to determine why these algal oozes do not decay are in progress, but as yet no satisfactory explanation is available. The ooze from Mud Lake, Florida, contains very few living bacteria but a great many bacterial spores, suggesting some active inhibitor. Gentle and slow anaerobic decay takes place in the ooze 1 foot or more below the mud-water interface. The algal ooze accumulates slowly. That at a depth of 3 feet below the mud-water interface has a C 14 age of 2280 ± 200 years. If compacted, this 3-foot layer would amount to a layer only about 0.5 inch thick. The air-dried algal mud (from Mud Lake) looks much like oil shale and has a C-H ratio essentially like that of the organic matter in oil shale. The oxygen of the mud, however, is roughly 5 times as high as in oil shale. The calorific value of dried Mud Lake algal ooze is about 6600 cal/g, whereas the organic matter from Green River oil shale averages about 9500 cal/g. Analyses show that the dried algal ooze from Mud Lake contains small quantities of higher fatty acids (C 12 –C 34 ), with C 16 being dominant. It also contains some unsaturated fatty acids and about 0.3 per cent of n-alkanes, predominantly odd carbons, with C 29 being dominant. A few qualitative analyses show that carotenoid pigments and terpenes are also present. A possible source of hydrocarbons is the long branched side chain of the chlorophyll molecule. Small crustaceans liberate this in the form of phytol, which, by dehydration, can go over into a series of saturated and unsaturated hydrocarbons, including phytanc and pristane, both of which are common in Green River oil shale. Search for other precursors of hydrocarbons continues.

GSA Bulletin↗