Showing papers by "United States Geological Survey published in 1979"

Submarine Thermal Springs on the Galápagos Rift

Abstract: The submarine hydrothermal activity on and near the Galapagos Rift has been explored with the aid of the deep submersible Alvin Analyses of water samples from hydrothermal vents reveal that hydrothermal activity provides significant or dominant sources and sinks for several components of seawater; studies of conductive and convective heat transfer suggest that two-thirds of the heat lost from new oceanic lithosphere at the Galapagos Rift in the first million years may be vented from thermal springs, predominantly along the axial ridge within the rift valley The vent areas are populated by animal communities They appear to utilize chemosynthesis by sulfur-oxidizing bacteria to derive their entire energy supply from reactions between the seawater and the rocks at high temperatures, rather than photosynthesis

The jupiter system through the eyes of voyager 1.

Abstract: The cameras aboard Voyager 1 have provided a closeup view of the Jupiter system, revealing heretofore unknown characteristics and phenomena associated with the planet's atmosphere and the surfaces of its five major satellites. On Jupiter itself, atmospheric motions-the interaction of cloud systems-display complex vorticity. On its dark side, lightning and auroras are observed. A ring was discovered surrounding Jupiter. The satellite surfaces display dramatic differences including extensive active volcanism on Io, complex tectonism on Ganymede and possibly Europa, and flattened remnants of enormous impact features on Callisto.

Formation of Martian flood features by release of water from confined aquifers

Abstract: It is proposed that the rapid release of water under great pressure from deeply buried aquifers is responsible for the formation of the Martian channels suggestive of catastrophic flooding (outflow channels). Fine channels in the Martian surface suggest the presence of surface water early in the history of the planet, which would have entered the ground water system through the porous near-surface rocks. Subsequent global cooling would have trapped the ground water under a thick permafrost layer and formed a system of confined aquifers. High pore pressures within the aquifers are considered to have triggered the breakout of water from the aquifers at rates of from 10 to the 5th to 10 to the 7th cu m/sec, which would be prevented from reentering the ground water system by the layer of permafrost. Outflow from the aquifer is also considered to have caused the undermining of adjacent areas and the collapse of the surface to form areas of chaos, often associated with channels.

The galilean satellites and jupiter: voyager 2 imaging science results.

Abstract: Voyager 2, during its encounter with the Jupiter system, provided images that both complement and supplement in important ways the Voyager 1 images. While many changes have been observed in Jupiter's visual appearance, few, yet significant, changes have been detected in the principal atmospheric currents. Jupiter's ring system is strongly forward scattering at visual wavelengths and consists of a narrow annulus of highest particle density, within which is a broader region in which the density is lower. On Io, changes are observed in eruptive activity, plume structure, and surface albedo patterns. Europa's surface retains little or no record of intense meteorite bombardment, but does reveal a complex and, as yet, little-understood system of overlapping bright and dark linear features. Ganymede is found to have at least one unit of heavily cratered terrain on a surface that otherwise suggests widespread tectonism. Except for two large ringed basins, Callisto's entire surface is heavily cratered.

Crystallization, fractionation and solidification of the Tuolumne intrusive series, Yosemite National Park, California

Abstract: Study of the Tuolumne Intrusive Series, a concentric texturally and compositionally zoned plutonic sequence in the eastern part of Yosemite National Park, was undertaken to develop and test a model for the origin of comagmatic plutonic sequences in the Sierra Nevada batholith. The granitoid units that make up the sequence are progressively younger and more felsic inward. The bulk of the rocks are granodiorite, but the outermost formation is quartz diorite, and the innermost one is granite porphyry. The compositional gradient changes both gradually within formations and abruptly between them. The change is greatest in the outer 1 km and lower toward the center of the sequence. Hornblende and biotite, abundant in the marginal rocks, decrease rapidly inward for 1 km as K-feldspar and quartz increase, but farther inward, they decrease slowly. The most conspicuous chemical changes are shown by the elements that are enriched in the mafic minerals. The compositional zoning indicates that with decreasing temperature, the sequence solidified from the margins inward. Solidification was interrupted repeatedly by surges of fluid core magma. The magma eroded the adjacent solidifying rock, and it expanded the area of the magma chamber at the exposed level by crowding the wall and roof rocks outward and upward and by breaking through the solidifying carapace into the wall rocks. The compositional zonation resulted from crystal fractionation that could have involved (1) preferential accretion of crystalline material present in the magma to the margins of the magma chamber, thus displacing the melt phase progressively inward, and/or (2) downward settling of crystals, probably accompanied by upward movement of melt and volatiles; the residual magma solidifying to form the granitoids. Although either mechanism can explain the observed relations, they lead to very different interpretations of the composition of the magma when the first exposed granitoids solidified at the margins of the magma chamber and as the sequence solidified inward.

Massive deep-sea sulphide ore deposits discovered on the East Pacific Rise

Abstract: Massive ore-grade zinc, copper and iron sulphide deposits have been found at the axis of the East Pacific Rise. Although their presence on the deep ocean-floor had been predicted there was no supporting observational evidence. The East Pacific Rise deposits represent a modern analogue of Cyprus-type sulphide ores associated with ophiolitic rocks on land. They contain at least 29% zinc metal and 6% metallic copper. Their discovery will provide a new focus for deep-sea exploration, leading to new assessments of the concentration of metals in the upper layers of the oceanic crust.

Estimation of fault-scarp ages from a scarp-height slope-angle relationship

Abstract: The age of fault scarps in unconsolidated deposits is commonly estimated by several criteria such as the extent of dissection, amount of rounding of the crest of the scarp, and the slope of the face of the scarp. To provide a more quantitative basis for evaluating the ages of fault scarps in western Utah, we have measured numerous profiles across late Quaternary fault scarps and studied the relationship between scarp height, slope angle, and age. Well-defined curves delineated by the data suggest that for a given age, (1) the slope angle of the scarp is proportional to the logarithm of the scarp height and (2) the slope angle decreases with estimated age for scarps of a given height. Owing to the lack of well-determined ages for the scarps studied, age assignments are only approximate; the available information provides a means of ranking scarps according to relative geomorphic age within a general age framework for scarps between several thousand and several hundred thousand years old.

Hydrogeological Processes and Chemical Reactions at a Landfill.

Abstract: Chemical and isotopic analyses were made of water from wells in and downgradient from a landfill to determine chemical and isotopic effects of generation and migration of leachate on ground water. The distribution and wide concentration range of oxygen and methane permit the delineation of an anaerobic zone, a regional oxygenated zone and an intermediate zone. The ratio of reduced nitrogen to nitrate indicates location of reducing fronts as the leachate migrates. The pH of the native ground water is low (≥5.0) primarily because of the low pH of rainfall and the lack of calcareous or other soluble minerals in the aquifer material. The pH is higher (∼6.6) in the leachate because of generation of carbon dioxide, ammonia, and methane. The native ground water has a low TDS (80 mg/l) while the leachate has an average TDS of 2800 mg/l and is primarily a NaHCO3 type water. Sulfate concentrations are extremely low and H2 S was not detected. We suggest that a major source of cations may be their exchange from the clays by the ammonium generated in the leachate. High concentrations of Fe and Mn are attributed to a source in the refuse but more important to reduction of oxide cements and coatings resulting from degradation of organic matter. The main source of bicarbonate is from organic degradation with minimal CO2 from the soil zone. At one landfill site 52% of the total alkalinity is attributed to organic compounds, mainly organic acid anions. The δ13 C of bicarbonate in the leachate is exceedingly heavy (+18.400 /00 ) which results from fractionation during the formation of methane. The 10 per mil deuterium enrichment of water may be due to decomposition of deuterium-enriched compounds and bacterial processes that preferentially consume the lighter hydrogen isotope.

U.s. Geological survey core drilling on the atlantic shelf.

Abstract: The first broad program of scientific shallow drilling on the U.S. Atlantic continental shelf has delineated rocks of Pleistocene to Late Cretaceous age, including phosphoritic Miocene strata, widespread Eocene carbonate deposits that serve as reflective seismic markers, and several regional unconformities. Two sites, off Maryland and New Jersey, showed light hydrocarbon gases having affinity to mature petroleum. Pore fluid studies showed that relatively fresh to brackish water occurs beneath much of the Atlantic continental shelf, whereas increases in salinity off Georgla and beneath the Florida-Hatteras slope suggest buried evaporitic strata. The sediment cores showed engineering properties that range from good foundation strength to a potential for severe loss of strength through interaction between sediments and man-made structures.

Distributary channels, sand lobes, and mesotopography of Navy Submarine Fan, California Borderland, with applications to ancient fan sediments

Abstract: The deep-tow instrument package of Scripps Institution of Oceanography provides a unique opportunity to delineate small-scale features of a size comparable to those features usually described from ancient deep-sea fan deposits. On Navy Fan, the deep-tow side-scanning sonar readily detected steep channel walls and steps and terraces within channels. The most striking features observed in side-scan are large crescentic depressions commonly occurring in groups. These appear to be large scours or flutes carved by turbidity currents. Four distinct acoustic facies were mapped on the basis of qualitative assessment of reflectivity of 4 kHz reflection profiles. There is a distinct increase in depth of acoustic penetration, number of sub-bottom reflectors, and reflector continuity from the upper fan-valley to the lower fan. These changes are accompanied by a decrease in surface relief. Navy Fan is made up of three active sectors. The active upper fan is dominated by a single channel with prominent levees that decrease in height downstream. The active mid-fan region or suprafan is where sand is deposited. Well defined distributary channels with steps, terraces, and other mesotopography terminate in depositional lobes. Interchannel areas are rough, containing giant scours as well as other relief. The active lower fan accumulates mud and silt and is without resolvable surface morphology. The morphological features seen on Navy Fan other than levees, interchannel areas, and lobes are principally erosional. The distributary channels are up to 0.5 km wide and 5–15 m deep. Such features, because of their large size and low relief, are rarely completely exposed or easily detectable in ancient rock sequences. Some flute-shaped scours are larger than channels in cross section but many are 5-30 m across and 1-2 m deep. If observed in ancient rocks transverse to palaeo-current direction, they would perhaps be indistinguishable from channels. Surface sediment distribution combined with fan morphology can be used to relate modern sediments to facies models for ancient fan sediments. Gravel and sand occur in the upper valley, massive sand beds in the mid-fan distributary channels, classical complete Bouma sequences on depositional lobes, incomplete Bouma sequences (lacking division a) on the lower mid-fan, and Bouma sequence with lenticular shape or other limited extent on mid-fan interchannel areas and on levees.

Landslides in Valles Marineris, Mars

Abstract: The morphology of the landslides in the Martian equatorial troughs, the geologic structure of the troughs, the time of emplacement, the similarity to terrestrial landslides, and the origin and mechanism of transport are analyzed. About 35 large landslides well-resolved on Viking images were examined, and it is found that the major landslides cover 31,000 sq km of the trough floors, and individual slides range in area from 40 to 7000 sq km. The morphologic variations of the landslides can be attributed mainly to their degree of confinement on trough floors. Many prominent landslides appear to be of similar age and were emplaced after a major faulting that dropped the trough floors. Most sliding occurred after the created scarps were dissected into spurs, gullies, and tributary canyons. Emplacement of the landslides approximately coincided with a late episode of major eruptive activity of the Tharsis volcanoes, and it is suggested that the slides may have originated as gigantic mudflows with slump blocks at their heads. The large size of many landslides is due to the fault scarps as high as 7 km on which they formed in the absence of vigorous fluvial erosion. The landslides suggest that Mars is earthlike in some respects, which may be important for further evaluations.

Morphology and distribution of common ‘sand’ dunes on Mars: Comparison with the Earth

Abstract: A comparative study of Martian and terrestrial dunes was made based on Viking Orbiter pictures and aerial pictures of terrestrial deserts The morphological similarity between the Martian dunes and terrestrial crescentic dunes implies that the dynamics of dune formation are similar on the two planets, despite Martian constraints on dune formation that include much higher velocity winds required to move 'sand' in saltation, the possible inhibition of sand movement by absorbed water vapor, the seasonal 'snow' cover in the north circumpolar erg, and a probably sparse sand supply The absence of longitudinal dunes and the restriction of massive crescentic dunes to a few sites on Mars suggests that Mars may have a long eolian history in which much of the sand suitable for saltation has already been transported to the north polar erg and crater floor fields

Sediment loads in the Amazon River

Abstract: ESTIMATES published in the past 20 years of the sediment load delivered to the sea by the Amazon River range from 4 to 10 × 108 tonnes yr−1 Estimates published around 1960, when few data were available on either the sediment concentration or the river discharge, were in the range 9–10 × 108 tonnes yr−1 (refs 1, 2). Estimates published in 1967 and 1968, after significant new data had been collected, were in the lower range of 4–5 × 108 tonnes yr−1 (refs 3, 4). Our more comprehensive data collected mostly since 1970 (and especially in 1977) suggest that the earlier higher estimates may have been more nearly correct. We show here that the mean annual load of suspended sediment at Obidos, Brazil is between 8 and 9 × 108 tonnes yr−1. Most of this sediment is discharged onto the continental shelf.

Depletion of adenosine triphosphate in Desulfovibrio by oxyanions of group VI elements

Abstract: Oxyanions of elements from group VI of the periodic table, i.e., analogs of SO4 2−, destroyed adenosine 5′-triphosphate (ATP) in cells of sulfate-respiring bacteria (Desulfovibrio spp.), probably via the ATP sulfurylase reaction. The approximate order of effectiveness was CrO4 2−> MoO4 2−=WO4 2−>SeO4 2−. Cultures of aerobically grown or nitrate-respiring bacteria were less susceptible and with fermentatively grownEscherichia coli the oxyanions even appeared to stimulate ATP levels. The selective depletion of ATP in sulfate-respiring bacteria might provide the basis for a rapid and simple assay of their biomass in mixed cultures or environmental samples.

Volcanic resurfacing rates and implications for volatiles on Io

Abstract: The rates of volcanic resurfacing on Io are estimated on the basis of two separate observations and the implications of these rates for the volatile history of Io and the supply of material to the Jovian torus are discussed. Rates of resurfacing based on the lack of observable impact craters and assuming a Jovian cratering rate similar to those of the moon and Mars are found to be on the order of 0.1 cm/year. Estimated deposition rates of volcanic matter are found to be in general agreement with cratering rate determinations, if large particle deposition, undetected volcanic activity, volcanic flows and gas condensation are taken into account. Escape rates from Io estimated for sulfur, oxygen and sodium, based on their concentrations around Io, indicate that only a fraction of the present volcanic material can escape. Thermal and nonthermal escape mechanisms are suggested to account for the current loss of sulfur and oxygen from Io's upper atmosphere, while sputtering of atoms from the surface by impacting magnetospheric ions is suggested as the mechanism of sodium supply.

Tosco-Abreojos fault zone: A Neogene transform plate boundary within the Pacific margin of southern Baja California, Mexico

Abstract: Single-channel seismic-reflection profiles across the Pacific margin of southern Baja California show a series of northwest-trending ridges, troughs, and faults The most significant feature is a lineament with a trend between N42°W and N32°W extending along the slope and outer shelf for at least 400 km and possibly more than 550 km The lineament is marked by a series of scarps, steep-sided ridges, and elongate intraslope basins as much as 17 km wide and 700 m deep Sea-floor morphology and deformation and/or truncation of subbottom reflectors along the lineament show that it is a continuous fault zone, named the Tosco-Abreojos fault zone We believe that this zone was a major part of the Pacific–North American transform plate boundary between 45 and 12 to 14 my ago Sea-floor offsets and disruption of the youngest sediments observed on some reflection profiles indicate that recent movement has occurred in some areas

The determination of erosion rates from exposed tree roots in the piceance basin, colorado

Abstract: Tree roots, exposed by hillslope erosion in the Piceance basin of Colorado, were inspected to determine average net erosion rates during the last four centuries. Twenty pinyon pine and juniper root sections were obtained from each of five sites in this region. The date when a root was first exposed by erosion was determined, for 83 of the sections collected, by one of three methods: 1. time of initial cambium dieback; 2. interpretation of annual ring growth pattern; and 3. the earliest occurrence of reaction wood. Analysis indicated no significant difference in erosion rates between the five study sites. However, a strong difference in erosion rates was noted between north-facing (0–56 mm/yr) and south-facing (1.18 mm/yr) slopes. No significant difference in erosion rates were found between various south-facing aspects and local steepness of slopes. Significant differences were noted between erosion rate and the length of time the root was exposed to erosion. Rates of erosion on south-facing slopes in the pinyon-juniper community during the last four centuries are as follows: period (years ago) 0-99 100-199 200-299 300-399 erosion rate (mm/yr) 1-79 0-49 0-33 0-22. Although there appears to be a slow increase in erosion rates during the three earliest centuries the dramatic increase during the last century may have been substantially augmented by the introduction of cattle into this region approximately one hundred years ago.