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At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Evaluation of the satellite derived snow cover area - Runoff forecasting models for the inaccessible basins of western Himalayas

In this study, the existing seasonal snow cover area runoff forecasting models of the Indus, Kabul, Sutlej and Chenab basins were evaluated with the concurrent flow correlation model for the period 1975-79. In all the basins under study, correlation of concurrent flow model explained the variability in flow better than by the snow cover area runoff models. Actually, the concurrent flow correlation model explained more than 90 percent of the variability in the flow of these rivers. Compared to this model, the snow cover area runoff models explained less of the variability in flow. In the Himalayan river basins under study and at least for the period under observation, the concurrent flow correlation model provided a set of results with which to compare the estimates from the snow cover area runoff models.

Dey, B.↗
NASA NTRS1986

Extension of continental lithosphere - A model for two scales of basin and range deformation

The development of a model for deformation in an extending continental lithosphere that is stratified in density and strength is described. The lithosphere model demonstrates that the necking instabilities at two wavelengths originate due to a strong upper crust, a mantle layer, and a weak lower crust. It is observed that the dominant wavelengths of necking are controlled by layer thickness and the strength of the layers control the amplitude of the instabilities. The model is applied to the Basin and Range Province of the western U.S. where deformations in ranges and tile domains are detected. The relation between the Bouguer gravity anomaly and the deformations is studied. The data reveal that the horizontal scale of short wavelength necking correlates with the spacings of individual basins and ranges, and the longer wavelength corresponds to the width of tilt domains. The control of the Basin and Range deformation by two scales of extensional instability is proposed.

Zuber, M. T.↗
NASA NTRS1986

Basalt depths in lunar basins using impact craters as stratigraphic probes: Evaluation of a method using orbital geochemical data

A rare look at the chemical composition of subsurface stratigraphy in lunar basins filled with mare basalt is possible at fresh impact craters. Mg/Al maps from orbital X-ray flourescence measurements of mare areas indicate chemical anomalies associated with materials ejected by large post-mare impacts. A method of constraining the wide-ranging estimates of mare basalt depths using the orbital MG/Al data is evaluated and the results are compared to those of investigators using different indirect methods. Chemical anomalies at impact craters within the maria indicate five locations where higher Mg/Al basalt compositions may have been excavated from beneath the surface layer. At eight other locations, low Mg/Al anomalies suggest that basin-floor material was ejected. In these two cases, the stratigraphic layers are interpreted to occur at depths less than the calculated maximum depth of excavation. In five other cases, there is no apparent chemical change between the crater and the surrounding mare surface. This suggests homogeneous basalt compositions that extend down to the depths sampled, i.e., no anorthositic material that might represent the basin floor was exposed.

Andre, C. G.↗
NASA NTRS1988

Boundary layer ozone - An airborne survey above the Amazon Basin

Ozone data obtained over the forest canopy of the Amazon Basin during July and August 1985 in the course of NASA's Amazon Boundary Layer Experiment 2A are discussed, and ozone profiles obtained during flights from Belem to Tabatinga, Brazil, are analyzed to determine any cross-basin effects. The analyses of ozone data indicate that the mixed layer of the Amazon Basin, for the conditions of undisturbed meteorology and in the absence of biomass burning, is a significant sink for tropospheric ozone. As the coast is approached, marine influences are noted at about 300 km inland, and a transition from a forest-controlled mixed layer to a marine-controlled mixed layer is noted.

Gregory, Gerald L.↗
NASA NTRS1988

Geological remote sensing of Palaeogene rocks in the Wind River Basin, Wyoming, USA

Remote sensing studies of Palaeogene sediments in the Wind River Basin (Wyoming) were used for mapping stratigraphic units, sedimentary features and facies, and structural patterns. Thematic Mapper principal component images for the central and eastern Wind River Basin along with geological investigations and spectral analyses allowed: mapping of the Fort Union, Wind River, and Wagon Bed formations (Fm) and their subunits; recognition of two subunits in the Wind River Fm, one of which can be traced for 75 km; determination of sediment source and depositional environment of units within the Wind River Fm; correlation of the Wagon Bed Fm across the basin; and apparent confirmation of different sources of volcanic debris in the western and southeastern exposures of the Wagon Bed Fm.

Krishtalka, L.↗
NASA NTRS1989

Geology and deposits of the lunar Nectaris basin

The geology and composition of Nectaris basin deposits have been investigated in order to provide information on the lunar basin-forming process and the regional geologic setting of the Apollo 16 landing site. Several outcrops of nearly pure anorthosite were noted in locations such as the walls of Kant crater, an inner ring of the basin, and the crater Bohnenberger F. The results suggest that the impact can be modeled as a proportional-growth crater, and that the Nectaris excavation cavity was about 470 km in diameter and as deep as 55 km.

Spudis, P. D.↗
NASA NTRS1990

Caloris Basin - An enhanced source for potassium in Mercury's atmosphere

Enhanced abundances of neutral K in the atmosphere of Mercury have been found above the longitude range containing Caloris Basin. Results of a large data set including six elongations of the planet between June 1986 and January 1988 show typical K column abundances of about 5.4 x 10 to the 8th K atmos/sq cm. During the observing period in October 1987, when Caloris Basin was in view, the typical K column was about 2.7 x 10 to the 9th K atoms/sq cm. Another large value was seen over the Caloris antipode in January 1988. This enhancement is consistent with an increased source of K from the well-fractured crust and regolith associated with this large impact basin. The phenomenon is localized because at most solar angles, thermal alkali atoms cannot move more than a few hundred kilometers from their source before being lost to ionization by solar ultraviolet radiation.

Sprague, Ann L.↗
NASA NTRS1991

Searching for Crisium Basin ejecta - Chemistry and ages of Luna 20 impact melts

Chemical (INAA) and chronological (Ar-40 - Ar-39) analyses of six Luna 20 impact melts are performed, and these are compared to the results of Podosek et al. (1973), commonly taken to be representative of the Crisium Basin impact. At least two chemical groups of impact melts are identified. One is interpreted as melts derived from the local crust by craters over the last 3.9 Ga. Another group, which includes one of the samples dated by Podosek et al. (1973), is chemically and chronologically (3.85 + or - 0.02 Ga) indistinguishable from Apollo 17 samples interpreted as Serenitatis impact melts, and hence could be melt formed by that event and deposited at the Luna 20 site. One sample (22023,3,F) has a well-defined age of 3.895 + or - 0.017 Ga, and is chemically similar to, but distinct from, impact melts from other basins. This sample, and its chemistry and age are tentatively identified with the Crisium Basin impact. Whether the age of the Crisium impact is given by 22023,3,F, the samples analyzed by Podosek et al. (1973), or neither, it is clear that Crisium impact melt is not abundant in the Luna 20 collection.

Swindle, T. D.↗
NASA NTRS1991

Global relationships between volcanic vents and fractures radial to large impact basins on Mars

The relation of volcanic vents on Mars to impact basins has been previously studied. It has been asserted that the concentric fractures around impact basins extend into the crust and might localize some features, including volcanoes. Herein, the possibility is assessed of radial fractures inferred to be associated with impact basins as an additional control on the location of volcanoes on Mars. Geologic mapping at 1:2 million scale enabled 250 central vents and fissure vents to be identified. Pattern of vent distribution superimposed on a globe show that most are located on three distinct circles. In addition, there are two more possible great circles which may be superimposed onto the Martian globe. These five Martian circles are briefly examined for their geological relationship to volcanoes.

Schneid, Byron D.↗
NASA NTRS1991

SO2-rich equatorial basins and epeirogeny of Io

Comparison of Io's large scale topography with an SO2 abundance map shows that SO2 is concentrated in equatorial topographic basins. In these basins, about 30 pct. of the surface is covered by SO2 at all elevations above the mean triaxial figure, and SO2 coverage increases with decreasing elevation to as much as 56 pct. at elevations below -1.5 km. The correlation is not good from long 240 to 360 degs where bright areas are covered by red, Pele type plume fallout, and in the polar regions where the topography is poorly known. The histogram of SO2 abundance binned by elevation appears bimodal, with a secondary concentration of SO2 at high elevations, but it is not certain that this is significant. Additional observations suggest that the basins have relatively little higher frequency topographic relief. The distribution of active plumes and hotspots show no obvious correlation with the topography. However, the Pele type plume all erupted from regions higher than the mean figure, and five of the eight Prometheus type plumes are more energetic and are associated with high temperature hotspots, whereas Prometheus type plumes are long lived and require large volatile reservoirs.

Mcewen, Alfred S.↗
NASA NTRS1992

Amazonis and Utopia Planitiae: Martian Lacustrine basins

Amazonis and Utopia Planitiae are two large (greater than 10(exp 6) sq. km) basins on Mars having morphological features commonly associated with former lakes. The investigation of these areas is an extension of our previous paleolake studies in the Elysium basin. Using Viking images, we are searching for familiar geologic forms commonly associated with standing bodies of water on Earth. Like Elysium, the two basins exhibit terraces and lineations resembling shorelines, etched and infilled floors with channel-like sinuous markings in places, inflow channels along their borders, and other geomorphic indicators believed to be related to the presence of water and ice. In some areas these features are better displayed than in others where they may be very tenuous; their value as indicators can be justified only by their association with related features. Even though these postulated paleolakes are very young in the Martian stratigraphic sequence, their shoreline features are poorly preserved and they are probably much older than large Pleistocene lakes on Earth.

Scott, David H.↗
NASA NTRS1992

Lunar impact basins and crustal heterogeneity - New western limb and far side data from Galileo

Multispectral images of the lunar western limb and far side obtained from Galileo reveal the compositional nature of several prominent lunar features and provide new information on lunar evolution. The data reveal that the ejecta from the Orientale impact basin (900 kilometers in diameter) lying outside the Cordillera Mountains was excavated from the crust, not the mantle, and covers pre-Orientale terrain that consisted of both highland materials and relatively large expanses of ancient mare basalts. The inside of the far side South Pole-Aitken basin (greater than 2000 kilometers in diameter) has low albedo, red color, and a relatively high abundance of iron- and magnesium-rich materials. These features suggest that the impact may have penetrated into the deep crust or lunar mantle or that the basin contains ancient mare basalts that were later covered by highlands ejecta.

Belton, Michael J. S.↗
NASA NTRS1992

New evidence of lacustrine basins on Mars - Amazonis and Utopia Planitiae

Amazonis and Utopia Planitiae are two large basins on Mars that have morphologic features commonly associated with former standing bodies of water. Like Elysium, the basins exhibit terraces and lineations resembling shorelines, etched and infilled floors marked by sinuous channels in places, inflow channels along their borders, and other geomorphic indicators believed to be related to the presence of water and ice. Moreover, most of the shoreline features have consistent elevations of about -1000 m, which suggests that the bodies of water thought to have occupied the basins may once have been connected. Although the concept of large paleolakes in the northern lowlands of Mars might be expanded to include inland seas, it is still premature to advance this hypothesis at the present stage of investigation. Even though these postulated paleolakes are very young in the Martian stratigraphic sequence, they are probably much older than large Pleistocene lakes on earth, and their shoreline features are less well preserved.

Scott, David H.↗
NASA NTRS1992

Saharan dust in the Amazon Basin

It is shown that Saharan dust enters the Central Amazon Basin in bursts that accompany major wet season rain systems. Low-level horizontal convergence feeding these rain systems draws dust from plumes that have crossed the tropical Atlantic under the large-scale circulation fields. Mass exchange of air between the surface and four kilometers over the eastern Amazon basin is calculated utilizing rawinsonde data collected during storm events. Mean concentrations of dust observed by aircraft over the western tropical Atlantic are employed to calculate the amount of dust injected into the basin.

Swap, R.↗
NASA NTRS1992

Geological evidence for a 2.6-Ga strewn field of impact spherules in the Hamersley Basin of Western Australia

Sand-sized spherules up to 1.7 mm across with spherulitic, vesicular, and other crystalline textures that consist mainly of K-feldspar help define a unique horizon in the well-preserved 2.6-Ga Wittenoom Formation in the Hamersley Basin of Western Australia. This layer is informally known as the spherule marker bed. In the northeastern part of the Hamersley Basin, similar spherules again occur at only one horizon, but here they are a minor constituent of a dolomitic debris-flow deposit known as the dolomixtite layer. The dolomixtite layer occurs in the Carawine Dolomite, which is stratigraphically equivalent to the Wittenoom Formation. Moreover, paleocurrent data from closely associated carbonate and volcaniclastic turbidites indicate the spherule marker bed was deposited in deeper-water paleoenvironments than the dolomixtite layer. Therefore, the dolomixtite layer is believed to be a proximal equivalent of the spherule marker bed. The layers that host the spherules are interpreted to be the deposits of a major sediment gravity flow that exhumed and redeposited most of the spherules after shallow burial, although the flow is not believed to have been a direct result of the proposed impact. The most likely site for the proposed impact would have been in the early Precambrian ocean close to the northeastern edge of the Pilbara Craton. Another thin horizon in the overlying Brockman Iron Formation contains spherules that again consist largely of K-feldspar and have internal textures strikingly similar to those of the Wittenoom Formation and Carawine Dolomite. The close resemblance of these spherules to those of the Wittenoom Formation and Carawine Dolomite suggests they also originated as impact melt droplets, even though they are admixed with volcaniclastic detritus. The stratigraphic separation between the two suggests that a second major impact occurred near the Hamersley Basin after a time interval of about 75 m.y. elapsed. This suggests the record of impacts in early Precambrian strata is richer than is generally appreciated.

Simonson, Bruce M.↗
NASA NTRS1992

The Serenitatis Basin and the Taurus-Littrow highlands: Geological context and history

The Apollo 17 mission was targeted to land at the southeastern edge of the Serenitatis Basin, one of a number of large impact basins on the Moon. The geologic setting of the Apollo 17 site is reviewed, the implications for the formation of basins from Apollo 17 results are assessed, and unanswered questions potentially addressable with existing and new data are outlined.

Head, James W.↗
NASA NTRS1992

The topographic distribution of annual incoming solar radiation in the Rio Grande River basin

We model the annual incoming solar radiation topoclimatology for the Rio Grande River basin in Colorado, U.S.A. Hourly pyranometer measurements are combined with satellite reflectance data and 30-m digital elevation models within a topographic solar radiation algorithm. Our results show that there is large spatial variability within the basin, even at an annual integration length, but the annual, basin-wide mean is close to that measured by the pyranometers. The variance within 16 sq km and 100 sq km regions is a linear function of the average slope in the region, suggesting a possible parameterization for sub-grid-cell variability.

Dubayah, R.↗
NASA NTRS1993

Hellas basin, Mars: Formation by oblique impact

Hellas, a 2,000-km-diameter, roughly circular multiring impact basin in the southern highlands of Mars, has a pronounced southeastern lobe of rim material that extends for some 1,500 km. This lobe and a system of ridges concentric to the southern part of the basin (including part of the lobe) were interpreted to be formed by an oblique impact that was inclined in the direction of the lobe. Our preliminary geologic mapping of the Hellas region (lat -20 to -65 deg, long 250 to 320 deg) at 1:5,000,000 scale gives this hypothesis additional supporting evidence, including a symmetric distribution of basin ejecta and volcanic centers across the inferred trend of the impact. Furthermore, measurements of relief indicate that the downrange ejecta may be about twice as thick as they are elsewhere around the rim.

Leonard, Gregory J.↗