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At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Rheological properties of ammonia-water liquids and crystal-liquid slurries - Planetological applications

The laboratory-measured viscosities of liquid mixtures representative of the variety of cryovolcanic substances of the icy satellites are presently noted to be much greater than could be expected on the assumption that end-member molecules are noninteractive; this observation is supported by others concerning molar volumes and vapor pressure relations, which indicate the presence of strong molecular-interaction forces that fundamentally affect the mixtures' physical properties. Since the rheological effects of partial crystallization parallel the characteristics of silicate lavas, icy satellite cryovolcanic morphologies are similarly interpretable with allowances for differences in surface gravities and lava densities.

Kargel, J. S.↗
NASA NTRS1991

Venus volcanism - Initial analysis from Magellan data

Magellan images confirm that volcanism is widespread and has been fundamentally important in the formation and evolution of the crust of Venus. High-resolution imaging data reveal evidence for intrusion (dike formation and cryptodomes) and extrusion (a wide range of lava flows). Also observed are thousands of small shield volcanoes, larger edifices up to several hundred kilometers in diameter, massive outpourings of lavas, and local pyroclastic deposits. Although most features are consistent with basaltic compositions, a number of large pancake-like domes are morphologically similar to rhyolite-dacite domes on earth. Flows and sinuous channels with lengths of many hundreds of kilometers suggest that extremely high effusion rates or very fluid magmas (perhaps komantiites) may be present. Volcanism is evident in various tectonic settings (coronae, linear extensional and compressional zones, mountain belts, upland rises, highland plateaus, and tesserae). Volcanic resurfacing rates appear to be low (less than 2 cu km/yr) but the significance of dike formation and intrusions, and the mode of crustal formation and loss remain to be established.

Head, James W.↗
NASA NTRS1991

Petrogenesis of Challis volcanics from central and southwestern Idaho - Trace element and Pb isotopic evidence

An analysis of the lava flows and ash-flow tuffs in Idaho is conducted to determine the composition of the volcanics in terms of major and trace elements and Pb isotopic substances. Al2O3 is found to be low, MgO content is high, and the concentration of K2O is higher or equal to that of Na2O with respect to the lavas of mafic to intermediate composition. Trace elements and element ratios are compatible with the crustal component, and the Pb isotopic compositions suggest a lack of assimilation during crystallization. The evidence does not support the notion of a magma system related to subduction, and the data regarding Pb isotopes and trace elements point to a connection with the lithosphere. A model is proposed for the Challis volcanics in which they resulted from completely melting within the lithosphere and then extending during the late Mesozoic and early Cenozoic compression.

Norman, Marc D.↗
NASA NTRS1991

Timing and formation of wrinkle ridges in the Tyrrhena Patera Region of Mars

Wrinkle ridges are distinctive linear to curvilinear arches topped by crenulated ridges and have been identified on the Moon, Mercury, and Mars. The presence of wrinkle ridges on other planetary surfaces has been used as a criterion for identifying volcanic plains. Recently, due to the presence of lava flow lobes and leveed channels, Greeley and Crown identified an area within Hesperia Planum as a flank flow unit associated with Tyrrhena Patera. Hesperia Planum surrounds Tyrrhena Patera and embays the eroded shield of the volcano to the north and south. The Tyrrhena Patera flank flow unit extends approx. 1000 km from the summit caldera to the southwest. More than 55 wrinkle ridges have been identified on this flank flow unit. The relationships between the lava flows and wrinkle ridges within the flank flow unit allow relative ages to be determined. Wrinkle ridges are classified as post flow if flow lobes appear to arch over the rises undeformed, with no evidence of flow ponding on the upstream side of the ridge, or of flows breaching the rises. Wrinkle ridges within Hesperia Planum and Tyrrhena Patera flank flow unit that trend NW-SE appear younger than the flank flow unit.

Porter, Tracy K.↗
NASA NTRS1991

Depth/diameter relationships of fresh craters within Hesperia Planum, Mars

Meteorite impact craters represent important geological features for revealing the near-surface layers of a planetary surface. In the case of Mars, this characteristic was proposed as a useful method to study spatial variations of such attributes as the distribution of sub-surface volatiles, and heat flow. Using the Planetary Image Cartography System (PICS) software, a quantitative analysis was completed of the geometry of fresh impact craters in the Hesperia Planum region of Mars, where an uniform target material and optimum viewing geometry make possible an analysis of target effects over a large geographic region. Because of the morphologic similarity to the lunar maria, it is likely that Hesperia Planum comprises a series of flood lavas that partially infilled topographic depressions within the Martian highlands. Measurements of partially buried crater rims suggest that the lava flows within Hesperia Planum are between 200-400 m thick.

Mouginis-Mark, P. J.↗
NASA NTRS1992

Influence of aerodynamic roughness length on aeolian processes: Earth, Mars, Venus

The aerodynamic roughness length (z sub 0) is the height at which a wind profile assumes a zero velocity. The lower part of the atmospheric boundary layer will be impeded by friction with the surface. An increase in surface roughness will also increase the shear stress required to initiate particle entrainment by the wind. Bagnold (1941) estimated z sub 0 as being 1/30 of the mean particle size. In Nature, surface roughness is composed of nonerodible elements as well as sand-size erodible particles. To assess z sub 0 values as a function of terrain, field experiments were conducted to obtain wind profiles monitored over natural surfaces at 15 sites in the Mojave Desert, Death Valley, and Nye County, Nevada. These sites span a variety of arid-land terrains, including smooth playas, alluvial fans, and lava flows; z sub 0 values ranged from 0.0001 cm to 1 cm. These values were incorporated in a threshold model and a flux model to assess transport efficiency over such terrains in three planetary environments (Venus, Earth, and Mars), and for particle sizes ranging from 60-500 micron. Threshold and flux are a function of planetary environment, particle density and size (Dp), and z sub 0, and the shear velocity of 1.2 x U sub *t (for Dp = 250 micron and z sub 0 = 0.84). Results show that flux on Mars is approximately 14 g/(cm x s), on Earth it is approximately 3 g/(cm x s), and on Venus 0.5 g/(cm x s). Under all planetary environments, the results also show a dramatic decrease in the flux for particles greater than 200 microns when z sub 0 increases above 0.0085 cm (corresponding to sites consisting of alluvium). When z sub 0 approaches 0.03 cm (corresponding to a mantled pahoehoe lava), the flux diminishes.

Blumberg, Dan G.↗
NASA NTRS1992

Mid-infrared spectra of Martian komantiite

Synthetic mid-infrared emissive spectra of basalts of possible Martian komatiitic compositions were generated to show what might be seen in data returned from the Thermal Emission Spectrometer (TES). TES is flying on the Mars Observer arriving at Mars in late 1993. The synthetic Martian komatiite spectra were generated using mineralogy based on Shergottite, Nakhlite, and Chassigny (SNC) meteorites and Viking X-Ray Fluorescence (XRF) data. These data sets provide strong evidence for the existence of ultramafic lavas on Mars, particularly lavas of komatiitic composition.

Reyes, David P.↗
NASA NTRS1992

Global scale concentrations of volcanic activity on Venus: A summary of three 23rd Lunar and Planetary Science Conference abstracts. 1: Venus volcanism: Global distribution and classification from Magellan data. 2: A major global-scale concentration of volcanic activity in the Beta-Atla-Themis region of Venus. 3: Two global concentrations of volcanism on Venus: Geologic associations and implications for global pattern of upwelling and downwelling

As part of the analysis of data from the Magellan Mission, we have compiled a global survey of the location, dimensions, and subsidiary notes of all identified volcanic features on Venus. More than 90 percent of the surface area was examined and the final catalog comprehensively identifies 1548 individual volcanic features larger than approximately 20 km in diameter. Volcanic features included are large volcanoes, intermediate volcanoes, fields of small shield volcanoes, calderas, large lava channels, and lava floods as well as unusual features first noted on Venus such as coronae, arachnoids, and novae.

Crumpler, L. S.↗
NASA NTRS1992

Effects of surficial modification processes on thermal infrared signatures in the arid southwestern United States

Thermal infrared spectra from both laboratory and remote sensing instruments were used to distinguish different age lava flows with varying amounts of surficial modification at Cima and Lunar Crater volcanic fields. The modification processes affecting the lava flows cause spectral differences that can be seen in remotely sensed emittance spectra from the thermal infrared multispectral scanner. Important influences on the thermal infrared spectra include aeolian mantling, vegetation, lave flow roughness, and rock varnish. Laboratory thermal infrared reflectance spectra of the subaerially exposed surfaces of 1-15 cm basalt fragments at Cima volcanic field show a feature attributable to rock varnish on the younger flows (0.14-0.75 m.y.) that is lacking on the older flows (greater than 0.8 m.y.). This suggests that rock varnish is thinner on the older flows at Cima volcanic field. Scanning electron microscope images and thin sections of the different age flows at Cima volcanic field support the conclusion that rock varnish is thinner and may be eroding on the older flow surfaces.

Weitz, Catherine M.↗
NASA NTRS1992

Canali-type channels on Venus - Some genetic constraints

Canali-type channels on Venus are unique because of their great lengths (up to 6800 km) and nearly constant channel cross sectional shapes along their paths. A simple model incorporating channel flow and radiative cooling suggests that common terrestrial-type tholeiite lava cannot sustain a superheated and turbulent state for the long distances required for thermal erosion of canali within allowable discharge rates. If canali formed mainly by constructional processes, laminar tholeiitic flow of relatively high, sustained discharge rates might travel the observed distances, but the absence of levees would need to be explained. An exotic low temperature, low viscosity lava like carbonatite or sulfur seems to be required for the erosional genesis of canali.

Komatsu, Goro↗
NASA NTRS1991

What heated the parent meteorite planets?

The plausibility of the two most wide discussed mechanisms, decay of short-lived Al-26 and solar wind induction heating, for heating the small planetesimals in which the meteorites formed are examined and shown to have significant problems. The main problem for the Al-26 decay mechanism is the fact that eucritic lavas, melted by the mysterious heating mechanism in some early planetesimal, did not contain enough Al-26 to decay to radiogenic Mg-26 when they erupted to their planetesimal surface and cooled. It is necessary to postulate that the lavas lingered underground while their Al-26 decayed away. The solar wind induction heat concept has the problem that astrophysical evidence has made is seem increasingly unlikely that an intense solar wind flux blew past planetesimals in the early solar system. Instead, it was probably collimated in the direction of the sun's poles by the persistence of the solar nebula during the T Tauri epoch.

Wood, John A.↗
NASA NTRS1992

Zagami - Product of a two-stage magmatic history

Results of petrologic studies of new large samples of the Zagami shergottite are presented. Pyroxene crystals have homogeneous Mg-rich pigeonite and augite cores, overgrown by Fe-rich zoned pyroxene rims. Amphibole-bearing magmatic inclusions occur exclusively in the cores. It is concluded that Zagami experienced a two-stage crystallization history. The first stage occurred in a deep-seated, slowly cooling magma chamber. There, the homogeneous Mg-rich cores of the pyroxenes crystallized during relatively slow cooling. During the second stage, the Mg-rich pyroxenes were entrained into a magma that either intruded to the near-surface and cooled in a relatively thin dike or sill, or extruded to the surface and crystallized in a lava flow greater than 10 m thick, again without indications of crystal settling. The estimated depth of the magma chamber for Zagami of greater than 7.5 km and thickness of the putative lava flow of greater than 10 m are consistent with calculations and observations of volcanic constructs and flows in the Tharsis region of Mars.

Mccoy, Timothy J.↗
NASA NTRS1992

Venus volcanism: A global overview from Magellan data

A preliminary analysis of a global survey of Magellan data covering over 90 percent of the surface and designed to document the characteristics, location, and dimensions of all major volcanic features on Venus has revealed over 1660 landforms and deposits. These include over 550 shield fields (concentrations of small volcanos less than 20 km in diameter), 274 intermediate volcanos between 20 and 100 km diameter with a variety of morphologies, 156 large volcanos in excess of 100 km diameter, 86 calderalike structures independent of those associated with shield volcanos and typically 60-80 km in diameter, 175 coronae (annulus of concentric ridges or fractures), 259 arachnoids (inner concentric and outer radial network pattern of fractures and ridges), 50 novae (focused radial fractures forming stellate patterns), and 53 lava flood-type flow fields, and 50 sinuous lava channels (all of which are in excess of 10(exp 2)-10(exp 3) km in length). The near-global coverage of Magellan data analyzed in this study confirms and extends the results of earlier observations that showed that volcanism is a widespread and significant process on the surface of Venus for the period of time in the presently observed record (less than about the last one billion years).

Head, James W., III↗
NASA NTRS1992

Comparison of Goldstone and Magellan radar data in the equatorial plains of Venus

Goldstone radar observations of the equatorial plains of Venus provide complementary information to that obtained by Magellan. Different radar scattering mechanisms dominate each system, leading to sampling of different surface properties. Comparison of image data and derived parameters indicate that: (1) relatively high dielectric constants on impact-related parabolic features are detected in Goldstone backscatter, Magellan reflectivity, and Magellan emissivity data; the dielectric effects are overwhelmed by roughness-related signatures in Magellan synthetic aperture radar (SAR) data; (2) lava flows in Navka Planitia show dielectric variations both among and within flows; higher dielectric constants on the perimeter of some flows may by due to a decrease in vesicularity; (3) some volcanic domes are relatively smooth at the wavelength scale and probably consist of low-density deposits; (4) comparisons of Magellan SAR data with rough surface scattering models and SAR data of terrestrial surfaces indicate that the roughness characteristics of the equatorial plains surfaces are comparable to modified terrestrial lava flows; and (5) scattering properties of an equatorial 'ridge belt' structure suggest highly weathered or soil-dominated surfaces.

Plaut, Jeffrey J.↗
NASA NTRS1992

Analysis of volcanic surface morphology on Venus from comparison of Arecibo, Magellan, and terrestrial airborne radar data

The paper compares Arecibo Observatory and Magellan radar data for Venus to airborne radar images for potential terrestrial analog surfaces. Volcanic deposits in western Eistla Regio and northern Sedna Planitia are characterized. It is shown that the expected-sense circularly polarized echoes in the 'dark plains' and broad flow aprons of Eistla Regio decrease rapidly with incidence angle. This angular scattering behavior implies surfaces no rougher than terrestrial pahoehoe flows. Polarization ratio comparisons show that the extensive lava flows in Western Eistla Regio and Sedna Planitia are generally consistent with the properties of terrestrial pahoehoe flows, with only limited occurrences of a'a morphology. Three scenarios are suggested. Many of the large flow units in the two study regions were emplaced as complexes of low-effusion rate pahoehoe flows, rather than as higher eruption rate events which might be expected to produce a'a surface textures; the long lava flows were originally emplaced as a'a but have since weathered to a smoother texture; or a combination of atmospheric and magma compositional effects combine to inhibit a'a formation even at high volume eruption rates.

Campbell, Bruce A.↗
NASA NTRS1993

Thermally altered palagonitic tephra - A spectral and process analog to the soil and dust of Mars

Six palagonitic soil samples (PH-1 through PH-6) which were collected at 30-cm intervals from a lava slab on Mauna Kea, Hawaii, are studied. The samples present an alteration sequence caused by heating during emplacement of molten lava over a preexisting tephra cone. Techniques employed include visible and near-IUR spectroscopy, Moessbauer spectroscopy, and magnetic analysis. The four samples closest to the slab (PH-1 through PH-4) were strongly altered in response to heating during its emplacement; their iron oxide mineralogy is dominated by nanophase ferric oxide. The sample adjacent to the slab (PH-1) has a factor of 3 less H2O and contains crystalline hematite and magnetite in addition to nanophase ferric oxide. It is argued that localized thermal alteration events may provide a volumetrically important mechanism for the palagonitization of basaltic glass and the production of crystalline ferric oxides on Mars.

Bell, James F., III↗
NASA NTRS1993

Volcanic recycling of carbonates on Mars

Thermal erosion of carbonate deposits by turbulently-flowing lava is investigated as a means of recycling carbon dioxide back into the atmosphere of Mars. Erosion rates of several meters/day are found, implying that up to hundreds of meters of carbonate could be removed over the lifetime of a flow. A large fraction of the northern plains and other parts of Mars were covered by lava during the Hesperian, and may have released the carbon dioxide trapped in carbonate deposits. This period of time, several times 10 exp 8 yrs, is comparable to that for the redeposition of such carbonate deposits. Therefore, there could have existed a relatively dense atmosphere, and enhanced weathering and erosion, after the Noachian era. This may help explain the apparent observational evidence for late fluvial and lacustrine activity on Mars.

Schaefer, M. W.↗
NASA NTRS1993

Basal scarp, paleoglacier, and fissure flows of Elysium Mons, Mars

Geological mapping at 1:500,000 scale of the Granicus Valles area west of Elysium Mons (MTM quadrangles 30227, 30222, and 25227) indicates that (1) the oldest deposits in the area are Upper Hesperian lavas of the Elysium shield; (2) a basal scarp formed by Early Amazonian faulting around the northwest flank of Elysium Mons triggered growth of Elysium Fossae; (3) a glacier or an ice sheet west and north of the scarp was of long duration; (4) water and lava flows from Elysium Fossae became dominant during and after glacial recession; and (5) the last volcanic-fissure-related flows resulted in linear chains of small domes on the Elysium shield.

Chapman, Mary G.↗