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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Silica activity in lunar lavas

Calculated values of log alpha SiO2 in lunar magmas range from approximately -0.8 to unity in the temperature range of 1100-1300 C. High-titanium mare basalts begin crystallizing at silica activities insufficient for orthopyroxene saturation; in contrast to terrestrial lavas, silica activities rise substantially with crystallization and cause silica saturation in the residuum. Igneous rocks of the highland regions have relatively higher initial silica activities than mare basalts. Thermodynamic calculations indicate that high-titanium mare basalts could be derived from a 90 to 240-km deep source region containing olivine and orthopyroxene in addition to other phases.

Nash, W. P.↗
NASA NTRS1975

A model for the evolution of opaques in mare lavas

The apparent 'reduced' state of the opaque mineral assemblages of mare basalts has led to various hypotheses on their origin through reduction by various media. A model is developed whereby the presence of trivalent titanium (Ti/3+/) and metallic iron in mare lavas at low oxygen fugacities automatically leads to the production of the observed assemblages by cooling near the mare basalt solidus. The 'reduced' assemblages may evolve isochemically at oxygen fugacities near the iron-ilmenite-ferropseudobrookite buffer by a reaction of the form Fe(2+)+2 Ti(3+) = metallic iron +2 Ti(4+).

Haselton, J. D.↗
NASA NTRS1979

Endogenic craters on basaltic lava flows - Size frequency distributions

Circular crater forms, termed collapse depressions, which occur on many basalt flows on the earth have also been detected on the moon and Mars and possibly on Mercury and Io. The admixture of collapse craters with impact craters would affect age determinations of planetary surface units based on impact crater statistics by making them appear anomalously old. In the work described in the present paper, the techniques conventionally used in planetary crater counting were applied to the determination of the size range and size frequency distribution of collapse craters on lava flows in Idaho, California, and New Mexico. Collapse depressions range in size from 3 to 80 m in diameter; their cumulative size distributions are similar to those of small impact craters on the moon.

Greeley, R.↗
NASA NTRS1982

Radar scatterometry of sand dunes and lava flows

Four frequency like polarized scatterometer data over a sand dune field and a volcanic field were analyzed to understand the scattering characteristics of these two terrain types as a function of frequency and incidence angle. For the frequency range studied (400 MHz to 13.3 GHz) unvegetated sand dunes are specular reflectors that return an echo to the radar antenna particularly when the geometry is such that the dune slope is nearly perpendicular to the antenna. Vegetation on the dunes can cause significant backscatter. Lava flows are strong diffuse scatterers which have backscatter values similar to coniferous forest at certain frequencies. Different observation frequencies are required for different situations. The scatterometer data correlate well with radar images.

Blom, R.↗
NASA NTRS1984

Classification of volcanoes of the Kane Patera Quadrangle of Io: Proportions of lava flows and pyroclastic flows

Voyager 1 images show 14 volcanic centers wholly or partly within the Kane Patera quadrangle of Io, which are divided into four major classes: (1) shield with parallel flows; (2) shield with early radial fan shapd flows; (3) shield with radial fan shaped flows, surfaces of flows textured with longitudinal ridges; and (4) depression surrounded by plateau-forming scarp-bounded, untextured deposits. The interpretation attempted here hinges largely on the ability to distinguish lava flows from pyroclastic flows by remote sensing.

Elston, W. E.↗
NASA NTRS1985

Geomorphic Classification of Lava Flows on Io

The lava flows on Io are classified into the following categories: broad, filamental, digitate, intercalated, sheet, and contained. Each classification is described according to flow distribution, geomorphology, color, thickness, and source.

Pieri, D. C.↗
NASA NTRS1985

Characteristics of Basaltic Lava Flows on Venus

Some ideas relating to the formation of lava flows on Venus are reviewed. The surface morphological features seen in the panoramic images made by the Venera 13 and 14 landers are examined in detail. The major element compositions measured by the Soviet probes indicate that the surface rocks at the Venera 13 site resemble a terrestrial tholeite composite whereas the Venera 14 rocks are similar to terrestrial alkali basalts. Few data exist on the rheological properties of such magma types on Earth; these properties are a strong function of magma volatile content, and there are important gaps in our knowledge of the typical volatiles to be associated with the magmas on Venus. However, the suggestion that Venusian magmas may be water poor together with consideration of the fact that the high Venusian surface temperatures may cause magmas to experience up to 50 K less cooling during their rise to the surface than corresponding terrestrial counterparts, leads to the finding that Venusian magmas may typically have plastic viscosities, E, up to a factor of three greater than terrestrial counterparts on eruption. A similar analysis of yield strength variations with temperature, magma composition and volatile content suggests that temperature will exert the main control and that Venusian magma yield strengths, Y, may be a factor of several times smaller than those of terrestrial equivalents.

Wilson, L.↗
NASA NTRS1985

Thermal Infrared Observations of Lava Flows During the 1984 Mauna Loa Eruption

Thermal infrared videotape images of the flowing lava streams and the vent areas at 10.6 microns were made, as well as some broadband images in the 8 to 12 micron range (for gas plume detection). These data were calibrated with on-site hand-held radiometer measurements, in-flow thermocouple measurements, and with later laboratory kiln measurements. Infrared video data are useful in quantitatively assessing the pattern and mode of flow thermal losses, particularly with regard to radiative losses from established/incipient floating crust. The general cooling of the flows downstream was readily apparent. Upper reaches of the active flow exhibited nearly crust-free main channels, radiating at about 700 to 800 degrees C. Below about the 7500 foot level (about 8 km from the vent) the flows formed nearly continuous crust and tended to spread, become less well-defined and founder due to a reduction in slope. Nevertheless, in thermal IR observations, the surface trace of the active subsurface channel was visible, radiating at about 500 to 700 degrees C. At the active flow front, most solid crust radiated at temperatures less than 500 to 600 degrees C, however bright high temperature interiors (approximately 900 to 1000 degrees C) were clearly visible though evolving fissures.

Pieri, D. C.↗
NASA NTRS1985

Hadley Rille, lava tubes and mare volcanism at the Apollo 15 site

Hadley Rille appears to be a collapsed lava tube/channel, whose formation history may be more intimately related to the mare units sampled at 15 than was previously thought. More work is needed relating samples and observations from Apollo 15 to the rille and its geologic evolution. As the only sinuous rille visited during the Apollo missions, Hadley Rille represents a data source that is directly applicable to the deciphering of processes involved in lunar mare volcanism.

Greeley, R.↗
NASA NTRS1986

The role of porosity in thermal inertia variations on basaltic lavas

Thermal inertia, defined as the square root of the product of thermal conductivity, density, and specific heat, has been noted to vary in inverse proportion to porosity in Hawaiian basalts. It is presently suggested that porosities of the order of more than 80 percent are required if the low thermal inertias observed in Martian shield volcanoes are the result of pristine lava flow surface properties. An aeolian origin is held to be most likely in view of thermal measurements on Mars; the volcanic surfaces in question are anticipated to have a short lifetime in their environment.

Zimbelman, James R.↗
NASA NTRS1987

Lava flows as kinematic waves

A recently proposed model for the emplacement of lava flows is reinterpreted as a kinematic wave theory for the depth of the flow. Explicit kinematic wave solutions and their properties are derived for three time-dependent boundary conditions of practical interest. These boundary conditions correspond to effusion rates that decrease, increase, and crest and broadly reflect types of eruption behavior documented in the geologic literature. Particular attention is given to the way source behavior propagates along the flow in relation to the advance of the flow itself.

Baloga, Stephen↗
NASA NTRS1988

Simulations of lava flows on Mars

One way to approach the understanding of the lava flows observed in the Viking images is to use well-documented terrestrial flows and to simulate comparable eruptions adjusted for Martian conditions. The detailed documentation available for several episodes of the 1983 to 1984 PuuOo eruption can be used in combination with an extension of the emplacement theory for solitary lobate flows to simulate comparable eruptions on the surface of Mars. For simplicity, the simulation is restricted to differences in the gravity between earth and Mars.

Baloga, S.↗
NASA NTRS1988

Relative dating of Hawaiian lava flows using multispectral thermal infrared images - A new tool for geologic mapping of young volcanic terranes

The weathering of Hawaiian basalts in arid and semiarid environments is accompanied by changes in their thermal infrared emittance spectra. The spectral differences can be measured and mapped with multispectral imaging systems. The differences appear to be related to the degree of development, preservation, and alteration of glassy crusts; the oxidation of iron; and the accretion of silica-rich surface veneers. Because the measurements are quantitative and in image format, they are useful for estimating relative ages in geologic mapping of lava flows. In Hawaii this technique is most diagnostic for distinguishing among sparsely vegetated flows less than 1.5 ka in age.

Kahle, Anne B.↗
NASA NTRS1988

Quenching and disruption of lunar KREEP lava flows by impacts

The results of a reexamination of petrography of the Apollo 15 KREEP basalts are reported. Several of the basalts contain yellow residual glasses which cross-cut the crystallized phases; some show more extreme disruption. The features of the glasses appear to be compatible only with impact disruption, ejection, and quenching from actively crystallizing flows, indicating a high impact flux immediately after the impact that formed the Imbrium basin. No other example of impacts into active lava flows is known in the solar system.

Ryder, Graham↗
NASA NTRS1989

Radar interpretation of lava fields as a function of incidence angle - Implications for interpretation of Magellan SAR data on Venus

The capability of a single frequency, single polarization radar to distinguish different lava flows solely on the basis of their relative radar backscatter as measured by scatterometer profiles is addressed. It is found that mantled and unmantled flow surfaces can be separated by their radar backscatter and become more distinct with increasing incidence angle. Pristine pahoehoe surfaces have backscatter coefficients distinctly different from older flows at small angles, whereas the most modified pahoehoe units are identifiable at larger incidence angles. At all latitudes on Venus, it should be possible to distinguish the style of volcanism responsible for volcanic plains emplacement.

Theilig, E.↗
NASA NTRS1990

A model for lava flows with two thermal components

This paper presents a mathematical model for the cooling of an active flow with two separate thermal components, one of which is a crust that cools by radiation and thickens with time and the other an inner core that is vertically isothermal and partially exposed at the top surface, where heat is lost by radiation. This model provides a more realistic description of active lava flows than the existing models that assume thermal homogeneity in each vertical cross section perpendicular to the direction of flow advance. The results of the model were found to compare favorably with existing field data. The effects of different crustal thickening rates, fractional areas of crust, and eruption temperatures on the cooling of the two thermal components were examined.

Crisp, Joy↗
NASA NTRS1990

Cosmic ray exposure dating with in situ produced cosmogenic He-3 - Results from young Hawaiian lava flows

Cosmogenic helium contents in a suite of Hawaiian radiocarbon-dated lava flows were measured to study the use of the production rate of spallation-produced cosmogenic He-3 as a surface exposure chronometer. Basalt samples from the Mauna Loa and Hualalai volcanoes were analyzed, showing that exposure-age dating is feasible in the 600-13000 year age range. The data suggest a present-day sea-level production rate in olivine of 125 + or - 30 atoms/g yr.

Kurz, Mark D.↗
NASA NTRS1991

Rheological analyses of lava flows on Mars

Researchers obtained 183 profiles of lava flows on Mars using photoclinometry. These photoclinometric profiles were leveled by adjusting them until the levee crests or bases had the same elevations (depending on the situation). Here, researchers report some of the results of their analysis of 27 flows on the flanks of Alba Patera (3 flows), near the summit of Ascraeus Mons (6 flows), the flanks of Arsia Mons (3 flows), and the flanks of Olympus Mons (15 flows). Results suggest that the flows examined to date are not felsic or ultramafic; rather, they probably range from basalts to basaltic andesites. Thus, the suggestion that flows on Olympus Mons and elsewhere may be more silicic than Hawaiian basalts is supported by the researchers' results. These suggestions are testable with suitable measurements of silica contents of the flows.

Moore, H. J.↗