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At least 811 records · Page 45

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NASA NTRS1979

The effects of nonideal surfaces on the derived thermal properties of Mars

The paper examines the effects of the observed brightness temperatures and the derived thermal inertias of some of the nonideal properties of the Martian surface. Attention is given to thermal models used for calculating the temperatures of the ideal and nonideal surfaces. Surfaces temperatures and derived thermal inertias for the various nonideal surfaces are presented. In addition, discussion covers the application of these models to the surface of Mars, the VL-1 landing site, the caldera atop Arsia Mons volcano, and the global relationships between thermal inertia and surface elevation.

Jakosky, B. M.↗

NASA NTRS1980

Time analysis of volcanic activity on Io by means of plasma observations

A model of Io volcanism in which the probability of activity obeys a binomial distribution is presented. Observed values of the electron density obtained over a 3-year period by ground-based spectroscopy are fitted to such a distribution. The best fit is found for a total number of 15 volcanoes with a probability of individual activity at any time of 0.143. The Pioneer 10 ultraviolet observations are reinterpreted as emissions of sulfur and oxygen ions and are found to be consistent with a plasma much less dense than that observed by the Voyager spacecraft. Late 1978 and the first half of 1979 are shown to be periods of anomalous volcanicity. Rapid variations in electron density are related to enhanced radial diffusion.

Mekler, Y.↗

NASA NTRS1980

Volcanic explosion clouds - Density, temperature, and particle content estimates from cloud motion

Photographic records of 10 vulcanian eruption clouds produced during the 1978 eruption of Fuego Volcano in Guatemala have been analyzed to determine cloud velocity and acceleration at successive stages of expansion. Cloud motion is controlled by air drag (dominant during early, high-speed motion) and buoyancy (dominant during late motion when the cloud is convecting slowly). Cloud densities in the range 0.6 to 1.2 times that of the surrounding atmosphere were obtained by fitting equations of motion for two common cloud shapes (spheres and vertical cylinders) to the observed motions. Analysis of the heat budget of a cloud permits an estimate of cloud temperature and particle weight fraction to be made from the density. Model results suggest that clouds generally reached temperatures within 10 K of that of the surrounding air within 10 seconds of formation and that dense particle weight fractions were less than 2% by this time. The maximum sizes of dense particles supported by motion in the convecting clouds range from 140 to 1700 microns.

Wilson, L.↗

NASA NTRS1980

Examples of realistic aerosol particles collected in a cascade impactor

In this paper some scanning electron microscope photomicrographs showing examples of a variety of particulate aerosol shapes are presented. Compositions of particles also are presented. These particles represent samples from a number of different sources and locations including: solid propellant rocket motor plumes, active volcano plumes, the lower stratosphere over Sondrestrom, Greenland, and the upper troposphere over northern Texas. The particles were collected from aboard an aircraft with a cascade impactor which classified them according to aerodynamic size into 10 size intervals ranging from submicron to greater than 25 micrometers in diameter. The cascade impactor also served to measure the mass concentration as a function of particle size. The variety of shapes and compositions found among these particles suggest difficulties in obtaining reliable size distribution data from light scattering measurements.

Woods, D. C.↗

NASA NTRS1980

Io - Are vapor explosions responsible for the 5-micron outbursts

It is proposed that a vapor explosion of a submerged pool of liquid sulfur will remove the crust overlying an area of about 50-km diam. Thermal radiation from the exposed liquid sulfur pool with a surface temperature of 600 K is then presumed to be responsible for the 5-micron outbursts that have been observed. The explosive volcanoes are expected to leave black sulfur calderas, which are, indeed, found on the surface. The 5-micron outburst observed by Sinton (1980), on June 11, 1979 (UT), is identified with a new caldera found on Voyager 2 photographs but which had not been present on Voyager 1 pictures.

Sinton, W. M.↗

NASA NTRS1981

An investigation of vegetation and other Earth resource/feature parameters using LANDSAT and other remote sensing data. 1: LANDSAT. 2: Remote sensing of volcanic emissions

A fanning technique based on a simplistic physical model provided a classification algorithm for mixture landscapes. Results of applications to LANDSAT inventory of 1.5 million acres of forest land in Northern Maine are presented. Signatures for potential deer year habitat in New Hampshire were developed. Volcanic activity was monitored in Nicaragua, El Salvador, and Guatemala along with the Mt. St. Helens eruption. Emphasis in the monitoring was placed on the remote sensing of SO2 concentrations in the plumes of the volcanoes.

Birnie, R. W.↗

NASA NTRS1976

Lidar measurements of the post-fuego stratospheric aerosol

Fifteen lidar observations of the stratospheric aerosol were made between February and November 1975. All observations revealed the greatly increased particulate backscattering that followed the eruption of the volcano Fuego in October 1974. Vertical structure consisted initially of multiple layers, which later merged to form a single, broader peak. Essentially all of the increased scattering was confined to altitudes below 20 km. Hence, aerosol layer centroids in 1975 were typically several km below their altitude prior to the eruption. Radiative and thermal consequences of the measured post-Fuego layer were computed using several recently published models. The models predict a temperature increase of several K at the altitude of the layer, caused by the infrared absorption bands of the sulfuric acid particles. The surface temperature decrease predicted by the models is considerably smaller than 1 K, partly because of the small optical thickness of the volcanic layer, and partly because of its short residence time relative to the earth-ocean thermal response time.

Russell, P. B.↗

NASA NTRS1980

Io - Ground-based observations of hot spots

Observations of Io in eclipse demonstrate conclusively that Io emits substantial amounts of radiation at 4.8 and 3.8 micrometers and a measurable amount at 2.2 micrometers. Color temperatures derived from the observations fit blackbody emission at 560 K. The required source area to yield the observed 4.8-micrometer flux is approximately 5 x 10 to the -5th of the disk of Io and is most likely comprised of small hot spots in the vicinity of the volcanoes.

Sinton, W. M.↗

NASA NTRS1980

Interpretation of postseismic deformation with a viscoelastic relaxation model

A viscoelastic relaxation model is used to interpret postseismic surface deformation for the large-magnitude Aleutian earthquakes of 1957 and 1965. The lithosphere and asthenosphere are modeled as elastic solids with an anomalous viscoelastic inclusion below the island arc volcanoes. It is found that the observed postseismic surface deformation is a corollary of the known island arc structure. A satisfactory fit to the uplift following the 1957 earthquake is found for a viscoelastic volume with 80-km width extending from a depth of 50 to 200 km.

Wahr, J.↗

NASA NTRS1980

Genesis of the Smartville arc-ophiolite, Sierra Nevada foothills, California

Rare earth element analyses of metavolcanic rocks from the Smartville, Calif. ophiolite divide the uniform suite of pillowed and massive lavas into the lower part consisting of massive, brecciated tholeiites, an intrusive dike-sill complex, and part of a plutonic suite. The tholeiites are light REE depleted with a (Ce)N range of 6.5 to 26.0 and (Yb)N of 6.0 to 30.0; it is suggested that the tholeiites were produced by partial melting of a LREE depleted source similar to MORB. The upper part of the volcanic pile is comprised of basaltic-andesitic flows and interbedded coarse to fine volcanic sediments; these 'calc-alkaline' rocks are light REE enriched with the (Ce)N range of 17.0-28.0 and (Yb)N of 8.0 to 12.0. Finally, petrographic investigations of volcanic sediments and sulfide ore deposits in the lava show that the ophiolite formed near a group of active submarine and subareal volcanoes.

Menzies, M.↗

NASA NTRS1981

Trajectories of the Mount St. Helens eruption plume

The plume of the major eruption of Mount St. Helens on May 18, 1980 penetrated 10 to 11 km into the stratosphere, attaining heights of 22 to 23 km. Wind shears rapidly converted the plume from an expanding vertical cone to a thin, slightly inclined lamina. The lamina was extruded zonally in the stratosphere as the lower part moved eastward at jet stream velocities, while the upper part slowly moved westward in the region of nonsteady transition from the westerlies to the summer stratospheric easterlies. Trajectories computed to position the NASA U-2 aircraft for sampling in the plume are described. Plume volume after 8 hours of strong volcanic emission is estimated at 2,000,000 cu km. Only about 1% of this volume is attributed to the volcano; the rest was entrained from the environment.

Danielsen, E. F.↗

NASA NTRS1981

Trace element composition of the Mount St. Helens plume - Stratospheric samples from the 18 May eruption

Atmospheric particulate material collected from the stratosphere in the plume of the 18 May 1980 eruption of the Mount St. Helens volcano was quite similar in composition to that of ash that fell to the ground in western Washington. However, there were small but significant differences in concentrations of some elements with altitude, indicating that the stratospheric material was primarily produced from fresh magma, not fragments of the mountain.

Vossler, T.↗

NASA NTRS1981

Characterization of aerosols from eruptions of Mount St. Helens

Measurements of mass concentration and size distribution of aerosols from eruptions of Mount St. Helens as well as morphological and elemental analyses were obtained between 7 April and 7 August 1980. In situ measurements were made in early phreatic and later, minor phreatomagmatic eruption clouds near the vent of the volcano and in plumes injected into the stratosphere from the major eruptions of 18 and 25 May. The phreatic aerosol was characterized by an essentially monomodal size distribution dominated by silicate particles larger than 10 micrometers in diameter. The phreatomagmatic eruption cloud was multimodal; the large size mode consisted of silicate particles and the small size modes were made up of mixtures of sulfuric acid and silicate particles. The stratospheric aerosol from the main eruption exhibited a characteristic narrow single mode with particles less than 1 micrometer in diameter and nearly all of the mass made up of sulfuric acid droplets.

Chuan, R. L.↗

NASA NTRS1981

Martian ages

Four discussions are conducted: (1) the methodology of relative age determination by impact crater statistics, (2) a comparison of proposed Martian impact chronologies for the determination of absolute ages from crater frequencies, (3) a report on work dating Martian volcanoes and erosional features by impact crater statistics, and (4) an attempt to understand the main features of Martian history through a synthesis of crater frequency data. Two cratering chronology models are presented and used for inference of absolute ages from crater frequency data, and it is shown that the interpretation of all data available and tractable by the methodology presented leads to a global Martian geological history that is characterized by two epochs of activity. It is concluded that Mars is an ancient planet with respect to its surface features.

Neukum, G.↗

NASA NTRS1982

An investigation into the utilization of HCMM thermal data for the discrimination of volcanic and Eolian geological units

The nature of the HCMM data set and the general geologic application of thermal inertia imaging using HCMM data were studied. The CCT's of five sites of interest were obtained and displayed. The upgrading of the image display system was investigated. Fragment/block size distributions in various terrain types wre characterized with emphasis on volcanic terrain. The SEASAT L-band radar images of volcanic landforms at Newberry Volcano, Oregon, were analyzed and compared to imagery from LANDSAT band 7.

Head, J. W., III↗

NASA NTRS1981

Spatial color variations in the volcanic plume at Loki, on Io

Multicolor Voyager 1 photographs of the Loki volcanic plume, on Io, have been analyzed to determine the nature and quantity of the scattering material within the plume. This work indicates that there are two particle populations. The first population consists of particles with radius of 0.001-0.01 microns, while the second population, which is concentrated near the source, comprises particles with radius greater than 1 micron. The population of smaller particles includes most of the particulate mass in the plume. This work increases the previously estimated particulate mass (Johnson et al., 1979) and suggests that the SO2 gas spectroscopically identified by Pearl et al. (1979) may represent transient flow from the volcano instead of an atmosphere in stable equilibrium with the local surface.

Collins, S. A.↗

NASA NTRS1981

Topography of Venus and earth - A test for the presence of plate tectonics

Comparisons of earth and Venus topography by use of Pioneer/Venus radar altimetry are examined. Approximately 93% of the Venus surface has been mapped with a horizontal resolution of 200 km and a vertical resolution of 200 m. Tectonic troughs have been indicated in plains regions which cover 65% of Venus, and hypsometric comparisons between the two planets' elevation distributions revealed that while the earth has a bimodal height distribution, Venus displays a unimodal configuration, with 60% of the planet surface within 500 m of the modal planet radius. The effects of mapping the earth at the same resolution as the Venus observations were explored. Continents and oceans were apparent, and although folded mountains appeared as high spots, no indications of tectonic activity were discernible. A NASA Venus Orbiting Imaging radar is outlined, which is designed to detect volcanoes, folded mountain ranges, craters, and faults, and thereby allow definition of possible plate-tectonic activity on Venus.

Head, J. W.↗

NASA NTRS1981

Volcanism on Mars

In situ chemical analyses of Martian soil by the Viking lander indicate mafic to ultramafic source rocks, consistent with both remote sensing data indicating the presence of pyroxene and olivine and with petrologic modeling which suggests that Martian lavas are iron-rich and ultramafic. Photogeological analysis of the Martian surface reveals two types of volcanic morphology: (1) central volcanoes, developed by continued and prolonged eruption from a point source vent; and (2) volcanic plains, recognized by mare ridges and flow lobes. When these volcanic morphologies are combined with relative age data, a volcanic history may be derived that is consistent with a moonlike thermal history involving a lithosphere of increasing thickness with time which gradually suppresses the volcanism.

Greely, R.↗