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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

An incursion of dust in the southwestern United States from April 1980 eruptions of Mount St. Helens

An intrusion of volcanic dust occurred over the northern Mojave Desert, one month before the explosive eruption of 18 May 1980. Visibility was reduced to 15 to 30 miles during meteorological conditions that should have yielded a visibility in excess of 100 miles. This intrusion was documented by particle size distributions, scanning electron microscope analysis of Nuclepore filter samples, insolation measurements, observations by Navy and NASA aircraft, and meteorological data. No further incidents have been observed to date because of a lack of simultaneous volcanic activity with the particular wind patterns that existed in April. Therefore, under certain meteorological conditions, the desert of the southwestern United States could be significantly affected by volcanic ash from an eruption of Mount St. Helens.

Mathews, L. A.↗
NASA NTRS1982

The faint young sun-climate paradox - Volcanic influences

It has been suggested that the early earth may have frozen over as a result of a fainter early sun (see Ulrich, 1975). If this had happened, climate models suggest the earth would have remained frozen through the present epoch and into the distant future. We suggest that volcanic influences could allow a passage from the frozen branch into the unfrozen branch of climate models should conditions on earth be suitable for the latter climate change. A broad equatorial belt of volcanic ash is one scenario which would allow a transfer from the frozen earth state into the unfrozen one.

Schatten, K. H.↗
NASA NTRS1982

Climatic influence of background and volcanic stratosphere aerosol models

A simple modelization of the earth atmosphere system including tropospheric and stratospheric aerosols has been derived and tested. Analytical expressions are obtained for the albedo variation due to a thin stratospheric aerosol layer. Also outlined are the physical procedures and the respective influence of the main parameters: aerosol optical thickness, single scattering albedo and asymmetry factor, and sublayer albedo. The method is applied to compute the variation of the zonal and planetary albedos due to a stratospheric layer of background H2SO4 particles and of volcanic ash.

Deschamps, P. Y.↗
NASA NTRS1983

The 1980 eruptions of Mount St. Helens - Physical and chemical processes in the stratospheric clouds

The large and diverse set of observational data collected in the high-altitude plumes of the May 18, May 25, and June 13, 1980 eruptions is organized and analyzed with a view to discerning the processes at work. The data serve to guide and constrain detailed model simulations of the volcanic clouds. For this purpose, use is made of a comprehensive one-dimensional model of stratospheric sulfate aerosols, sulfur precursor gases, and volcanic ash and dust. The model takes into account gas-phase and condensed-phase (heterogeneous) chemistry in the clouds, aerosol nucleation and growth, and cloud expansion. Computational results are presented for the time histories of the gaseous species concentrations, aerosol size distributions, and ash burdens of the eruption clouds. Also investigated are the long-term buildup of stratospheric aerosols in the Northern Hemisphere and the persistent effects of injected chlorine and water vapor on stratospheric ozone. It is concluded that SO2, water vapor, and ash were probably the most important substances injected into the stratosphere by the Mount St. Helens volcano, both with respect to their widespread effects on composition and their effect on climate.

Turco, R. P.↗
NASA NTRS1983

Erosion and transport of eolian materials on Mars

An abrasion chamber was constructed to produce grain to grain impacts and to eliminate, as far as possible, grain to wall impact. Quartz, basalt, olivine, and volcanic ash were used as abrasives to determine particle longevity on Mars during eolian abrasion. The various abrasion velocities, measured velocity or particles, calculated velocity of collision, time during which abrasion took place, the charge (material) in grams, and the percent remaining after completion are tabulated. The tests show that if coarse sand-sized particles of the composition presumably present on Mars are moved at the wind velocities given, almost complete destruction can occur in geologically insignificant time periods. Grain to rock collisions are not necessary for almost complete destruction; grain to grain collisions are sufficient.

Krinsley, D.↗
NASA NTRS1983

The faint young sun-climate paradox - Crustal influences

The various mechanisms which have been proposed to compensate for the climatic effects of a 30 percent increase in the solar constant during the past 4.5 billion years are examined. Mechanisms besides the greenhouse effect could have provided significant compensation during the second half of this period. It is proposed that the development of continents during the past 2.5 billion years caused a secular evolution of the atmosphere-ocean heat transport system. As a result, past climates were less susceptible to complete freeze-over. The lower albedo of water would be another factor in this effect insofar as the early earth had smaller land masses. A complete or nearly complete freeze-over may have occurred as past glaciations were widespread. Climate models then suggest that the earth would have remained frozen through the present epoch and into a distant future. It is suggested that volcanic influences could allow a passage from the frozen branch onto the unfrozen branch of climate models should conditions on earth be suitable for that climate change. A broad equatorial belt of volcanic ash is one scenario which would allow a transfer from the frozen earth state into the unfrozen one.

Schatten, K. H.↗
NASA NTRS1983

Size-specific composition of aerosols in the El Chichon volcanic cloud

A NASA U-2 research aircraft flew sampling missions in April, May, July, November, and December 1982 aimed at obtaining in situ data in the stratospheric cloud produced from the March-April 1982 El Chichon eruptions. Post flight analyses provided information on the aerosol composition and morphology. The particles ranged in size from smaller than 0.05 m to larger than 20 m diameter and were quite complex in composition. In the April, May, and July samples the aerosol mass was dominated by magmatic and lithic particles larger than about 3 m. The submicron particles consisted largely of sulfuric acid. Halite particles, believed to be related to a salt dome beneath El Chichon, were collected in the stratosphere in April and May. On the July 23 flight, copper-zinc oxide particles were collected. In July, November, and December, in addition to the volcanic ash and acid particles, carbon-rich particles smaller than about 0.1 m aerodynamic diameter were abundant.

Woods, D. C.↗
NASA NTRS1985

The Effect of Particle Density on Aeolian Transport

A set of experiments using a wide range of particle densities was performed in an open-circuit, terrestrial-atmospheric-pressure wind tunnel at Arizona State University. The results show that saltation flux equations derived for typical geologic material overpredict the flux of low-density particles. Walnut shells (approximately 1.1 g/cc) were used in the experiment and correspond to volcanic ash or ice. Less mass is transported by the wind in the case of low particle density because the style of transport is different. There is a direct, counter-intuitive relationship between particle density and transport height. Measurements of the vertical distribution of material show that the low-density walnut shells travel in a zone within 10 cm of the surface while high-density (approximately 4.5 g/cc) chromite particles travel as 50 cm. Furthermore, the overall saltation rate of the chromite is approximately four times greater than the walnut shells at the same freestream wind speed, even though the wind is much further above threshold for the walnut shells.

Williams, S. H.↗
NASA NTRS1985

Accurate stratospheric particle size distributions from a flat plate collection surface

Flat plate particle collections have revealed the presence of a remarkable variety of both terrestrial and extraterrestrial material in the stratosphere. It is found that the ratio of terrestrial to extraterrestrial material and the nature of the material collected may vary significantly over short time scales. These fluctuations may be related to massive injections of volcanic ash, emissions from solid fuel rockets, or variations in the micrometeoroid flux. The variations in particle number density can be of great importance to the earth's atmospheric radiation balance, and, therefore, its climate. With the objective to assess the number density of solid particles in the stratosphere, an examination has been conducted of all particles exceeding 1 micron in average diameter for a representative suite of particles obtained from a single flat plate collection surface. Attention is given to solid particle size distributions in the stratosphere, and the origin of important stratospheric particle types.

Zolensky, M. E.↗
NASA NTRS1985

Nd and Sr isotopic compositions of tektite material from Barbados and their relationship to North American tektites

The isotopic composition of microtektites from Barbados was determined to establish their possible source and their relationship to known tektite strewn fields. Analyzed samples included microtektites and tektite fragments from the Barbados oceanic beds, samples of deep sea ooze, in which they occur, and of underlying volcanic ash, as well as glass beads from Lake Wanapitei Crater. Isotope ratios (Sr-87/Sr-86, Nd-143/Nd-144, Rb-87/Sr-86, and Sm-147/Nd-144) were determined, and the epsilon values for Sr and Nd plotted on the diagram available for the fields of North America, Australia, Ivory Coast, and Moldavite tektites. The epsilon coordinates of all Barbados microtektite and bulk tektite samples plot precisely within the narrow field determined by North American tektites (epsilon Sr, 111; epsilon Nd, -6.2), yield an Nd model age of 0.6 AE, and are distinct from all other fields. The isotopic signatures of samples from sea ooze, ash layer, and of the Lake Wanapitei glass beads are clearly different from all known tektite classes. It is concluded that the Barbados tektites are of the same source and temporal event as the North American tektites.

Ngo, H. H.↗
NASA NTRS1986

Electrostatic aggregation of finely-comminuted geological materials

Electrostatic forces are known to have a significant effect on the behavior of finely comminuted particulate material: perhaps the most prevalent expression of this being electrostatic aggregation of particles into relatively coherent clumps. However, the precise role of electrostatic attraction and repulsion in determining the behavior of geological materials (such as volcanic ash and aeolian dust) is poorly understood. Electrostatic aggregation of fine particles is difficult to study on Earth either in the geological or laboratory environment principally because the material in an aggregated state remains airborne for such a short period of time. Experiments conducted in the NASA/JCS - KC135 aircraft are discussed. The aircraft experiments are seen as precursors to more elaborate and scientifically more comprehensive Shuttle or Space Station activities.

Marshall, J. R.↗
NASA NTRS1985

Halite particles injected into the stratosphere by the 1982 El Chichon eruption

A cascade impactor was flown on board a U-2 aircraft to gather particulate samples in the stratosphere at 18-21 km altitude after the El Chichon eruptions of 1982. Halite particles were observed, which posed a hazard for the catalytic destruction of ozone. No halite particles were observed a month after the eruptions, while a 40 percent increase in HCl was detected at 12 km, an increase which could have been augmented by halite transformations. The halite proportion of the volcanic clouds was of the same proportion of NaCl as in the volcanic ash around El Chichon. The results indicate that halite forms in eruption clouds of volcanos with alkalic magmas.

Woods, D. C.↗
NASA NTRS1986

On the colors of Jupiter's satellite Io - Irradiation of solid sulfur at 77 K

The colors of seven sulfur allotropes at 77 K have been investigated both before and after irradiation by a high-pressure mercury lamp. S8 is white at 77 K but turns intense yellow within a few minutes on irradiation through quartz or DURAN. On warming, the yellow species (presumably chain-like sulfur diradicals characterized by an absorption at 430 nm) decomposes near 260 K and polymeric sulfur (S-infinity) is formed; the sample color changes gradually to the very similar color of an S8-S-infinity mixture, resulting in no visually detectable color change with temperatures from 77 K to 260 K. This is consistent with the lack of posteclipse brightening on Io. Other sulfur forms also turn intense yellow (S7, S10), grayish yellow (S12, S20, S-infinity), or brownish yellow (S6) on irradiation at 77 K, and these colors also change to the normal colors of the starting materials on warming to 298 K. It is suggested that the yellowish features on Io are caused by the effect of solar radiation on elemental sulfur. The yellow color thus produced may subsequently be modified by deposits of SO2 frosts and volcanic ash.

Steudel, R.↗
NASA NTRS1985

Approximation methods for the solution of inverse problems in lake and sea sediment core analysis

A theoretical model employing one-dimensional (depth) transport equations to describe vertical redistribution of ocean-floor and lake-floor sediment (particulates, volcanic ash, microtektites, or radioactive tracers) by episodic and nonepisodic events including bioturbation is developed analytically and demonstrated. The principles underlying the model are explained; the model equations are derived; the inverse problem of identifying the depth-dependent bioturbation coefficient is addressed; two approximation theorems are presented; and numerical results for two sample problems are presented graphically. It is suggested that compatification, porosity effects, and depth-dependent sedimentation be taken into account when formulating future models.

Banks, H. T.↗
NASA NTRS1987

Laser remote sensing of the atmosphere

Laser beams can be used as long-range spectroscopic probes of the chemical composition and physical state of the atmosphere. The spectroscopic, optical, and laser requirements for atmosphheric laser remote sensing are reviewed, and the sensitivity and limitations of the technique are described. A sampling of recent measurements includes the detection of urban air pollution and toxic chemicals in the atmosphere, the measurement of global circulation of volcanic ash in the upper atmosphere, and the observation of wind shear near airports.

Killinger, Dennis K.↗
NASA NTRS1987

Electrostatic aggregation of finely-comminuted geological materials

Electrostatic forces are known to have a significant effect on the behavior of finely comminuted particulate material: perhaps the most prevalent expression of this being electrostatic aggregation of particles into relatively coherent clumps. However, the precise role of electrostatic attraction and repulsion in determining the behavior of geological materials (such as volcanic ash and aeolian dust) is poorly understood. Electrostatic aggregation of fine particles is difficult to study on earth either in the geological or laboratory environment principally because the material in an aggregated state remains airborne for such a short period of time. Experiments conducted in the NASA/JSC - KC135 aircraft are discussed. The aircraft experiments are seen as precursors to more elaborate and scientifically more comprehensive Shuttle or Space Station activities.

Marshall, John R.↗
NASA NTRS1988

Effects of variation in look angle and wavelength in radar images for geologic applications: Implications for SIR-C and Magellan

Implications for SIR-C and Magellan of Seasat, SIR-A/B, and aircraft radar images which show that a variety of geologic targets can have similar backscatter and be indistinguishable under given observing wavelengths and/or look angles are discussed. The SIR-C/X-SAR combination provides three wavelengths, each of which may provide significant information not provided by another, and HH, VV, and one cross polarization each provide different and significant information. For study of unvegetated geological targets in relatively flat terrain, images made at smaller look angles probably provide more information than images from larger look angles. For Magellan, the possible existence of aeolian landforms such as sand dunes or sand sheets on Venus cannot be ruled out simply because they are not seen on radar images. The problem of dissimilar features having identical backscatter must also be considered in the Venusian context, where perhaps lava flows and impact ejecta could have similar high backscatter, or conversely, smooth aeolian materials and smooth volcanic ash (if either exist) could have a similar backscatter.

Blom, R. G.↗
NASA NTRS1989

Radar imaging of glaciovolcanic stratigraphy, Mount Wrangell caldera, Alaska - Interpretation model and results

Glaciological measurements and an airborne radar sounding survey of the glacier lying in Mount Wrangell caldera raise many questions concerning the glacier thermal regime and volcanic history of Mount Wrangell. An interpretation model has been developed that allows the depth variation of temperature, heat flux, pressure, density, ice velocity, depositional age, and thermal and dielectric properties to be calculated. Some predictions of the interpretation model are that the basal ice melting rate is 0.64 m/yr and the volcanic heat flux is 7.0 W/sq m. By using the interpretation model to calculate two-way travel time and propagation losses, radar sounding traces can be transformed to give estimates of the variation of power reflection coefficient as a function of depth and depositional age. Prominent internal reflecting zones are located at depths of approximately 59-91m, 150m, 203m, and 230m. These internal reflectors are attributed to buried horizons of acidic ice, possibly intermixed with volcanic ash, that were deposited during past eruptions of Mount Wrangell.

Clarke, Garry K. C.↗