Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “eruptions”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,117 records · Page 62
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Magma reservoirs and neutral buoyancy zones on Venus - Implications for the formation and evolution of volcanic landforms

The production of magma reservoirs and neutral buoyancy zones (NBZs) on Venus and the implications of their development for the formation and evolution of volcanic landforms are examined. The high atmospheric pressure on Venus reduces volatile exsolution and generally serves to inhibit the formation of NBZs and shallow magma reservoirs. For a range of common terrestrial magma-volatile contents, magma ascending and erupting near or below mean planetary radius (MPR) should not stall at shallow magma reservoirs; such eruptions are characterized by relatively high total volumes and effusion rates. For the same range of volatile contents at 2 km above MPR, about half of the cases result in the direct ascent of magma to the surface and half in the production of neutral buoyancy zones. NBZs and shallow magma reservoirs begin to appear as gas content increases and are nominally shallower on Venus than on earth. For a fixed volatile content, NBZs become deeper with increasing elevation: over the range of elevations treated in this study (-1 km to +4.4 km) depths differ by a factor of 2-4. Factors that may account for the low height of volcanoes on Venus are discussed.

Head, James W.↗
NASA NTRS1992

Energy buildup in sheared force-free magnetic fields

Photospheric displacement of the footpoints of solar magnetic field lines results in shearing and twisting of the field, and consequently in the buildup of electric currents and magnetic free energy in the corona. The sudden release of this free energy may be the origin of eruptive events like coronal mass ejections, prominence eruptions, and flares. An important question is whether such an energy release may be accompanied by the opening of magnetic field lines that were previously closed, for such open field lines can provide a route for matter frozen into the field to escape the sun altogether. This paper presents the results of numerical calculations showing that opening of the magnetic field is permitted energetically, in that it is possible to build up more free energy in a sheared, closed, force-free magnetic field than is in a related magnetic configuration having both closed and open field lines. Whether or not the closed force-free field attains enough energy to become partially open depends on the form of the shear profile; the results presented compare the energy buildup for different shear profiles. Implications for solar activity are discussed briefly.

Wolfson, Richard↗
NASA NTRS1992

Catastrophic loss of stratospheric ozone in dense volcanic clouds

Rapid, localized loss of ozone is predicted to occur in the midlatitude and tropical stratosphere in the presence of very large concentrations of sulfate aerosols. Volcanic eruptions can increase the effective surface area of sulfuric acid so that heterogeneous reactions involving ClONO2, and secondarily N2O5, are able to suppress NO(x) abundances by more than a factor of 10 relative to gas phase chemistry. When NO(x) levels fall below a threshold, e.g., 0.6 ppb at 24 km in mid-latitudes, the chlorine-catalyzed loss of O3 proceeds at rates comparable to those during the formation of the Antarctic ozone hole, more than 50 ppb per day. If such losses occurred following the eruption of Mount Pinatubo in the most volcanically perturbed regions over the tropics and mid-latitudes, this model predicts that they are driven primarily by the suppression of NO(x) below these critical levels. The increase in stratospheric chlorine since El Chichon has made Mount Pinatubo more than twice as effective in causing rapid O3 loss.

Prather, Michael↗
NASA NTRS1992

Venus steep-sided domes: Relationships between geological associations and possible petrogenetic models

Venus domes are characterized by steep sides, a circular shape, and a relatively flat summit area. In addition, they are orders of magnitude larger in volume and have a lower height/diameter ratio than terrestrial silicic lava domes. The morphology of the domes is consistent with formation by lava with a high apparent viscosity. Twenty percent of the domes are located in or near tessera (highly deformed highlands), while most other (62 percent) are located in and near coronae (circular deformational features thought to represent local mantle upwelling). These geological associations provide evidence for mechanisms of petrogenesis and several of these models are found to be plausible: remelting of basaltic or evolved crust, differentiation of basaltic melts, and volatile enhancement and eruption of basaltic foams. Hess and Head have shown that the full range of magma compositions existing on the Earth is plausible under various environmental conditions on Venus. Most of the Venera and Vego lander compostional data are consistent with tholeiitic basalt; however, evidence for evolved magmas was provided by Venera 8 data consistent with a quartz monzonite composition. Pieters et al. have examined the color of the Venus surface from Venera lander images and interpret the surface there to be oxidized. Preliminary modeling of dome growth has provided some interpretations of lava rheology. Viscosity values obtained from these models range from 10(exp 14) - 10(exp 17) pa*s, and the yield strength has been calculated to be between 10(exp 4) and 10(exp 6) Pa, consistent with terrestrial silicic rocks. The apparent high viscosity of the dome lavas suggests that the domes have a silicic composition or must augment their viscosity with increased visicularity or crystal content. Sixty-two percent of the Venus domes are associated with coronae, circular features that have been proposed as sites of mantle upwelling, and 20 percent of the domes are located near tessera, relatively high areas of complex deformed terrain. We have investigated several models that are consistent with these geologic associations. The first case involves the differentiation of basalt in a magma reservoir in the crust, perhaps produced by partial melting within a mantle plume. The second case is melting at the base of thickened basaltic crust, and the final case is volatile exsolution and enhancement within a basaltic magma reservoir. The association of domes with tessera might be explained by crustal remelting, while the association with coronae may be consistent with chemical differentiation of a magma reservoir or the exsolution and concentration of volatiles in the reservoir before eruption.

Pavri, B.↗
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 NTRS1992

Solidification and morphology of submarine lavas - A dependence on extrusion rate

The results of recent laboratory experiments with wax extruded beneath relatively cold water may be extrapolated to predict the surface morphology of submarine lavas as a function of the extrusion rate and melt viscosity. The experiments with solidifying wax indicated that the surface morphology was controlled by a single parameter, the ratio of the time taken for the surface to solidify, and a time scale for lateral flow. For submarine basalts a solution of the cooling problem (which is dominated by conduction in the lava but convective heat transfer in the water) and estimates of lava viscosities place this parameter within the empirically determined 'pillowing' regime over a wide range of extrusion rates. This results is consistent with the observation that pillow basalts are the most common products of submarine eruptions. Smoother surfaces corresponding to the various types of submarine sheet flows are predicted for sufficiently rapid extrusion of basaltic magma. Still higher eruption rates in regions of low topographic relief may produce submarine lava lakes. Minimum emplacement times can be calculated for submarine volcanic constructs of a single lava flow type.

Griffiths, Ross W.↗
NASA NTRS1992

Ramgarh Crater, Rajasthan, India - Study of multispectral images obtained by Indian remote sensing satellite (IRS-IA)

Ramgarh Crater, Rajasthan, India is a potential impact crater that has not been studied so far. The proximity of Ramgarh Crater to the Deccan flood basalt terrain makes it important to examine the spatial and temporal relationship of this crater to Deccan Volcanism because recent studies propose a strong link between impact cratering and major flood basalt eruptions. A detailed multidisciplinary study is necessary to evaluate the structure and lithology of Ramgarh Crater and its temporal relationship to the emplacement of Deccan eruptions in India. Application of the IRS-IA data to study the lithologic/surface characteristics of Ramgarh Crater (attempted for the first time) indicates the potential application of remote sensing data in these studies. The IRS-IA data are of good quality and resolution. Our preliminary assessment has shown that these data are helpful in generating lithology soil vegetation profiles of Ramgarh Crater region. These 'profile maps' would be useful for targeting the specific areas in the region for a closer look and ground truth verification during the field work and sample collection in the region.

Murali, A. V.↗
NASA NTRS1993

The concentration and isotopic composition of carbon in basaltic glasses from the Juan de Fuca Ridge, Pacific Ocean

The abundance and C-13/C-12 ratios of carbon were analyzed in basaltic glass from twenty locations along the Juan de Fuca Ridge using a 3-step combustion/extraction technique. Carbon released during the first two combustion steps at 400-500 C and 600-650 C is interpreted to be secondary, and only the carbon recovered during a final combustion step at about 1200 C is thought to be indigenous to the samples. For carbon released at about 1200 C, glasses analyzed as 1-2 mm chips contained 23-146 ppm C with delta C-13 values of -4.8 to -9.3 per mil, whereas samples crushed to 38-63 microns or 63-90 microns yielded 56-103 ppm C with delta C-13 values of -6.1 to -9.2 per mil. The concentrations and isotopic compositions of the primary carbon dissolved in the glasses and present in the vesicles are similar to those previously reported for other ocean-ridge basalts. The Juan de Fuca basaltic magmas were not in equilibrium with respect to carbon when they erupted and quenched on the sea floor. Evidence of disequilibrium includes (1) a large range of carbon contents among glasses collected at similar depths, (2) a highly variable calculated carbon isotopic fractionation between melt and vapor determined by comparing crushed and uncrushed splits of the same sample, and (3) a lack of correlation between vesicle abundance, carbon concentration, and depth of eruption. Variations in carbon concentration and delta C-13 ratios along the ridge do not correlate with major element chemistry. The observed relationship between carbon concentrations and delta C-13 values may be explained by late-stage, variable degrees of open-system (Rayleigh-like) degassing.

Blank, Jennifer G.↗
NASA NTRS1993

Modified HNO3 seasonality in volcanic layers of a polar ice core - Snow-pack effect or photochemical perturbation?

Changes in atmospheric HNO3 chemistry following the Laki (1783), Tambora (1815), and Katmai (1912) volcanic eruptions are presently investigated in view of a central Greenland ice core's chemical composition. Attention is given to the concentration of several cations and anions, using ion chromatography. Following the eruptions, the ratio of winter to summer depositions of NO3(-) was significantly higher than during nonvolcanic periods. While this may be due to ice pack effects, it is proposed that large concentrations of the stratospheric H2SO4 particles ejected by the volcanoes favored HNO3 removal during Arctic winter.

Laj, Paolo↗
NASA NTRS1990

Explosive volcanism and associated pressures - Implications for models of endogenically shocked quartz

The nature of explosive volcanic phenomena and associated pressures, both from field and theoretical perspectives, is discussed. An endogenic origin for shocked quartz at the K/T boundary requires impulsive pressures greater than 60 kbars to be generated during explosive volcanism. Explosive volcanic eruptions which are events of sustained decompression may be initiated by impulsive explosions while the magnitudes of the overpressures are small. These maximum overpressures can be controlled mainly by the tensile strength of the rock surrounding the magma chamber-conduit system. Thus maximum overpressures in the volcanic environment are limited to less than 500 bars which are orders of magnitude less than those required for shock quartz (greater than 60 kbars). This observation is found to be consistent with the complete lack of field or petrographic evidence in support of shock metamorphism associated with volcanic eruptions and their products.

De Silva, S. L.↗
NASA NTRS1993

Ozone depletion at northern and southern latitudes derived from January 1979 to December 1991 Total Ozone Mapping Spectrometer data

An extended version of the Nimbus 7/TOMS ozone data set from the period January 1, 1979 to December 31, 1991 is presented. It is shown that the ozone-trend data indicate that regions of enhanced ozone depletion rates have formed at middle and high latitudes during recent years. The seasonal dependence and geographical extent of the enhanced ozone-depletion rates for the Northern and Southern hemispheres are examined. The variability of the long-term ozone trend determination is discussed via consideration of the differences among 11-, 12-, and 13-yr trend calculations. The effects of the Mount Pinatubo eruption and other volcanic eruptions on the TOMS equatorial zonal average ozone measurements, and its influence on long-term trend determinations are discussed. On the basis of a determination of the aerosol phase function using TOMS data, the effect of stratospheric aerosols on determination of ozone amounts from TOMS are shown to be less than 1 percent.

Herman, J. R.↗
NASA NTRS1993

Th-230 - U-238 series disequilibrium of the Olkaria rhyolites Gregory Rift Valley, Kenya: Residence times

U-series disequilibrium analyses have been conducted on samples from Olkaria rhyolite centers with ages being available for all but one center using both internal and whole rock isochrons. 67 percent of the rhyolites analyzed show U-Th disequilibrium, ranging from 27 percent excess thorium to 36 percent excess uranium. Internal and whole rock isochrons give crystallization/formation ages between 65 ka and 9 ka, in every case these are substantially older than the eruptive dates. The residence times of the rhyolites (U-Th age minus the eruption date) have decreased almost linearly with time, from 45 ka to 7 Ka suggesting a possible increase of activity within the system related to increased basaltic input. The long residence times are mirrored by large Rn-222 fluxes from the centers which cannot be explained by larger U contents.

Black, S.↗
NASA NTRS1993

Mode of emplacement of lunar mare volcanic deposits: Graben formation due to near surface deformation accompanying dike emplacement at Rima Parry 5

Theoretical analyses, together with the observed style of emplacement of lunar mare volcanic deposits, strongly suggest that mare volcanic eruptions are fed by dikes from source regions at the base of the crust or deeper in the lunar mantle. Some dikes intrude into the lower crust, while others penetrate to the surface and are the sources for voluminous outpourings of lava. Still others stall near the surface generating a near-surface extensional stress field. We have investigated the hypothesis that some lunar linear rilles (graben) are the near-surface manifestations of dikes intruded to shallow depths. For a specific example (Rima Parry 5), we show that the geometry of the faults implies a mean dike width of about 150 m and depth to the dike top of about 500 m, values consistent with other theoretical and observational data on lunar dike geometry. Localized pyroclastic deposits along Rima Parry 5 are evidence for the presence of near-surface magma, and are interpreted to be the result of degassing and pyroclastic eruption subsequent to the emplacement of the dike.

Head, J. W.↗
NASA NTRS1993

Thermal and rheological controls on magma migration in dikes: Examples from the east rift zone of Kilauea volcano, Hawaii

Long-lived eruptions from basaltic volcanoes involving episodic or steady activity indicate that a delicate balance has been struck between the rate of magma cooling in the dike system feeding the vent and the rate of magma supply to the dike system from a reservoir. We describe some key factors, involving the relationships between magma temperature, magma rheology, and dike geometry that control the nature of such eruptions.

Parfitt, E. A.↗
NASA NTRS1994

Mount Rainier active cascade volcano

Mount Rainier is one of about two dozen active or recently active volcanoes in the Cascade Range, an arc of volcanoes in the northwestern United States and Canada. The volcano is located about 35 kilometers southeast of the Seattle-Tacoma metropolitan area, which has a population of more than 2.5 million. This metropolitan area is the high technology industrial center of the Pacific Northwest and one of the commercial aircraft manufacturing centers of the United States. The rivers draining the volcano empty into Puget Sound, which has two major shipping ports, and into the Columbia River, a major shipping lane and home to approximately a million people in southwestern Washington and northwestern Oregon. Mount Rainier is an active volcano. It last erupted approximately 150 years ago, and numerous large floods and debris flows have been generated on its slopes during this century. More than 100,000 people live on the extensive mudflow deposits that have filled the rivers and valleys draining the volcano during the past 10,000 years. A major volcanic eruption or debris flow could kill thousands of residents and cripple the economy of the Pacific Northwest. Despite the potential for such danger, Mount Rainier has received little study. Most of the geologic work on Mount Rainier was done more than two decades ago. Fundamental topics such as the development, history, and stability of the volcano are poorly understood.

Source record↗
NASA NTRS1994

Theoretical studies of the solar atmosphere and interstellar pickup ions

Solar atmosphere research activities are summarized. Specific topics addressed include: (1) coronal mass ejections and related phenomena; (2) parametric instabilities of Alfven waves; (3) pickup ions in the solar wind; and (4) cosmic rays in the outer heliosphere. Also included is a list of publications covering the following topics: catastrophic evolution of a force-free flux rope; maximum energy release in flux-rope models of eruptive flares; sheet approximations in models of eruptive flares; material ejection, motions of loops and ribbons of two-ribbon flares; dispersion relations for parametric instabilities of parallel-propagating; parametric instabilities of parallel-propagating Alfven waves; beat, modulation, and decay instabilities of a circularly-polarized Alfven wave; effects of time-dependent photoionization on interstellar pickup helium; observation of waves generated by the solar wind pickup of interstellar hydrogen ions; ion thermalization and wave excitation downstream of the quasi-perpendicular bowshock; ion cyclotron instability and the inverse correlation between proton anisotrophy and proton beta; and effects of cosmic rays and interstellar gas on the dynamics of a wind.

Source record↗
NASA NTRS1993

Physical mechanism of comet outbursts - An experimental result

Attention is given to an experimental investigation of the physical mechanism of comet outbursts which is consistent with the general picture of mantle presence on comets and clarifies the relation of mantles to eruptive activity. The experiment and closeup observation of Comet P/Halley suggest a result different from most mathematical models in that the release of gas pressure does not occur only from uniform gas flow out of the entire surface. In some active comets near perihelion within a few AU of the sun, gas production rates and disturbance of the surface may be so high that the outflow is nearly continuous, with the regolith being entirely stripped away, as in many of the models. The present model provides a cyclic eruption and recharge mechanism which is lacking in most other models.

Hartmann, William K.↗
NASA NTRS1994

Counting Condensation Nuclei in the Antarctic Ozone Mission

The work done on this grant primarily concerns the measurement of aerosol in the stratosphere from NASA ER-2 aircraft in studies of stratospheric ozone depletion in the northern and southern hemispheres. The ER-2 Condensation Nucleus Counter (CNC) measures the number concentration of particles in the diameter range of approximately 0.01 to 1 micron. The Passive Cavity Aerosol Spectrometer measures size distributions in the 0.17 to 3 micron diameter range. This instrument was upgraded during this grant period to a Focused Cavity Aerosol Spectrometer (FCAS). This upgrade permitted the instrument to measure particles as small as 0.05 micron in diameter. The inlet for the PCAS and FCAS was modified and characterized under this grant so that the modifications to the aerosol due to anisokinetic sampling and heating upon sampling and in transport to the measurement location were accounted for in the data analysis. These measurements permitted observations of particle production in the southern hemisphere winter polar vortex and observation of the impact of denitrification on the number concentration of the aerosol in the denitrified air. In the northern polar vortex, the measurements provided a characterization of the sulfate aerosol. Following the eruption of Mount Pinatubo in 1991, the measurements permitted an accurate characterization of the sulfate aerosol enhancements resulting from the eruption. This led to studies of the impact of heterogeneous chemistry on the partitioning of the partitioning of the reactive nitrogen species and the partitioning of the chlorine reservoir.

Wilson, James Charles↗